A method for rapid preparation of hard carbon anode materials, the resulting products, and sodium-ion batteries

Abstract

This invention discloses a method for rapidly preparing hard carbon anode materials, the resulting product, and a sodium-ion battery, belonging to the field of sodium-ion battery technology. The method includes pretreating biomass materials to obtain a precursor material, and then subjecting the precursor material to Joule heating carbonization under an inert atmosphere to obtain the hard carbon anode material. The pretreatment of the biomass material includes sequential preliminary treatment, pre-carbonization treatment, activation treatment, and post-treatment. This invention utilizes the Joule effect to achieve rapid heating in a very short time, significantly shortening the preparation cycle of hard carbon materials, reducing the energy consumption in the preparation of hard carbon materials in existing technologies, and producing hard carbon materials with excellent electrochemical performance. When applied to sodium-ion batteries, it can effectively improve the reversible capacity, initial coulombic efficiency, and capacity retention after 100 cycles.

Description

Technical Field

[0001] This invention belongs to the field of hard carbon material preparation technology, and more specifically, relates to a method for rapidly preparing hard carbon anode materials from biomass materials based on Joule heating synergistic alkaline activation, the resulting products, and sodium-ion batteries. Background Technology

[0002] Currently, lithium-ion batteries have become the primary energy storage medium for portable electronic devices and electric vehicles. However, limited lithium resources and the ever-increasing demand for energy storage devices have spurred the development of low-cost, high-performance sustainable energy systems. Sodium-ion batteries (SIBs), due to their abundant and widely distributed resources, have attracted significant research interest as cost-effective energy storage devices with potential for large-scale applications.

[0003] Due to their desirable electrochemical properties and low cost, carbon materials are the primary electrode materials for electrochemical energy storage devices. Among various types of carbon materials, hard carbon, as the anode in sodium-ion batteries, exhibits excellent electrochemical properties, including a considerable reversible capacity and a low operating potential (average 0.3V compared to Na+). + Sodium-ion batteries (Na) are currently considered the most promising candidate for anodes in sodium-ion batteries due to their relatively high capacity, low cost, and good scalability.

[0004] In existing technologies, carbonization of biomass materials to prepare hard carbon anode materials typically employs carbonization equipment such as pusher kilns, pot furnaces, and rotary kilns. The pusher kiln operates by using pushers to control airflow and temperature distribution within the furnace, thus controlling the firing process. During firing, fuel burns at the bottom of the kiln, generating hot airflow. The pushers can block this hot airflow, preventing it from flowing within the furnace and thus controlling the temperature. Simultaneously, air above the pushers exchanges with the outside environment, allowing for gas exhaust. However, because pusher kilns typically operate at relatively low temperatures, the firing cycle is usually long, resulting in low carbonization efficiency. Compared to pusher kilns, pot furnaces offer more stable firing quality, less material oxidation loss, higher purity of the calcined material, and higher overall furnace thermal efficiency. However, the furnace body is large and complex, requiring large quantities of steel and various types of refractory bricks, demanding advanced construction techniques, a long construction period, and significant investment. Rotary kilns have a simple structure, high production capacity, and long service life, but they suffer from significant oxidation loss of materials, typically around 10%, which greatly reduces production capacity. Furthermore, because the kiln body rotates around a certain axis and the calcined material rotates inside, it easily causes wear and detachment of the refractory lining, leading to increased ash content and frequent maintenance.

[0005] Limited by equipment and existing conventional carbonization processes, the preparation of hard carbon anode materials currently suffers from problems such as high energy consumption, long processing time, complex processes, and high requirements for production equipment. Furthermore, the prepared hard carbon anode materials also have certain defects, making it difficult for them to fully realize their application performance.

[0006] A search revealed relevant patents regarding rapid preparation methods for hard carbon anode materials. For example, Chinese Patent Publication No. CN116462176A, published on July 21, 2023, is entitled "An Ultra-Fast Preparation Method for Hard Carbon Anode Materials for Sodium-Ion Batteries." This patent discloses a method for preparing hard carbon anode materials for sodium-ion batteries, including (1) pretreatment of biomass raw materials to obtain a hard carbon precursor; (2) purification and drying of the hard carbon precursor to obtain a purified hard carbon precursor; and (3) ultra-fast heat treatment of the purified hard carbon precursor in a protective environment to obtain a hard carbon anode material. In step (1), the pretreatment is drying and pulverizing; in step (2), the purification is washing with water, alcohol solution, acid solution, and alkali solution for 3-24 hours at a purification temperature of 20-80°C; and the rapid heat treatment method in step (3) is based on the Joule heating effect. The protective environment is an inert atmosphere or a vacuum environment.

