Preparation method and device of biomass hard carbon negative electrode material

Abstract

The application discloses a preparation method of a biomass hard carbon negative electrode material, and comprises the following steps: (1) pre-carbonizing a biomass raw material, and then uniformly mixing the pre-carbonized biomass raw material with an alkali solution to obtain wet material; (2) high-temperature carbonizing the wet material in an inert atmosphere, and then rapidly cooling the high-temperature carbonized wet material to obtain carbonized biomass; the cooling rate is controlled to be 10-30 DEG C / min during the rapid cooling; and (3) physically stripping the crystalline substances on the surface of the carbonized biomass, and then crushing the carbonized biomass to obtain the biomass hard carbon negative electrode material. The biomass hard carbon needs high-temperature carbonization during processing, and the high-temperature carbonization process is used for impurity removal, so that the energy consumption is not additionally increased. The impurities are separated by using a physical method, and the process is simple and environment-friendly. Overall, the material prepared by the method has low impurity content, excellent sodium storage performance, low energy consumption in the preparation process, simple process and environment-friendly.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and particularly relates to a method and apparatus for preparing an electrode material. Background Technology

[0002] Due to the consumption of fossil fuels and increasing environmental pollution, wind and solar power have developed rapidly. However, these two energy sources are limited by natural conditions, exhibiting intermittent and uneven distribution characteristics, thus requiring energy storage systems to improve their stability. Chemical energy storage, as a technology with long cycle life, high conversion efficiency, and flexibility, is considered one of the most promising energy storage technologies. Lithium-ion batteries, as an energy storage device with long cycle life, no pollution, and high energy density, have been widely used in electronic devices, automobiles, computers, and other small devices. However, the rising price of lithium resources has hindered its large-scale application in the energy storage field.

[0003] Sodium-ion batteries possess comprehensive advantages such as abundant resources, low cost, adaptability to low temperatures and safety, and rapid industrialization, making them one of the most promising new energy storage systems to replace lithium-ion batteries. Biomass-based hard carbon, as a low-cost material with abundant raw material resources, is considered the most likely anode material for sodium-ion batteries to achieve industrialization. Biomass contains abundant natural porous structures, and the hard carbon materials prepared from it have excellent sodium storage performance. However, biomass contains a large number of heteroatoms, especially silicon, which lacks sodium storage properties, severely affecting the reversible capacity of hard carbon materials.

[0004] Currently, biomass-based hard carbon anodes use chemical purification methods to remove silicon and metal impurities, typically strong alkali or hydrofluoric acid systems. These methods are complex, energy-intensive, operate in hazardous environments, and are difficult to recycle. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the shortcomings and defects mentioned in the background art above, and to provide a method and apparatus for preparing biomass hard carbon anode materials with a simple impurity removal process. To solve the above technical problem, the technical solution proposed by this invention is as follows:

[0006] A method for preparing a biomass hard carbon anode material includes the following steps:

[0007] (1) The biomass raw material is pre-carbonized and then mixed evenly with alkaline solution to obtain wet material;

[0008] (2) The wet material is carbonized at high temperature under an inert atmosphere and then rapidly cooled to obtain carbonized biomass; the cooling rate is controlled at 10-30℃ / min during rapid cooling.

[0009] (3) Physically peel off the crystalline material on the surface of the carbonized biomass and then crush it to obtain the biomass hard carbon anode material.

[0010] In the above preparation method, preferably, the alkaline solution is a sodium hydroxide solution with a concentration of 0.1-1 mol / L, and the solid-liquid ratio when mixed with the alkaline solution is 0.1-4 g / mL. Immersion in sodium hydroxide solution can achieve the initial transformation of impurity silica, and a deeper transformation to sodium silicate during the two-stage carbonization process, facilitating subsequent crystallization of sodium silicate.

[0011] In the above preparation method, preferably, the thickness of the wet material pile during high-temperature carbonization in an inert atmosphere is controlled to not exceed 0.8 cm. The principle of rapid cooling for impurity removal is that the sodium silicate on the surface undergoes nucleation and macroscopically connects together, which can be peeled off with tweezers. If the pile thickness is too large, impurities may be removed from the surface, but the internal impurities will still not be removed, resulting in a high overall impurity content and poor impurity removal effect.

