CN116692832A - Hard carbon anode material and preparation method and application thereof - Google Patents

Hard carbon anode material and preparation method and application thereof Download PDF

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CN116692832A
CN116692832A CN202310995732.8A CN202310995732A CN116692832A CN 116692832 A CN116692832 A CN 116692832A CN 202310995732 A CN202310995732 A CN 202310995732A CN 116692832 A CN116692832 A CN 116692832A
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hard carbon
carbon
starch
negative electrode
sodium
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CN116692832B (en
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钟应声
江柯成
刘娇
张�浩
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Jiangsu Zenergy Battery Technologies Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection 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
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The invention discloses a hard carbon negative electrode material, a preparation method and application thereof, wherein the preparation of the hard carbon negative electrode material comprises the following steps: (1) Mixing starch, a dispersing agent and a modifying agent in water, and drying to obtain a carbon precursor; (2) Sequentially carrying out high-temperature dehydration and carbonization treatment on the carbon precursor to obtain a hard carbon substrate; (3) Mixing the hard carbon substrate with a fluorine-containing substance in water or an organic solvent, and drying to obtain a hard carbon substrate coated with the fluorine-containing substance on the surface; (4) And placing the hard carbon substrate coated with the fluorine-containing substance on the surface under a mixed atmosphere containing hydrocarbon, and filling surface carbon to obtain the hard carbon anode material. The hard carbon negative electrode material prepared by the method has stable structure, the fluorine-containing substance coated on the surface of the hard carbon substrate forms an interface activation layer, and the negative electrode material filled with carbon free radicals can effectively improve the initial coulomb efficiency and the cycle performance of the battery.

Description

Hard carbon anode material and preparation method and application thereof
Technical Field
The invention relates to the technical field of batteries, relates to a hard carbon negative electrode material, a preparation method and application thereof, and in particular relates to preparation and application of a modified hard carbon negative electrode material.
Background
Currently, disordered carbon represented by hard carbon is a cathode material with great prospect in sodium ion battery industrialization due to the characteristics of rich raw materials, simple synthesis, low working potential and the like.
Researchers in the field tend to prefer to introduce various porous structures when designing carbon materials, and the pore-rich design can generally increase the amorphous degree of the carbon materials and provide active sites for disordered carbon cathodes, thereby enhancing the ion transport capacity of sodium ion batteries. However, the high production cost and low initial coulombic efficiency limit the practical use of the hard carbon negative electrode in sodium ion batteries, so how to solve the above problems by designing better materials to improve electrochemical performance is still the key direction of the current development of hard carbon negative electrode materials.
Disclosure of Invention
The invention provides a hard carbon negative electrode material, a preparation method and application thereof, which takes starch with low cost and wide sources as a carbon source, and carries out surface modification treatment on the starch before carbonization, so that starch particles can be carbonized to prepare a hard carbon substrate with stable structure and high carbon residue rate, and the surface of the hard carbon substrate is coated with fluorine-containing substances to form an artificial interface activation layer and carbon filling is carried out on the surface of the hard carbon substrate, thus obtaining the hard carbon negative electrode material which can lead a battery to have high initial coulombic efficiency and excellent cycle performance.
In order to solve the technical problems, the invention provides the following technical scheme:
the first aspect of the invention provides a preparation method of a hard carbon anode material, which comprises the following steps:
(1) Mixing starch, a dispersing agent and a modifying agent in water, and drying to obtain a carbon precursor; the modifier is R 1 COOR 2 And/or (R) 1 COO） 2 R 2 Wherein R is 1 One selected from C1-C12 alkyl, C3-C12 cycloalkyl, phenyl, C6-C12 substituted phenyl, R 1 COOR 2 R in (a) 2 Is CH 3 、H、K、Na, li or NH 4 ，（R 1 COO） 2 R 2 R in (a) 2 Is Mg or Ca;
(2) Sequentially dehydrating and carbonizing the carbon precursor prepared in the step (1) to obtain a hard carbon substrate;
(3) Mixing the hard carbon substrate prepared in the step (2) with an aqueous solution or an organic solution of a fluorine-containing substance, and drying to obtain a hard carbon substrate with a surface modified with the fluorine-containing substance;
(4) Placing the hard carbon substrate with the surface modified with the fluorine-containing substances prepared in the step (3) under a mixed atmosphere, and sweeping for 10 min-1 h at 300-700 ℃ to fill surface carbon, so as to obtain the hard carbon negative electrode material; the mixed atmosphere is composed of hydrocarbon and inert gas.
