Method for preparing hard carbon negative material by activating lignite with ferric chloride and application of the hard carbon negative material in sodium ion battery

Abstract

The application discloses a method for preparing hard carbon negative materials from lignite activated by ferric chloride and application of the hard carbon negative materials in sodium ion batteries. The method comprises the following steps: firstly, pretreating the lignite by washing, drying and crushing to remove surface impurities; then, mixing the lignite with anhydrous ferric chloride as an activator, and performing one-step carbonization / activation treatment; finally, purifying the lignite by dilute acid washing to obtain lignite-derived hard carbon negative materials with good sodium storage performance. The method has the characteristics of low-cost raw materials, simple process, low carbonization temperature and low cost, and realizes high-value utilization of low-rank coal resources. The lignite-based hard carbon negative materials prepared by the method have high initial coulombic efficiency, high reversible specific capacity and excellent cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries and relates to a method for preparing a hard carbon anode material, specifically a method for preparing a hard carbon anode material by activating lignite with ferric chloride and its application in sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries, due to their abundant sodium resources, low cost, and good safety, have shown broad application prospects in the field of large-scale energy storage. Hard carbon materials, with their advantages of high sodium storage capacity and good cycle stability, are considered the most commercially promising anode materials for sodium-ion batteries. Currently, the precursors for hard carbon mainly include biomass (coconut shells, straw, fruit shells, etc.), resins, and coal-based raw materials. Among them, lignite, as a low-rank coal, is abundant and extremely inexpensive (approximately 100-300 yuan / ton), making it an ideal precursor for preparing hard carbon anodes. However, direct carbonization of lignite easily produces a partially graphitized structure with a small carbon interlayer spacing (<0.37 nm), which is not conducive to the reversible insertion / extraction of sodium ions.

[0003] Chemical activation is an effective means of controlling the pore structure of carbon materials. Commonly used activators include KOH, NaOH, ZnCl2, and H3PO4, but these methods have problems such as high activation temperature, strong corrosivity, and low yield. In recent years, transition metal chlorides (such as FeCl3, CuCl2, and NiCl2) have attracted attention as a new type of activator. Among them, FeCl3 has the following advantages: (1) strong oxidizing power, which can react with carbon precursors at lower temperatures; (2) the reduction product Fe 0 It can be easily removed by acid; (3) It is inexpensive and environmentally friendly. However, there are currently no reports on the preparation of hard carbon anode materials for sodium-ion batteries using FeCl3-activated lignite. Summary of the Invention

[0004] This invention provides a method for preparing hard carbon anode materials by activating lignite with ferric chloride and its application in sodium-ion batteries. The method utilizes the redox reaction between FeCl3 and lignite at high temperature, where FeCl3... 3+ Reduced to Fe 0 Simultaneously, HCl gas is released to etch the carbon skeleton, forming abundant micropores and defect structures, and expanding the carbon layer spacing. This invention uses inexpensive lignite as raw material and employs a one-step FeCl3 activation method, which features inexpensive raw materials, simple process, low carbonization temperature, and low cost, realizing the high-value utilization of low-rank coal resources. Using this method, lignite-based hard carbon anode materials with high initial coulombic efficiency, high reversible specific capacity, and excellent cycle stability can be prepared.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing hard carbon anode materials from lignite activated with ferric chloride involves first pretreating the lignite by washing, drying, and crushing to remove surface impurities. Then, anhydrous ferric chloride is used as an activator, mixed with the lignite, and subjected to a one-step carbonization / activation treatment. Finally, the mixture is purified by washing with dilute acid to obtain lignite-derived hard carbon anode materials with good sodium storage performance. The method includes the following steps:

[0007] Step (1) Pretreatment: The lignite is ultrasonically washed sequentially with deionized water and anhydrous ethanol to remove impurities from the surface of the material. After ultrasonic treatment, it is dried in a forced-air drying oven. The dried lignite is then crushed to obtain lignite powder, wherein: the lignite is low-rank lignite with a carbon content of 50-70 wt%, a volatile matter content of 25-45 wt%, and an ash content of 5-20 wt%; the ultrasonic washing time is 0.5-2 h; the drying temperature is 60-80℃ and the time is 6-12 h.

