Biomass-based hard carbon negative electrode material and preparation method thereof

Abstract

The application discloses a preparation method of a biomass-based hard carbon negative material, and comprises the following steps: (1) one-time pore forming by using a pore forming agent; (2) twice pore forming by using O2 and CO2 in a cycle; (3) coating a carbohydrate on the surface of the twice-pore-formed pyrolytic carbon after pyrolysis to obtain a coated material; and (4) calcining the coated material to obtain the biomass-based hard carbon negative material. The application also provides a biomass-based hard carbon negative material. The biomass-based hard carbon negative material is prepared by the following steps: pore forming by using a pore forming agent, then alternately passing in oxygen and carbon dioxide, and finally coating a carbohydrate, so that the biomass-based hard carbon negative material with high porosity and high slope capacity ratio is obtained; the hard carbon negative material has high capacity, large pore volume, high slope capacity ratio and suitable specific surface area, and has excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and particularly relates to a negative electrode material and its preparation method. Background Technology

[0002] Sodium-ion batteries, as a new generation of energy storage batteries, have rapidly entered the energy storage market due to their high energy storage capacity and fast charge / discharge capabilities. As an excellent high-energy storage battery, the anode material is key to limiting its electrochemical performance. Hard carbon is considered the best anode material for sodium-ion batteries, exhibiting a structure of "short-range order and long-range disorder," possessing a larger interlayer spacing than graphite, making it highly suitable for sodium-ion intercalation and storage. Currently, biomass materials are the main precursors for hard carbon materials. Biomass materials are characterized by low cost and high capacity. Pyrolytic carbon materials can be obtained through low-temperature oxygen-free calcination, and then hard carbon materials can be prepared by high-temperature sintering of the pyrolytic carbon materials. However, hard carbon materials prepared by conventional methods suffer from relatively low capacity, especially a low slope capacity ratio. Furthermore, even if the capacity is increased, the excessively large specific surface area makes it difficult to process into batteries. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a biomass-based hard carbon anode material with high porosity and high slope capacity ratio and its preparation method, so as to solve the technical problems of low capacity, small pore volume, low slope capacity ratio and large specific surface area of ​​biomass-based hard carbon anode materials in the prior art.

[0004] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for preparing a biomass-based hard carbon anode material includes the following steps: (1) Use a pore-forming agent to create pores in the pyrolytic carbon (obtained by anaerobic roasting of biomass materials) to obtain pyrolytic carbon with one-time pore-forming. (2) The primary pore-forming pyrolytic carbon is placed in an inert atmosphere and kept at a first temperature, during which O2 is introduced; the first temperature is 180-280℃; the O2 is introduced and then the first temperature is changed to a second temperature, and it is kept in an inert atmosphere, during which CO2 is introduced; the second temperature is 780-990℃; this step is repeated once or multiple times, and O2 and CO2 are cyclically introduced to treat the pyrolytic carbon to obtain secondary pore-forming pyrolytic carbon; (3) Add the secondary pore-forming pyrolytic carbon to the carbohydrate solution, stir, place it in a hydrothermal reactor, use microwave heating to make the secondary pore-forming pyrolytic carbon and carbohydrates come into uniform contact, raise the temperature to make the carbohydrates pyrolyze and coat the surface of the secondary pore-forming pyrolytic carbon, and obtain the coating material. (4) The coating material is calcined to obtain the biomass-based hard carbon anode material.

[0005] In this invention, biomass materials include bamboo, coconut shells, reeds, walnut shells, etc.

[0006] In the above preparation method, preferably, the secondary pore-forming pyrolytic carbon is used to form pores a third time using a pore-forming agent, and after the third pore-forming, it is subjected to a carbon loading process before being added to a carbohydrate solution. The first carbon loading is carried out by cracking hydrocarbon carbon source gas.

[0007] In the above preparation method, preferably, the pore-forming agent includes one or more of KOH, K2CO3, Na2CO3, and NaOH, the mass ratio of pyrolytic carbon to the pore-forming agent is (95-99.9):(0.1-5), the pore-forming temperature is 800-1000℃, and the pore-forming time is 30-300 min. The use of the above pore-forming agent utilizes alkaline etching to create deep pores. Pore-forming depth is not significant below the above process parameters, while exceeding the above parameters will lead to over-activation, resulting in an increase in large open pores in the material.

