Coal-based carbon negative electrode material, preparation method thereof and full-carbon-based lithium ion capacitor

Abstract

The invention discloses a coal-based carbon negative electrode material, a preparation method thereof and a full-carbon-based lithium ion capacitor, and the preparation method comprises the following steps: S1, crushing and screening coal to obtain coal powder, mixing the coal powder with an alkaline solution, stirring at a high temperature, and cooling to room temperature to obtain pre-oxidized coal; s2, deionized water is added into the coal pre-oxidized in the step S1, heating and boiling are carried out, washing and suction filtration are carried out multiple times with boiling water, and purified raw materials are obtained after aftertreatment; and S3, roasting the raw material purified in the step S2 at a high temperature of 600-2400 DEG C in an inert gas or vacuum environment, and performing post-treatment to prepare the coal-based carbon negative electrode material of high-conductivity soft carbon. The coal-based carbon negative electrode material prepared by the invention is applied to a lithium ion capacitor, so that the lithium ion capacitor has relatively high capacity, energy density and power density, stable cycle performance and good safety performance.

Description

Technical Field

[0001] This invention belongs to the technical field, and in particular relates to a coal-based carbon anode material, its preparation method, and an all-carbon-based lithium-ion capacitor. Background Technology

[0002] Lithium-ion capacitors are a new type of high-power energy storage device. During charging and discharging, ion adsorption and desorption occur at the positive electrode, while ion intercalation and deintercalation occur at the negative electrode. To improve the energy storage capacity and rate capability of lithium-ion capacitors, porous capacitive carbon active materials are used for the positive electrode, and rate-capable lithium intercalation and deintercalation energy storage materials are used for the negative electrode.

[0003] Soft carbon is an amorphous carbon material that is easily graphitized after high-temperature treatment. Its disordered structure can be easily eliminated. Due to its excellent rate performance, it has attracted widespread attention from researchers in recent years, leading to its increasing research and application in energy storage devices such as soft carbon lithium-ion capacitors. Currently, the main raw material for commercial soft carbon is petroleum. By separating components such as petroleum coke from petroleum and subjecting it to high-temperature heat treatment, the prepared soft carbon has high purity and uniform particle size. However, due to the special strategic importance of petroleum, the production cost of soft carbon is higher than that of other carbon materials such as graphite and hard carbon. To enhance the market competitiveness of soft carbon anodes, it is necessary to develop new precursors for soft carbon preparation. Coal has the highest carbon content among various types of coal, typically around 90%, and is inexpensive. The internal structure of coal is very complex. In addition to carbon, coal also contains some mineral elements such as silicon, aluminum, calcium, and magnesium, as well as organic matter. Therefore, it needs to be purified before being used as an energy storage material. Summary of the Invention

[0004] In view of this, the present invention aims to provide a coal-based carbon anode material and its preparation method, as well as an all-carbon-based lithium-ion capacitor, to solve at least one technical problem in the background art.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A method for preparing a coal-based carbon anode material includes the following steps: S1: Coal is crushed and sieved to obtain coal powder. The coal powder is mixed with an alkaline solution, stirred at high temperature, and cooled to room temperature to obtain pre-oxidized coal. S2: Add the pre-oxidized coal from step S1 to deionized water, heat to boiling, wash and filter repeatedly with boiling water, and obtain the purified raw material after post-treatment. S3: The raw material purified in step S2 is calcined at a high temperature of 600~2400℃ in an inert gas or vacuum environment, and then post-treated to prepare a coal-based carbon anode material with high conductivity soft carbon.

[0006] Furthermore, the coal in step S1 includes one or more of anthracite, lean coal, semi-lean coal, coking coal, fat coal, gas coal, weakly caking coal, non-caking coal, long-flame coal, lignite, and sub-flame coal. Preferably, the coal is anthracite. And / or, the average particle size of the coal powder in step S1 is ≤10μm; And / or, the mass ratio of pulverized coal to weakly alkaline solution in step S1 is 1:(1~20). And / or, the alkaline solution includes one or more of KOH, NaOH, LiOH, Na2CO3, NaHCO3, and NH3·H2O; And / or, the concentration of the alkaline solution is 1–30 mol / L; And / or, in step S1, high-temperature stirring is carried out in an air atmosphere for 1 to 8 hours, and the high-temperature stirring temperature is 120 to 500°C. Preferably, the high-temperature stirring temperature is 170 to 190°C.