[0007] This patent document utilizes the Joule heating effect, a simple method with a short carbonization time, while maintaining good electrochemical performance. The resulting biomass-derived sodium-ion battery hard carbon anode material exhibits high initial coulombic efficiency and reversible specific capacity when applied to sodium-ion batteries, solving the problem of sodium-ion battery anode materials struggling to achieve both initial coulombic efficiency and reversible specific capacity. However, on the one hand, the hard carbon material prepared directly through Joule heating has a relatively small number of internal closed pores, resulting in limited capacity improvement. On the other hand, the internal distribution of closed pores in the prepared material is uneven, making it prone to material cracking due to uneven local stress during charge and discharge, leading to loss of active lithium. Summary of the Invention

[0008] 1. The problem to be solved

[0009] The purpose of this invention is to overcome the shortcomings of existing hard carbon materials, such as high energy consumption, long processing time, and complex processes, and to provide a method for rapidly preparing hard carbon anode materials, which effectively solves the above problems.

[0010] Furthermore, the present invention also provides a hard carbon anode material prepared by the above method, which exhibits excellent electrochemical performance. When applied to sodium-ion batteries, it can effectively improve the reversible capacity, initial coulombic efficiency, and capacity retention rate after 100 cycles of the prepared sodium-ion batteries.

[0011] 2. Technical Solution

[0012] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0013] This invention provides a method for rapidly preparing hard carbon anode materials, comprising pretreating biomass materials to obtain precursor materials, and then subjecting the precursor materials to Joule heating carbonization in an inert atmosphere to obtain hard carbon anode materials. This invention utilizes the principle of the Joule effect, i.e., the heat generated by a stable current (defined as the heat generated by a stable current per unit time equal to the product of the square of the current and the resistance of the conductor), to apply a controllable current to a heating carrier, enabling the carrier to rapidly heat up in a very short time, thus shortening the preparation cycle of hard carbon materials and significantly reducing the energy consumption of conventional carbonization devices such as pusher kilns and pot furnaces used in the prior art for carbonizing biomass materials.

[0014] Specifically, to further improve the electrical properties and sodium storage capacity of the obtained hard carbon material, the pretreatment of the biomass material in this invention includes sequential preliminary treatment, pre-carbonization treatment, activation treatment, and post-treatment: wherein:

[0015] The preliminary treatment includes washing, drying and crushing the biomass material. This can remove dust and other impurities from the surface of the biomass and crush it through a 100-mesh sieve, which helps the material to be heated more evenly during the pre-carbonization process.

[0016] Pre-carbonization treatment involves heating and carbonizing pre-treated biomass materials at low temperature under an inert atmosphere to obtain pre-carbonized materials.

[0017] The activation treatment involves mixing the obtained pre-carbonized material with an activator and then subjecting it to Joule heating under an inert atmosphere. By combining Joule heating with activator treatment, the pre-carbonized material undergoes two main processes: firstly, alkali activation etches a microporous structure onto the carbon material surface, and high-temperature treatment increases the closed-pore content, providing more sites for sodium storage and resulting in excellent electrochemical performance of the prepared hard carbon material. Secondly, the instantaneous high-temperature Joule heating rapidly raises the carbon material to a certain temperature, accelerating raw material decomposition and preventing the rapid aggregation of metal impurities at high temperatures, which is beneficial for subsequent impurity removal. Furthermore, the instantaneous high-temperature Joule heating accelerates the diffusion of the alkali activator, promoting a more complete activation reaction and resulting in a more uniform pore size and distribution. This contributes to uniform stress distribution during charge-discharge processes and improves the material's cycle stability. Additionally, it is worth noting that Joule heating at high current densities can induce directional rearrangement of the carbon structure, forming a highly ordered pseudo-graphite structure, thus exhibiting excellent conductivity.

[0018] The post-processing includes acid washing, water washing and drying of the carbon material after ultrafast Joule heating to obtain the precursor material. Acid washing can effectively remove the precursor material.

[0019] As a further improvement of the present invention, the activator is at least one of sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate, and the mass ratio of pre-carbonized material to activator is 1:(0.1~1). By controlling this mass ratio, the number of activated pores inside the material can be effectively controlled, avoiding over-activation or under-activation, which would affect the physicochemical and electrochemical properties of the final hard carbon material.

