CN114044513A - Preparation method of coal-based graphite/carbon composite negative electrode material for power type lithium ion battery - Google Patents

Preparation method of coal-based graphite/carbon composite negative electrode material for power type lithium ion battery Download PDF

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CN114044513A
CN114044513A CN202111330723.4A CN202111330723A CN114044513A CN 114044513 A CN114044513 A CN 114044513A CN 202111330723 A CN202111330723 A CN 202111330723A CN 114044513 A CN114044513 A CN 114044513A
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negative electrode
coal
lithium ion
pressure
electrode material
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CN114044513B (en
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侯春平
马少宁
王兴蔚
侯佼
马勇
贺超
杨丹
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Bolt New Materials Yinchuan Co ltd
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    • CCHEMISTRY; METALLURGY
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    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00Carbon; Compounds thereof
    • C01B32/20Graphite
    • C01B32/205Preparation
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00Carbon; Compounds thereof
    • C01B32/05Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/052Li-accumulators
    • H01M10/0525Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/362Composites
    • H01M4/366Composites as layered products
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/58Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/62Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M2004/026Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027Negative electrodes
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries

Abstract

The invention discloses a preparation method of a coal-based graphite/carbon composite negative electrode material for a power type lithium ion battery, which comprises the steps of wetting and mixing, heating and pressurizing, pressure relief treatment, coating modification, carbonization treatment and the like. The invention takes graphitized anthracite micro powder as a raw material, adopts an environment-friendly solid phase, low-temperature low-pressure controllable micro expansion technology, coating, carbonization and other processes, and the prepared cathode material has a porous structure and a microcrystal particle structure on the microcosmic aspect, and the distance between graphite flake layers is enlarged, and the cathode material is represented as micron-scale particles on the macroscopic aspect, so that the specific surface area is greatly reduced, a short and developed diffusion channel is easily provided for lithium ion diffusion, the diffusion of lithium ions is accelerated, the lithium ion is suitable for being embedded and embedded in the charging and discharging process under the conditions of high power and low temperature, and meanwhile, the amorphous carbon shell protective layer enables the microcrystal structure to have structural stability and can meet the charging and discharging under the long-cycle condition. The material has excellent multiplying power, low temperature and cycle performance, and is suitable for being used as a negative electrode material of a power type lithium ion battery.

Description

Preparation method of coal-based graphite/carbon composite negative electrode material for power type lithium ion battery
Technical Field
The invention relates to the technical field of new energy lithium ion battery materials, in particular to a preparation method of a coal-based graphite/carbon composite negative electrode material for a power type lithium ion battery.
Background
As the most important basic energy and energy safety ballast stone in China, the coal has to go the way of innovation of intelligent green development and clean low-carbon utilization, and the coal resource is promoted to become the most competitive energy and raw material resource through continuous technical innovation. The non-combustion utilization technology for developing coal has a very wide market space and higher economic value in the fields of chemical industry, materials and the like, while the lithium ion battery is used as one of key energy storage devices and technologies for developing and utilizing new energy, and the development and utilization of coal as a lithium ion battery cathode material becomes an important subject in the cross research direction of new materials and new energy. The industrial report of producing the lithium ion battery cathode material by taking the Taixi coal even the coal as the raw material is not available, so that the realization of the research and the development and the industrialization of the Taixi coal cathode material can promote the transformation and the upgrade of the coal industry and the high-value clean utilization of the Taixi coal, generate good economic benefit and social benefit, meet the low-carbon development strategy of the 'double-carbon' target in China, and have strong practical significance for the healthy and sustainable development of the national economy and the society.
At present, the negative electrode materials of the lithium ion battery mainly use artificial graphite and natural graphite. China has abundant natural graphite resources which account for about 70 percent of the global reserves, but has the problems of uneven distribution, low carbon content, high mining and processing cost, serious pollution and the like, and meanwhile, the cost of the artificial graphite is high under the influence of factors such as raw materials, environmental protection and the like, so people have to find cheap and abundant substitutes. Coal is used as a resource with high carbon content, has an aromatic ring structure similar to graphite, has a compact structure layer of carbon atoms in the coal, has good orientation, has the potential of converting to the graphite structure at high temperature, and is a high-quality raw material for producing graphitized products. The coal has a microcrystalline structure after graphitization treatment, and the low-temperature performance and the rate capability of the material are excellent. The coal resource reserves in China are rich, the anthracite is used for preparing the negative electrode material of the lithium ion battery, the high-efficiency clean utilization of the coal can be realized, the production cost of the negative electrode material is reduced, the additional value of the coal can be greatly improved, and the lithium ion battery has wide market application prospects.