[0012] In the above preparation method, preferably, the carbonization temperature of the high-temperature carbonization is controlled to be 1200-1800℃, the heating rate is 2-8℃ / min, and the holding time is 1-4h; the inert atmosphere is nitrogen and / or argon, and the gas flow rate of the inert atmosphere is controlled to be 0.1-5L / h.

[0013] In the above preparation method, preferably, the cooling method for rapid cooling is cold gas cooling, with the cold gas temperature controlled at 0-15℃ and the introduction rate at 0.5-10L / h, to ensure a cooling rate of 10-30℃ / min. By controlling the cold gas temperature and introduction rate as described above, sufficient heat can be removed to meet the cooling rate requirements.

[0014] In the above preparation method, preferably, the biomass raw material is first subjected to pre-purification before pre-carbonization. The pre-purification involves soaking, washing, and drying the crushed biomass raw material in distilled water for 1-48 hours, at a drying temperature of 60-90℃, and for 6-24 hours. The pre-carbonization is carried out under an inert atmosphere, with the pre-carbonization temperature controlled at 400-800℃, a heating rate of 2-8℃ / min, and a holding time of 1-4 hours. The inert atmosphere is nitrogen and / or argon, and the gas flow rate is controlled at 0.1-3 L / h. The purpose of soaking and washing with distilled water is to remove impurities such as soil from the surface of the biomass.

[0015] In the above preparation method, preferably, the ash content of the biomass hard carbon anode material after physical stripping is ≤2.0% (mass content), and the silicon content is less than 0.5% (Note: the biomass carbonization yield is about 20-25%, and impurities in the raw materials will be enriched 4-5 times); the particle size D50 of the pulverized biomass hard carbon anode material is 6-12μm. The main impurity elements in biomass-based hard carbon are silicon and metal elements. The main impurity element removed in this invention is silicon, which crystallizes in the form of sodium silicate, and metal chlorides can also be removed.

[0016] In this invention, the biomass raw material is one of wood, coconut shell, nut shell, or bamboo.

[0017] In this invention, rapid cooling achieves rapid temperature reduction, the material surface is rapidly cooled, and the supercooling provides the driving force for crystallization, increasing the crystallization rate, causing nucleation to occur explosively, the crystal nucleus generation time is short, the number of crystal nuclei increases, and impurities are macroscopically linked together, which can be separated by physical means.

[0018] The specific principle is as follows: Supercooling is a necessary condition for crystallization. Every substance has its theoretical crystallization temperature, but in the actual crystallization process, the actual crystallization temperature is always lower than the theoretical crystallization temperature; the difference between these two temperatures is called supercooling. Supercooling refers to the theoretical crystallization temperature (T) of a substance under a certain pressure. 理论 ) and actual temperature (T) 实际 The difference between ) is, i.e., ΔT = T 理论 -T 实际 When the temperature drops to T 实际 Previously, heat was continuously lost and the temperature was continuously decreasing. When the temperature dropped to T... 实际 Near the crystallization point, some solid begins to appear, but the phase transition from liquid to solid releases latent heat, causing the temperature to stop decreasing during crystallization. In the subsequent process, heat continues to be lost, resulting in more solid phase. At this point, the heat loss and latent heat of phase transition reach equilibrium, and the system temperature remains constant. This continues until complete crystallization occurs, the latent heat of phase transition disappears, the thermal equilibrium is broken, and T... 实际 Continue to decrease.

[0019] The degree of supercooling is closely related to the cooling rate during crystallization. The lower the cooling rate, the higher the actual temperature, and the lower the supercooling. With a lower supercooling, atoms in the liquid phase can move freely, making it difficult to form new crystal nuclei. The longer solidification time allows sufficient growth time for the crystals, resulting in more complete crystals (slow cooling leads to better, more complete, larger, and fewer crystals, appearing as small particles). Conversely, a higher cooling rate results in a lower actual temperature and a greater supercooling. The increase in nucleation rate is faster than the growth rate of the crystal nuclei, leading to explosive nucleation and smaller, more numerous crystals. This results in finer and more abundant crystals, causing impurities to aggregate macroscopically and allowing for physical separation. Therefore, this invention controls the cooling rate, causing impurities to crystallize and aggregate on the material surface, which can then be easily removed using simple physical methods. The process is short, environmentally friendly, low-cost, and suitable for industrial production.