[0007] Furthermore, the post-processing in step S2 includes placing the coal, which has been washed and filtered multiple times with boiling water, in an acidic solution, stirring and letting it stand at a certain temperature, repeatedly washing and filtering with deionized water, and then drying it to obtain the purified raw material. Preferably, the acidic solution includes one or more of HCl, H2SO4, and HNO3, and the concentration of the acidic solution is 0.1–2 mol / L; Preferably, the stirring temperature is 80~120℃. Preferably, the stirring and standing time is 1 to 6 hours; Preferably, the filtrate is repeatedly washed and filtered with deionized water until the pH of the filtrate is neutral. And / or, the mass ratio of coal in step S1, weak alkaline solution in step S1, and deionized water in step S2 is 1:(1~20):(1:50).

[0008] Furthermore, in step S3, the high-temperature calcination temperature is 1200~1600℃, the heating rate is 3~30℃ / min, the cooling method is furnace cooling, and the high-temperature calcination time is 0.5~12h; the pyrolysis carbonization is carried out at 800-1600℃ to prepare high-conductivity soft carbon anode material.

[0009] Preferably, the inert gas in step S3 includes one or more of argon, nitrogen, and helium.

[0010] And / or, a pore-forming agent is added during the high-temperature calcination in step S3; And / or, the pore-forming agent includes one or more of ZnCl2, NaCl, NaOH, Na2CO3, NaNO3, KCl, KOH, K2CO3, and KNO3; And / or, the mass ratio of coal to pore-forming agent is 1:(0.1~5).

[0011] Furthermore, the post-processing in step S3 includes high-temperature roasting, cooling of the raw material, adding it to an acidic solution, stirring at room temperature, followed by vacuum filtration and drying to finally obtain a coal-based carbon anode material with high conductivity soft carbon. Preferably, the acidic solution is dilute hydrochloric acid or dilute sulfuric acid, and the mass fraction of the acidic solution is 2% to 10%. Preferably, the stirring time at room temperature is 0.5 to 48 hours.

[0012] The coal-based carbon anode material prepared by the above-mentioned method is a coal-based carbon anode material.

[0013] A lithium-ion capacitor negative electrode sheet includes a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, wherein the negative electrode material includes the aforementioned coal-based carbon negative electrode material, a conductive agent, and a binder.

[0014] Furthermore, the negative electrode current collector is a porous current collector; The porous current collector is a metal conductive layer with a porous structure; The conductive metal layer is a metal wire or a conductive carbon material coating applied to the surface of a metal foil and a metal wire. The metal wire is woven into a porous metal layer, wherein the mesh is polygonal. Polygons include squares, rhombuses, and rectangles.

[0015] Alternatively, the conductive metal layer can be a porous metal foil or a porous foam metal layer with a porous structure. Alternatively, the conductive metal layer may be formed by mechanical stamping, laser drilling, or chemical etching of a porous metal plate or foil. Preferably, the material of the metal conductive layer is one or more of stainless steel, copper, nickel, titanium, silver, tin, tin-plated copper, nickel-plated copper, and silver-plated copper; And / or, the conductive agent includes one or more of acetylene black, Ketjen black, furnace black, conductive carbon black, conductive graphite, Super P, carbon nanotubes, graphene, onion carbon, and fullerene.

[0016] And / or, the adhesive comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride hexafluoropropylene, polyacrylic acid, and acrylonitrile copolymer; And / or, the solvent includes one of NMP (N-methylpyrrolidone) or deionized water; And / or, the mass ratio of coal-based carbon anode material to conductive agent and binder is (80%~96%): (10%~1%): (10%~2%), and the mass ratio of the sum of the mass of coal-based carbon anode material to conductive agent and binder to the mass of solvent is (35%~60%): (40%~65%).