[0008] Step (2) Mixing: Mix the lignite powder obtained in step (1) with anhydrous ferric chloride evenly, wherein: the mass ratio of lignite powder to anhydrous ferric chloride is 1:1 to 1:6, preferably 1:2 to 1:4; the lignite powder is sieved through a 30 to 50 mesh sieve, and the anhydrous ferric chloride powder is sieved through a 50 to 100 mesh sieve.

[0009] Step (3) Carbonization / Activation: The mixed powder obtained in step (2) is placed in a tube furnace, a protective gas is introduced, and carbonization is carried out. After the tube furnace is cooled to room temperature, the carbonization product of lignite is obtained, wherein: the protective gas is nitrogen or argon, the heating rate is 1~10℃ / min, preferably 2~8℃ / min, the carbonization temperature is 700~1100℃, preferably 800~1000℃, and the holding time is 1~5 h, preferably 2~4 h;

[0010] Step (4) Acid washing and purification: The carbonized product obtained in step (3) is transferred to a dilute hydrochloric acid or dilute sulfuric acid solution and stirred. Then, it is washed with deionized water and filtered until pH=7. Finally, the material obtained by filtration is placed in a drying oven to dry, and lignite-derived hard carbon anode material is obtained. The concentration of dilute hydrochloric acid or dilute sulfuric acid is 0.1~1.0 mol / L, the stirring time is 6~24 h, preferably 8~16 h, the stirring speed is 200~400 rpm, the drying temperature is 100~150℃, and the time is 8~16 h. The specific surface area of ​​the lignite-derived hard carbon anode material is 400~900 m². 2 / g, with an interlayer spacing of 0.38~0.42 nm and an average pore size of 1.5~3.5 nm.

[0011] Application of a lignite-derived hard carbon anode material prepared by the above method in the anode of sodium-ion batteries.

[0012] The design concept of this invention is to use lignite as a carbon precursor and anhydrous ferric chloride as an activator. During the high-temperature carbonization process, FeCl3 undergoes a redox reaction with lignite, and Fe... 3+ Reduced to Fe 0 Simultaneously, HCl gas is released. The escaping HCl gas chemically etches the carbon framework, forming abundant micropores and mesopores. The generated nano-iron particles dispersed in the carbon matrix can inhibit the orderly stacking of carbon layers and expand the interlayer spacing. Furthermore, the catalytic effect of FeCl3 promotes the release of volatiles and the formation of cross-linked structures in lignite. Subsequent acid washing removes residual elemental iron and impurities, yielding pure hard carbon material. By controlling the ratio of FeCl3 to lignite, the carbonization temperature, and the time, precise control over the pore structure and interlayer spacing of hard carbon can be achieved, resulting in excellent sodium storage performance.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. Low-temperature carbonization: Utilizing the strong oxidizing and catalytic properties of FeCl3, efficient carbonization and activation of lignite can be achieved at low temperatures of 700~1100℃, which significantly reduces energy consumption compared to traditional hard carbon preparation (usually ≥1300℃).

[0015] 2. One-step process: Carbonization and activation are completed simultaneously, without the need for additional pre-oxidation or pre-carbonization steps. The process is simple and suitable for industrial production.

[0016] 3. Adjustable pore structure: By adjusting the ratio of FeCl3 to lignite (1:1~1:6), the specific surface area of ​​hard carbon (400~900 m²) can be adjusted. 2 Precise control of (g / g) and pore size distribution (1.5~3.5 nm).

[0017] 4. Excellent performance: The prepared lignite-based hard carbon anode material has a large interlayer spacing (0.38~0.42 nm), abundant defect sites, and a reasonable pore structure. At 20 mA g... -1 Reversible capacity at current density reaches 290~330 mAh g -1 The initial coulomb efficiency is 82-89%, at 1 Ag. -1 After 2000 cycles at a current density, the capacity retention rate is >87%, and after 1000 cycles, the capacity retention rate still reaches over 80%.

[0018] 5. Low cost: The price of lignite raw material is about 100-300 yuan / ton, and the price of FeCl3 is about 3000-5000 yuan / ton. The overall cost is far lower than that of biomass-based and resin-based hard carbon. Attached Figure Description

[0019] Figure 1This is a transmission electron microscope (TEM) image of the lignite-based hard carbon anode material for sodium-ion batteries prepared in Example 1.