Further, in the step (1), starch and a dispersing agent are firstly added into water, uniformly stirred at 25-60 ℃, then a modifying agent is added, the mixture is continuously stirred and reacted for 30 min-12 h, and the carbon precursor is obtained after drying treatment.
Further, in the step (1), the starch is selected from one or more of wheat starch, corn starch, soybean starch, mung bean starch, pea starch, potato starch, rice starch, millet starch, potato starch and tapioca starch.
Further, in the step (1), the dispersing agent is selected from one or more of sodium chloride, dimethylformamide, sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, sodium alkyl sulfonate, sodium stearate, magnesium stearate, calcium stearate and copper stearate.
Further, in step (1), the C1-C12 alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, sec-butyl, n-pentyl, n-heptyl, n-octyl, and the like;
the C3-C12 cycloalkyl includes, but is not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and the like;
the C6-C12 substituted phenyl represents a phenyl group substituted with one or more substituents including, but not limited to, methyl, ethyl, propyl, and the like.
Further, the steps of(1) In which the modifier is more preferably CH 3 COONa and/or CH 3 COONH 4 。
Further, in the step (1), the feeding mass ratio of the starch, the dispersing agent and the modifying agent is 0.1-45:0.05-10:0.05-22.
Further, in step (2), the dehydrating step includes: heating to 100-400 ℃ at a heating rate of 1-5 ℃/min under inert atmosphere, and preserving heat for 1-8 h.
Further, in the step (2), the carbonization treatment step includes: heating to 300-700 ℃ at a heating rate of 2-10 ℃/min, and preserving heat for 2-16 h.
Further, in the step (3), the aqueous solution or the organic solution of the fluorine-containing substance is obtained by dispersing the fluorine-containing substance in water or an organic solvent.
Further, in the step (3), the fluorine-containing substance is selected from one or more of sodium fluoride, sodium fluorophosphate and sodium fluorophosphate.
Further, in the step (3), the mass ratio of the fluorine-containing substance in the aqueous solution or the organic solution of the fluorine-containing substance is 0.05-wt-8-wt%; the mass ratio of the hard carbon substrate to the aqueous solution or the organic solution of the fluorine-containing substance is 100:0.05-8.
Further, in the step (4), the hydrocarbon-containing compound is selected from one or more of methane, ethane, acetylene, butyne, propane and butane.
Further, in the step (4), the inert gas is nitrogen, helium, neon or argon.
Further, in the step (4), the volume ratio of hydrocarbon to inert gas in the mixed atmosphere is 1-8:5-50.
The second aspect of the invention provides the hard carbon anode material prepared by the preparation method of the first aspect, wherein the hard carbon anode material comprises a hard carbon core, a fluorine-containing interface activation layer and a carbon coating layer which are sequentially distributed from inside to outside.
Further, the specific surface area of the hard carbon anode material is preferably 0.4-35 m 2 /g。
Further, the porosity of the hard carbon anode material is preferably 1.2 to 28%.
Further, the particle diameter D50 corresponding to 50% on the particle size cumulative percentage curve of the hard carbon negative electrode material is preferably between 1.2 and 35 μm.
Further, in the XRD pattern of the hard carbon anode material, the diffraction peak of the crystal face of the carbon material (002) is corresponding to the vicinity of 23-24 degrees of 2 theta, the peak intensity is marked as P (002), the diffraction peak of the crystal face of the carbon material (100) is corresponding to the vicinity of 43-44 degrees of 2 theta, the peak intensity is marked as P (100), and the ratio between P (002) and P (100) is 1.01-16.7; the XRD test conditions were as follows: the X-ray diffraction analysis ray source adopts Cu-K alpha radiation, the wavelength is 1.5406A, the tube voltage is 20-50kV, the tube current is 15-60mA, the stepping scanning mode is adopted, and the angle range is 0-90 degrees.
