CN114335522A - Coal-based carbon negative electrode material, preparation method and application thereof, and battery containing coal-based carbon negative electrode material - Google Patents
Coal-based carbon negative electrode material, preparation method and application thereof, and battery containing coal-based carbon negative electrode material Download PDFInfo
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Abstract
The invention discloses a coal-based carbon negative electrode material, a preparation method and application thereof, and a battery containing the coal-based carbon negative electrode material. The preparation method comprises the following steps: s1: pretreating a coal-based raw material to obtain coal powder; d50 of the coal powder is 1-35 mu m; the pretreatment sequentially comprises crushing, oxidation and re-crushing; s2: uniformly mixing volatile organic compounds with the pulverized coal, and performing low-temperature heat treatment to obtain modified pulverized coal; s3: and carrying out high-temperature heat treatment on the modified coal powder to obtain the coal-based carbon negative electrode material. The lithium battery and the sodium battery which take the coal-based carbon as the negative electrode material have better electrical properties, meet the commercial performance requirements of the lithium ion and sodium ion batteries with high energy density and high first coulombic efficiency, and are particularly suitable for the fields of lithium batteries, sodium ion batteries and super capacitors such as consumer electronics, large-scale energy storage, low-cost batteries and low-temperature fields.
Description
Technical Field
The invention relates to a coal-based carbon negative electrode material, a preparation method and application thereof, and a battery containing the coal-based carbon negative electrode material.
Background
The lithium ion battery has the advantages of high energy density, long cycle life, stable work, environmental protection, no pollution and the like, and is widely applied to the fields of electronics and energy. The graphite material is used as a raw material for preparing the traditional lithium ion battery cathode material, has the advantages of definite crystal form, stable performance, lower potential platform, mature processing technology and the like, but the artificial graphite material needs a graphitization process at the temperature of more than 2500 ℃, and the process needs to consume a large amount of energy and auxiliary materials, consume heat-insulating materials, and release environmental harmful substances such as dust, oxynitride, sulfide and the like.
For lithium batteries, lithium as a raw material is unevenly distributed on the earth, and the total amount thereof cannot support the increasing consumer demand of lithium batteries. In addition, the lithium ion battery made of the traditional graphite cathode material is difficult to be widely applied to power type energy devices and low-temperature environments, and the graphite crystal (002) has small interplanar spacing (D002 is approximately equal to 0.3354nm), so that the lithium ion battery is not favorable for quick intercalation, deintercalation and diffusion of lithium ions.
The sodium ion battery has electrochemical mechanism, structural form, processing mode and performance similar to those of the lithium ion battery, and sodium resources are widely distributed and can be extracted by a chlor-alkali process and the like. Therefore, there is no problem of resource limitation in developing sodium ion batteries. At present, the main limiting factor of the development of the sodium ion battery is the negative electrode material. Because the crystal interlayer spacing of the graphite material and the hexagonal arrangement mode of carbon atoms are not suitable for embedding sodium ions, the traditional graphite material cannot be applied to the field of sodium ion batteries. Amorphous carbon materials, particularly hard carbon materials, made from coal having a relatively high carbon content are likely to be core materials for the negative electrode of sodium ion batteries. Coal-based carbon materials represented by bituminous coal, lignite and peat are abundant in resources and low in price. The development of the carbonaceous material taking coal-based carbon as the main raw material and the application of the carbonaceous material to the lithium ion battery and the sodium ion battery are beneficial to saving energy, reducing pollution, improving the power characteristic and low-temperature applicability of the battery and effectively reducing the cost of the battery.
Chinese patent CN111293309A discloses a method for improving the performance of a coal-based sodium ion battery cathode material and application thereof, the method comprises the steps of mixing a coal-based material with a soft carbon precursor, treating at a low temperature of 300-500 ℃ in an air atmosphere, and carbonizing at a high temperature to obtain an amorphous carbon material, wherein the sodium storage capacity is about 220mAh/g, and the first coulombic efficiency is 80%. The amorphous carbon material takes a coal-based material as a raw material, but the capacity and the efficiency of the amorphous carbon material cannot meet the requirements of a commercial sodium-ion battery. Chinese patent CN113381013A discloses a sodium ion battery coal-based hard carbon negative electrode material, a preparation method and application thereof, wherein the patent firstly carries out deashing treatment on raw material coal to obtain a carbon precursor; and then, placing the carbon precursor in an inert atmosphere for high-temperature carbonization, and performing programmed cooling to obtain the coal-based hard carbon material, wherein the sodium storage capacity is about 330mAh/g, and the first coulombic efficiency is 80%. Although the specific capacity of the carbon material is greatly improved, the carbon material is difficult to be practically and commercially applied due to the first coulombic efficiency of only 80%.
Disclosure of Invention
The invention aims to overcome the defects of low first coulombic efficiency, unsatisfactory quick charging performance, complex production process and unfavorable industrial production and commercial development of a sodium ion battery cathode material in the prior art, and provides a coal-based carbon cathode material, a preparation method and application thereof and a battery containing the coal-based carbon cathode material. The invention takes coal-based carbon materials with wide resources and low price as main materials, adopts simplified process, and reduces environmental pollution and carbon emission. In addition, the lithium battery and the sodium battery which take the coal-based carbon as the negative electrode material have better electrical properties, meet the commercial performance requirements of the lithium ion and sodium ion batteries with high energy density and high first coulombic efficiency, and are particularly suitable for the fields of lithium batteries, sodium ion batteries and super capacitors such as consumer electronics, large-scale energy storage, low-cost batteries and low-temperature fields.