[0020] As a further improvement of this invention, during the activation treatment, the Joule heating temperature is 700–900°C, the heating rate is 80–200°C / min, and the holding time is 10–30 min. The temperature setting for the activation treatment is crucial. If the temperature is set too high, the reaction rate is too fast, resulting in excessively large pore size and specific surface area, affecting the compaction performance of the final product. If the temperature is set too low, an effective activation reaction cannot occur. Furthermore, the heating rate is also critical. An excessively fast heating rate can easily lead to uneven physical and chemical structures on the material surface and inside, resulting in incomplete or over-carbonization. An excessively slow heating rate will prolong the preparation cycle and affect production efficiency.

[0021] As a further improvement of the present invention, the inert atmosphere is one or more mixed gases selected from nitrogen, argon and helium, and the biomass material is one of ginkgo leaves, bamboo, coconut shells, cotton, nut shells, etc. Using these biomass materials, the material sources are extensive, which can not only provide a good way to dispose of agricultural residues and transform them into high-value battery negative electrode materials, thus improving the resource recycling rate, but also further reduce the manufacturing cost of hard carbon materials.

[0022] As a further improvement of this invention, the pre-carbonization process parameters are as follows: pre-carbonization temperature is 400–600℃; heating rate is 1–5℃ / min; and holding time is 1–5h. Pre-carbonization promotes the pyrolysis of biomass to form carbon materials, effectively improving the uniformity of the reaction between the carbon materials and the activator, avoiding localized over- or under-activation. Furthermore, setting the pre-carbonization temperature within this range ensures a more uniform internal structure of the carbon materials. Lower pre-carbonization temperatures result in excessive volatile substances remaining in the pyrolysis products, affecting subsequent activation efficiency. Excessively high pre-carbonization temperatures lead to significant heat loss and low economic efficiency. Further optimization involves controlling the heating rate to promote uniform pyrolysis of the biomass materials. In addition, the controlled holding time ensures complete pyrolysis of the biomass materials into carbon materials.

[0023] As a further improvement of the present invention, the acid used during pickling is at least one of dilute sulfuric acid, dilute nitric acid, dilute hydrochloric acid, dilute acetic acid, and hydrofluoric acid, with an acid concentration of 1-5 mol / L. This not only removes impurity elements from biomass and improves the purity of the final hard carbon material, effectively reducing the self-discharge of the battery, but also prevents impurity metal elements from being reduced on the negative electrode surface during charging and discharging, thus improving the safety performance of the battery. Furthermore, it can further react with unreacted alkaline activator to eliminate residual alkaline activator, thereby preventing the residual alkaline activator from further activating and etching during final carbonization, which could lead to problems such as excessively large surface area of ​​the hard carbon material and low initial coulombic efficiency.

[0024] As a further improvement of the present invention, the mass ratio of carbon material to acid is 1:(1-5); the pickling time is 0.5-5 hours, and the temperature is 20-70°C. Through optimized design of the pickling process, the present invention can ensure that the ash content of the carbon material is reduced to below 0.2%. Furthermore, after pickling, a water wash is performed to remove residual acid, and then the material is dried, with the drying temperature controlled at 80°C-120°C and the drying time at 6-10 hours.

[0025] As a further improvement of the present invention, the process parameters for Joule heating carbonization of the precursor material are as follows: carbonization temperature of 1100–1500°C, heating rate of 80–200°C / min, and holding time of 10–30 min. By controlling the above process parameters, further rearrangement of carbon atoms is promoted, thereby closing the open pores of the activated etching and increasing the closed pore content of the material. This provides more sites for sodium storage in the material, resulting in the prepared hard carbon material exhibiting excellent electrochemical performance.

[0026] The hard carbon material prepared by the above method has a specific surface area of ​​4–6 m². 2 / g, conductivity ≥25.9S / cm under 25MPa pressure.

[0027] This invention also provides a sodium-ion battery, prepared using the hard carbon material of this invention as the negative electrode material, which simultaneously possesses: an initial charge capacity ≥310 mAh·g -1 The capacity in the slope region (>0.1V) is ≥95mAh·g. -1 Platform capacity (≤0.1V) ≥216mAh·g -1 The initial coulomb efficiency is ≥88%, and the retention rate after 100 cycles is ≥86.7%.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention improves upon existing methods for preparing hard carbon materials by employing a Joule heating-assisted alkali activation method to prepare high-performance hard carbon anode materials. This simplifies the existing preparation process of hard carbon materials, significantly shortens the preparation time, reduces energy consumption, and contributes to energy conservation and improved production efficiency.

[0030] Meanwhile, this invention obtains precursor materials by pre-carbonizing, activating and post-treating biomass materials, and finally performs Joule heating carbonization on the precursor materials in an inert atmosphere. The resulting hard carbon anode material has excellent electrochemical performance, effectively solving the problems of long preparation cycle, large specific surface area, poor conductivity, and low capacity and first coulombic efficiency of hard carbon anode materials.