Further, the oxygen content of the carbon cladding is lower than the oxygen content of the hard carbon core.
The third aspect of the invention provides a negative electrode plate, which comprises the hard carbon negative electrode material in the second aspect.
Further, the preparation method of the negative electrode plate comprises the following steps:
(1) Weighing a hard carbon anode material, a conductive material and a bonding substance according to the mass ratio of each component in an anode active material layer of an anode piece, and stirring and mixing the hard carbon anode material, part of the conductive material, part of the bonding substance and water for the first time to obtain a primary mixture;
(2) Stirring and mixing the primary mixture prepared in the step (1) with the rest of conductive materials, the rest of bonding substances and water for the second time to obtain a secondary mixture, wherein the content of solid substances in the secondary mixture is 40-60%, and the viscosity is 1-8 Pa.s;
(3) And (3) coating the secondary mixture prepared in the step (2) on the negative electrode fluid, and drying, cold pressing and cutting to obtain the negative electrode plate.
Further, the rotation speed of the first stirring is preferably 200-1500 r/min, and the time is preferably 5-30 min; the rotation speed of the second stirring is preferably 800-3000 r/min, and the time is preferably 30-200 h.
Further, the content of solid matters in the secondary mixture is more preferably 45-55%, and the viscosity is more preferably 2.5-3.5 Pa.s.
Further, the mass ratio of the hard carbon anode material to the conductive material to the bonding substance in the secondary mixture is as follows: 85-98.5:0.2-7:0.2-8.
Further, the conductive material is selected from one or more of conductive carbon black, acetylene black, graphite, graphene, carbon micro-wires, carbon nano-wires, carbon micro-tubes and carbon nano-tubes.
Further, the bonding substance is one or more selected from polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyamide, polyimide, polyacrylate, styrene-butadiene rubber, sodium alginate, chitosan and polyethylene glycol.
Further, the negative electrode current collector is selected from one or more of aluminum foil, porous aluminum foil, foam nickel/aluminum foil, galvanized aluminum foil, nickel-plated aluminum foil, carbon-coated aluminum foil, nickel foil, and titanium foil, and more preferably aluminum foil, nickel-plated aluminum foil, and carbon-coated aluminum foil.
A fourth aspect of the present invention provides a secondary battery comprising the hard carbon negative electrode material of the second aspect or the negative electrode tab of the third aspect.
Compared with the prior art, the invention has the beneficial effects that:
the invention takes starch with low cost and wide sources as a carbon source, but the starch is easy to depolymerize in the dehydration and carbonization heat treatment process to form volatile pyrolysis micromolecule products such as water, carbon dioxide, nitrogen oxides and the like, and the pyrolysis products can cause the starch to melt or expand, so that the starch with a spherical structure is structurally collapsed in the carbonization process and is converted into a carbon material with a foaming and fluffy structure, and the carbon material has poor structural stability. Based on the method, the starch is subjected to surface modification treatment before carbonization, the starch is rich in primary hydroxyl groups and secondary hydroxyl groups, the hydroxyl groups of the single chains and adjacent chains react with carboxyl groups or ester groups of the modifier, and a crosslinking protective layer is formed on the surface of the starch; the crosslinking protective layer can reduce the breaking degree of intramolecular and intermolecular bonds on the surface of the starch, enhance the heat resistance of the starch, and ensure that the starch can keep a spherical structure of the starch after being dehydrated and carbonized, thereby preparing the spherical hard carbon substrate with stable structure. Meanwhile, due to the existence of the cross-linking protective layer, the obtained hard carbon substrate has higher carbon residue rate, improves the heat treatment efficiency, reduces the cost and is beneficial to reducing the irreversible capacity in the primary charge and discharge process. In addition, the fluorine-containing substance is introduced into the surface of the spherical hard carbon substrate prepared by the method to form an artificial interface activation layer so as to optimize the structure and composition of an SEI film formed on the surface of the modified anode material in the secondary battery, thereby reducing the occurrence of side reaction, effectively inhibiting the growth of sodium dendrite, reducing the accumulation and consumption of dead sodium, and being beneficial to improving the initial coulombic efficiency of the modified anode material and the cycle performance of the secondary battery. In addition, small carbon species (such as carbon free radicals and the like) carry out surface defect filling and carbon molecule curing on the hard carbon substrate through hydrocarbon pyrolysis at high temperature, and surface repair is carried out to form a carbon surface layer with an amorphous structure and fewer residual oxygen atoms and defects, so that the irreversible capacity in the primary charge and discharge process can be further reduced; meanwhile, in the surface carbon filling process, the carbon layer formed on the hard carbon surface layer can wrap and protect the artificial interface activation layer, so that the stability of the artificial interface activation layer is improved.