The invention mainly solves the technical problems through the following technical means:
the invention discloses a preparation method of a coal-based carbon negative electrode material, which comprises the following steps:
s1: pretreating a coal-based raw material to obtain coal powder; d50 of the coal powder is 1-35 mu m; the pretreatment sequentially comprises crushing, oxidation and re-crushing;
s2: uniformly mixing volatile organic compounds with the pulverized coal, and performing low-temperature heat treatment to obtain modified pulverized coal;
s3: and carrying out high-temperature heat treatment on the modified coal powder to obtain the coal-based carbon negative electrode material.
At S1, the coal-based raw material may be a carbonaceous-rich amorphous material conventional in the art, preferably a young coal and/or a washed coal of a young coal; the annual light coal can be one or more of bituminous coal, lignite and peat. The annual light coal is a coal-based raw material with light metamorphism degree and short coal forming time.
Wherein, the volatile content of the clean coal is generally 20-50%, preferably 45%.
Wherein the ash content of the clean coal is less than 5%, preferably 2.1%.
Wherein the volatile components of the bituminous coal and the lignite are generally 8-60%.
Wherein the ash content of the bituminous coal and the lignite is 8 percent.
Wherein, the volatile components and the deterioration degree of the coal-based raw materials are moderate. The volatile components and the deterioration degree of the coal-based raw materials have a large relationship with the sources, the surrounding environment, the deterioration history and the components of the coal-based raw materials.
Generally, coal-based raw materials with low volatile components have high deterioration degree, high carbon element content in the coal-based raw materials and high carbon atom arrangement order degree. The microcosmic expression is that the graphite microcrystals in the coal are greatly developed, and the interlayer spacing of the layered arrangement of the carbon atom six-membered rings in the graphite microcrystals is reduced. The larger graphite microcrystal and the smaller graphene layer interval are not beneficial to the embedding and diffusion of sodium ions, so that the electrochemical performance of the material is poor when the material is used as a negative electrode material of a sodium ion battery.
Generally, coal-based raw materials with higher volatile content have lower deterioration degree, lower carbon content and higher impurity content. Higher impurity element content is not beneficial to improving the performance of the sodium-ion battery, and potential safety hazards can be brought.
Wherein the coal-based raw material is generally obtained by ore mining, crushing, flotation and mechanical processing treatment so as to reduce ash content and sulfur content and remove partial impurities. If necessary, the coal-based raw material can be subjected to conventional technology impurity removal in the field in advance so as to reduce inorganic mineral components in the coal, stabilize the quality of the raw material coal and reduce material pollution and energy consumption in the processing process.
In S1, the coal-based raw material is pulverized to 20 to 100 μm, preferably 50 μm.
In S1, the reactor in which the oxidation takes place is an electrically heated reaction furnace, preferably an electrically heated ribbon blender.
Wherein the volume of the pulverized coal-based raw material is preferably 50% of the effective volume of the electrically heated reaction furnace.
In S1, the oxidation is a redox reaction between part of organic matter in the coal-based raw material and oxygen, sulfur, and halogen elements. The elements react with functional groups in organic matters to cause the reconstruction and crosslinking of molecular chains, the active groups are converted into inactive groups, the active groups are converted into thermosetting groups, the small molecules react to generate macromolecules, and impurity atoms are introduced into the molecular chains. The thermosetting coal-based carbon particles are obtained through oxidation treatment, so that the structure and the appearance of the coal-based carbon particles are maintained in subsequent treatment. So as to obtain the nano-pores and sub-nano-pores through impurity atom discharge, molecular chain breakage, small molecule separation and the like in subsequent heat treatment.
In S1, the oxidizing reagent may be one or more of an oxygen-containing reagent, an oxidizing sulfur-containing reagent, and an oxidizing halogen-containing reagent.
Wherein, the oxygen-containing reagent is preferably one or more of peroxide, aqueous solution of peroxide, inorganic oxidant, aqueous solution of inorganic oxidant and oxygen-containing gas, preferably oxygen-containing gas, more preferably one or more of air, oxygen and ozone, such as air, for the purpose of convenient use and cost control; the peroxide can be benzoyl peroxide and/or hydrogen peroxide; the inorganic oxidant can be one or more of nitric acid, sulfuric acid, potassium permanganate, potassium perchlorate and potassium dichromate.
Wherein the sulfur-containing agent having oxidizing properties is preferably an aqueous solution of a persulfate and/or a persulfate, such as one or more of ammonium persulfate, hydrogen persulfate and a sulfur-containing carbon disulfide solution.
Among them, the oxidizing halogen-containing reagent is preferably one or more of fluorine gas, chlorine gas, liquid bromine, and hydrogen chloride.
In S1, the oxidation may be performed by microwave or ultraviolet light.
At S1, the oxidation involves volatile emissions; the volatile component discharge means that the content of volatile small molecules in coal is reduced through heating and oxidation, and the bonding and structural damage of coal particles in subsequent heat treatment are reduced.
In S1, the temperature of the oxidation is preferably 200-500 ℃.
The oxidation can be realized by a segmented temperature control manner or a continuous temperature control manner, preferably a segmented temperature control manner, and more preferably a three-segment temperature control manner, for example, the first-segment temperature is 200 ℃, the second-segment temperature is 250 ℃, and the third-segment temperature is 320 ℃. The rate of temperature increase from the second-stage temperature to the third-stage temperature is preferably 20 ℃/hour.