[0031] Furthermore, the coin cell prepared using the hard carbon material of the present invention as the negative electrode material has a reversible capacity of ≥310mAh / g, an initial coulombic efficiency of ≥88%, and a capacity retention rate of ≥86% after 100 cycles. Attached Figure Description

[0032] Figure 1 SEM image of the hard carbon anode material prepared by Joule heating in Example 1;

[0033] Figure 2 The XRD comparison diagrams are of the hard carbon materials prepared by the Joule heating synergistic alkali activation method and the conventional heating method in Example 1.

[0034] Figure 3 This is a comparison of Raman tests of hard carbon materials prepared by Joule heating synergistic alkali activation method and conventional heating in Example 1;

[0035] Figure 4 This is a comparison of nitrogen adsorption-desorption curves of hard carbon materials prepared by Joule heating synergistic alkali activation method and conventional heating in Example 1;

[0036] Figure 5 This is a schematic diagram of the Joule heating device used in this invention. Detailed Implementation

[0037] This invention provides a method for rapidly preparing hard carbon anode materials, specifically comprising the following steps:

[0038] Step 1: Clean one of the following biomass materials, such as ginkgo leaves, bamboo, coconut shells, cotton, nut shells, etc., with deionized water, dry them, crush them, and then pass them through a 100-mesh sieve.

[0039] Step 2: Place the crushed biomass material from Step 1 into a tube furnace and heat it to 400-600℃ at a heating rate of 1-5℃ / min under an inert atmosphere. Hold the temperature for 1-5 hours to perform pre-carbonization treatment and obtain pre-carbonized material.

[0040] Step 3: Mix the pre-carbonized material and activator from Step 2 at a mass ratio of 1:(0.1~1), and then perform Joule heating treatment under an inert atmosphere. A schematic diagram of the Joule heating device used is shown below. Figure 5 As shown, the temperature is increased to 700–900℃ at a heating rate of 80–200℃ / min and held for 10–30 min. The resulting carbon material and acid are then pickled at a mass ratio of 1:(1–5) at 20–70℃ for 0.5–5 h. The acid used for pickling is at least one of dilute sulfuric acid, dilute nitric acid, dilute hydrochloric acid, dilute acetic acid, and hydrofluoric acid, with an acid concentration of 1–5 mol / L. After pickling, the material is washed with deionized water until neutral, and finally dried at 80–120℃ for 6–10 h to obtain the precursor material.

[0041] Step 4: The precursor material is subjected to Joule heating carbonization treatment in an inert atmosphere. The temperature is increased to the carbonization temperature of 1100-1500℃ at a heating rate of 80-200℃ / min, and held at this temperature for 10-30min to obtain hard carbon anode material.

[0042] The present invention will be further described below with reference to specific embodiments.

[0043] Example 1

[0044] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0045] Step 1: Clean the bamboo biomass material with deionized water, dry it, then crush it and pass it through a 100-mesh sieve.

[0046] Step 2: Place the crushed biomass material from Step 1 into a tube furnace, heat it to 500°C at a heating rate of 2°C / min under an inert atmosphere, and hold it at that temperature for 2 hours to perform pre-carbonization treatment, thereby obtaining pre-carbonized material.

[0047] Step 3: Mix the pre-carbonized material and activator (potassium hydroxide) from Step 2 at a mass ratio of 1:0.5, and then perform Joule heating treatment under an inert atmosphere. Specifically, heat to 850℃ at a rate of 100℃ / min and hold for 20 min. Next, acid-wash the resulting carbon material and acid at a mass ratio of 1:3 at 45℃ for 4 h. The acid used for acid washing is 4 mol / L dilute hydrochloric acid. After acid washing, wash with deionized water until neutral, and finally dry at 80℃ for 10 h to obtain the precursor material.

[0048] Step 4: The precursor material is subjected to Joule heating carbonization treatment in an inert atmosphere, heated to 1400℃ at a heating rate of 100℃ / min, and held for 20min to obtain hard carbon anode material.

[0049] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 4.23 m². 2 / g, tap density is 0.81g / cm³ 3 The conductivity is 30.2 S / cm at a pressure of 25 MPa.

[0050] Example 2

[0051] The preparation method of the hard carbon material in this embodiment is basically the same as that in Example 1. The difference between the two is that in step four, the Joule heating carbonization temperature is 1100°C.