The hard carbon negative electrode material prepared by the preparation method provided by the invention has a stable spherical structure, has few surface defects and excellent chemical stability through the introduction of the interface activation layer and the surface carbon filling treatment, shows high initial coulomb efficiency which can be up to 89.8%, and the secondary electrode containing the hard carbon negative electrode material shows excellent cycle performance, and has a capacity fading of 672 cycles corresponding to 80%.
Drawings
FIG. 1 is an SEM image of a hard carbon anode material prepared according to example 1;
FIG. 2 is an SEM image of a hard carbon anode material prepared according to comparative example 1;
fig. 3 shows XRD patterns of the hard carbon negative electrode materials prepared in example 1 and comparative example 1, with the XRD pattern of comparative example 1 above and the XRD pattern of example 1 below.
Detailed Description
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items. The term "comprising" or "comprises" as used herein means that it may include or comprise other components in addition to the components described. The term "comprising" or "comprising" as used herein may also be replaced by "being" or "consisting of" closed.
As described in the background art, disordered carbon represented by hard carbon is a cathode material with great prospect in sodium ion battery industrialization due to the characteristics of abundant raw materials, simple synthesis, low working potential and the like, but the hard carbon cathode material is also greatly limited in practical use in sodium ion batteries due to higher production cost, low initial coulombic efficiency and poor cycle performance.
In order to solve the technical problems, the embodiment of the invention provides a preparation method of a hard carbon anode material, which comprises the following steps:
(1) Mixing starch, a dispersing agent and a modifying agent in water, and drying to obtain a carbon precursor; the modifier is R 1 COOR 2 And/or (R) 1 COO） 2 R 2 Wherein R is 1 One selected from C1-C12 alkyl, C3-C12 cycloalkyl, phenyl, C6-C12 substituted phenyl, R 1 COOR 2 R in (a) 2 Is CH 3 H, K, na, li or NH 4 ，（R 1 COO） 2 R 2 R in (a) 2 Is Mg or Ca;
(2) Sequentially dehydrating and carbonizing the carbon precursor prepared in the step (1) to obtain a hard carbon substrate;
(3) Mixing the hard carbon substrate prepared in the step (2) with an aqueous solution or an organic solution of a fluorine-containing substance, and drying to obtain a hard carbon substrate with a surface modified with the fluorine-containing substance;
(4) Placing the hard carbon substrate with the surface modified with the fluorine-containing substances prepared in the step (3) under a mixed atmosphere, and sweeping for 10 min-1 h at 400-900 ℃ to fill surface carbon, so as to obtain the hard carbon negative electrode material; the mixed atmosphere is composed of hydrocarbon and inert gas.