In S1, the time for oxidation is preferably 0.5-48 hours, the oxidation is stopped until the volatile component of the coal-based carbon is less than 10% and the coal-based carbon is heated to 500 ℃ and no melting occurs; wherein the melting is in a liquid state as is conventional in the art.
In S1, the aeration frequency of the oxidation may be 0.1 to 5 times/min, preferably 0.2 times/min.
In S1, D50 of the pulverized coal obtained after the regrinding is preferably 8 μm. When the D50 of the coal powder is larger than 35 mu m, the poor dynamic performance and the poor rate capability of the electrode material can be caused; poor electrode processing, difficult coating, scratches, unevenness and the like.
In S1, the pulverized coal obtained after the re-pulverization preferably has a volatile content of 10% or less, but not zero, and more preferably 8%. The volatile component of the coal dust is more than 10 percent, which can cause the adhesion of material particles in the subsequent treatment, thereby causing poor pretreatment effect, difficult screening of finished products and no adhesion property of the coal dust.
In S1, the pulverization and the re-pulverization are both performed by using techniques and equipment known in the art, preferably by using pulverization equipment, and further preferably by using one or more of jet milling, roll milling, mechanical milling and ball milling.
In S1, the regrinding is to crush to a target particle size, and it is further preferable to shape the crushed or reground coal-based carbon to optimize parameters such as morphology, aspect ratio, sphericity, and the like of the coal-based carbon particles. During the pretreatment process, the coal-based raw materials may undergo morphology changes such as pulverization and adhesion, and particle size distribution changes. Therefore, the pretreated coal-based raw material needs to be pulverized to achieve the particle size distribution of the target product.
At S1, the pulverization and the re-pulverization are respectively followed by a sieving operation as is conventional in the art.
In S1, the pulverization before oxidation provides a relatively large solid-gas reaction interface for the oxidation heat treatment, which facilitates the reaction. Since the smaller particles are locally inhomogeneous in the reaction, the size of the pulverized particles is not preferably smaller than the target particle size for the re-pulverization. In the oxidation process, the coal-based carbon particles are bonded to a certain extent, so that the bonding capability of the oxidized coal-based carbon particles is damaged in order to ensure the particle size of the product after the oxidation and the subsequent treatment is basically free of bonding.
At S2, the volatile organic compound may be a meltable carbonaceous material below 500 ℃, which means a carbonaceous material that can be melted into a liquid state, preferably one or more of a thermoplastic, a thermoplastic resin, and a low molecular organic compound, more preferably one or more of polyethylene, polyvinyl chloride, polypropylene, polystyrene, petroleum resin, tar, heavy oil, residual oil, coal tar, naphthalene, phenanthrene, anthracene, and pyrene, such as coal tar or anthracene.
In S2, the dosage of the volatile organic compound is preferably 5-20%;
wherein, when the volatile organic compound is coal tar pitch, the coal tar pitch is preferably 5-10% of the mass of the coal powder in S1.
When the volatile organic compound is anthracene, the anthracene is preferably 10-20% of the mass of the coal powder in S1.
In a preferred embodiment of the present application, the volatile organic compound is coal tar pitch, the coal tar pitch has a carbon residue value of 5-40%, a softening point of 180 ℃, D50 of 5 μm, and the coal tar pitch is 8% of the mass of the coal powder in S1.
In another preferred embodiment of the present application, the volatile organic compound is anthracene, and the anthracene accounts for 15% of the mass of the coal powder in S1.
In S2, the mixing may be performed by a mechanical device with high shear force, such as a fusion machine or a kneader, which is conventional in the art, to improve the dispersion and surface fusion bonding of the volatile organic compounds in the pretreated pulverized coal.
In S2, the low temperature heat treatment is performed in a rotary furnace conventional in the art.
S2, the low-temperature heat treatment may be performed in one or more of an oxidizing atmosphere, a reducing atmosphere, and an inert atmosphere; wherein, the oxidizing atmosphere can be air and/or ozone-nitrogen mixed gas; wherein the reducing atmosphere can be one or more of ammonia gas, hydrogen gas and a mixed gas of 5% hydrogen gas and 95% argon gas; wherein the inert atmosphere can be nitrogen and/or argon; when the low-temperature heat treatment is carried out in the oxidizing atmosphere, the ventilation frequency of the oxidizing atmosphere is 0.1-5 times/min; when the low-temperature heat treatment is carried out in the reducing atmosphere and the inert atmosphere, the ventilation frequency of the reducing atmosphere and the inert atmosphere is 0.1-3 times/minute.
In S2, the temperature of the low temperature heat treatment may be generally 200 ℃ to 800 ℃, preferably 350 ℃ to 600 ℃.
In S2, the temperature rise rate of the low-temperature heat treatment may be 0 to 20 ℃/min, preferably 3 ℃/min.
In S2, the time of the low temperature heat treatment may be 3 to 9 hours, preferably 6 hours.
In S2, the ventilation frequency of the low-temperature heat treatment may be 0.05 to 0.2 times/min.
In S2, the low-temperature heat treatment is performed in an oxidizing atmosphere and/or an inert atmosphere.
In a preferred embodiment of the present application, the low temperature heat treatment can be divided into a first stage and a second stage.
Wherein the first stage is carried out under an oxidizing atmosphere; the rate of temperature rise in the first stage may be 3 ℃/minute; the temperature of the first stage may be 360 ℃; the time for the first stage may be 3 hours; the aeration frequency of the oxidizing atmosphere may be 0.2 times/min.
Wherein the second stage is carried out under an inert atmosphere; the temperature rise rate of the second stage can be 3 ℃/min; the temperature of the second stage may be 600 ℃; the time for the second stage may be 3 hours; the inert atmosphere may be ventilated at a frequency of 0.05 times/minute.