[0008] In the above preparation method, preferably, during the first pore-forming stage, the amount of pore-forming agent and / or the pore-forming temperature and / or the pore-forming time are greater than those during the second pore-forming stage. The first pore-forming stage is the main pore-forming process, and the third pore-forming stage is an auxiliary pore-forming process. The third pore-forming stage mainly supplements the second pore-forming stage. Therefore, the process conditions for the third pore-forming stage can be lower than those for the first pore-forming stage to avoid excessively large pores.

[0009] In the above preparation method, preferably, the hydrocarbon carbon source gas includes one or more of methane, ethane, acetylene, and propane; the flow rate of the hydrocarbon carbon source gas is 0.5-1.5 L / min; the introduction time of the hydrocarbon carbon source gas is 30-420 min; and the decomposition temperature of the hydrocarbon carbon source gas is 800-1000℃. During a single carbon loading operation, carbon loading is achieved through the decomposition of the hydrocarbon carbon source gas to repair pores. If the gas flow rate and time are too low, or the temperature is too low, the carbon decomposition effect will be insignificant; if the temperature is too high, an excessively thick carbon coating will form, resulting in an excessively large distance between the closed pores and the material surface, making it difficult for sodium to enter the closed pores under the influence of current.

[0010] This invention employs a three-step pore-forming process. The first pore-forming step creates deep pores on the surface of pyrolytic carbon. The second pore-forming step further creates pores on the pyrolytic carbon surface and within the larger pores created in the first step, increasing porosity and adding more sodium ion adsorption sites. During the second pore-forming step, due to the varying etching effects of carbon dioxide at different sites, some sites may create pores with very small diameters, unsuitable for sodium storage. Therefore, performing a third deep pore-forming step after carbon dioxide etching effectively enlarges these small pores to the point where sodium storage is possible. After the three-step pore-forming process, the material's specific surface area is too large, resulting in many large pores that cannot be repaired by subsequent carbohydrate solutions. Furthermore, the large pores may allow carbohydrates to enter, completely filling the pores and rendering the pore-forming process ineffective. This invention first uses a carbon loading treatment, followed by a first-step vapor deposition process to repair the excessively large pores, transforming them into closed pores that can be processed later. This avoids the low initial coulombic efficiency caused by the presence of excessively large pores and also prevents the direct filling of large pores. The second carbon coating process then closes most of the suitable open pores, transforming them all into closed pores, thereby further improving the material's capacity. This two-step coating process adjusts the porosity of the initial pore-forming stage, further enhancing the material's initial efficiency and capacity.

[0011] Furthermore, the carbon film coating does not cover the active sites caused by oxygen treatment. The interlayer spacing of carbon is sufficient for sodium ions to enter, so it does not affect the binding of sodium ions with active sites. Moreover, for the pores caused by carbon dioxide etching, carbon atoms do not enter the pores during the carbon coating process, but are coated at the pore openings to form closed pores, which is more conducive to sodium storage (pores with excessively large openings cannot achieve stable sodium storage).

[0012] In the above preparation method, preferably, when introducing O2, the O2 gas flow rate is 0.5-1.5 L / min, and the time for a single O2 introduction is 5-60 min; when introducing CO2, the CO2 gas flow rate is 0.5-2.5 L / min, and the time for a single O2 introduction is 10-360 min; when heating from the first temperature to the second temperature, the heating rate is 1-10 °C / min; and step (2) is repeated 2-5 times. If the oxygen and carbon dioxide gas flow rates are less than the above ranges, the effect is very minimal; if the oxygen flow rate is too high, it will cause the material to ignite and burn; while excessive carbon dioxide will cause excessive etching of the material, resulting in an excessively large specific surface area that cannot be reduced by subsequent coating, leading to a decrease in the material's initial coulombic efficiency. Too many repetitions will also cause an excessively large specific surface area. The above-mentioned oxygen and carbon dioxide flow rates and the number of repetitions need to be matched with the first and third pore formations.

[0013] In the above preparation method, preferably, the carbohydrates in the carbohydrate solution include one or more of starch, glucose, maltose, and fructose; the mass concentration of the carbohydrates in the carbohydrate solution is 1-30%; the solvent in the carbohydrate solution is anhydrous ethanol; and the mass ratio of the carbohydrates to the secondary pore-forming pyrolytic carbon is 1:(4-99). When coating with the carbohydrate solution, coating effects are not significant below the above process parameters; above the above parameters, excessive carbon coating will result in an excessively large distance between the closed pores and the material surface, making it difficult for sodium to enter the closed pores under the influence of current.