[0052] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 5.79 m². 2 / g, tap density is 0.75g / cm³ 3 The conductivity is 26.8 S / cm at a pressure of 25 MPa.

[0053] Example 3

[0054] The preparation method of the hard carbon material in this embodiment is basically the same as that in Example 1. The difference between the two is that in step four, the Joule heating carbonization temperature is 1500℃.

[0055] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 4.51 m². 2 / g, tap density is 0.79g / cm³ 3 The conductivity is 27.3 S / cm at a pressure of 25 MPa.

[0056] Example 4

[0057] The preparation method of the hard carbon material in this embodiment is basically the same as that in Example 1. The difference between the two is that in step three, the Joule heating temperature is 700°C during the activation treatment.

[0058] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 5.58 m². 2 / g, tap density is 0.76g / cm³ 3 The conductivity is 28.1 S / cm at a pressure of 25 MPa.

[0059] Example 5

[0060] The preparation method of the hard carbon material in this embodiment is basically the same as that in Example 1. The difference between the two is that in step three, the Joule heating temperature is 900°C during the activation treatment.

[0061] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 5.72 m². 2 / g, tap density is 0.77g / cm³ 3 The conductivity is 28.4 S / cm at a pressure of 25 MPa.

[0062] Example 6

[0063] The preparation method of hard carbon material in this embodiment is basically the same as that in Example 1. The difference between the two is that in step three, during the activation treatment, the mass ratio of pre-carbonized material to potassium hydroxide is 1:0.1.

[0064] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 4.37 m². 2 / g, tap density is 0.79g / cm³ 3 The conductivity is 25.9 S / cm at a pressure of 25 MPa.

[0065] Example 7

[0066] The preparation method of the hard carbon material in this embodiment is basically the same as that in Example 1. The difference between the two is that in step three, during the activation treatment, the mass ratio of the pre-carbonized material to potassium hydroxide is 1:1.

[0067] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 5.87 m². 2 / g, tap density is 0.75g / cm³ 3 The conductivity is 27.1 S / cm at a pressure of 25 MPa.

[0068] Comparative Example 1

[0069] The preparation method of the hard carbon material in this comparative example is basically the same as that in Example 1. The difference between Example 1 and Example 1 is that in step three, the pre-carbonized material obtained in step two is pre-carbonized in an argon atmosphere using a conventional heating method. Specifically, the temperature is raised to 850°C at a heating rate of 2°C / min and held for 2 hours.

[0070] In step four, the precursor material is heated to 1400℃ at a heating rate of 2℃ / min under an argon atmosphere and held at that temperature for 2 hours to obtain the hard carbon anode material.

[0071] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 12.54 m². 2 / g, tap density is 0.63g / cm³ 3The conductivity is 18.8 S / cm at a pressure of 25 MPa.

[0072] Comparative Example 2

[0073] The preparation method of the hard carbon material in this comparative example is basically the same as that in Example 1. The difference between this method and Example 1 is that the pre-carbonization treatment in step two is omitted. The biomass material after being crushed in step one is directly mixed with the activator and then subjected to the treatment in steps three and four to obtain the hard carbon anode material.

[0074] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 9.27 m². 2 / g, tap density is 0.68g / cm³ 3 The conductivity is 20.1 S / cm at a pressure of 25 MPa.

[0075] Comparative Example 3

[0076] The preparation method of the hard carbon material in this comparative example is basically the same as that in Example 1. The difference between Example 1 and Example 1 is that the acid washing step in step three is omitted. That is, the pre-carbonized material obtained in step two is subjected to Joule heating treatment with the activator. After cooling, the carbon material obtained is directly used as a precursor to enter step four for processing to obtain the hard carbon anode material.

[0077] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 7.83 m². 2 / g, tap density is 0.70g / cm³ 3 The conductivity is 20.5 S / cm at a pressure of 25 MPa.

[0078] Comparative Example 4

[0079] The preparation method of the hard carbon material in this comparative example is basically the same as that in Example 1. The difference between the two examples is that in step three, the pre-carbonized material obtained in step two is directly subjected to Joule heating treatment without adding an activator. Finally, after step four, the hard carbon anode material is obtained.

[0080] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 8.84 m². 2 / g, tap density is 0.71g / cm³ 3 The conductivity is 21.1 S / cm at a pressure of 25 MPa.

[0081] Comparative Example 5

[0082] The preparation method of the hard carbon material in this comparative example is basically the same as that in Example 1. The difference between Example 1 and Example 1 is that in step four, the precursor material obtained by acid washing in step three is carbonized in an argon atmosphere using a conventional heating method. Specifically, the temperature is raised to 1400°C at a heating rate of 2°C / min and held for 2 hours.