There are not too many scientific research institutes and enterprises developing research on anthracite negative electrode materials in China, such as Hunan university, Shenzhen fibrate, Shanghai fir science and Jiangxi Zi essence, but no commercialized products are reported.
The King crystal of Beijing university of science and technology and the like take low-cost high-quality anthracite rich in resources in China as a raw material, the negative electrode material for the lithium battery is prepared by high-temperature purification and graphitization at 2800 ℃, and the same means is used for processing the precursor petroleum coke of the commercial graphite and comparing the precursor petroleum coke with the graphitization anthracite. The result shows that the graphitization degree of the anthracite-based graphitized negative electrode material can reach 95.44 percent, and the specific surface area is 1.1319m2g-1And the graphite sheet layer structure is smooth and flat. The graphitized anthracite has the initial coulombic efficiency of 87 percent as a negative electrode material of a lithium ion battery, and has 345.3mAh g under the current density of 0.1C-1And the material shows better lithium storage performance than graphitized petroleum coke material at high magnification, which is attributed to the more regular and highly ordered structure of graphitized anthracite.
Jianninglin of Shanghai fir technology Limited company takes Ningxia Taixi anthracite as raw material and is subjected to coarse crushing, grinding, graphitization and the likeThe anthracite-based lithium ion battery cathode material is prepared by a single process. The test result shows that the graphitized anthracite-based negative electrode has the graphitization degree of 92.23 percent and shows 340.2mAh g-1The reversible capacity of the graphite is equivalent to the negative electrode capacity of the petroleum coke-based graphite before calcination.
The structure and the performance of anthracite are analyzed by Wangxianfei of the New energy Material Ltd of Beijing City, Shenzhen, and the like, and the synthesis method of anthracite as the lithium ion battery cathode material and the research progress thereof are summarized, so that the research direction of preparing the lithium ion battery cathode material by anthracite is pointed out, and a large amount of research needs to be continued to prepare the lithium ion battery cathode material by taking anthracite as the raw material, so that the performances of all aspects of the lithium ion battery can be continuously improved. Once the anthracite-based negative electrode material successfully enters the market, the cost of the negative electrode material is necessarily greatly reduced. Meanwhile, after the anthracite is graphitized, a mesoporous and macroporous structure appears, and the specific surface area is also increased, which has great significance for developing power batteries and low-temperature batteries.
The use of anthracite as the negative electrode material of sodium ion battery is also a focus of research in recent years by the researchers and the industry. The Huyong problem group of physics of Chinese academy of sciences adopts anthracite as precursor, and utilizes the processes of pulverizing and one-step carbonization to obtain a carbon negative electrode material with excellent sodium storage property, and utilizes the cracked anthracite to obtain a soft carbon material, but is different from soft carbon material from asphalt, and still has high disorder degree below 1600 deg.C, its carbon yield is up to 90%, and sodium storage capacity is up to 220mAh g-1The cyclic stability is excellent, and the performance is also excellent in the aspects of rate performance and low-temperature performance.
The research and the invention generally prepare the composite cathode material by crushing the smokeless coal, mixing the pulverized smokeless coal with a binder, needle coke, or an oxide, or a silicon oxide and other substances, and then carrying out processes such as molding, graphitization and the like.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a preparation method of a coal-based graphite/carbon composite negative electrode material for a power type lithium ion battery, which adopts an environment-friendly controllable low-temperature low-pressure micro-expansion technology to solve the problems of solvent treatment and environmental protection caused by wet processes such as oxidation stripping reduction and electrochemical expansion adopted by conventional graphite layer expansion and the problem that the expansion degree of the conventional process layer expansion is difficult to control, thereby improving the power of the coal-based graphite/carbon composite negative electrode material, prolonging the cycle life, reducing the production cost and being suitable for large-scale industrialization.
The invention provides a preparation method of a coal-based graphite/carbon composite negative electrode material for a power type lithium ion battery, which comprises the following steps:
(1) wetting and mixing: fully and uniformly mixing the graphitized anthracite micro powder with a certain amount of deionized water and surfactant to ensure that water molecules can enter pores and gaps of the graphitized anthracite particles to obtain a wetting mixture;
(2) temperature rising and pressure increasing: placing the wetted mixture obtained in the step (1) in a pressure container, heating to a heat preservation temperature, keeping the temperature constant until the heat preservation pressure is reached in the pressure container, and then continuing to preserve heat for a certain time;
(3) pressure relief treatment: releasing the pressure of the pressure container subjected to heat preservation and pressure maintaining in the step (2) to the standard atmospheric pressure within 3-30 s to complete the pressure release process, so as to obtain a micro-expanded graphitized anthracite precursor;
(4) coating modification: placing the micro-expanded graphitized anthracite precursor prepared in the step (3) and an organic carbon source accounting for 1-20% of the mass of the precursor in a mixer, stirring and mixing under the protection of inert atmosphere, simultaneously heating to 150-350 ℃, and preserving heat for 0.5-10 hours under the stirring state to prepare a precursor composite material;
(5) carbonizing treatment: and (3) placing the precursor composite material prepared in the step (4) in a crucible, heating to 650-1400 ℃ at a heating rate of 2-10 ℃/min in an inert atmosphere protection furnace, carrying out heat preservation carbonization treatment for 3-20 h, then naturally cooling to room temperature, and carrying out scattering and sieving treatment to prepare the coal-based graphite/carbon composite negative electrode material.