[0014] In the above preparation method, preferably, the microwave heating power is 1-100 GHz, the hydrothermal pyrolysis temperature of the carbohydrates is 120-200℃, and the time is 0.5-24 h. This invention uses microwave heating, resulting in a better carbon coating effect.

[0015] In the above preparation method, preferably, the calcination temperature is 1100-1600℃, and the calcination time is 0.5-3h. During calcination, if the calcination temperature is below 1100℃, the material's pore structure is less likely to become closed-cell, and if the calcination temperature is above 1600℃, the interlayer spacing of the material is too low, which is not conducive to sodium storage.

[0016] As a general technical concept, the present invention also provides a biomass-based hard carbon anode material prepared by the above-described preparation method.

[0017] The preparation method of biomass-based hard carbon anode material in this invention specifically includes the following steps: S1. Use a pore-forming agent to create pores in pyrolytic carbon to obtain pyrolytic carbon with primary pores.

[0018] S2. Place the pyrolytic carbon from the first pore-forming process in a rotary kiln and heat it to the first temperature at a certain heating rate under an inert atmosphere. During the holding stage, ensure that O2 is introduced under the working state of the inert gas to introduce more oxygen atom functional groups on the surface of the material. After a certain time, stop introducing O2 and change to the second temperature. During the holding stage, ensure that CO2 is introduced under the working state of the inert gas. After a certain time, stop introducing O2 and change the temperature again. Repeat the steps of introducing O2 and CO2 multiple times.

[0019] S3. Use the pore-forming agent to create pores a third time.

[0020] S4. Heat to a certain temperature, introduce a certain amount of hydrocarbon carbon source gas for a period of time, and let it decompose to form a carbon film on the surface of the material. S5. Add the carbohydrate solution together to the reaction vessel, stir, and then use microwave heating to make the two evenly contact each other. The temperature is raised to pyrolyze the carbohydrate material and then coat it to obtain the coated material.

[0021] S6. Calcine the coating material obtained in step S5 to obtain the biomass-based hard carbon anode material.

[0022] The inert gas introduced is one or more of nitrogen, helium, argon, neon, etc. The flow rate of the inert gas is 1.0-4.5 L / min.

[0023] The preparation method of biomass-based hard carbon anode material of the present invention involves alternating the introduction of oxygen and carbon dioxide during the secondary pore-forming process. This not only increases the porosity of the material but also introduces oxygen-containing functional groups to the material surface. The alternating introduction of the two gases effectively prevents over-activation of the material by a single gas, avoiding structural collapse caused by over-activation. The etching effect of carbon dioxide can effectively improve the internal pore structure of the material, increase the porosity, and provide more sodium storage sites; however, excessive pore structure can reduce the kinetic performance of the material to some extent. The pre-oxidation effect of oxygen can effectively introduce oxygen-containing functional groups to the material surface, providing more sodium ion adsorption sites, significantly enhancing the kinetic performance of the material, increasing the slope capacity during charge and discharge, mitigating the etching effect of carbon dioxide, and further improving the sodium storage capacity of the material, effectively solving the problem of low slope capacity in current biomass-based hard carbon materials in the industry. At the same time, during the oxygen introduction process, oxygen also produces a certain pore-forming effect, forming a synergistic effect with carbon dioxide etching.

[0024] Regarding the oxygen introduction process, using an inert gas as a protective agent can effectively prevent the material from burning. Below 180°C, oxygen cannot pre-oxidize the material, and above 280°C, oxygen will cause localized over-oxidation, leading to overall structural collapse and significantly reducing material performance. Regarding the carbon dioxide introduction process, compared to other gases, carbon dioxide's carbon-oxygen bond structure makes it easier to penetrate the material's pores. Below 780°C, the etching effect of carbon dioxide is weak, and above 990°C, the material will be over-etched and activated, forming numerous large pores, resulting in a significant decrease in the material's electrochemical capacity.