[0017] A method for preparing a negative electrode sheet for a lithium-ion capacitor includes the following steps: mixing a coal-based carbon negative electrode material with a conductive agent and a binder, and then stirring it in a solvent to prepare a negative electrode slurry, which is then coated onto a negative electrode current collector and dried in a vacuum drying oven at 80~160℃ for 6~12h to obtain a negative electrode sheet for a lithium-ion capacitor.

[0018] A carbon-based lithium-ion capacitor, using the aforementioned lithium-ion capacitor negative electrode, is applied to one or more of the following: regenerative braking energy recovery in rail transit, auxiliary power supply for new energy vehicles, industrial lifting machinery, or energy-saving elevators.

[0019] Compared with existing technologies, the coal-based carbon anode material, its preparation method, and the all-carbon-based lithium-ion capacitor described in this invention have the following advantages: The coal-based carbon anode material prepared in this application is used in lithium-ion capacitors, which enable lithium-ion capacitors to have high capacity, energy density and power density, stable cycle performance and good safety performance. It has broad application prospects in fields such as short-term high-frequency energy storage, regenerative braking energy recovery in rail transit, auxiliary power supply for new energy vehicles, industrial hoisting machinery, and energy-saving elevators. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The physical properties of the anthracite raw coal described in Example 1 of this invention are characterized (a is the X-ray diffraction of the anthracite, and b is the thermogravimetric image of the anthracite). Figure 2 The images shown are SEM images of coal powder as described in Embodiment 1 of the present invention (a is a 500x SEM image of coal powder, and b is a 3000x SEM image of coal powder). Figure 3 The three self-made soft carbon Raman spectra described in Example 1 of this invention; Figure 4 The soft carbon TEM characterization described in Example 1 of this invention (a is the internal carbon layer structure of 1000-SC, b is the internal carbon layer structure of 1200-SC, and c is the internal carbon layer structure of 1400-SC). Figure 5The lithium storage performance of soft carbon under three different temperatures as described in Example 1 of this invention is shown in Figure a (CV curve at a scan rate of 0.1 mV / s; and charge-discharge curve at a current density of 0.05 A / g during the first week). Figure 6 The charging and discharging curves of the lithium-ion capacitor under different current densities are shown in Embodiment 2 of the present invention. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0022] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] Example 1 The method for preparing soft carbon: Step 1, crushing and screening: Anthracite is selected as raw material, and it is crushed and screened to obtain coal powder with an average particle size of ≤10μm.

[0024] Figure 1 The image shows the XRD diffraction pattern of raw anthracite coal. The results indicate that the raw coal contains many impurity diffraction peaks, with carbon as the main component. Figure 1 (b) is the thermogravimetric analysis (TGA) image of raw anthracite coal. The heating rate was 10℃ / min, and the test atmosphere was nitrogen. The TGA image shows that the mass of the coal powder decreased slightly before 600℃, which was due to the volatilization of moisture and organic volatiles in the material. The mass decreased significantly between 600-800℃, which was due to the cracking of carbon rings in the coal powder. When the heat treatment temperature was higher than 1000℃, the mass of the coal powder decreased very slowly. At this time, the main component remaining in the coal powder was carbon. After testing, the content of the anthracite coal used was close to 86%.

[0025] Figure 2 Images (a) and (b) are SEM images of the anthracite powder at 500x and 3000x magnification. The images show that the particle size of the anthracite powder is entirely in the micrometer range; however, the particle size distribution is uneven, ranging from a few micrometers to tens of micrometers, indicating a mixture of particles of different sizes and low uniformity. In addition to particle size, the anthracite powder also exhibits inconsistent particle morphology. SEM images reveal that the anthracite powder is a mixture of spherical and flaky particles, likely due to the inability of mechanized grinding to control the particle morphology. In conclusion, the prepared anthracite powder meets the requirements for use as an electrode material in terms of carbon content and particle size.