Preferably, in step (1): the mass percentage of the graphitized anthracite micro powder, deionized water and a surfactant is 1: (0.5-20): (0.05-2).
Preferably, in step (1): the particle size D50 of the graphitized anthracite is 4.0-18.0 mu m, the carbon content is more than 99.0%, the graphitized anthracite is obtained by graphitizing, crushing and sieving anthracite raw materials, and the anthracite raw materials are one of taixi anthracite, artificial graphite with a micropore/porous structure or natural graphite; the surfactant is ethanol, or stearic acid, or oleic acid, or lauric acid, or sodium dodecyl benzene sulfonate, or fatty glyceride and the like; the mixing and dispersing equipment used for mixing is a VC mixer, a fusion machine, a stirring mixer or the like.
Preferably, in step (2): the heating rate is 1-20 ℃/min, the heat preservation temperature is 120-350 ℃, the heat preservation pressure is 0.15-1.0 MPa, and the continuous heat preservation time is 2-10 min after the heat preservation pressure is reached.
Preferably, in step (2): the pressure vessel is a pressure cooker, a popcorn machine, a reaction kettle, a hydrothermal reaction kettle or an autoclave, and is provided with an air pressure gauge and an explosion-proof valve; the heating mode of the pressure container for heating is electric heating, coal gas heating or microwave heating.
Preferably, in step (4): the organic carbon source is one or more of epoxy resin, asphalt, phenolic resin, acrylic resin, furan resin, ethyl methyl carbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyimide, styrene-butadiene rubber and carboxymethyl cellulose.
Preferably, in step (4): the heating and temperature rising speed of the mixer is 1-10 ℃/min, and the mixer is a VC mixer, a reaction kettle, a kneading machine, a mixing roll or an internal mixer; the stirring speed is 50-200 rpm; the inert atmosphere is one or more of nitrogen, argon and helium.
Preferably, in step (5): the crucible is one of a graphite crucible, a corundum crucible and a ceramic crucible.
Preferably, in step (5): the inert gas is one or more of nitrogen, argon and helium, and the inert gas flowThe amount of the surfactant is 0.1 to 1.2m3H; the inert atmosphere protection furnace is a tube furnace, a box furnace, a rotary furnace or a tunnel kiln;
preferably, in step (5): the scattering equipment used for scattering treatment is a planetary ball mill, a universal pulverizer, a jet mill or an ultrafine pulverizer.
The working principle of the invention is as follows: the invention discloses a coal-based graphite/carbon composite negative electrode material for a power type lithium ion battery and a preparation method thereof, which takes graphitized anthracite as a raw material and adopts a low-temperature low-pressure controllable micro-expansion technology, namely a popcorn principle: firstly, slightly wetting graphite with the carbon content of more than 99 percent, and putting the graphite into a pressure container; heating the pressure container, and increasing the pressure of the gas in the pressure container with the continuous increase of the temperature of the pressure container; when the temperature reaches a certain degree, the pressure inside and outside the graphite particles is balanced; when the pressure of the pressure vessel continues to rise to a certain degree, a pressure relief valve of the pressure vessel is suddenly opened, gas in the pressure vessel rapidly expands, the pressure rapidly decreases, so that the pressure difference between the inside and the outside of the graphite particles is increased, high-pressure water vapor in the graphite particles also rapidly expands, and the high-pressure water vapor instantaneously expands to form expanded graphite; the purpose of controlling the expansion degree of the graphite can be achieved by controlling the water content, the heating temperature and the pressure relief pressure of the graphite. And finally, coating and carbonizing the prepared graphite with enlarged interlayer spacing so as to reduce the influence of expansion and layer expansion on the increase of the specific surface area of the material. Wherein: compared with spherical and spheroidal natural graphite and artificial graphite, the graphitized anthracite in the step (1) has the characteristics of microcrystalline particles, porous structure, large specific surface area and high mechanical strength; the key link of the step (2) is that the temperature control and the pressure control of the pressure container can be adjusted, and the pressure maintaining pressure is within the safe pressure of the pressure container, so as to ensure that the expansion degree of the graphitized anthracite is controllable; the key point of the step (3) is that the pressure drop in the pressure relief process is uniform and controllable, and the powder cannot burst, and the interlayer spacing expansion is uncontrollable due to the fact that the powder expands too much due to sudden burst; the graphitized anthracite treated by the low-temperature low-pressure controllable micro-expansion in the step (4) has the problems of large specific surface area, low tap density, low first coulombic efficiency of charging and discharging, complex electrode preparation process and the like, is difficult to directly apply without coating modification, and after coating modification, the specific surface area of the material is reduced, the tap density is increased, the first coulombic efficiency is improved, and the electrode preparation process is simple and easy to implement; the coal-based graphite/carbon composite negative electrode material prepared in the step (5) forms an amorphous carbon shell protective layer on the surfaces of porous and microcrystalline graphitized anthracite particles through the coating of an organic carbon source and the subsequent carbonization, which is beneficial to the formation of an SEI film and the improvement of the initial coulomb efficiency of the material.