[0083] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 7.52 m². 2 / g, tap density is 0.66g / cm³ 3 The conductivity is 18.5 S / cm at a pressure of 25 MPa.

[0084] Comparative Example 6

[0085] The preparation method of the hard carbon material in this comparative example is basically the same as that in Example 1. The difference between Example 1 and Example 1 is that the amount of activator added is larger, and the mass ratio of activator to pre-carbonized material is 1.5:1.

[0086] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 21.4 m². 2 / g, tap density is 0.56g / cm³ 3 The conductivity is 13.7 S / cm at a pressure of 25 MPa.

[0087] Comparative Example 7

[0088] The preparation method of the hard carbon material in this comparative example is basically the same as that in Example 1. The difference between Example 1 and Example 1 is that during the activation treatment, the temperature is raised to 1000°C at a heating rate of 100°C / min and held for 20min.

[0089] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 36.7 m². 2 / g, tap density is 0.51g / cm³ 3 The conductivity is 15.5 S / cm at a pressure of 25 MPa.

[0090] Comparative Example 8

[0091] The preparation method of the hard carbon material in this comparative example is basically the same as that in Example 1. The difference between Example 1 and Example 1 is that during the activation treatment, the temperature is raised to 600°C at a heating rate of 100°C / min and held for 20min.

[0092] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 5.73 m². 2 / g, tap density is 0.72g / cm³ 3 The conductivity is 11.5 S / cm at a pressure of 25 MPa.

[0093] Comparative Example 9

[0094] The preparation method of the hard carbon material in this comparative example is basically the same as that in Example 1. The difference between the two examples is that during the activation treatment, the temperature is raised to 850°C at a heating rate of 250°C / min and held for 20min.

[0095] The specific surface area of ​​the hard carbon anode material obtained in this comparative example is 8.43 m². 2 / g, tap density is 0.77g / cm³ 3 The conductivity is 24.6 S / cm at a pressure of 25 MPa.

[0096] Example 8

[0097] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0098] Step 1: Clean the ginkgo leaf biomass material with deionized water, dry it, crush it, and then pass it through a 100-mesh sieve.

[0099] Step 2: Place the crushed biomass material from Step 1 into a tube furnace, heat it to 400°C at a heating rate of 1°C / min under an inert atmosphere, and hold it at that temperature for 5 hours to perform pre-carbonization treatment, thereby obtaining pre-carbonized material.

[0100] Step 3: Mix the pre-carbonized material and activator (sodium carbonate) from Step 2 at a mass ratio of 1:0.1, and then perform Joule heating treatment under an inert atmosphere. Specifically, heat to 900℃ at a rate of 200℃ / min and hold for 10 min. Next, acid-wash the resulting carbon material and acid at a mass ratio of 1:1 at 70℃ for 5 h. The acid used for acid washing is 5 mol / L dilute acetic acid. After acid washing, wash with deionized water until neutral, and finally dry at 120℃ for 10 h to obtain the precursor material.

[0101] Step 4: The precursor material is subjected to Joule heating carbonization treatment in an inert atmosphere, heated to 1500℃ at a heating rate of 200℃ / min, and held for 10min to obtain hard carbon anode material.

[0102] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 5.26 m². 2 / g, tap density is 0.76g / cm³ 3 The conductivity is 28.8 S / cm at a pressure of 25 MPa.

[0103] Example 9

[0104] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0105] Step 1: Clean the coconut shell biomass material with deionized water, dry it, then crush it and pass it through a 100-mesh sieve.

[0106] Step 2: Place the crushed biomass material from Step 1 into a tube furnace, heat it to 600°C at a heating rate of 5°C / min under an inert atmosphere, and hold it at that temperature for 1 hour to perform pre-carbonization treatment, thereby obtaining pre-carbonized material.

[0107] Step 3: Mix the pre-carbonized material and activator (sodium hydroxide) from Step 2 at a mass ratio of 1:1, and then perform Joule heating treatment under an inert atmosphere. Specifically, heat to 700℃ at a rate of 80℃ / min and hold for 30 min. Next, acid-wash the resulting carbon material and acid at a mass ratio of 1:5 at 20℃ for 0.5 h. Use 1 mol / L dilute sulfuric acid for acid washing. After acid washing, wash with deionized water until neutral, and finally dry at 90℃ for 8 h to obtain the precursor material.

[0108] Step 4: The precursor material is subjected to Joule heating carbonization treatment in an inert atmosphere, with a heating rate of 80℃ / min to 1100℃ and a holding time of 30min to obtain hard carbon anode material.