[0020] In this invention, to ensure rapid cooling for impurity removal, strict control of the cooling rate and material thickness is necessary. For the cooling rate, rapid cooling is required to induce nucleation, resulting in numerous small crystals that are macroscopically connected and can be removed through physical exfoliation. If the cooling rate is slow, the supercooling is low, the crystallization driving force is weak, and the crystals are more complete, larger, and fewer, uniformly dispersed on the hard carbon surface, making them difficult to remove. Regarding material thickness, if the material thickness is too large, while surface impurities are removed by rapid cooling, internal impurities remain dispersed on the hard carbon surface, leading to a high overall impurity concentration and poor electrochemical performance in the hard carbon material.

[0021] As a general technical concept, the present invention also provides a preparation apparatus for the above-mentioned preparation method of biomass hard carbon anode material, including a heating furnace tube, a sagger, and a ventilation assembly for introducing inert gas or cooling gas into the heating furnace tube, wherein the sagger is disposed inside the heating furnace tube.

[0022] In the above-mentioned preparation apparatus, preferably, the ventilation assembly includes a main air inlet pipe, a normal temperature air inlet pipe, a low temperature air inlet pipe, and a cooler. An air inlet pipe knob is provided at the junction of the main air inlet pipe, the normal temperature air inlet pipe, and the low temperature air inlet pipe, and the cooler is located on the low temperature air inlet pipe.

[0023] More specifically, the preparation apparatus of the present invention includes a main air inlet pipe, an air inlet pipe knob, a normal temperature air inlet pipe, a low temperature air inlet pipe, a cooler, an air inlet pipe valve, an air inlet flange, a support frame, a heating furnace tube, a heat insulation layer, a sagger, an air outlet flange, a feed flange, a pressure gauge, an air outlet valve, and an air outlet pipe.

[0024] Furthermore, the heating furnace tube is supported and fixed by a support frame, and a heat insulation layer is installed on the outside of the heating furnace tube. The two ends of the heating furnace tube are connected by an inlet flange and an outlet flange.

[0025] Furthermore, a protective atmosphere is introduced into the main intake pipe. An intake pipe valve is installed on the intake pipe to control the opening and closing of the intake port for checking airtightness and vacuuming. The main intake pipe is adjusted by an intake pipe knob to allow the gas to be introduced into the heating furnace tube via either the ambient temperature intake pipe or the cryogenic intake pipe. When heating up, the gas enters the heating furnace tube through the ambient temperature intake pipe. When cooling down rapidly, the gas enters the heating furnace tube through the cryogenic intake pipe, which is cooled by a chiller to increase the cooling rate.

[0026] Furthermore, the gas outlet discharges gas from the heating furnace tube. The gas outlet is equipped with an outlet valve to control the opening and closing of the outlet, so as to check the airtightness and evacuate the vacuum. The pressure gauge observes the pressure of the heating furnace tube to check the airtightness and ensure experimental safety.

[0027] Furthermore, the sagger enters the heating furnace tube through the feed flange and is placed in the middle of the heating furnace tube to ensure uniform heating.

[0028] This invention discloses a method and apparatus for rapidly cooling and preparing biomass hard carbon anode materials. Using inexpensive biomass as raw material, the process begins by soaking and washing to remove surface-adsorbed impurities. The pre-carbonized biomass is then mixed with a small amount of sodium hydroxide and placed in a tube furnace for high-temperature carbonization. Rapid cooling provides a significant degree of supercooling, resulting in finer and more numerous microscopically and macroscopically interconnected crystals. Impurities are separated using physical methods, minimizing the use of large amounts of chemical reagents (especially strong alkalis or hydrofluoric acid systems) for impurity removal, thus simplifying the process and reducing environmental pollution. Furthermore, rapid cooling preserves the high-temperature morphology of the carbon layer, resulting in larger interlayer spacing, increased sodium storage capacity, improved kinetic performance, and enhanced ion diffusion.