The invention has the beneficial effects that:
(1) the performance is excellent: the coal-based graphite/carbon composite negative electrode material with the graphite layer spacing controllably expanded is prepared by adopting a controllable low-temperature low-pressure micro-expansion layer technology, the material has a porous structure and a microcrystal particle structure in a microcosmic aspect, the graphite sheet spacing is expanded, the material is represented as particles with a micrometer scale in a macroscopic aspect, the specific surface area is greatly reduced, a short and developed diffusion channel is easily provided for lithium ion diffusion, the diffusion of lithium ions is accelerated, and the material is suitable for embedding and embedding lithium ions in a charging and discharging process under the conditions of high power and low temperature. Meanwhile, the amorphous carbon shell protection layer enables the microcrystalline structure to have structural stability, can meet charge and discharge under a long cycle condition, shows excellent rate performance, low-temperature performance and cycle performance, and is suitable for being used as a negative electrode material of a power type lithium ion battery.
(2) Safety and environmental protection: the low-temperature low-pressure controllable micro-expansion technology is adopted, the process is easy to control, the water treatment problem caused by electrochemistry and chemical oxidation methods adopted by the common graphite expansion is not involved in the preparation process, the problem of environmental pollution caused in the preparation process is avoided, and the process technical route is environment-friendly;
(3) the method is easy to implement: the anthracite is used for preparing the cathode material of the lithium ion battery, the raw material cost is low, the preparation method is simple, the process is easy to control, and the method is suitable for industrial production and industrial application and popularization.
Drawings
FIG. 1 is an SEM photograph of example 1 and comparative samples;
FIG. 2 is an XRD pattern of the samples of example 1 and comparative example;
FIG. 3 is a first charge and discharge curve at a rate of 0.1C at 25 ℃ and a first charge and discharge curve at a rate of 0.5C for example 1 and comparative example;
FIG. 4 is a graph showing the cycle curves at 25 ℃ and 0.5C magnification of example 1 and comparative example.
Detailed Description
In order to make the technical scheme of the invention easier to understand, the technical scheme of the invention is clearly and completely described by adopting a mode of a specific embodiment in combination with the attached drawings.
Detailed description of the preferred embodiments
Example 1:
the preparation method of the coal-based graphite/carbon composite negative electrode material for the power type lithium ion battery comprises the following steps:
(1) graphitized anthracite with the granularity D50 of 8.0 mu m, deionized water with the mass percentage of 9 percent and surfactant stearic acid with the mass percentage of 1 percent are fully and evenly mixed for 2 hours by a ZSJ-8 fusion machine at the rotating speed of 500rpm to obtain a wetting mixture.
(2) Placing the wetted mixture obtained in the above steps in a 2.5kg popcorn machine, sealing the cover, heating to 280 deg.C at 10 deg.C/min by gas heating, and maintaining at the temperature until the pressure is 0.5MPa for 5 min.
(3) And (3) decompressing the popcorn machine with the heat preservation and pressure maintaining to the normal pressure within 10s to complete the decompression process, thus preparing the precursor of the micro-expansion graphitized anthracite.
(4) And adding the micro-expanded graphitized anthracite precursor prepared in the step and pitch with the softening point of 150 ℃ accounting for 10% of the mass of the precursor into a 3L kneader, heating to 220 ℃ at the heating speed of 5 ℃/min under the protection of argon, preserving the heat for 3 hours, and stirring and mixing the kneader at the rotating speed of 150rpm in the process to prepare the precursor composite material.