[0109] The specific surface area of ​​the hard carbon anode material obtained in this embodiment is 5.13 m². 2 / g, tap density is 0.79g / cm³ 3 The conductivity is 29.6 S / cm at a pressure of 25 MPa.

[0110] The hard carbon anode materials of Examples 1-9 and Comparative Examples 1-9 were used to prepare CR2032 coin cells for electrochemical performance testing. The specific steps were as follows: Hard carbon anode material, PVDF, and SP in a mass ratio of 92:5:3 were added to an appropriate amount of NMP and dispersed using a homogenizer at 2000 rpm for 30 min to obtain a uniform slurry. The slurry was coated onto copper foil, vacuum dried at 110℃ (vacuum degree -80 kPa) for 8 h, and then rolled and punched to prepare the positive electrode sheet. Sodium sheets were used as the anode material, and the electrolyte was a 1 mol / L NaPF6 solution with a solvent of EC and PC in a volume ratio of 1:1. Glass fiber was used as the separator, and the coin cells were assembled in a glove box filled with Ar atmosphere. The charge / discharge voltage range for cycle performance testing was 0.01–2.0 V, and the nominal capacity was 300 mAh / g. The experimental results are shown in Table 1 below.

[0111] Table 1 shows the performance test results of batteries prepared using the hard carbon anode materials obtained in the various embodiments and comparative examples of this invention.

[0112]

[0113] As shown in Table 1, the battery prepared using the hard carbon anode material obtained in the embodiments of the present invention has good reversible specific capacity, high initial coulombic efficiency, and cycle retention rate. Changing any step in the preparation method of the present invention will lead to a decrease in initial coulombic efficiency and cycle performance. Comparative Example 1 is a conventional heating preparation of hard carbon anode material. Compared with the Joule heating synergistic alkaline activation process used in the embodiments of the present invention, the conventionally prepared hard carbon anode material has a significant decrease in initial charge capacity, initial coulombic efficiency, and cycle stability.

[0114] Comparative Examples 2, 3, and 4, after omitting the pre-carbonization, acid washing, and alkali activation steps of the present invention, all resulted in a significant decrease in initial charge capacity, initial coulombic efficiency, and cycle stability.

[0115] In Comparative Example 5, the use of conventional heating methods for carbonization to prepare hard carbon materials resulted in a significant decrease in initial charge capacity, initial coulombic efficiency, and cycle stability.

[0116] The addition of too much activator in Comparative Example 6 resulted in over-activation, leading to an excessively large specific surface area of ​​the resulting hard carbon material. Ultimately, this resulted in a decrease in the initial coulombic efficiency and capacity performance of the prepared sodium-ion battery.

[0117] Comparative Examples 7, 8, and 9 investigated the effects of high and low activation temperatures and excessively high activation temperature heating rates on the performance of the resulting hard carbon materials. Excessively high activation temperatures resulted in excessively large specific surface areas of the resulting hard carbon materials, which did not meet the requirements of this invention. Conversely, excessively low activation temperatures could not effectively activate the materials. Furthermore, excessively high heating rates could easily lead to uneven chemical structures on the surface and inside of the material, affecting the subsequent carbonization effect and ultimately causing a decline in the electrochemical performance of the material.

[0118] Furthermore, it is worth noting that, Figure 1 This is a SEM image of the hard carbon anode material prepared by Joule heating in Example 1. The image shows that the prepared hard carbon material has a relatively uniform particle distribution, a smooth surface, and a particle size D50 of 6–10 μm, which is beneficial for Na… + The de-embedding process improves dynamic performance.

[0119] Figure 2 The XRD patterns of the hard carbon materials prepared by Joule heating synergistic alkali activation and conventional heating in Example 1 are shown. Both samples show two broad peaks, corresponding to the (002) and (100) crystal planes, respectively. Compared with conventional heating, the (002) peak of the carbon material prepared by Joule heating is shifted to the left. According to the Bragg equation, the lattice spacing of the carbon material prepared by Joule heating is increased, which is beneficial to the transport of sodium ions between layers.

[0120] Figure 3 This is a comparison of Raman spectroscopy results for hard carbon materials prepared by the Joule heating synergistic base activation method and conventional heating in Example 1. Both samples exhibit disorder-induced D bands (~1350 cm⁻¹). -1 ) and in-plane vibration G-band (~1600cm) -1 Meanwhile, it was observed that the AD / AG ratio of Joule heating increased from 2.21 to 2.60 compared to conventional heating, indicating that the hard carbon material prepared by Joule heating formed more defects, thus providing more active sites for sodium ion storage.