[0025] Pore ​​formation (tertiary pore formation) and pre-oxidation can effectively improve the sodium storage capacity and slope capacity of materials, but they can also lead to an excessively large specific surface area, affecting the material processing performance in battery slurry processes. In this invention, a hydrocarbon carbon source gas is first introduced. Taking advantage of the characteristics of hydrocarbon carbon source gas decomposition under high temperature and catalysis, a thin carbon film is coated onto the material surface, thus initially reducing the specific surface area to some extent. Next, carbohydrates are used as a coating agent, mixed with the precursor through stirring. Microwave heating is then used to achieve uniform heating of the material, promoting full and uniform contact between the carbohydrates in the solution and the material, achieving uniform coating of the precursor by the carbohydrates, and avoiding the phenomenon of uneven coating of pyrolytic carbon.

[0026] The specific principle of carbohydrate coating in this invention is as follows: Carbohydrates are mainly composed of C, H, and O elements. Under high pressure (closed reactor) at 120-200℃, their multi-branched long-chain structure gradually transforms into a three-dimensional network chain structure (in which most of the C-O, C=O, and C-H bonds break), and trace amounts of gases such as H2O and CO2 are produced. The final three-dimensional network chain structure is mainly composed of C-C and C=C bonds, containing a small amount of C-O, C=O, and C-H bonds. This three-dimensional network chain structure forms a thin film on the surface of the biomass-based hard carbon material, achieving the coating effect on the material (specifically by...). Figure 1 (As shown).

[0027] Compared with the prior art, the advantages of the present invention are as follows: The preparation method of the biomass-based hard carbon anode material of the present invention involves creating pores with a pore-forming agent, then alternately introducing oxygen and carbon dioxide, and finally coating with carbohydrates to obtain a biomass-based hard carbon anode material with high porosity and high slope capacity ratio. The biomass-based hard carbon anode material has high capacity, large pore volume, high slope capacity ratio, and suitable specific surface area, and has excellent electrochemical performance. Attached Figure Description

[0028] 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.

[0029] Figure 1 This is a TEM image of the biomass-based hard carbon material prepared in Example 1. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The pyrolytic charcoal in the following examples and comparative examples is obtained by anaerobic roasting of biomass materials, such as coconut shells.

[0034] Example 1: A method for preparing a biomass-based hard carbon anode material includes the following steps: Mix 600g of pyrolytic carbon with 20g of NaOH, heat to 900℃ and hold for 300min to create a single pore, thus obtaining a single-pore pyrolytic carbon.

[0035] The primary pore-forming pyrolysis carbon was placed in a rotary kiln, and nitrogen was introduced at a rate of 2.0 L / min. The temperature was increased to 200 °C at a rate of 3 °C / min. After reaching 200 °C, oxygen was introduced at a rate of 0.8 L / min for 25 min. Then, the oxygen was stopped, and the temperature was increased to 800 °C at a rate of 3 °C / min. After reaching 800 °C, carbon dioxide was introduced at a rate of 1.5 L / min for 240 min. Then, the carbon dioxide was stopped, and the furnace cavity was cooled to 200 °C. Oxygen was then introduced at a rate of 0.8 L / min for 25 min. The above gas introduction steps were repeated three times to obtain secondary pore-forming pyrolysis carbon.

[0036] 400g of secondary pore-forming pyrolytic carbon was mixed with 5g of NaOH and heated to 800℃ and held for 100min to form pores for the third time, thus obtaining tertiary pore-forming pyrolytic carbon.

[0037] The pyrolytic carbon with 3-stage pore formation was placed in a rotary kiln, and the kiln was heated to 900°C. Methane gas was then introduced at a rate of 1.0 L / min for 180 min. After cooling, a precursor containing more oxygen atom functional groups and initially coated was obtained.

[0038] Add 50g of starch to 2000mL of anhydrous ethanol and mix. Stir to obtain a carbohydrate solution and place the solution in a reaction vessel.

[0039] 200g of precursor carbon was added to a reaction vessel containing a carbohydrate solution. After stirring, the mixture was heated to 150℃ using a microwave at 50GHz and kept at that temperature for 20 hours to allow the carbohydrates to react and then coat the surface of the precursor, thus obtaining the coated material.

[0040] The above-mentioned coating material was calcined at 1300℃ for 2 hours to obtain a biomass-based hard carbon anode material (TEM image as shown). Figure 1 (As shown).

[0041] The specific surface area of ​​the above-mentioned biomass-based hard carbon anode material was determined to be 4.58 m² using the static volumetric method. 2 / g, the total pore volume of the material is 0.065cm³. 3 / g.