(5) Placing the precursor composite material prepared in the step into a graphite crucible, and keeping the flow of argon gas at 0.5m3Heating to 1000 deg.C at a rate of 5 deg.C/min in a box furnace, carbonizing for 8h, naturally cooling to room temperature, and pulverizing with JXFT-53 universal pulverizerAnd (4) scattering to obtain the coal-based graphite/carbon composite negative electrode material.
The particle size D50 of the graphitized anthracite/carbon composite negative electrode material obtained in the embodiment is 14.45 microns, and the specific surface area is 4.58m2(ii)/g, tap density 0.95g/cm3The first capacity at 0.1C rate was 326.3mAh/g, and the first efficiency was 89.40%. At room temperature of 25 ℃ and under the multiplying power of 0.5C, the first capacity is 303.6mAh/g, and the capacity retention rate is 96.50% after 35 weeks of circulation; the initial capacity at 0 ℃ and 0.5 ℃ is 257.1mAh/g, and the capacity retention rate of the sample at 0 ℃/25 ℃ is 84.68%. Analysis by XRD test gave the graphite interlayer spacing d of example 10020.3460 nm. SEM photographs of example 1 and comparative example are shown in figure 1; the XRD patterns of the example 1 and the comparative sample are shown in figure 2; the first charge and discharge curves at 25 ℃ and 0.1C magnification and the first charge and discharge curves at 0 ℃ and 0.5C magnification of example 1 and comparative example are shown in FIG. 3; the 25 ℃ 0.5C-rate cycling curves for example 1 and the comparative example are shown in FIG. 4.
Example 2:
the preparation method of the coal-based graphite/carbon composite negative electrode material for the power type lithium ion battery comprises the following steps:
(1) graphitized anthracite with the granularity D50 of 4.0 mu m, deionized water with the mass percentage of 20 percent and sodium dodecyl benzene sulfonate as a surfactant with the mass percentage are fully and evenly mixed for 0.5 hour by a VC mixer at the rotating speed of 150rpm to obtain a wetting mixture.
(2) Placing the obtained wet mixture in a pressure cooker of Supor SY-30FC8058Q, covering, heating to 130 deg.C at 20 deg.C/min by electric heating, and maintaining at 0.15MPa for 10 min.
(3) And (3) decompressing the pressure cooker with the heat preservation and pressure maintaining to the normal pressure within 30s to finish the decompression process, thus preparing the precursor of the micro-expansion graphitized anthracite.
(4) And adding the micro-expanded graphitized anthracite precursor prepared in the step and acrylic resin accounting for 20% of the mass of the precursor into a 5L VC mixer, heating to 350 ℃ at a heating speed of 10 ℃/min under the protection of nitrogen, preserving the heat for 0.5 hour, and stirring and mixing at a rotating speed of 200rpm by the VC mixer in the process to prepare the precursor composite material.
(5) Placing the precursor composite material prepared in the above steps in a corundum crucible, and controlling the flow of helium gas at 1.2m3Heating to 1400 ℃ in a rotary furnace at the heating rate of 10 ℃/min, carbonizing for 3h, naturally cooling to room temperature, and performing ball milling and scattering treatment by using a QM-3SP2 planetary ball mill of Nanjing university instruments factory to obtain the coal-based graphite/carbon composite negative electrode material.
The particle size D50 of the graphitized anthracite composite negative electrode material obtained in the embodiment is 8.62 μm, and the specific surface area is 5.21m2(ii)/g, tap density 0.90g/cm3The first capacity at 0.1C rate is 330.5mAh/g, and the first efficiency is 90.25%. Under the room temperature of 25 ℃, under the multiplying power of 0.5C, the capacity retention rate is 95.83 percent after 35 weeks of circulation at 304.3 mAh/g. The initial capacity at 0 ℃ and 0.5 ℃ is 262.7mAh/g, and the capacity retention rate of the sample at 0 ℃/25 ℃ is 86.33%. Analysis by XRD test gave the graphite interlayer spacing d of example 20020.3458 nm. The test results are shown in Table 1.
Example 3:
the preparation method of the coal-based graphite/carbon composite negative electrode material for the power type lithium ion battery comprises the following steps:
(1) graphitized anthracite with the granularity D50 of 18.0 mu m, 1.0 percent of deionized water and 0.05 percent of surfactant ethanol by mass percent are fully and uniformly mixed for 3 hours by a stirring mixer at the rotating speed of 35rpm to obtain a wetting mixture.
(2) And (3) placing the wetting mixture prepared in the step into a Qiuzo scientific FCF-5 reaction kettle, heating to 350 ℃ at a speed of 2 ℃/min in a microwave heating mode, and then keeping the temperature at the temperature until the pressure is 1.0MPa, and maintaining for 2 min.