In S2, the modified coal powder may be a surface-modified coal powder. Due to the internal and external unevenness of the oxidation reaction and the discharge of volatile components, the coal powder obtained by pretreatment has larger specific surface area and increased surface cracks and defects. The first coulombic efficiency and the cycle instability are shown in the electrochemical test. Volatile organic compounds are used for low-temperature treatment, a coating layer can be formed on the surface of the pretreated pulverized coal, and the surface of the pores in the particles is partially blocked, so that small-bellied pores are formed in the subsequent treatment, and the capacity of the sodium ion battery is improved; the degree of roundness of the particles with more sharp corners on the surface after being crushed can be improved in a coating mode; the surface cracks and defects of the coal powder can be modified, and the purposes of reducing the defects, reducing the specific surface area, improving the flowability of the powder and the like are achieved.
In S2, the specific surface area of the modified coal powder is preferably not more than 5m2(ii)/g; the volatile matter of the modified coal dust is preferably not higher than 8%.
S3, the high-temperature heat treatment is carried out in one or more of inert atmosphere, reducing atmosphere and vacuum; preferably a reducing atmosphere or vacuum; more preferably a vacuum; wherein the inert atmosphere is preferably argon and/or nitrogen; wherein the reducing atmosphere is preferably one or more of ammonia gas, hydrogen gas and a mixed gas of 5% hydrogen gas and 95% argon gas.
In S3, the high-temperature heat treatment may be a constant-temperature heat treatment, a continuous-temperature-rise heat treatment or a temperature-programmed heat treatment; preferably a programmed temperature rise-holding heat treatment.
In S3, the ventilation frequency of the high-temperature heat treatment is preferably 0.1 to 3 times/min.
In S3, the high-temperature heat treatment is preferably performed in a temperature-raising and holding apparatus, such as a kiln or a vacuum furnace; when a vacuum furnace is used, the pressure is preferably 5kPa or less.
In S3, the high temperature heat treatment is preferably 1000 to 1800 ℃, and more preferably 1300 to 1750 ℃.
In S3, the high temperature heat treatment is preferably performed for 1 to 8 hours, and more preferably for 1 to 4 hours.
In S3, the content of nitrogen in the coal-based carbon negative electrode material is preferably not higher than 0.5%, and the interlayer spacing of (002) crystal face corresponding to the maximum value of the (002) crystal face diffraction peak of the coal-based carbon negative electrode material 2 theta approximately equal to 26 degrees in XRD test is 0.34-0.38 nm. The high-temperature heat treatment is used for discharging impurity elements such as nitrogen, oxygen, metal and the like in the materials after the low-temperature heat treatment.
The invention also provides the coal-based carbon negative electrode material prepared by the preparation method of the coal-based carbon negative electrode material.
The invention also provides application of the coal-based carbon negative electrode material in a battery and/or a super capacitor.
Wherein the battery is a liquid battery and/or a solid-state battery, more preferably a lithium ion or sodium ion battery.
The invention also provides a battery containing the coal-based carbon negative electrode material, and the battery comprises a lithium ion battery or a sodium ion battery.
Wherein the lithium ion battery preferably has the following properties: the button half-cell 3C rapid discharge constant current ratio is higher than 40%; the first charging capacity is higher than 400mAh/g, and the first coulombic efficiency is higher than 85%; the capacity retention rate can reach more than 85% after 1000 cycles.
Wherein the sodium ion battery preferably has the following properties: the first charge capacity of the button half-cell is higher than 280mAh/g under the charge-discharge current density of 100mA/g, and the first coulombic efficiency is higher than 90%.
On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.
The positive progress effects of the invention are as follows:
(1) the coal-based carbon cathode material has the characteristics of low price, stable batch and easiness in large-scale industrial production, reduces environmental pollution and carbon emission, is green in development and beneficial to resource utilization of coal and commercial application of boosted sodium-ion batteries.
(2) The coal-based carbon negative electrode material prepared by the invention is applied to a lithium battery, and has excellent lithium ion intercalation and deintercalation capability and excellent cycle capability. The performance can reach: the button half-cell 3C quick discharge constant current ratio is higher than 40%, the first charge capacity is higher than 400mAh/g, the first coulombic efficiency is higher than 85%, and the capacity retention rate can reach more than 85% after 1000 cycles, so that the commercial performance requirements of lithium ions with high energy density and high first coulombic efficiency can be met.
(3) The coal-based carbon negative electrode material prepared by the invention is applied to a sodium ion battery, and has excellent sodium ion intercalation and deintercalation capability and excellent circulation capability. The performance can reach: the first charge capacity of the button half-cell is higher than 280mAh/g under the charge-discharge current density of 100mA/g, the first coulombic efficiency is higher than 90%, and the commercial performance requirements of the sodium-ion cell with high energy density and high first coulombic efficiency can be met.
Drawings
FIG. 1 is an XRD pattern of a coal-based carbon negative electrode material obtained in example 1 of the present invention;
fig. 2 is an SEM image of the coal-based carbon negative electrode material obtained in example 1 of the present invention.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The reagents and starting materials used in the present invention are commercially available. Reference may be made to conventional methods in the art or to descriptions of related materials, equipment, and equipment for methods and methods not specifically described herein. Unless otherwise specified, the tests described in the present invention are performed according to the current national standards.