[0042] The above-mentioned biomass-based hard carbon anode material was fabricated into a coin cell according to the following steps: Biomass-based hard carbon anode material, PVDF, and acetylene black were mixed and ground in a mass ratio of 90:5:5. After grinding for 5 minutes, polyvinylidene fluoride binder was added dropwise, and grinding continued for another 5 minutes until a thin slurry was obtained. The ground slurry was uniformly coated onto the surface of aluminum foil with a thickness of 100 μm, dried at 120°C, and then sliced ​​to obtain the battery anode sheet. In a glove box under oxygen- and water-free conditions, the anode battery casing, the aforementioned anode sheet, separator, electrolyte, sodium sheet (counter electrode), and positive electrode battery casing were assembled in sequence. After assembly, the battery was compacted using a small hydraulic press to obtain the battery. After the battery was left to stand naturally for 6 hours, its electrochemical performance was tested using an electrochemical testing system.

[0043] According to the test, the battery has an initial coulombic efficiency of 90%, an initial reversible specific capacity of 351.6 mAh / g, and a ramp capacity ratio of 41.6%.

[0044] Example 2: A method for preparing a biomass-based hard carbon anode material includes the following steps: Mix 600g of pyrolytic carbon with 15g of KOH, heat to 860℃ and hold for 230min to create a single pore, thus obtaining a single-pore pyrolytic carbon.

[0045] The primary pore-forming pyrolysis carbon was placed in a rotary kiln, and nitrogen was introduced at a rate of 2.0 L / min. The temperature was increased to 190°C at a rate of 3°C / min. After reaching 190°C, oxygen was introduced at a rate of 1.0 L / min for 45 min. Then, the oxygen was stopped, and the temperature was increased to 850°C at a rate of 3°C / min. After reaching 850°C, carbon dioxide was introduced at a rate of 1.8 L / min for 190 min. Then, the carbon dioxide was stopped, and the furnace cavity was cooled to 190°C. Oxygen was then introduced at a rate of 1.0 L / min for 45 min. The above gas introduction steps were repeated four times to obtain secondary pore-forming pyrolysis carbon.

[0046] 400g of secondary pore-forming pyrolytic carbon was mixed with 8g of KOH and heated to 810℃ and held for 130min to form pores for the third time, thus obtaining tertiary pore-forming pyrolytic carbon.

[0047] The pyrolytic carbon with 3-stage pore formation was placed in a rotary kiln, and the rotary kiln was heated to 950°C. Propane gas was then introduced at a rate of 0.7 L / min for 200 min. After cooling, a precursor containing more oxygen atom functional groups and initially coated was obtained.

[0048] Add 40g of glucose to 2000mL of anhydrous ethanol and mix. Stir to obtain a carbohydrate solution and place the solution in a reaction vessel.

[0049] 200g of precursor was added to a reaction vessel containing a carbohydrate solution, stirred, and then heated to 130℃ using a microwave at 50GHz and held for 16h to allow the carbohydrates to react and then coat the surface of the precursor, thus obtaining the coated material.

[0050] The above-mentioned coating material is calcined at 1200℃ for 1.5 hours to obtain biomass-based hard carbon anode material.

[0051] The specific surface area of ​​the above-mentioned biomass-based hard carbon anode material was determined to be 5.87 m² using the static volumetric method. 2 / g, the total pore volume of the material is 0.059cm³. 3 / g.

[0052] The above-mentioned biomass-based hard carbon anode material was made into a button cell according to the steps in Example 1. After testing, the initial coulombic efficiency of the above cell was 89%, the initial reversible specific capacity was 348.8 mAh / g, and the slope capacity ratio was 40.3%.

[0053] Example 3: A method for preparing a biomass-based hard carbon anode material includes the following steps: 600g of pyrolytic carbon was mixed with 28g of Na2CO3 and heated to 840℃ and held for 170min to create a single pore, thus obtaining a single-pore pyrolytic carbon.