[0029] This invention utilizes the high-temperature carbonization process required in biomass hard char processing for impurity removal, without increasing energy consumption. Furthermore, it separates impurities through physical means, resulting in a simple and environmentally friendly process. Overall, the material prepared by this invention has low impurity content, excellent sodium storage performance, low energy consumption, and a simple and environmentally friendly preparation process.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] 1. The preparation method of biomass hard carbon anode material of the present invention uses biomass as raw material. During the high-temperature carbonization cooling stage, it is rapidly cooled to provide sufficient supercooling, so that impurity elements such as silicon can be rapidly crystallized on the surface of the material and macroscopically linked together. They are then peeled off by simple physical means. This process does not use conventional strong alkali or hydrofluoric acid systems for impurity removal. The process is simple, environmentally friendly, low in cost, and can be industrialized.

[0032] 2. The preparation method of the biomass hard carbon anode material of the present invention uses biomass as raw material, and obtains hard carbon material through high-temperature carbonization. During the high-temperature carbonization cooling stage, the material is rapidly cooled, and the prepared material retains the morphology at high temperature. The large interlayer spacing increases the specific capacity and facilitates the diffusion rate of sodium ions, thereby improving the kinetic performance.

[0033] 3. The preparation device for biomass hard carbon anode material of the present invention can control the cooling rate during the high-temperature stage, achieve impurity removal and provide a large interlayer spacing, improve the reversible capacity and kinetic performance of the material, and synergistically improve the sodium storage performance of biomass hard carbon material. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the apparatus for preparing the biomass hard carbon anode material of the present invention.

[0036] Figure 2 This is a photograph of the hard carbon material obtained in Example 1 after high-temperature carbonization.

[0037] Figure 3 The first charge-discharge curve of the sodium-ion battery in Example 1 is shown.

[0038] Figure 4 The image shows the SEM image of the hard carbon material obtained by high-temperature carbonization in Comparative Example 1.

[0039] Legend:

[0040] 1. Main air inlet pipe; 2. Air inlet pipe knob; 3. Normal temperature air inlet pipe; 4. Low temperature air inlet pipe; 5. Cooler; 6. Air inlet pipe valve; 7. Air inlet flange; 8. Support frame; 9. Heating furnace tube; 10. Insulation layer; 11. Sagger; 12. Air outlet flange; 13. Feed flange; 14. Pressure gauge; 15. Air outlet pipe valve; 16. Air outlet pipe. Detailed Implementation

[0041] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0042] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0043] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0044] like Figure 1 As shown, the preparation apparatus for the preparation method of biomass hard carbon anode material in the following embodiments and comparative examples includes a main air inlet pipe 1, an air inlet pipe knob 2, a normal temperature air inlet pipe 3, a low temperature air inlet pipe 4, a cooler 5, an air inlet pipe valve 6, an air inlet flange 7, a support frame 8, a heating furnace tube 9, a heat insulation layer 10, a sagger 11, an air outlet flange 12, a feed flange 13, a pressure gauge 14, an air outlet pipe valve 15, and an air outlet pipe 16.

[0045] The heating furnace tube 9 is supported and fixed by the support frame 8. The heating furnace tube 9 is provided with a heat insulation layer 10 on the outside. The two ends of the heating furnace tube 9 are connected by an air inlet flange 7 and an air outlet flange 12.

[0046] The main intake pipe 1 is filled with a protective atmosphere. The intake pipe 1 is equipped with an intake pipe valve 6 to control the opening and closing of the intake port for checking air tightness and vacuuming. The main intake pipe 1 is adjusted by the intake pipe knob 2 to allow the gas to be introduced into the heating furnace tube 9 through the ambient temperature intake pipe 3 or the low temperature intake pipe 4. When heating up, the gas enters the heating furnace tube 9 through the ambient temperature intake pipe 3. When cooling down rapidly, the gas enters the heating furnace tube 9 through the low temperature intake pipe 4. The low temperature intake pipe 4 is cooled by the chiller 5 to improve the cooling rate.

[0047] The gas outlet 16 discharges gas from the heating furnace tube 9. The gas outlet 16 is equipped with a gas outlet valve 15 to control the opening and closing of the gas outlet, so as to check the airtightness and evacuate the vacuum. The pressure gauge 14 observes the pressure of the heating furnace tube 9 to check the airtightness and ensure experimental safety.

[0048] The sagger 11 enters the heating furnace tube 9 through the feed flange 13 and is placed in the middle of the heating furnace tube 9 to ensure uniform heating.