[0026] Step 2, Pre-oxidation and impurity removal: Mix coal powder and 15 mol / L KOH solution at a mass ratio of 1:10, place in a furnace and stir at 180°C in air atmosphere for 4 hours, then cool to room temperature; Acid washing: The coal is placed in a 1 mol / L HCl solution, stirred and allowed to stand at 90°C for 4 hours. Then it is repeatedly washed and filtered with deionized water to remove excess acid and salt ions generated in the reaction. The washing is continued until the pH of the filtrate is 7 or close to 7, and then it is dried.

[0027] Step 3, Washing: Deionized water is injected into the furnace. The mass ratio of coal, weakly alkaline solution, and deionized water is 1:10:25. The mixture is then heated to boiling. The coal is repeatedly washed and filtered with boiling water to remove excess alkali and salt ions generated in the reaction. The boiling water washing continues until the filtrate's pH is 7 or close to 7. The mixture is then dried to obtain high-quality, impurity-free coal raw material. This process also modifies the surface microstructure of the anthracite, resulting in coal with increased interlayer spacing and partially oxidized and purified surface.

[0028] Step 4, High-temperature carbonization: The purified coal is placed into a carbonization furnace and roasted at high temperature for 5 hours under a flowing nitrogen atmosphere. The heating rate is 15℃ / min, and the cooling method is furnace-cooled.

[0029] The high-temperature roasting was carried out at temperatures of 1000℃, 1200℃, and 1400℃ respectively; To verify the change in the degree of order of the internal carbon layer arrangement of soft carbon with increasing temperature, Raman scattering tests were performed on the three materials.

[0030] Figure 3 The Raman scattering spectra are shown for the 1000-SC, 1200-SC, and 1400-SC materials at 1343 cm⁻¹. -1 and 1589cm -1 Obvious D and G peaks were observed at all locations. After comparison, the ID / IG values ​​of the three materials, 1000-SC, 1200-SC and 1400-SC, were 1.0072, 0.9919 and 0.9618, respectively, indicating that as the heat treatment temperature increased, the orderliness of the self-made soft carbon continued to increase and the internal carbon layer arrangement tended to be more ordered.

[0031] The increased orderliness of the self-made coal-based carbon anode material with temperature was also verified in transmission electron microscopy images. Figure 4 (a) shows the internal carbon layer structure of 1000-SC, where the internal carbon layers are arranged in a basically completely disordered manner. Figure 4 (b) shows the internal carbon layer structure of 1200-SC, in which ordered and disordered structures of the internal carbon layers are interwoven. Figure 4 (c) is the internal carbon layer structure of 1400-SC, and the degree of order of its internal carbon layers is significantly higher than that of 1000-SC and 1200-SC.

[0032] During the high-temperature carbonization process, a pore-forming agent, KOH, is added to the anthracite. The mass ratio of coal to pore-forming agent is 1:3.

[0033] After the above steps, the cooled soft carbon powder is added to 5% dilute hydrochloric acid and stirred at room temperature for 24 hours. Following this, it is vacuum filtered and dried to obtain the final coal-based high-conductivity soft carbon anode material. The acid washing process aims to further improve the purity of the soft carbon material. The prepared coal-based high-conductivity soft carbon anode material contains macropores, mesopores, or micropores, exhibiting a microstructural characteristic of short-range order and long-range disorder.

[0034] Figure 5 (a) shows the cyclic voltammetry curves of three coal-based carbon anode materials at a scan rate of 0.1 mV / s, with a voltage window of 0-2.0 V. The scan curves are normal in shape, with no redox peaks appearing. The three materials have almost no capacity after 1.5 V. The capacity of the soft carbon above 1.5 V is mainly provided by adsorption, and a peak appears at around 0.25 V throughout the cycle. The higher the temperature, the sharper the peak becomes, which is due to the gradual graphitization of the material. Figure 5 (b) shows the first-cycle charge-discharge curves of the three anode material samples at a current density of 0.05 A / g. The 1400-SC sample has the lowest potential during charge-discharge. This is because the higher the temperature, the more crystalline carbon in the material, and the lower the lithium intercalation potential. However, 1400℃ is far from the temperature for complete graphitization, and the crystalline carbon in the material is much less than that in graphite. Therefore, it is impossible to form a low and stable charge-discharge curve plateau similar to that of graphite. The 1000-SC sample has the highest first-cycle discharge specific capacity. This is because the higher the disorder of the soft carbon, the more carbon layer edges are exposed. Side reactions occur at the carbon layer edges during the first-cycle discharge, which increases the first-cycle specific capacity of the material. However, the increase in side reactions reduces the first-cycle coulombic efficiency of the battery.