The invention takes the starch with wide sources and low cost as a carbon source, is used for preparing the hard carbon material, has low preparation cost and is suitable for industrialized development; however, starch is easily depolymerized to form volatile pyrolysis micromolecule products such as water, carbon dioxide, nitrogen oxides and the like in the actual dehydration and carbonization heat treatment processes, and the pyrolysis products can cause the starch to melt or expand, so that the starch with a spherical structure is structurally collapsed in the carbonization process and is converted into a carbon material with a foaming and fluffy structure, the carbon material has poor structural stability, and if the carbon material is directly used as a cathode active material in a battery, the cycle performance is extremely poor. Based on the method, the starch is subjected to surface modification treatment before carbonization, the starch is rich in primary hydroxyl groups and secondary hydroxyl groups, the hydroxyl groups of the single chains and adjacent chains react with carboxyl groups or ester groups of the modifier, and a crosslinking protective layer is formed on the surface of the starch; the crosslinking protective layer can reduce the breaking degree of intramolecular and intermolecular bonds on the surface of the starch, enhance the heat resistance of the starch, and ensure that the starch can keep a spherical structure of the starch after being dehydrated and carbonized, thereby preparing the spherical hard carbon substrate with stable structure. Meanwhile, due to the existence of the cross-linking protective layer, the obtained hard carbon substrate has higher carbon residue rate, improves the heat treatment efficiency, reduces the cost and is beneficial to reducing the irreversible capacity in the primary charge and discharge process.
In addition, the fluorine-containing substance is introduced into the surface of the hard carbon substrate prepared by the method to form the artificial interface activation layer, and the artificial interface activation layer can optimize the structure and the composition of an SEI film formed on the surface of the anode material in the secondary battery, so that the occurrence of side reaction is reduced, the growth of sodium dendrite can be effectively inhibited, the accumulation and the consumption of dead sodium can be reduced, and the initial coulombic efficiency of the modified anode material and the cycle performance of the secondary battery can be improved. In addition, the invention enables small carbon species (such as carbon free radicals and the like) to fill surface defects and solidify carbon molecules on the hard carbon substrate through hydrocarbon pyrolysis at high temperature, and surface repair is carried out, so that the carbon surface layer with an amorphous structure and fewer residual oxygen atoms and defects is formed, and the irreversible capacity in the first charge and discharge process can be further reduced; meanwhile, in the surface carbon filling process, the carbon layer formed on the hard carbon surface layer can wrap and protect the artificial interface activation layer, so that the stability of the artificial interface activation layer is improved. According to the invention, under the synergistic effect of surface modification before carbonization of starch, introduction of the interfacial active layer and surface carbon filling, the prepared hard carbon negative electrode material has high initial coulombic efficiency, and the secondary battery containing the hard carbon negative electrode material shows excellent cycle performance.
In some preferred embodiments, in step (1), C1-C12 alkyl includes, but is not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, sec-butyl, n-pentyl, n-heptyl, n-octyl, and the like; the C3-C12 cycloalkyl includes, but is not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and the like; the C6-C12 substituted phenyl represents phenyl substituted with one or more substituents including, but not limited to, methyl, ethyl, propyl, and the like.
In some preferred embodiments, in the step (1), starch and a dispersing agent are firstly added into water, uniformly stirred at 25-60 ℃, then a modifying agent is added, the stirring reaction is continued for 30 min-12 h, and the carbon precursor is obtained after drying treatment. Specifically, the starch may be one or more selected from wheat starch, corn starch, soybean starch, mung bean starch, pea starch, potato starch, rice starch, millet starch, potato starch, and tapioca starch; the dispersant may be one or more selected from sodium chloride, dimethylformamide, sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, sodium alkylsulfonate, sodium stearate, magnesium stearate, calcium stearate, and copper stearate. Starch and a dispersing agent are mixed in water to uniformly disperse starch particles, and then a modifying agent is added to fully react the modifying agent with the starch particles so as to form a uniform crosslinking protective layer on the surfaces of the starch particles; more preferably, the mass ratio of the starch, the dispersant and the modifier is 0.1-45:0.05-10:0.05-22.
In some preferred embodiments, the modifier may be CH 3 COONa and/or CH 3 COONH 4 Such carboxylates are hydrolyzed and then react with hydroxyl groups on the starch, thereby modifying the starch surface to form a corresponding protective layer.
In some preferred embodiments, in the step (2), the dehydration treatment is performed by heating to 100-400 ℃ at a heating rate of 1-5 ℃/min under an inert atmosphere, and preserving heat for 1-8 h; and then heating to 300-700 ℃ at a heating rate of 2-10 ℃/min, preserving heat for 2-16 h, and carbonizing to obtain the hard carbon substrate.