The coal-based raw material is obtained by carrying out ore opening, crushing, flotation and mechanical processing on the coal-based raw material, and is clean coal with 45% of volatile content and 2.1% of ash content, the asphalt adopts commercially available petroleum asphalt with a softening point of 180 ℃, and other reagents are commercially available and have purity Analytical Reagent (AR) and above.
Example 1
Pretreatment of coal-based raw materials
Firstly, fine coal washing is pulverized until D50 is 50 micrometers, then the fine coal washing is put into an electric heating spiral ribbon type mixer, air is continuously introduced into the electric heating spiral ribbon type mixer for oxidation operation, the volume of the pulverized coal-based raw material is 50% of the effective volume of the electric heating spiral ribbon type mixer, the temperature is raised to 200 ℃, and the ventilation frequency is 0.2 times/minute. After the temperature is continuously raised to 250 ℃, the temperature is raised to 350 ℃ according to the temperature raising rate of 20 ℃/hour, and the oxidation time is 6 hours. After the reaction is finished, the material is cooled to room temperature, and pulverized coal with 8 μm D50 and 8% of volatile component is obtained by airflow crushing and sieving.
② low-temperature heat treatment
Adding coal tar pitch with the mass percentage of 5%, the softening point of 180 ℃, the carbon residue value of 38% and the D50 of 5 mu m into the pretreated coal dust, uniformly mixing the coal tar pitch and the pretreated coal dust in a fusion machine, putting the mixture into a rotary furnace for low-temperature heat treatment, introducing air, raising the ventilation frequency to 360 ℃ at 3 ℃/min, keeping the temperature for 3 hours, switching to nitrogen protection, wherein the ventilation frequency is 0.05 times/min, and the temperature is 3 DEG CHeating to 600 ℃ per minute and keeping the temperature for 3 hours to obtain the product with the specific surface area of 3m2(ii)/g, surface-modified coal powder with a volatile content of 5%.
High temperature heat treatment
And putting the modified coal powder into a vacuum furnace for high-temperature heat treatment, maintaining the pressure at 0-1 kPa, and carrying out heat treatment on the material at 1300 ℃ for 3 hours to obtain the coal-based carbon negative electrode material with the nitrogen content not higher than 0.5%.
Example 2
Preprocessing a coal-based raw material: same as example 1
② low-temperature heat treatment: same as example 1
High temperature heat treatment
And (3) putting the material subjected to low-temperature heat treatment into an argon protection ceramic tube furnace, keeping the ventilation frequency at 0.3 time/min under normal pressure, and maintaining the material at 1500 ℃ for 3 hours to obtain the coal-based carbon negative electrode material. The argon was purged at 0.05 times/min.
Example 3
Preprocessing a coal-based raw material: same as example 1
② low-temperature heat treatment
Adding 15 percent by mass of anthracene into pretreated coal powder, uniformly mixing in a fusion machine, putting into a rotary furnace, carrying out low-temperature heat treatment, introducing air firstly, wherein the ventilation frequency is 0.2 times/min, heating to 360 ℃ at 3 ℃/min, preserving heat for 3 hours, switching to nitrogen protection, the ventilation frequency is 0.05 times/min, heating to 600 ℃ at 3 ℃/min, preserving heat for 3 hours, and obtaining the specific surface area of 3m2(ii)/g, surface-modified coal powder with a volatile content of 5%.
High-temperature heat treatment: same as example 2
Example 4
Pretreatment of coal-based raw materials
Firstly, fine coal is pulverized until D50 is 50 μm, then the pulverized coal is put into a rotary furnace lined with ceramic, and hydrogen chloride gas is continuously introduced: oxidizing the mixed gas with the air volume ratio of 1:5, wherein the volume of the pulverized coal-based raw material is 50% of the effective volume of the electric heating helical ribbon mixer, heating to 200 ℃, and the ventilation frequency is 0.2 times/min. After the temperature is continuously raised to 250 ℃, the temperature is raised to 350 ℃ according to the temperature raising rate of 20 ℃/hour, and the oxidation time is 2 hours. After the reaction is finished, the material is cooled to room temperature, and pulverized coal with 8 μm volume distribution D50 and 8% volatile component is obtained by airflow re-crushing and sieving.
② low-temperature heat treatment
Same as example 3
High temperature heat treatment
The same as in example 2.
Comparative example 1
In this comparative example, no volatile organic compound was added before the low-temperature heat treatment of step S2.
Comparative example 2
In this comparative example, the washed fine coal powder which had not been subjected to the pretreatment and the low-temperature heat treatment was pulverized to D50 of 10 μm, and then the high-temperature heat treatment of step S3 in example 2 was directly applied to reduce the temperature of the material to room temperature and agglomerate the material, and pulverized again to D50 of 8 μm.
Comparative example 3
Pretreatment of coal-based raw materials
Firstly, fine coal washing is pulverized until D50 is 50 mu m, 5 mass percent of coal pitch with the softening point of 180 ℃, the carbon residue value of 38 percent and the D50 value of 5 mu m is added into the fine coal washing, then the fine coal washing is put into an electric heating spiral belt type mixer, air is continuously introduced into the electric heating spiral belt type mixer for oxidation operation, the volume of the material is 50 percent of the effective volume of the electric heating spiral belt type mixer, the temperature is raised to 200 ℃, and the ventilation frequency is 0.2 times/min. After 250 ℃, the temperature is raised to 350 ℃ according to the temperature raising rate of 20 ℃/hour, and the oxidation time is 6 hours. After the reaction is finished, the material is cooled to room temperature along with equipment, and pulverized coal with 8 μm of D50 and 8% of volatile component is obtained by airflow re-crushing and screening.