[0035] Example 2 A negative electrode sheet for a lithium-ion capacitor includes a negative current collector and a negative electrode material coated on the negative current collector.

[0036] The negative material includes the coal-based soft carbon negative electrode material prepared above, a conductive agent, and a binder.

[0037] Coal-based soft carbon anode material is mixed with conductive agent and binder in a certain proportion and placed in solvent and stirred to prepare anode slurry. Then, it is coated on anode current collector and dried in a vacuum drying oven at 120°C for 8 hours to obtain soft carbon anode for lithium-ion capacitors.

[0038] The negative electrode current collector is a porous current collector. The porous current collector is a metal conductive layer with a porous structure. The metal conductive layer is a metal wire or a metal foil and a metal wire coated with a conductive carbon material. The metal wire is woven into a porous metal layer, wherein the mesh is square. The material of the metal conductive layer of the negative electrode current collector is stainless steel.

[0039] The conductive agent includes acetylene black.

[0040] Using coal-derived soft carbon as the negative electrode material and porous capacitor carbon as the positive electrode material, lithium-ion capacitors were fabricated and charge-discharge tests were conducted. Figure 6 The charge-discharge curves of lithium-ion capacitors at different current densities are shown.

[0041] Example 3 The difference from Example 1 is that the acid washing in step 4 is performed using dilute hydrochloric acid (5 wt%) at 80°C for 12 hours to dissolve most of the metal oxides. Subsequently, an aminopolycarboxylic acid complexing agent (EDTA) is introduced to selectively chelate residual Fe³⁺ and Ca²⁺ ions, reducing the ash content from 8.7% of the raw material to below 0.3%. The soft carbon material prepared from the purified precursor exhibits a gas production rate reduced to one-quarter of that of the untreated sample, significantly improving the safety performance of lithium-ion capacitors.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a coal-based carbon anode material, characterized in that: The method comprises the following steps: S1: crushing and screening coal to obtain coal powder, mixing the coal powder with an alkaline solution, high-temperature stirring, and cooling to room temperature to obtain pre-oxidized coal; S2: adding the pre-oxidized coal in step S1 to deionized water, heating and boiling, washing and filtering with boiling water multiple times, and obtaining the purified raw material after post-processing; S3: high-temperature calcining the purified raw material in step S2 under an inert gas or in a vacuum environment at 600-2400 DEG C, and obtaining the coal-based carbon negative material of high-soft carbon after post-processing.

2. The method according to claim 1, wherein: The coal in step S1 comprises one or more of anthracite, lean coal, lean coal, coking coal, fat coal, gas coal, weakly coking coal, non-coking coal, long-flame coal, lignite, and sub-flame coal, and preferably, the coal is anthracite; And / or, the average particle size of the coal powder in step S1 is ≤10 μm; And / or, the mass ratio of the coal powder to the weak alkaline solution in step S1 is 1:(1-20); And / or, the alkaline solution comprises one or more of KOH, NaOH, LiOH, Na2CO3, NaHCO3, and NH3·H2O; And / or, the concentration of the alkaline solution is 1-30 mol / L; And / or, the high-temperature stirring in step S1 is performed in an air atmosphere, the high-temperature stirring time is 1-8 h, and the high-temperature stirring temperature is 120-500 DEG C, and preferably, the high-temperature stirring temperature is 170-190 DEG C.

3. The method of claim 1, wherein: The post-processing in step S2 comprises placing the coal washed and filtered multiple times with boiling water in an acidic solution, stirring and standing at a certain temperature, repeatedly washing and filtering with deionized water, and drying to obtain the purified raw material; Preferably, the acidic solution comprises one or more of HCl, H2SO4, and HNO3, and the concentration of the acidic solution is 0.1-2 mol / L; Preferably, the stirring temperature is 80-120 DEG C; Preferably, the stirring and standing time is 1-6 h; Preferably, the repeatedly washing and filtering with deionized water is performed until the pH of the filtrate is neutral; And / or, the mass ratio of the coal in step S1, the weak alkaline solution in step S1, and the deionized water in step S2 is 1:(1-20):(1:50).