[0049] Example 1:

[0050] A method for preparing a biomass hard carbon anode material includes the following steps:

[0051] Step 1: Soak crushed bamboo (ash content 1.09%, silicon content 0.26%) through a 20-mesh sieve in distilled water for 24 hours, changing the water every 12 hours to prevent biomass fermentation; wash repeatedly with deionized water until the filtrate is clear, then transfer to a forced-air drying oven and dry at 80℃ for 12 hours; pre-carbonize by raising the temperature to 600℃ at 5℃ / min and holding for 2 hours, adding sodium hydroxide solution with a concentration of 0.3mol / L and a solid-liquid ratio of 0.5g / mL to the carbonized material (silicon content 1.02%).

[0052] Step 2: Spread the wet material evenly in the crucible to a thickness of 0.2 cm, and place it in the middle of the heating furnace tube through the feed flange; argon gas is introduced into the heating furnace tube through the main gas inlet pipe and controlled by the gas inlet pipe knob from the ambient temperature gas inlet pipe to provide an inert atmosphere. The high-temperature carbonization temperature is 1500℃, the heating rate is 5℃ / min, the holding time is 2h, and the gas flow rate is 1.5L / min. When cooling, argon gas is introduced into the heating furnace tube through the low-temperature gas inlet pipe and the cooler through the gas inlet pipe knob. The temperature of the cooler is set to 6℃, the gas flow rate is 2L / min, and the cooling rate is 20℃ / min. After cooling to room temperature, the high-temperature carbonization product is obtained.

[0053] Step 3: Physically remove the white impurities from the surface of the prepared hard carbon material; then, perform air jet milling on the physically removed material to obtain a material with a D50 of 9 μm, which is the biomass hard carbon anode material. Testing showed that the ash content was 0.99%, with a silicon content of 0.21%, achieving the purpose of impurity removal. The methods for detecting impurity elements are as follows: Metal impurities: ICP measurement after digestion with perchloric acid and nitric acid; Silicon: ICP measurement after digestion with aqua regia and hydrofluoric acid.

[0054] The macroscopic image of the high-temperature carbonization product prepared in this embodiment is shown below. Figure 2 As shown in the picture, there is a layer of white impurities on the surface of the material, which can be removed by physical means.

[0055] The hard carbon material prepared above is used as the active material of the negative electrode in the preparation of sodium-ion batteries.

[0056] The prepared hard carbon material powder was mixed evenly with acetylene black and PVDF at a mass ratio of 80:10:10. An appropriate amount of organic solvent NMP was added and the mixture was ground to form a slurry. The evenly ground slurry was then uniformly coated onto a current collector copper foil. After drying, the slurry was cut into circular electrode sheets. The electrode sheets were dried at 120°C for 6 hours under vacuum and then transferred to a glove box for later use.

[0057] The simulated battery was assembled in an Ar atmosphere glove box, using metallic sodium as the counter electrode and 1 mole of NaPF6 dissolved in 1 L of a 1:1 volume ratio solution of ethylene carbonate and diethyl carbonate as the electrolyte, to form a CR2032 coin cell. Figure 3 As shown, under the conditions of a discharge cutoff voltage of 0.01V and a charge cutoff voltage of 2.0V, the reversible specific capacity is 322.78mAh / g and the first-cycle coulombic efficiency is 86.23%.

[0058] Example 2:

[0059] A method for preparing a biomass hard carbon anode material includes the following steps:

[0060] Step 1: Soak the crushed bamboo (same as in Example 1) through a 20-mesh sieve in distilled water for 36 hours, changing the water every 12 hours to prevent biomass fermentation; wash repeatedly with deionized water until the filtrate is clear, then transfer it to a forced-air drying oven and dry at 80°C for 12 hours; pre-carbonize the material by raising the temperature to 600°C at 5°C / min and holding for 2 hours, adding sodium hydroxide solution with a concentration of 0.5 mol / L and a solid-liquid ratio of 0.5 g / mL to the carbonized material (same as in Example 1);

[0061] Step 2: Spread the wet material evenly in the crucible to a thickness of 0.15cm, and place it in the middle of the heating furnace tube through the feed flange; introduce nitrogen into the heating furnace tube through the main gas inlet pipe and control it with the gas inlet pipe knob to provide an inert atmosphere. The high-temperature carbonization temperature is 1500℃, the heating rate is 7℃ / min, the holding time is 2h, and the gas flow rate is 1.5L / min. When cooling, introduce nitrogen from the low-temperature gas inlet pipe through the cooler into the heating furnace tube through the gas inlet pipe knob. Control the cooler temperature to 4℃, the gas flow rate to 2L / min, and the cooling rate to 25℃ / min. After cooling to room temperature, the high-temperature carbonization product is obtained.