② low-temperature heat treatment
Firstly introducing air, wherein the ventilation frequency is 0.2 times/min, heating to 360 ℃ at 3 ℃/min, preserving heat for 3 hours, switching to nitrogen protection, wherein the ventilation frequency is 0.05 times/min, heating to 600 ℃ at 3 ℃/min, preserving heat for 3 hours, and obtaining the coal powder after low-temperature heat treatment.
High temperature heat treatment
Same as example 1
Effect example 1
The carbon negative electrode materials prepared in examples 1-4 and comparative examples 1-3 were subjected to physical and chemical property tests by a conventional method in the art, and the test results are shown in fig. 1-2 and table 1.
Wherein the particle size D50 is measured by Mastersize 2000 (Malvern 2000);
the apparent morphology is measured by a ZEISS 500 field emission scanning electron microscope;
the crystal structure was measured by a Brookfield D8X-ray diffractometer in a scanning mode of theta-2 theta with a step of 2 deg/s.
Fig. 1 is an XRD pattern of the coal-based carbon negative electrode material obtained in example 1 of the present invention. As can be seen from the figure, the XRD pattern of the coal-based carbon anode material obtained by the invention shows typical amorphous carbon characteristics, namely, a hump-like bulge appears near 2 theta-26 degrees, the position of the highest peak obviously shifts to the low-angle direction, and the peak width span is large. This indicates that the average (002) crystal face interlayer spacing of the coal-based carbon negative electrode material prepared by the invention is larger, and the (002) crystal face size is smaller. The peak value of the (002) crystal face interlayer spacing in the embodiment 1 of the invention is 0.375nm which is far larger than 0.335nm of graphite, which is very beneficial to the intercalation, diffusion and desorption of sodium ions and the rapid diffusion of lithium ions in the carbon cathode material.
Fig. 2 is an SEM image of the coal-based carbon negative electrode material obtained in example 1 of the present invention. As can be seen from fig. 2, the coal-based carbon negative electrode material obtained by the present invention has a single-particle characteristic, and the particle surface is smooth and has few defects that may cause deterioration of the negative electrode material, such as sharp angles, local protrusions, cracks, and the like. The single particle distribution of the coal-based carbon negative electrode material is that in the pretreatment process, the adhesive volatile components of the coal-based material are fully volatilized and react to form thermosetting components, so that the adhesive property of the coal-based material particles is greatly reduced. The volatile organic compounds are introduced to deposit on the surface concave part of the coal particles in the heat treatment process and finally become amorphous carbon, so that the coal-based negative electrode material has full particles and smaller specific surface area, and further shows better electrochemical performance.
Effect example 2
(1) Preparation of the electrodes
Mixing the carbon negative electrode materials obtained in examples 1-4 and comparative examples 1-3 with an acetylene black conductive agent and a PVDF binder at a mass ratio of 8:1:1 and NMP as a solvent at room temperature to prepare a uniform slurry, uniformly coating the slurry on a copper foil, wherein the coating surface density is about 6mg/cm2Then, the copper foil was put into a vacuum drying oven and dried at 80 ℃ for 12 hours. Cutting the dried copper foil into 2cm in area2The wafer of (a) is made into a working electrode.
(2) Assembly of button cell
Assembling the lithium ion button cell: under the condition of room temperature, taking a metal lithium sheet as a negative electrode and a counter electrode, taking the product obtained in the step (1) as a working electrode, taking a Celgard2400 polypropylene porous membrane as a diaphragm, and taking 1mol/L LiPF6The electrolyte solution of EC and DEC (volume ratio of 1: 1) is assembled into a CR-2032 type button cell in a vacuum glove box, and is sealed mechanically.
Assembling a sodium ion button cell: under the condition of room temperature, taking a metal sodium sheet as a negative electrode and a counter electrode, taking the product obtained in the step (1) as a working electrode, taking a GE-Whatman glass fiber diaphragm as a diaphragm, and taking 1mol/L NaPF6The electrolyte solution of EC and DMC (volume ratio of 1: 1) is assembled into a CR-2032 type button cell in a vacuum glove box, and is sealed mechanically.
(3) Specific capacity and capacity retention rate test
Testing the specific capacity and capacity retention rate of the lithium ion button cell: electrochemical testing was started after the assembled cell was allowed to stand at room temperature for 24 h. On an Arbin battery test system, the design capacity is 360mAh/g, the current of 0.1C is adopted in the first test cycle, the discharge is firstly carried out to 0V, and the charging voltage interval is 0V-2V. And standing for 5min after the charging or discharging is finished, and then carrying out the next process step. The button cell 3C rapid discharge constant current ratio test adopts the button cell after 3 weeks of 0.1C circulation, firstly carries out 0.1C charge to 2V, then uses 3C to discharge to 5mV to obtain the capacity a, and then uses 0.1C to discharge to 5mV to obtain the capacity b. The 3C fast discharge constant current ratio is a/(a + b) × 100%.
Testing the specific capacity and capacity retention rate of the sodium ion button cell: electrochemical testing was started after the assembled cell was allowed to stand at room temperature for 24 h. On an Arbin battery test system, the current of 100mA/g is adopted in the first test cycle according to the mass of active substances, the discharge is firstly carried out to 0V, and the charging voltage interval is 0V-2V. Standing for 5min after charging or discharging.
Through tests, the particle size and the specific surface area of the coal-based carbon negative electrode materials prepared in the examples 1 to 4 and the comparative examples 1 to 3, and the capacity and the 3C fast discharge constant current ratio of the coal-based carbon negative electrode materials when the coal-based carbon negative electrode materials are used in lithium ion batteries and sodium ion batteries are shown in the table 1.