[0054] The primary pore-forming pyrolysis carbon was placed in a rotary kiln, and nitrogen was introduced at a rate of 2.0 L / min. The temperature was increased to 250°C at a rate of 5°C / min. After reaching 250°C, oxygen was introduced at a rate of 0.5 L / min for 38 min. Then, the oxygen was stopped, and the temperature was increased to 920°C at a rate of 5°C / min. After reaching 920°C, carbon dioxide was introduced at a rate of 2.0 L / min for 260 min. Then, the carbon dioxide was stopped, and the furnace cavity was cooled to 250°C. Oxygen was then introduced at a rate of 0.5 L / min for 38 min. The above gas introduction steps were repeated four times to obtain secondary pore-forming pyrolysis carbon.

[0055] 400g of secondary pore-forming pyrolytic carbon was mixed with 11g of Na2CO3 and heated to 800℃ and held for 130min to form pores for the third time, thus obtaining pyrolytic carbon with pores formed for the third time.

[0056] The pyrolytic carbon with 3-stage pore formation was placed in a rotary kiln, and the rotary kiln was heated to 850°C. Then, acetylene gas was introduced at a rate of 1.2 L / min for 80 min. After cooling, a precursor containing more oxygen atom functional groups and initially coated was obtained.

[0057] Add 40g of fructose to 2000mL of anhydrous ethanol and mix. Stir to obtain a carbohydrate solution and place the solution in a reaction vessel.

[0058] 500g of precursor was added to a reaction vessel containing a carbohydrate solution, stirred, and then heated to 130℃ using a microwave at 70GHz and held for 20h to allow the carbohydrates to react and then coat the surface of the precursor, thus obtaining the coated material.

[0059] The above-mentioned coating material is calcined at 1400℃ for 2 hours to obtain biomass-based hard carbon anode material.

[0060] The specific surface area of ​​the above-mentioned biomass-based hard carbon anode material was determined to be 4.68 m² using the static volumetric method. 2 / g, the total pore volume of the material is 0.063cm³. 3 / g.

[0061] The above-mentioned biomass-based hard carbon anode material was made into a button cell according to the steps in Example 1. After testing, the initial coulombic efficiency of the above cell was 89%, the initial reversible specific capacity was 352.4 mAh / g, and the slope capacity ratio was 42.1%.

[0062] Example 4: A method for preparing a biomass-based hard carbon anode material includes the following steps: Mix 600g of pyrolytic carbon with 20g of K2CO3, heat to 980℃ and hold for 230min to create a single pore, thus obtaining a single-pore pyrolytic carbon.

[0063] The primary pore-forming pyrolysis carbon was placed in a rotary kiln, and nitrogen was introduced at a rate of 2.0 L / min. The temperature was increased to 260°C at a rate of 3°C / min. After reaching 260°C, oxygen was introduced at a rate of 0.7 L / min for 16 min. Then, the oxygen was stopped, and the temperature was increased to 820°C at a rate of 3°C / min. After reaching 820°C, carbon dioxide was introduced at a rate of 1.7 L / min for 160 min. Then, the carbon dioxide was stopped, and the furnace cavity was cooled to 260°C. Oxygen was then introduced at a rate of 0.7 L / min for 16 min. The above gas introduction steps were repeated three times to obtain secondary pore-forming pyrolysis carbon.

[0064] 400g of secondary pore-forming pyrolytic carbon was mixed with 9g of K2CO3 and heated to 870℃ and held for 180min to form pores for the third time, thus obtaining pyrolytic carbon with pores formed for the third time.

[0065] The pyrolytic carbon with 3-stage pore formation was placed in a rotary kiln, and the rotary kiln was heated to 980°C. Then, a bowl of gas was introduced at a rate of 0.7 L / min for 30 min. After cooling, a precursor containing more oxygen atom functional groups and initially coated was obtained.

[0066] Add 30g of maltose to 2000mL of anhydrous ethanol and mix. Stir to obtain a carbohydrate solution and place the solution in a reaction vessel.

[0067] 300g of precursor was added to a reaction vessel containing a carbohydrate solution. After stirring, the mixture was heated to 200℃ using microwave at 80GHz and held for 12 hours to allow the carbohydrates to react and coat the surface of the precursor, thus obtaining a coated material. The coated material was then calcined at 1600℃ for 3 hours to obtain a biomass-based hard carbon anode material.

[0068] The specific surface area of ​​the above-mentioned biomass-based hard carbon anode material was determined to be 5.02 m² using the static volumetric method. 2 / g, the total pore volume of the material is 0.067cm³. 3 / g.