[0062] Step 3: Physically remove the white impurities from the surface of the prepared hard carbon material. Then, subject the material to airflow milling to obtain a material with a D50 of 9 μm, which is the biomass hard carbon anode material. Testing revealed an ash content of 0.73% and a silicon content of 0.11%, using the same testing method as in Example 1.

[0063] The hard carbon material prepared above was used as the active material for the negative electrode of a sodium-ion battery. Electrochemical charge-discharge tests were conducted, and the preparation process and testing methods were the same as in Example 1. The results are as follows: the reversible specific capacity was 331.23 mAh / g, and the first-cycle coulombic efficiency was 84.89%.

[0064] Example 3:

[0065] A method for preparing a biomass hard carbon anode material includes the following steps:

[0066] Step 1: Soak the crushed bamboo (same as in Example 1) through a 20-mesh sieve in distilled water for 24 hours, changing the water every 12 hours to prevent biomass fermentation; wash repeatedly with deionized water until the filtrate is clear, then transfer it to a forced-air drying oven and dry at 80°C for 12 hours; pre-carbonize the material by raising the temperature to 600°C at 5°C / min and holding for 2 hours, adding sodium hydroxide solution with a concentration of 0.2 mol / L and a solid-liquid ratio of 0.5 g / mL to the carbonized material (same as in Example 1);

[0067] Step 2: Spread the wet material evenly in the crucible to a thickness of 0.35cm, and place it in the middle of the heating furnace tube through the feed flange; argon gas is introduced into the heating furnace tube through the main gas inlet pipe and controlled by the gas inlet pipe knob to provide an inert atmosphere. The high-temperature carbonization temperature is 1400℃, the heating rate is 5℃ / min, the holding time is 2h, and the gas flow rate is 1.5L / min. When cooling, argon gas is introduced into the heating furnace tube through the low-temperature gas inlet pipe and the cooler through the gas inlet pipe knob. The temperature of the cooler is controlled at 8℃, the gas flow rate is 2L / min, and the cooling rate is 17℃ / min. After cooling to room temperature, the high-temperature carbonization product is obtained.

[0068] Step 3: Physically remove the white impurities from the surface of the prepared hard carbon material. Then, subject the physically purified material to airflow milling to obtain a material with a D50 of 9 μm, which is the biomass hard carbon anode material. Testing revealed an ash content of 1.51%, with a silicon content of 0.41%, using the same testing method as in Example 1.

[0069] The hard carbon material prepared above was used as the active material for the negative electrode of a sodium-ion battery. Electrochemical charge-discharge tests were conducted, and the preparation process and testing methods were the same as in Example 1. The results are as follows: the reversible specific capacity was 303.44 mAh / g, and the first-cycle coulombic efficiency was 85.80%.

[0070] Example 4:

[0071] Step 1: Soak the wood (ash content 1.49%, of which silicon content is 0.48%) that has been crushed through a 20-mesh sieve in distilled water for 24 hours, changing the water every 12 hours to prevent biomass fermentation; wash repeatedly with deionized water until the filtrate is clear, then transfer it to a forced-air drying oven and dry at 80℃ for 12 hours; pre-carbonize by raising the temperature to 600℃ at 5℃ / min and holding for 2 hours, adding sodium hydroxide solution with a concentration of 0.6mol / L and a solid-liquid ratio of 0.3g / mL to the carbonized material (silicon content 1.92%);

[0072] Step 2: Spread the wet material evenly in the crucible to a thickness of 0.7cm, and place it in the middle of the heating furnace tube through the feed flange; argon gas is introduced into the heating furnace tube through the main gas inlet pipe and controlled by the gas inlet pipe knob from the ambient temperature gas inlet pipe to provide an inert atmosphere. The high-temperature carbonization temperature is 1500℃, the heating rate is 5℃ / min, the holding time is 2h, and the gas flow rate is 1.5L / min. When cooling, argon gas is introduced into the heating furnace tube through the low-temperature gas inlet pipe and the cooler through the gas inlet pipe knob. The temperature of the cooler is set to 10℃, the gas flow rate is 2L / min, and the cooling rate is 12℃ / min. After cooling to room temperature, the high-temperature carbonization product is obtained.