In some preferred embodiments, in the step (3), firstly dispersing fluorine-containing substances in water or an organic solvent, stirring uniformly to obtain a mixed solution, then adding the hard carbon substrate prepared in the step (2) into the mixed solution, stirring and mixing, and vacuum drying at 30-60 ℃ to obtain the hard carbon substrate with the surface modified with the fluorine-containing substances; wherein, the fluorine-containing substance is preferably one or more of sodium fluoride, sodium monofluorophosphate and sodium fluometaphosphate, and the mass ratio of the fluorine-containing substance in the mixed solution is 0.05-8 wt%, for example 0.6-wt%; the organic solvent may be ethanol, but may be other usable solvents, which is not limited in the present invention; more preferably, the mass ratio of the hard carbon substrate to the mixed solution is 100:0.05-8.
In some preferred embodiments, in step (4), the volume ratio of hydrocarbon to inert gas in the mixed atmosphere is preferably 1-8:5-50, e.g. 5:10; wherein the hydrocarbon can be selected from one or more of methane, ethane, acetylene, butyne, propane and butane, and the inert gas is nitrogen, helium, neon or argon. The invention can fill the defects of the surface of the hard carbon substrate by cracking hydrocarbon at high temperature to form small carbon species such as carbon free radicals and the like, and improve the initial coulomb efficiency of the anode material, wherein the effect cannot be achieved if a carbon coating layer is prepared on the surface of the hard carbon substrate by adopting other carbon-containing material coating and calcining methods.
The embodiment of the invention also provides the silicon-carbon anode material prepared by the preparation method, which comprises a hard carbon core, a fluorine-containing interface activation layer and a carbon coating layer which are sequentially distributed from inside to outside.
In some preferred embodiments, the silicon carbon anode material satisfies at least one of the following conditions:
the specific surface area of the hard carbon anode material is 0.4-35 m 2 /g；
The porosity of the hard carbon anode material is 1.2-28%;
the particle diameter D50 corresponding to 50% of the particle size cumulative percentage curve of the hard carbon negative electrode material is 1.2-35 mu m;
In the XRD pattern of the hard carbon anode material, diffraction peaks of the crystal face of the carbon material (002) are corresponding to the vicinity of 23-24 degrees of 2 theta, the peak intensity is marked as P (002), diffraction peaks of the crystal face of the carbon material (100) are corresponding to the vicinity of 43-44 degrees of 2 theta, the peak intensity is marked as P (100), and the ratio between P (002) and P (100) is 1.01-16.7; the XRD test conditions were as follows: the X-ray diffraction analysis ray source adopts Cu-K alpha radiation, the wavelength is 1.5406A, the tube voltage is 20-50kV, the tube current is 15-60mA, the stepping scanning mode is adopted, and the angle range is 0-90 degrees;
the oxygen content of the carbon coating layer is lower than the oxygen content of the inner hard carbon core, illustratively, when the oxygen content of the carbon coating layer is Ha, the oxygen content of the inner hard carbon core is Oa, more preferably Ha is less than or equal to Oa <5 wt%.
In addition, the embodiment part of the invention provides a negative electrode plate which comprises the hard carbon negative electrode material.
In some preferred embodiments, the negative electrode piece comprises a current collector and a negative electrode active material layer coated on the surface of the current collector, wherein the negative electrode active material layer of the negative electrode piece comprises the following components in percentage by mass: 85-98.5% of hard carbon cathode material, 0.2-7% of conductive material and 0.2-8.0% of bonding substance.
In some preferred embodiments of the present invention, the negative electrode current collector is selected from one or more of aluminum foil, porous aluminum foil, nickel foam/aluminum foil, zinc-plated aluminum foil, nickel-plated aluminum foil, carbon-coated aluminum foil, nickel foil, titanium foil, more preferably aluminum foil, nickel-plated aluminum foil, or carbon-coated aluminum foil; the conductive material is selected from one or more of conductive carbon black, acetylene black, graphite, graphene, carbon micro-nano linear conductive material and carbon micro-nano tubular conductive material; polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacryloyl, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyamide, polyimide, polyacrylate, styrene-butadiene rubber, sodium alginate, chitosan and polyethylene glycol.