[0069] The above-mentioned biomass-based hard carbon anode material was made into a button cell according to the steps in Example 1. After testing, the initial coulombic efficiency of the above cell was 89%, the initial reversible specific capacity was 358.6 mAh / g, and the slope capacity ratio was 38.6%.

[0070] Example 5: A method for preparing a biomass-based hard carbon anode material without hydrocarbon gas coating is described. The main difference between this method and Example 1 is that it does not involve a single carbon coating process (hydrocarbon gas pyrolysis), while all other conditions remain the same.

[0071] The specific surface area of ​​the above-mentioned biomass-based hard carbon anode material was determined to be 24.31 m² using the static volumetric method. 2 / g, the total pore volume of the material is 0.066cm³. 3 / g.

[0072] The above-mentioned biomass-based hard carbon anode material was made into a button cell according to the steps in Example 1. After testing, the initial coulombic efficiency of the above cell was 81%, the initial reversible specific capacity was 342.1 mAh / g, and the slope capacity ratio was 39.9%.

[0073] Example 6: A method for preparing a biomass-based hard carbon anode material without three-stage pore formation is described. The main difference between this method and Example 1 is that it does not involve three-stage pore formation, while all other conditions remain the same.

[0074] The specific surface area of ​​the above-mentioned biomass-based hard carbon anode material was determined to be 4.25 m² using the static volumetric method. 2 / g, the total pore volume of the material is 0.048cm³. 3 / g.

[0075] The above-mentioned biomass-based hard carbon anode material was made into a button cell according to the steps in Example 1. After testing, the initial coulombic efficiency of the above cell was 86%, the initial reversible specific capacity was 302.1 mAh / g, and the slope capacity ratio was 39.1%.

[0076] Example 7: A method for preparing a biomass-based hard carbon anode material without hydrocarbon gas coating and three-stage pore formation is disclosed. The main difference between this method and Example 1 is that it does not involve a single carbon coating (hydrocarbon gas pyrolysis) and three-stage pore formation, while all other conditions remain the same.

[0077] The specific surface area of ​​the above-mentioned biomass-based hard carbon anode material was determined to be 19.76 m² using the static volumetric method. 2 / g, the total pore volume of the material is 0.053cm³. 3 / g.

[0078] The above-mentioned biomass-based hard carbon anode material was made into a button cell according to the steps in Example 1. After testing, the initial coulombic efficiency of the above cell was 83%, the initial reversible specific capacity was 316.9 mAh / g, and the slope capacity ratio was 38.7%.

[0079] Comparative Example 1: A method for preparing a biomass-based hard carbon anode material that does not employ hydrocarbon gas and carbohydrate coating differs from Example 1 mainly in that it does not undergo primary carbon coating (hydrocarbon gas pyrolysis) and secondary carbon coating (carbohydrate pyrolysis), while all other conditions remain the same.

[0080] The specific surface area of ​​the above-mentioned biomass-based hard carbon anode material was determined to be 57.86 m² using the static volumetric method. 2 / g, the total pore volume of the material is 0.068cm³. 3 / g.

[0081] The above-mentioned biomass-based hard carbon anode material was made into a button cell according to the steps in Example 1. After testing, the initial coulombic efficiency of the above cell was 72%, the initial reversible specific capacity was 335.7 mAh / g, and the slope capacity ratio was 38.4%.

[0082] Comparative Example 2: A method for preparing a negative electrode material that does not employ carbon dioxide pore-forming and oxygen pre-oxidation treatment differs from Example 1 mainly in that it does not involve secondary pore-forming, while all other conditions remain the same.

[0083] The specific surface area of ​​the above-mentioned biomass-based hard carbon anode material was determined to be 3.98 m² using the static volumetric method. 2 / g, the total pore volume of the material is 0.038cm³. 3 / g.

[0084] The above-mentioned biomass-based hard carbon anode material was made into a button cell according to the steps in Example 1. After testing, the initial coulombic efficiency of the above cell was 87%, the initial reversible specific capacity was 289.7 mAh / g, and the slope capacity ratio was 30.1%.

[0085] Comparative Example 3: A method for preparing a negative electrode material without primary pore formation is described. The main difference between this method and Example 1 is that it does not involve primary pore formation, while all other conditions remain the same.

[0086] The specific surface area of ​​the above-mentioned biomass-based hard carbon anode material was determined to be 4.03 m² using the static volumetric method. 2 / g, the total pore volume of the material is 0.049cm³. 3 / g.