[0073] Step 3: Physically remove the white impurities from the surface of the prepared hard carbon material. Then, subject the material to airflow milling to obtain a material with a D50 of 9 μm, which is the biomass hard carbon anode material. Testing revealed an ash content of 1.88%, with a silicon content of 0.48%, using the same testing method as in Example 1.

[0074] The hard carbon material prepared above was used as the active material for the negative electrode of a sodium-ion battery. Electrochemical charge-discharge tests were conducted, and the preparation process and testing methods were the same as in Example 1. The results are as follows: the reversible specific capacity was 295.11 mAh / g, and the first-cycle coulombic efficiency was 82.76%.

[0075] Comparative Example 1:

[0076] A method for preparing a biomass hard carbon anode material includes the following steps:

[0077] Step 1: Soak the crushed bamboo (same as in Example 1) through a 20-mesh sieve in distilled water for 24 hours, changing the water every 12 hours to prevent biomass fermentation; wash repeatedly with deionized water until the filtrate is clear, then transfer it to a forced-air drying oven and dry at 80°C for 12 hours; pre-carbonize the material by raising the temperature to 600°C at 5°C / min and holding for 2 hours, adding sodium hydroxide solution with a concentration of 0.3 mol / L and a solid-liquid ratio of 0.5 g / mL to the carbonized material (same as in Example 1);

[0078] Step 2: Spread the wet material evenly in the crucible to a thickness of 0.2 cm, and place it in the middle of the heating furnace tube through the feed flange; argon gas is introduced into the heating furnace tube through the main gas inlet pipe and controlled by the gas inlet pipe knob from the ambient temperature gas inlet pipe to provide an inert atmosphere. The high-temperature carbonization temperature is 1500℃, the heating rate is 5℃ / min, the holding time is 2h, and the gas flow rate is 1.5L / min. When cooling, argon gas is introduced into the heating furnace tube through the low-temperature gas inlet pipe and the cooler through the gas inlet pipe knob. The temperature of the cooler is set to 14℃, the gas flow rate is 1L / min, and the cooling rate is 6℃ / min. After cooling to room temperature, the high-temperature carbonization product is obtained.

[0079] Step 3: The prepared hard carbon material is subjected to air jet milling to obtain a material with a D50 of 9 μm, which is the biomass hard carbon anode material. Testing showed that the ash content was 2.75%, and the silicon content was 0.80%, using the same testing method as in Example 1.

[0080] The biomass hard carbon anode material obtained in this comparative example was characterized by SEM, and the results are as follows: Figure 4 As shown in the SEM image, during the high-temperature carbonization stage, the temperature slowly decreased, and white substances appeared on the surface of the hard carbon material. This indicates that the impurities crystallized slowly during the slow cooling process. The crystals were large and few, adhering to the surface of the hard carbon. The white substances were not visible macroscopically and could not be removed by physical means.

[0081] The hard carbon material prepared above was used as the active material for the negative electrode of a sodium-ion battery. Electrochemical charge-discharge tests were conducted, and the preparation process and testing methods were the same as in Example 1. The results are as follows: the reversible specific capacity was 286.21 mAh / g, and the first-cycle coulombic efficiency was 80.50%.

[0082] The difference between Comparative Example 1 and Example 1 is that the cooling rate during the high-temperature carbonization process is slower. The remaining steps are the same as in Example 1, but the final results show that the product performance in Example 1 is significantly better than that in Comparative Example 1.