(3) And (3) decompressing the reaction kettle with the heat preservation and pressure maintaining to the normal pressure within 3s to complete the decompression process, thus preparing the precursor of the micro-expansion graphitized anthracite.
(4) Adding the micro-expanded graphitized anthracite precursor prepared in the above step and polyacrylonitrile with the mass of 1% of the precursor into a 5L reaction kettle, heating to 150 ℃ at a heating speed of 1 ℃/min under the protection of helium, preserving the heat for 10 hours, and stirring and mixing the reaction kettle at a rotating speed of 50rpm in the process to prepare the precursor composite material.
(5) Placing the precursor composite material prepared in the above step in a ceramic crucible, and keeping the nitrogen flow at 0.1m3Heating to 650 ℃ in a tubular furnace at the heating rate of 2 ℃/min, carbonizing for 20h, naturally cooling to room temperature, and scattering by using a CEF-300 pulverizer in the ancient cooking calendar to obtain the coal-based graphite/carbon composite negative electrode material.
The particle size D50 of the graphitized anthracite composite negative electrode material obtained in the embodiment is 12.74 microns, and the specific surface area is 3.85m2(ii)/g, tap density 0.97g/cm3The first capacity at 0.1C rate was 328.7mAh/g, and the first efficiency was 91.1%. The primary capacity is 300.9mAh/g under the multiplying power of 0.5C at the room temperature of 25 ℃, and the capacity retention rate is 96.28 percent after 35 weeks of circulation. The first capacity at 0 ℃ and 0.5 ℃ is 260.3mAh/g, and the capacity retention rate of the sample at 0 ℃/25 ℃ is 86.51%. Analysis by XRD test gave the graphite interlayer spacing d of example 30020.3452 nm. The test results are shown in Table 1.
Comparative example:
comparative example a commercial graphitized mesocarbon microbead ground negative electrode with a particle size D50 of 8.36 μm was used without any further treatment, and the specific surface area of the material was measured to be 1.21m2(ii)/g, tap density 1.30g/cm3The first capacity at 0.1C rate was 332.7mAh/g, and the first efficiency was 93.73%. The capacity retention rate after 35 weeks of circulation is 50.30% at room temperature 25 ℃ and 0.5C multiplying power of 263.7 mAh/g. The initial capacity at 0 ℃ and 0.5 ℃ is 72.8mAh/g, and the capacity retention rate of the sample at 0 ℃/25 ℃ is 27.61%. The graphite interlayer spacing d of the comparative sample is measured by XRD test analysis0020.3385 nm. The test results are shown in Table 1.
Second, performance characterization method
(1) Characterization of the morphology of the examples and comparative examples to which the invention relates:
the coal-based graphite/carbon composite negative electrode material for the power type lithium ion battery prepared by the method provided by the invention adopts a Zeiss Gemini SEM 500 field emission scanning electron microscope to observe the appearance of the composite negative electrode material; the crystal structure characteristics of the graphitized anthracite and the composite cathode material are analyzed by adopting an XRD-6000X-ray diffractometer of Shimadzu corporation; testing the powder tap density of the composite cathode material by using an Auto tap type tap density instrument of the American Congta company; testing the specific surface area of the composite negative electrode material by adopting a JW-DX type specific surface area tester of the Jingwei Gaobo company; the electrical property of the composite cathode material button cell is tested by adopting a CT2001A type blue cell test system of blue electric company in Wuhan city.
(2) The electrode materials of the examples and comparative examples to which the present invention relates were subjected to half-cell tests:
pole pieces were fabricated using the coal-based composite negative electrode material samples prepared in examples 1 to 3 and comparative examples, and half-cell tests were performed. According to the active substance: SP: CMC: SBR 95: 2: 1.5: 1.5 pulping, evenly mixing, coating on a copper foil, drying for 10 hours at 110 ℃, rolling and punching, using a metal lithium sheet as a counter electrode, using FEC: EC: EMC 1: 2: 7 as electrolyte, and preparing into CR2032 button experimental cell in a German Braun MBRAUN glove box protected by high-purity argon. Under room temperature (25 ℃), the charging and discharging voltage range is 0.003-1.5V, 0.1C first capacity mAh/g and first efficiency are measured, 0.5C charging and discharging cycle test is carried out after 0.1C charging and discharging activation for 2 weeks, and the cycle capacity retention rate of 35 weeks is calculated by utilizing the ratio of the specific capacity of the composite negative electrode material at 35 weeks to the specific capacity of the composite negative electrode material at 0.5C 1 weeks; under room temperature (25 ℃), the charging and discharging voltage range is 0.003-1.5V, after 0.1C is activated for 2 weeks, 0.5C charging and discharging cycle test is carried out at 0 ℃, and the capacity retention rate at 0 ℃/25 ℃ is calculated by utilizing the ratio of the 0.5C specific capacity of the composite negative electrode material at 0 ℃ in 1 week to the 0.5C specific capacity at 25 ℃ in 1 week.