[0087] The above-mentioned biomass-based hard carbon anode material was made into a button cell according to the steps in Example 1. After testing, the initial coulombic efficiency of the above cell was 87%, the initial reversible specific capacity was 300.4 mAh / g, and the slope capacity ratio was 39.1%.

[0088] Table 1 compares the battery electrochemical performance test results of Examples 1-7 with those of Comparative Examples 1-3.

[0089] Table 1: Comparison of Battery Electrochemical Performance Test Results

[0090] As shown in the table above, the electrochemical performance of Examples 5-7 decreased significantly compared to Example 1. Comparative Examples 1-3 also showed the same decreasing trend compared to Example 1.

Claims

1. A method for preparing a biomass-based hard carbon anode material for sodium-ion batteries, characterized in that, Includes the following steps: (1) Use a pore-forming agent to create pores in pyrolytic carbon to obtain pyrolytic carbon with one-time pore-forming. (2) The primary pore-forming pyrolytic carbon is placed in an inert atmosphere and kept at a first temperature, during which O2 is introduced; the first temperature is 180-280℃; the O2 is introduced and then the first temperature is changed to a second temperature, and it is kept in an inert atmosphere, during which CO2 is introduced; the second temperature is 780-990℃; this step is repeated once or multiple times, and O2 and CO2 are cyclically introduced to treat the pyrolytic carbon to obtain secondary pore-forming pyrolytic carbon; (3) Add the secondary pore-forming pyrolytic carbon to the carbohydrate solution, stir, place it in a hydrothermal reactor, use microwave heating to make the secondary pore-forming pyrolytic carbon and carbohydrates come into uniform contact, raise the temperature to make the carbohydrates pyrolyze and coat the surface of the secondary pore-forming pyrolytic carbon, and obtain the coating material. (4) The coating material is calcined to obtain the biomass-based hard carbon anode material; The pyrolytic carbon from the secondary pore-forming process is then used to create pores a third time using a pore-forming agent. After the third pore-forming process, the carbon is loaded once more before being added to a carbohydrate solution. The first carbon loading is achieved by cracking hydrocarbon carbon source gas.

2. The preparation method according to claim 1, characterized in that, The pore-forming agent includes one or more of KOH, K2CO3, Na2CO3, and NaOH. The mass ratio of the pyrolytic carbon to the pore-forming agent is (95-99.9):(0.1-5). The pore-forming temperature is 800-1000℃, and the pore-forming time is 30-300 min.

3. The preparation method according to claim 2, characterized in that, During the first pore formation, the amount of pore-forming agent used and / or the pore-forming temperature and / or the pore-forming time are greater than those used in the second pore formation.

4. The preparation method according to claim 1, characterized in that, The hydrocarbon carbon source gas includes one or more of methane, ethane, acetylene, and propane. The flow rate of the hydrocarbon carbon source gas is 0.5-1.5 L / min, the introduction time of the hydrocarbon carbon source gas is 30-420 min, and the decomposition temperature of the hydrocarbon carbon source gas is 800-1000℃.

5. The preparation method according to claim 1, characterized in that, When introducing O2, the O2 gas flow rate is 0.5-1.5 L / min, and the time for introducing O2 once is 5-60 min; when introducing CO2, the CO2 gas flow rate is 0.5-2.5 L / min, and the time for introducing CO2 once is 10-360 min; when heating from the first temperature to the second temperature, the heating rate is 1-10℃ / min; the number of times step (2) is repeated is 2-5 times.

6. The preparation method according to any one of claims 1-5, characterized in that, The carbohydrates in the carbohydrate solution include one or more of starch, glucose, maltose, and fructose. The mass concentration of the carbohydrates in the carbohydrate solution is 1-30%. The solvent of the carbohydrate solution is anhydrous ethanol. The mass ratio of the carbohydrates to the secondary pore-forming pyrolytic carbon is 1:(4-99).

7. The preparation method according to any one of claims 1-5, characterized in that, The temperature for hydrothermal pyrolysis of carbohydrates is 120-200℃, and the time is 0.5-24h.

8. The preparation method according to any one of claims 1-5, characterized in that, The calcination temperature is 1100-1600℃, and the calcination time is 0.5-3h.

9. A biomass-based hard carbon anode material prepared by any one of claims 1-8.

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