[0121] Figure 4 This is a comparison of nitrogen adsorption-desorption curves for hard carbon materials prepared by the Joule heating synergistic alkali activation method and conventional heating in Example 1. The materials exhibit typical type II isotherms. The specific surface areas of the samples prepared in Example 1 and Comparative Example 1 are 4.23 m², respectively. 2 / g and 12.54m 2 The / g is mainly attributed to the directional rearrangement of the carbon structure caused by high current density, forming a highly ordered pseudo-graphite structure, thereby reducing the specific surface area.

[0122] More specifically, although exemplary embodiments of the invention have been described herein, the invention is not limited to these embodiments, but includes any and all embodiments modified, omitted, such as combinations between various embodiments, adaptive changes, and / or substitutions, as would be apparent to those skilled in the art from the foregoing detailed description. The limitations in the claims are to be interpreted broadly as used in the language of the claims and are not limited to the examples described in the foregoing detailed description or during the implementation of this application, which should be considered non-exclusive. Any step listed in any method or process claim may be performed in any order and is not limited to the order set forth in the claims. Therefore, the scope of the invention should be determined solely by the appended claims and their legal equivalents, and not by the description and examples given above.

[0123] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the definitions in this specification shall prevail. When a rate, pressure, temperature, time, or other value or parameter is expressed as a range, preferred range, or a range defined by a series of upper and lower preferred values, this shall be understood to specifically disclose all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether such range is disclosed individually. For example, the range 1-50 should be understood to include any number, combination of numbers, or subrange selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50, as well as all decimal values ​​between the integers mentioned above, such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, and 1.9. Regarding subranges, specifically consider "nested subranges" extending from any endpoint of the range. For example, nested sub-ranges of the exemplary range 1-50 may include 1-10, 1-20, 1-30 and 1-40 in one direction, or 50-40, 50-30, 50-20 and 50-10 in another direction.

Claims

1. A method for rapidly preparing hard carbon anode materials, characterized in that, The process includes pretreating biomass materials to obtain precursor materials, and then subjecting the precursor materials to Joule heating carbonization in an inert atmosphere to obtain hard carbon anode materials. The pretreating of biomass materials includes sequential preliminary treatment, pre-carbonization treatment, activation treatment, and post-treatment. Preliminary processing includes washing, drying, and crushing the biomass materials; Pre-carbonization treatment involves heating and carbonizing pre-treated biomass materials at low temperature under an inert atmosphere to obtain pre-carbonized materials. The activation process involves mixing the obtained pre-carbonized material with an activator and then subjecting it to Joule heating under an inert atmosphere. The activator is at least one of sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate, and the mass ratio of precarbonated material to activator is 1:(0.1~1); During the activation treatment, the Joule heating temperature is 700–900℃, the heating rate is 80–200℃ / min, and the holding time is 10–30min; The post-processing includes acid washing, water washing and drying of the carbon material after ultrafast Joule heating to obtain the precursor material.

2. The method for rapidly preparing hard carbon anode materials according to claim 1, characterized in that, The inert atmosphere is one or more mixed gases selected from nitrogen, argon, and helium, and the biomass material is one of ginkgo leaves, bamboo, coconut shells, cotton, nut shells, etc.

3. The method for rapidly preparing hard carbon anode materials according to any one of claims 1-2, characterized in that, The pre-carbonization process parameters are as follows: pre-carbonization temperature is 400-600℃; heating rate is 1-5℃ / min; and holding time is 1-5h.

4. The method for rapidly preparing hard carbon anode materials according to any one of claims 1-2, characterized in that, During pickling, at least one of dilute sulfuric acid, dilute nitric acid, dilute hydrochloric acid, dilute acetic acid, and hydrofluoric acid is used, with an acid concentration of 1–5 mol / L.

5. The method for rapidly preparing hard carbon anode materials according to claim 4, characterized in that, The mass ratio of carbon material to acid is 1:(1~5); the pickling time is 0.5~5h, and the temperature is 20~70℃; during drying, the drying temperature is 80℃~120℃, and the drying time is 6~10hh.

6. The method for rapidly preparing hard carbon anode materials according to any one of claims 1-2, characterized in that, The process parameters for Joule heating carbonization of precursor materials are as follows: carbonization temperature is 1100-1500℃, heating rate is 80-200℃ / min, and holding time is 10-30min.

7. A hard carbon material, characterized in that, It is prepared by the method described in any one of claims 1-6.

8. A sodium-ion battery, characterized in that, A sodium-ion battery prepared using the hard carbon material described in claim 7 as the negative electrode material.

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