Thirdly, analyzing physical characteristics and electrochemical performance results of the cathode material
Table 1: physical and chemical property test results of the samples of examples and comparative examples
Figure BDA0003348730240000121
FIG. 1 is SEM photographs of example 1 and a comparative example, and it can be seen from FIG. 1 that the milled material of the comparative example commercial mesophase carbon microspheres is denser and irregular in morphology, no distinct layering occurs between graphite sheets, and the texture and structure of the particles are more uniform, so that the material has a smaller specific surface area and a higher tap density. The particles of example 1 are relatively fluffy and mainly comprise particles of two morphologies, one is a lamellar structure similar to a graphite flake, and graphite microcrystal particles with the size of about 100nm are arranged between the lamellar structures, so that the micro-expanded sample has a large specific surface area and a low tap density, and the microcrystal particles and a porous channel formed by the microcrystal particles and the graphite lamellar layers are convenient for the infiltration of electrolyte and the transmission of lithium ions, thereby achieving the effect of improving the electrochemical performance of the material.
FIG. 2 is an XRD pattern of example 1 and a comparative example, and it can be seen from FIG. 2 that example 1 and the comparative example both have 3 distinct characteristic peaks, which are located around 26.5 °, 45 ° and 55 °, respectively, but compared with the comparative example, the diffraction peaks of the example are shifted to the left, which shows that the disorder degree of the crystal is increased, and the interlayer spacing of the material is larger than that of the comparative example, so that the material is suitable for the intercalation and deintercalation of lithium ions, thereby increasing the diffusion rate of lithium ions.
FIG. 3 is a first charge and discharge curve at 25 ℃ and 0.1C rate and a first charge and discharge curve at 0 ℃ and 0.5C rate of example 1 and comparative example; FIG. 4 is a graph showing the cycle curves of example 1 and comparative example at 25 ℃ and 0.5C magnification. Table 1 shows the results of the physical and chemical property tests of the samples of examples and comparative examples. As can be seen from FIGS. 3 and 4 and Table 1, the samples prepared in examples 1 to 3 had a first capacity of 325mAh/g or more at 25 ℃ and 0.1C, a capacity retention rate of more than 95% and a capacity retention rate of more than 84% at 0 ℃/25 ℃ after 35 weeks of cycling at 25 ℃ and 0.5C. The samples prepared in the comparative examples, though the initial capacity at 25 ℃ and 0.1C was similar to those of comparative examples 1 to 3, had a capacity retention rate of only 50.30% and a capacity retention rate at 0 ℃/25 ℃ of only 27% after 35 weeks of cycling at 25 ℃ and 0.5C. It is demonstrated that examples 1-3 all exhibit better power, cycle and low temperature performance than comparative examples because the graphitized anthracite composite negative electrode material prepared by the present invention has a porous structure and a microcrystalline particle structure on the micro-scale and the graphite layer spacing is controllably enlarged. In addition, an amorphous carbon shell protective layer is formed on the surfaces of graphitized anthracite particles with porous and microcrystalline structures through the coating of an organic carbon source and the subsequent carbonization, and the protective layer is macroscopically represented as micron-scale particles, and the specific surface area is greatly reduced. The porous and microcrystalline structure with the expanded graphite interlayer spacing can easily provide a short and developed diffusion channel for lithium ion diffusion, is suitable for embedding and embedding lithium ions in the charging and discharging process under high-power and low-temperature conditions, and simultaneously, the microcrystalline structure has structural stability due to the amorphous carbon shell protective layer, and can meet the charging and discharging under the long-cycle condition. The structural change obviously improves the high-power charge-discharge performance, the rate capability and the low-temperature charge-discharge performance of the cathode material.
It should be noted that the embodiments described herein are only some embodiments of the present invention, and not all implementations of the present invention, and the embodiments are only examples, which are only used to provide a more intuitive and clear understanding of the present invention, and are not intended to limit the technical solutions of the present invention. All other embodiments, as well as other simple substitutions and various changes to the technical solutions of the present invention, which can be made by those skilled in the art without inventive work, are within the scope of the present invention without departing from the spirit of the present invention.