[0020] Figure 2 The first charge-discharge curve of the lignite-based hard carbon anode material prepared in Example 1 at a current density of 20 mA / g is shown.

[0021] Figure 3 The graph shows the cycling performance of the lignite-based hard carbon anode material prepared in Example 1 at a current density of 1 A / g. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0023] Example 1

[0024] This embodiment provides a method for preparing hard carbon anode materials by activating lignite with ferric chloride, the method comprising the following steps:

[0025] (1) Pretreatment: The lignite (carbon content of about 62 wt%, ash content of about 14 wt%, and volatile matter of about 36 wt%) was washed sequentially with deionized water and anhydrous ethanol for 0.5 h each to remove impurities from the surface of the material. After the ultrasonic treatment was completed, it was placed in a forced-air drying oven and dried at 70℃ for 10 h. The dried lignite was crushed and passed through a 40-mesh sieve to obtain lignite powder.

[0026] (2) Mixing: Mix the lignite powder obtained in step (1) with anhydrous ferric chloride (analytical grade, passed through an 80-mesh sieve) at a mass ratio of 1:3, and grind it thoroughly in a mortar for 15 min to make it evenly mixed.

[0027] (3) Carbonization / activation: Place the mixed powder obtained in step (2) in a magnetic boat, transfer it into a tube furnace, introduce nitrogen gas (flow rate 100 mL / min), heat it to 900℃ at a heating rate of 5℃ / min, keep it at a constant temperature for 3 h, and take out the carbonized product after the tube furnace has cooled to room temperature naturally.

[0028] (4) Acid washing and purification: The carbonized product obtained in step (3) was transferred into a 0.5 mol / L hydrochloric acid solution with a solid-liquid ratio of 1:10 and stirred for 12 h (300 rpm). Then, it was washed with deionized water and filtered until pH=7. Finally, the material obtained by filtration was placed in a vacuum drying oven and dried at 120℃ for 12 h to obtain lignite-derived hard carbon anode material, labeled as HC-1.

[0029] Figure 1This is a transmission electron microscope (TEM) image of the lignite-based hard carbon anode material for sodium-ion batteries prepared in this embodiment. Figure 1 As shown, the material exhibits a typical amorphous structure, composed of randomly stacked graphite microcrystals, rich in defects and closed pores. Its carbon interlayer spacing, measured to be approximately 0.38 nm, combined with the abundant microstructure, provides numerous active sites for the reversible storage of sodium ions.

[0030] Figure 2 This is the first charge-discharge curve of the lignite-based hard carbon anode material prepared in this embodiment at a current density of 20 mA / g. Figure 2 It can be seen that the coal-based hard carbon material prepared in this embodiment has an initial coulombic efficiency of ≥87% and an initial reversible specific capacity of ≥320 mAh / g.

[0031] Figure 3 This is a graph showing the cycling performance of the lignite-based hard carbon anode material prepared in this embodiment at a current density of 1 A / g. Figure 3 It can be seen that the capacity retention rate after 1000 cycles is >80%.

[0032] Example 2

[0033] The difference between this embodiment and Embodiment 1 is that in step (2), the mass ratio of lignite powder to anhydrous ferric chloride is 1:2. The resulting material is labeled as HC-2.

[0034] Example 3

[0035] The difference between this embodiment and Embodiment 1 is that in step (2), the mass ratio of lignite powder to anhydrous ferric chloride is 1:4. The resulting material is labeled HC-3.

[0036] Example 4

[0037] The difference between this embodiment and Embodiment 1 is that the carbonization temperature in step (3) is 800°C. The resulting material is labeled HC-4.

[0038] Example 5

[0039] The difference between this embodiment and Embodiment 1 is that the carbonization temperature in step (3) is 1000℃. The resulting material is labeled HC-5.

[0040] Example 6

[0041] The difference between this embodiment and Embodiment 1 is that in step (4), acid washing and purification are performed using a 0.5 mol / L sulfuric acid solution. The resulting material is labeled as HC-6.

[0042] Application Example 1: Electrochemical Performance Testing

[0043] (1) Electrode preparation: The hard carbon samples prepared in Example 1 and Comparative Example 1 were ground into fine particles and sieved through a 300-mesh sieve. The active material, conductive agent (super P), and binder (2% sodium alginate) were mixed in a mass ratio of 8:1:1, and an appropriate amount of deionized water was added and ground evenly to obtain an electrode slurry. The slurry was evenly coated on aluminum foil and dried in a vacuum oven at 90°C for 12 h, and then cut into 10 mm circular electrode sheets.