TABLE 1 Performance test results of coal-based carbon negative electrode materials
As can be seen from table 1, in comparative example 1, when no volatile organic compound was added, the coal-based negative electrode material can exhibit the first capacity of the lithium ion battery similar to that of the examples, but the capacity of the sodium ion battery is greatly different, and the first coulombic efficiency is also significantly lower than that of examples 1 to 4. Comparative example 2 adopts a direct coal carbonization mode, and the prepared coal-based carbon negative electrode material is remarkably lower than that of examples 1-4 in capacity and efficiency. Comparative example 3 employs the addition of volatile organic compounds at the pretreatment stage, but the reversible capacity of both lithium and sodium batteries is lower than that of examples 1-4. This is because the addition of volatile organic compounds in the pretreatment stage is not conducive to the oxidation reaction of pulverized coal, and finally results in higher structural order degree, fewer micropores and lower capacity. In the embodiments 1 to 4 of the present invention, the following effects are produced by adding the volatile organic compound after oxidation: (1) the volatile components in the coal lose the adhesive property through oxidation; (2) part of substances in the coal react with oxygen to interfere the arrangement of carbon atoms in the coal so as to realize larger interlayer spacing; (3) the oxygen atoms occupy certain positions after entering the coal, and are removed together with H or C in the subsequent high-temperature carbonization to form micropores.
In example 1, the high-temperature heat treatment in the vacuum furnace showed a high lithium storage capacity due to a developed pore structure, but the sodium storage capacity was inferior to that of example 4 because some of the pores were small. Example 4 a part of hydrogen chloride gas was introduced in the pretreatment of the coal-based material, which can effectively remove a part of metallic and non-metallic impurities from the raw material coal and form a suitable pore structure in the coal-based material, so that the capacity and efficiency of the coal-based material are both better. The coal-based carbon negative electrode material obtained in any one of the embodiments 1 to 4 is superior to that of the comparative example. The reason is that proper oxidation pretreatment can not only promote thermoplastic substances in the coal to be converted into thermosetting property, but also introduce non-carbon elements into the coal and remove the non-carbon elements in subsequent treatment to interfere the carbon atoms to develop towards the direction of graphite, so that the amorphous carbon material with larger (002) crystal plane interlayer spacing and smaller graphite microcrystallines is obtained.
Claims (10)
1. The preparation method of the coal-based carbon negative electrode material is characterized by comprising the following steps of:
s1: pretreating a coal-based raw material to obtain coal powder; d50 of the coal powder is 1-35 mu m; the pretreatment sequentially comprises crushing, oxidation and re-crushing;
s2: uniformly mixing volatile organic compounds with the pulverized coal, and performing low-temperature heat treatment to obtain modified pulverized coal;
s3: and carrying out high-temperature heat treatment on the modified coal powder to obtain the coal-based carbon negative electrode material.
2. The method for preparing the coal-based carbon negative electrode material according to claim 1, wherein in S1, the coal-based raw material is washed clean coal of light and/or young coal; the annual light coal is one or more of bituminous coal, lignite and peat; wherein the content of the first and second substances,
the volatile content of the clean coal is 20-50%, preferably 45%;
and/or the ash content of the clean coal is less than 5%, preferably 2.1%;
and/or the volatile components of the bituminous coal and the lignite are 8-60%, and the ash content is 8%.
3. The method for preparing the coal-based carbon negative electrode material as claimed in claim 1, wherein in S1, the coal-based raw material is pulverized to 20 to 100 μm;
and/or the reactor for oxidation is an electric heating reaction furnace or an electric heating ribbon blender mixer;
and/or, in the crushing process, the volume of the crushed coal-based raw material is 50% of the effective volume of the reactor in which the oxidation occurs;
and/or the oxidizing reagent is one or more of an oxygen-containing reagent, a sulfur-containing reagent with oxidizing property and a halogen-containing reagent with oxidizing property;
and/or, the oxidation is carried out by adopting a microwave or ultraviolet mode;
and/or the temperature of the oxidation is 200-500 ℃;
and/or the oxidation time is 0.5-48 hours;
and/or the ventilation frequency of the oxidation is 0.1-5 times/min.
4. The method for preparing the coal-based carbon negative electrode material as claimed in claim 3, wherein in S1, the coal-based raw material is pulverized to 50 μm;
and/or the oxygen-containing reagent is one or more of peroxide, aqueous peroxide solution, inorganic oxidant, aqueous inorganic oxidant solution and oxygen-containing gas, preferably oxygen-containing gas, more preferably one or more of air, oxygen and ozone, such as air; the peroxide is benzoyl peroxide and/or hydrogen peroxide; the inorganic oxidant is one or more of nitric acid, sulfuric acid, potassium permanganate, potassium perchlorate and potassium dichromate;
and/or, the sulfur-containing agent having oxidizing properties is an aqueous solution of a persulfate and/or a persulfate, such as one or more of ammonium persulfate, hydrogen persulfate, and a sulfur-containing carbon disulfide solution;
and/or the oxidizing halogen-containing reagent is one or more of fluorine gas, chlorine gas, liquid bromine and hydrogen chloride;
and/or, the oxidation adopts a segmented temperature control mode or a continuous temperature control mode, preferably a segmented temperature control mode, more preferably a three-segment temperature control mode, for example, the first segment temperature is 200 ℃, the second segment temperature is 250 ℃, and the third segment temperature is 320 ℃;
and/or the heating rate from the second section temperature to the third section temperature is 20 ℃/hour;
and/or, the aeration frequency of the oxidation is 0.2 times/min;
and/or the D50 of the pulverized coal obtained after the re-crushing is 8 μm;
and/or the volatile content of the pulverized coal obtained after the re-crushing is less than or equal to 10 percent but not zero, preferably 8 percent;
and/or, the pulverization and the re-pulverization adopt one or more of jet milling, roll milling, mechanical milling and ball milling;
and/or, respectively carrying out screening operation after the crushing and the re-crushing.