4. The method according to claim 1, characterized in that: The high-temperature calcining temperature in step S3 is 1200-1600 DEG C, the heating rate is 3-30 DEG C / min, the cooling mode is furnace cooling, and the high-temperature calcining time is 0.5-12 h; Preferably, the inert gas in step S3 comprises one or more of argon, nitrogen, and helium; And / or, a pore-forming agent is added in the high-temperature calcining in step S3; And / or, the pore-forming agent comprises one or more of ZnCl2, NaCl, NaOH, Na2CO3, NaNO3, KCl, KOH, K2CO3, and KNO3; And / or, the mass ratio of the coal to the pore-forming agent is 1:(0.1-5).

5. The method according to claim 1, wherein: The post-treatment in step S3 includes cooling the raw material after high-temperature calcination, adding an acidic solution, stirring at room temperature, vacuum filtration and drying to obtain the coal-based carbon negative electrode material with high conductivity soft carbon. Preferably, the acidic solution is dilute hydrochloric acid or dilute sulfuric acid, and the mass fraction of the acidic solution is 2% to 10%. Preferably, the stirring time at room temperature is 0.5 to 48 h.

6. A coal-based carbon negative electrode material prepared by the method of any one of claims 1 to 5.

7. A lithium-ion capacitor negative electrode sheet comprising a negative electrode current collector, a negative electrode material coated on the negative electrode current collector, characterized by: The negative material comprises the coal-based carbon negative electrode material of claim 6, a conductive agent and a binder.

8. The lithium-ion capacitor negative electrode sheet according to claim 7, characterized by: The negative current collector is a porous current collector. The porous current collector is a metal conductive layer with a porous structure. The metal conductive layer is a metal wire or a metal foil with a conductive carbon material coating on the surface of the metal wire or the metal foil, and the metal wire is woven into a porous metal layer, wherein the mesh holes are polygonal. Alternatively, the metal conductive layer is a porous metal foil or a porous foam metal layer with a porous structure. Alternatively, the metal conductive layer is a porous metal plate or a metal foil formed by mechanical stamping, laser punching or chemical etching. Preferably, the metal conductive layer is made of one or more of stainless steel, copper, nickel, titanium, silver, tin, tinned copper, nickel-plated copper and silver-plated copper. Preferably, the conductive agent comprises one or more of acetylene black, ketjen black, furnace black, conductive carbon black, conductive graphite, Super P, carbon nanotubes, graphene, onion carbon and fullerenes. Preferably, the binder comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride hexafluoropropylene, polyacrylic acid and acrylonitrile multivariate copolymer. Preferably, the solvent comprises one of NMP and deionized water. Preferably, the mass ratio of the coal-based carbon negative electrode material to the conductive agent and the binder is (80% to 96%):(10% to 1%):(10% to 2%), and the mass ratio of the sum of the mass of the coal-based carbon negative electrode material, the conductive agent and the binder to the mass of the solvent is (35% to 60%):(40% to 65%).

9. The method for preparing a negative electrode sheet for a lithium-ion capacitor according to claim 8, characterized in that: The method comprises the following steps: mixing the coal-based carbon negative electrode material, the conductive agent and the binder, stirring in the solvent to prepare a negative electrode slurry, coating the negative electrode slurry on the negative electrode current collector, and drying the negative electrode slurry in a vacuum drying oven at 80 to 160°C for 6 to 12 h to obtain a lithium ion capacitor negative electrode sheet.

10. A full carbon-based lithium-ion capacitor using the lithium-ion capacitor negative electrode sheet according to claim 8, characterized by: The lithium ion capacitor is applied to one or more of rail transit regenerative braking energy recovery, new energy vehicle auxiliary power supply, industrial hoisting machinery or energy-saving elevators.

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