[0044] (2) Sodium-ion half-cell assembly: Using metallic sodium as the counter electrode, 1M NaPF6+DEGDME as the electrolyte, and glass fiber (GF / C) as the separator, the CR2032 button cell was assembled in an argon-protected glove box.

[0045] (3) Electrochemical performance testing: The electrochemical performance of the battery was tested using a LAND CT2001 A tester. The charge / discharge voltage range was 0~2.5 V (vs. Na). + The first charge-discharge curves were tested at a current density of 20 mA / g, and the cycling performance was tested at a current density of 1 A / g. The prepared coal-based hard carbon material achieved an initial coulombic efficiency ≥87% and an initial reversible specific capacity ≥320 mAh / g. The capacity retention after 1000 cycles was >80%.

Claims

1. A method for preparing hard carbon anode materials by activating lignite with ferric chloride, characterized in that... The method includes the following steps: Step (1) Pretreatment: The lignite is ultrasonically washed with deionized water and anhydrous ethanol for 0.5-2 h to remove impurities from the surface of the material. After ultrasonic treatment, it is dried in a forced-air drying oven. The dried lignite is then crushed to obtain lignite powder. Step (2) Mixing: Mix the lignite powder obtained in step (1) with anhydrous ferric chloride until homogeneous; Step (3) Carbonization / Activation: The mixed powder obtained in step (2) is placed in a tube furnace, a protective gas is introduced, and carbonization is carried out. After the tube furnace is cooled to room temperature, the carbonization product of lignite is obtained. Step (4) Acid washing and purification: The carbonized product obtained in step (3) is transferred into dilute hydrochloric acid or dilute sulfuric acid solution and stirred. Then, it is washed with deionized water and filtered until pH=7. Finally, the material obtained by filtration is placed in a drying oven to dry, and lignite-derived hard carbon anode material is obtained.

2. The method for preparing hard carbon anode materials by activating lignite with ferric chloride according to claim 1, characterized in that... In step (1), the lignite is low-rank lignite with a carbon content of 50-70 wt%, a volatile matter content of 25-45 wt%, and an ash content of 5-20 wt%; the ultrasonic washing time is 0.5-2 h; the drying temperature is 60-80℃ and the time is 6-12 h.

3. The method for preparing hard carbon anode materials by activating lignite with ferric chloride according to claim 1, characterized in that... In step (2), the mass ratio of lignite powder to anhydrous ferric chloride is 1:1 to 1:6; the lignite powder is sieved through a 30-50 mesh sieve, and the anhydrous ferric chloride powder is sieved through a 50-100 mesh sieve.

4. The method for preparing hard carbon anode materials by activating lignite with ferric chloride according to claim 3, characterized in that... The mass ratio of the lignite powder to anhydrous ferric chloride is 1:2 to 1:

4.

5. The method for preparing hard carbon anode materials by activating lignite with ferric chloride according to claim 1, characterized in that... In step (3), the protective gas is nitrogen or argon; the heating rate is 1~10℃ / min, the carbonization temperature is 700~1100℃, and the holding time is 1~5 h.

6. The method for preparing hard carbon anode materials by activating lignite with ferric chloride according to claim 5, characterized in that... The heating rate is 2~8℃ / min, the carbonization temperature is 800~1000℃, and the holding time is 2~4 h.

7. The method for preparing hard carbon anode materials by activating lignite with ferric chloride according to claim 1, characterized in that... In step (4), the concentration of dilute hydrochloric acid or dilute sulfuric acid is 0.1~1.0 mol / L, the stirring time is 6~24 h, the stirring speed is 200~400 rpm, the drying temperature is 100~150℃, and the drying time is 8~16 h.

8. The method for preparing hard carbon anode materials by activating lignite with ferric chloride according to claim 7, characterized in that... The stirring time is 8~16 h.

9. A lignite-derived hard carbon anode material prepared by the method according to any one of claims 1-8.

10. The application of a lignite-derived hard carbon anode material prepared by the method of any one of claims 1-8 in a sodium-ion battery anode.

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