[0083] Comparative Example 2:

[0084] A method for preparing a biomass hard carbon anode material includes the following steps:

[0085] Step 1: Soak the crushed bamboo (same as in Example 1) through a 20-mesh sieve in distilled water for 24 hours, changing the water every 12 hours to prevent biomass fermentation; wash repeatedly with deionized water until the filtrate is clear, then transfer it to a forced-air drying oven and dry at 80°C for 12 hours; pre-carbonize the material by raising the temperature to 600°C at 5°C / min and holding for 2 hours, adding sodium hydroxide solution with a concentration of 0.3 mol / L and a solid-liquid ratio of 0.5 g / mL to the carbonized material (same as in Example 1);

[0086] Step 2: Spread the wet material evenly in the crucible to a thickness of 1.2cm, and place it in the middle of the heating furnace tube through the feed flange; argon gas is introduced into the heating furnace tube through the main gas inlet pipe and controlled by the gas inlet pipe knob to provide an inert atmosphere. The high-temperature carbonization temperature is 1500℃, the heating rate is 5℃ / min, the holding time is 2h, and the gas flow rate is 1.5L / min. During cooling, nitrogen and argon gas are introduced into the heating furnace tube through the low-temperature gas inlet pipe and the cooler through the gas inlet pipe knob. The temperature of the cooler is set to 6℃, the gas flow rate is 2L / min, and the cooling rate is 20℃ / min. After cooling to room temperature, the high-temperature carbonization product is obtained.

[0087] Step 3: Physically remove the white impurities from the surface of the prepared hard carbon material. Then, perform air jet milling on the physically removed material to obtain a material with a D50 of 9 μm, which is the biomass hard carbon anode material. Testing showed that the ash content was 2.79%, and the silicon content was 0.82%, using the same testing method as in Example 1.

[0088] The hard carbon material prepared above was used as the active material for the negative electrode of a sodium-ion battery. Electrochemical charge-discharge tests were conducted, and the preparation process and testing methods were the same as in Example 1. The results are as follows: the reversible specific capacity was 278.89 mAh / g, and the first-cycle coulombic efficiency was 79.93%.

[0089] The difference between Comparative Example 2 and Example 1 is that the thickness of the material in the sagger is increased. The rest of the steps are the same as in Example 1, but the final results show that the product performance in Example 1 is significantly better than that in Comparative Example 2.

Claims

1. A method for preparing a biomass hard carbon anode material, characterized in that, Includes the following steps: (1) The biomass raw material is pre-carbonized and then mixed evenly with alkaline solution to obtain wet material; (2) The wet material is carbonized at high temperature in an inert atmosphere and then rapidly cooled to obtain carbonized biomass; the cooling rate is controlled at 10-30℃ / min during rapid cooling; the thickness of the wet material pile is controlled not to exceed 0.8cm during the high-temperature carbonization of the wet material in an inert atmosphere. (3) Physically peel off the crystalline material on the surface of the carbonized biomass and then crush it to obtain the biomass hard carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that, The alkaline solution is a sodium hydroxide solution with a concentration of 0.1-1 mol / L, and the solid-liquid ratio when mixed with the alkaline solution is 0.1-4 g / mL.

3. The preparation method according to claim 1, characterized in that, The carbonization temperature for the high-temperature carbonization is controlled at 1200-1800℃, the heating rate is 2-8℃ / min, and the holding time is 1-4h; the inert atmosphere is nitrogen and / or argon, and the gas flow rate of the inert atmosphere is controlled at 0.1-5L / h.

4. The preparation method according to claim 1, characterized in that, The cooling method during rapid cooling is cold air cooling, with the cold air temperature controlled at 0-15℃ and the airflow rate at 0.5-10L / h.

5. The preparation method according to any one of claims 1-4, characterized in that, The biomass raw material is first subjected to pre-purification and then pre-carbonization. The pre-purification involves soaking, washing, and drying the crushed biomass raw material in distilled water for 1-48 hours, drying at 60-90℃ for 6-24 hours. The pre-carbonization is carried out under an inert atmosphere, with the pre-carbonization temperature controlled at 400-800℃, the heating rate at 2-8℃ / min, and the holding time at 1-4 hours. The inert atmosphere is nitrogen and / or argon, and the gas flow rate of the inert atmosphere is controlled at 0.1-3L / h.

6. The preparation method according to any one of claims 1-4, characterized in that, The ash content in the biomass hard carbon anode material after physical stripping is ≤2.0%.

7. The preparation method according to any one of claims 1-4, characterized in that, The particle size D50 of the pulverized biomass hard carbon anode material is 6-12 μm.

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