5. The method for preparing the coal-based carbon negative electrode material according to claim 1, wherein in S2, the volatile organic compound is a carbon-containing substance meltable below 500 ℃, preferably one or more of thermoplastics, thermoplastic resins and low molecular organic compounds, more preferably one or more of polyethylene, polyvinyl chloride, polypropylene, polystyrene, petroleum resins, tar, heavy oil, residual oil, coal pitch, naphthalene, phenanthrene, anthracene and pyrene, such as coal pitch or anthracene;
and/or the using amount of the volatile organic compounds is 5-20%; wherein when the volatile organic compound is coal tar pitch, the coal tar pitch is 5-10% of the mass of the coal powder in S1; wherein when the volatile organic compound is anthracene, the anthracene accounts for 10-20% of the mass of the coal powder in S1;
and/or, the mixing adopts a fusion machine or a kneader;
and/or, the low temperature heat treatment is carried out in a rotary furnace;
and/or, the low-temperature heat treatment is carried out in one or more of an oxidizing atmosphere, a reducing atmosphere and an inert atmosphere; wherein the oxidizing atmosphere is air and/or ozone-nitrogen mixed gas; wherein the reducing atmosphere is one or more of ammonia gas, hydrogen gas and a mixed gas of 5% hydrogen gas and 95% argon gas; wherein the inert atmosphere is nitrogen and/or argon; when the low-temperature heat treatment is carried out in the oxidizing atmosphere, the ventilation frequency of the oxidizing atmosphere is 0.1-5 times/min; when the low-temperature heat treatment is carried out in the reducing atmosphere and the inert atmosphere, the ventilation frequency of the reducing atmosphere and the inert atmosphere is 0.1-3 times/minute;
and/or the temperature of the low-temperature heat treatment is 200-800 ℃, preferably 350-600 ℃;
and/or the heating rate of the low-temperature heat treatment is 0-20 ℃/min, preferably 3 ℃/min;
and/or the time of the low-temperature heat treatment is 3 to 9 hours, preferably 6 hours;
and/or the ventilation frequency of the low-temperature heat treatment is 0.05-0.2 times/min;
and/or, the low temperature heat treatment is carried out under an oxidizing atmosphere and/or an inert atmosphere;
and/or the specific surface area of the modified coal powder is not higher than 5m2(ii)/g; the volatile component of the modified coal powder is not higher than 8%.
6. The preparation method of the coal-based carbon negative electrode material as claimed in claim 5, wherein in S2, the volatile organic matter is coal pitch, the coal pitch has a carbon residue value of 5-40%, a softening point of 180 ℃, D50 of 5 μm, and the coal pitch is 8% of the mass of the coal powder in S1; or the volatile organic matter is anthracene, and the anthracene accounts for 15% of the mass of the coal powder in S1;
and/or, the low temperature heat treatment is divided into a first stage and a second stage; wherein the first stage is carried out under an oxidizing atmosphere; the temperature rise rate of the first stage is 3 ℃/min; the temperature of the first stage is 360 ℃; the time of the first stage is 3 hours; the ventilation frequency of the oxidizing atmosphere is 0.2 times/min; wherein the second stage is carried out under an inert atmosphere; the temperature rise rate of the second stage is 3 ℃/min; the temperature of the second stage is 600 ℃; the time of the second stage is 3 hours; the aeration frequency of the inert atmosphere was 0.05 times/min.
7. The method for preparing the coal-based carbon negative electrode material as claimed in claim 1, wherein, in S3, the high-temperature heat treatment is performed in one or more of an inert atmosphere, a reducing atmosphere, and a vacuum; preferably a reducing atmosphere or vacuum; more preferably a vacuum; wherein the inert atmosphere is argon and/or nitrogen; wherein the reducing atmosphere is one or more of ammonia gas, hydrogen gas and a mixed gas of 5% hydrogen gas and 95% argon gas;
and/or the high-temperature heat treatment is constant-temperature heat treatment, continuous heating heat treatment or programmed heating heat treatment; preferably, the temperature rise-heat preservation heat treatment is controlled by a program;
and/or the ventilation frequency of the high-temperature heat treatment is 0.1-3 times/min;
and/or, the high temperature heat treatment is carried out in a temperature-raising and holding apparatus, such as a kiln or a vacuum furnace; when a vacuum furnace is used, the pressure is preferably 5kPa or less;
and/or, the high-temperature heat treatment is 1000-1800 ℃, preferably 1300-1750 ℃;
and/or, the high-temperature heat treatment is carried out for 1 to 8 hours, preferably 1 to 4 hours.
8. The coal-based carbon negative electrode material prepared by the preparation method of the coal-based carbon negative electrode material as claimed in any one of claims 1 to 7.
9. The use of the coal-based carbon negative electrode material of claim 8 in a battery and/or a supercapacitor; wherein the battery is a liquid battery and/or a solid-state battery, preferably a lithium ion or sodium ion battery.
10. A battery comprising the coal-based carbon negative electrode material of claim 8, the battery comprising a lithium ion battery or a sodium ion battery.
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