Claims (10)

1. A preparation method of a coal-based graphite/carbon composite negative electrode material for a power type lithium ion battery is characterized by comprising the following steps:
(1) wetting and mixing: fully and uniformly mixing the graphitized anthracite micro powder with a certain amount of deionized water and surfactant to ensure that water molecules can enter pores and gaps of the graphitized anthracite particles to obtain a wetting mixture;
(2) temperature rising and pressure increasing: placing the wetted mixture obtained in the step (1) in a pressure container, heating to a heat preservation temperature, keeping the temperature constant until the heat preservation pressure is reached in the pressure container, and then continuing to preserve heat for a certain time;
(3) pressure relief treatment: releasing the pressure of the pressure container subjected to heat preservation and pressure maintaining in the step (2) to the standard atmospheric pressure within 3-30 s to complete the pressure release process, so as to obtain a micro-expanded graphitized anthracite precursor;
(4) coating modification: placing the micro-expanded graphitized anthracite precursor prepared in the step (3) and an organic carbon source accounting for 1-20% of the mass of the precursor in a mixer, stirring and mixing under the protection of inert atmosphere, simultaneously heating to 150-350 ℃, and preserving heat for 0.5-10 hours under the stirring state to prepare a precursor composite material;
(5) carbonizing treatment: and (3) placing the precursor composite material prepared in the step (4) in a crucible, heating to 650-1400 ℃ at a heating rate of 2-10 ℃/min in an inert atmosphere protection furnace, carrying out heat preservation carbonization treatment for 3-20 h, then naturally cooling to room temperature, and carrying out scattering and sieving treatment to prepare the coal-based graphite/carbon composite negative electrode material.
2. The preparation method of the coal-based graphite/carbon composite negative electrode material for the power lithium ion battery according to claim 1, wherein in the step (1): the mass percentage of the graphitized anthracite micro powder, deionized water and a surfactant is 1: (0.5-20): (0.05-2).
3. The preparation method of the coal-based graphite/carbon composite negative electrode material for the power lithium ion battery according to claim 1, wherein in the step (1): the particle size D50 of the graphitized anthracite is 4.0-18.0 mu m, the carbon content is more than 99.0%, the graphitized anthracite is obtained by graphitizing, crushing and sieving anthracite raw materials, and the anthracite raw materials are one of taixi anthracite, artificial graphite with a micropore/porous structure or natural graphite; the surfactant is ethanol, or stearic acid, or oleic acid, or lauric acid, or sodium dodecyl benzene sulfonate, or fatty glyceride and the like; the mixing and dispersing equipment used for mixing is a VC mixer, a fusion machine, a stirring mixer or the like.
4. The preparation method of the coal-based graphite/carbon composite negative electrode material for the power lithium ion battery according to claim 1, wherein in the step (2): the heating rate is 1-20 ℃/min, the heat preservation temperature is 120-350 ℃, the heat preservation pressure is 0.15-1.0 MPa, and the continuous heat preservation time is 2-10 min after the heat preservation pressure is reached.
5. The preparation method of the coal-based graphite/carbon composite negative electrode material for the power lithium ion battery according to claim 1, wherein in the step (2): the pressure vessel is a pressure cooker, a popcorn machine, a reaction kettle, a hydrothermal reaction kettle or an autoclave, and is provided with an air pressure gauge and an explosion-proof valve; the heating mode of the pressure container for heating is electric heating, coal gas heating or microwave heating.
6. The preparation method of the coal-based graphite/carbon composite negative electrode material for the power lithium ion battery according to claim 1, wherein in the step (4): the organic carbon source is one or more of epoxy resin, asphalt, phenolic resin, acrylic resin, furan resin, ethyl methyl carbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyimide, styrene-butadiene rubber and carboxymethyl cellulose.
7. The preparation method of the coal-based graphite/carbon composite negative electrode material for the power lithium ion battery according to claim 1, wherein in the step (4): the heating and temperature rising speed of the mixer is 1-10 ℃/min, and the mixer is a VC mixer, a reaction kettle, a kneading machine, a mixing roll or an internal mixer; the stirring speed is 50-200 rpm; the inert atmosphere is one or more of nitrogen, argon and helium.
8. The preparation method of the coal-based graphite/carbon composite negative electrode material for the power lithium ion battery according to claim 1, wherein in the step (5): the crucible is one of a graphite crucible, a corundum crucible and a ceramic crucible.
9. The method for preparing the coal-based graphite/carbon composite negative electrode material for the power lithium ion battery according to claim 1, which comprisesCharacterized in that, in the step (5): the inert gas is one or more of nitrogen, argon and helium, and the flow rate of the inert gas is 0.1-1.2 m3H; the inert atmosphere protection furnace is a tube furnace, a box furnace, a rotary furnace or a tunnel kiln;
10. the preparation method of the coal-based graphite/carbon composite negative electrode material for the power lithium ion battery according to claim 1, wherein in the step (5): the scattering equipment used for scattering treatment is a planetary ball mill, a universal pulverizer, a jet mill or an ultrafine pulverizer.
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