In some preferred embodiments, the preparation method of the negative electrode piece includes the following steps:
(1) Weighing a hard carbon anode material, a conductive material and a bonding substance according to the mass ratio of each component in an anode active material layer of an anode piece, and stirring and mixing the hard carbon anode material, part of the conductive material, part of the bonding substance and water for the first time to obtain a primary mixture;
(2) Stirring and mixing the primary mixture prepared in the step (1) with the rest of conductive materials, the rest of bonding substances and water for the second time to obtain a secondary mixture, wherein the content of solid substances in the secondary mixture is 40-60%, and the viscosity is 1-8 Pa.s;
(3) And (3) coating the secondary mixture prepared in the step (2) on the negative electrode fluid, and drying, cold pressing and cutting to obtain the negative electrode plate.
In some preferred embodiments of the present invention, the rotation speed of the first stirring is preferably 200-1500 r/min, and the time is preferably 5-30 min; the rotation speed of the second stirring is preferably 800-3000 r/min, and the time is preferably 30-200 min.
In some preferred embodiments of the present invention, the content of the solid matters in the secondary mixture is more preferably 45-55%, and the viscosity is more preferably 2.5-3.5 pa.s.
The embodiment of the invention provides a secondary battery, which comprises the hard carbon negative electrode material or the negative electrode plate.
In some preferred embodiments of the present invention, the secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; the positive electrode active material in the positive electrode sheet can be one or more of sodium nickel manganese oxide, sodium nickel cobalt aluminate, sodium vanadium fluorophosphate, sodium iron manganese fluorophosphate, sodium nickel iron manganese oxide, sodium nickel copper manganese ferrite, sodium hexacyanoferrate, sodium hexacyanomanganate, sodium hexacyanonickelate, sodium hexacyanoferrate nickelate, sodium hexacyanoferrate, sodium titanium phosphate and sodium titanium manganese phosphate; the isolating film may be at least one polymer organic matter diaphragm of polyethylene, polypropylene, polyacrylonitrile, polyvinyl alcohol and polyvinylidene fluoride.
The present invention will be further described with reference to specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the present invention and practice it.
Example 1
The embodiment relates to a preparation method of a hard carbon anode material and a secondary battery, which comprises the following specific preparation processes:
(1) Adding 35 parts of corn starch and 0.5 part of sodium tripolyphosphate into water according to parts by weight, stirring uniformly at 45 ℃ to obtain a solution with uniformly dispersed starch, and adding 6 parts of CH 3 Stirring COONa to obtain a mixed solution, reacting 4 h, carrying out suction filtration to obtain a filter cake, washing with water, carrying out suction filtration, and drying to obtain a carbon precursor;
(2) Delivering the carbon precursor into a carbonization furnace, heating to 240 ℃ at a heating rate of 5 ℃ per min under inert gas, staying at 2 h, carrying out dehydration treatment, heating to 1300 ℃ at a heating rate of 4 ℃ per min, staying at 5 h, cooling, and crushing to obtain a hard carbon substrate material;
(3) Dispersing sodium fluorophosphate into ethanol to prepare an ethanol solution of 0.6 wt% sodium fluorophosphate, stirring and mixing 100 parts of hard carbon substrate and 3 parts of the ethanol solution containing sodium fluorophosphate, and vacuum drying at 55 ℃ to obtain a sodium fluorophosphate modified hard carbon substrate;
(4) Placing the hard carbon substrate material prepared in the step (3) in a heating furnace of a fluidized bed, and under inert gas argon: hydrocarbon methane = 10: and 5 (air flow ratio) is carried out at 550 ℃ for 20 min in an atmosphere, surface carbon filling (hydrocarbon cracking, surface defect filling and carbon molecule solidification) is carried out, the heating rate is 5 ℃/min, and then the temperature is reduced, so that the hard carbon anode material is obtained.
The prepared hard carbon negative electrode material was tested for specific surface area, porosity, particle diameter and carbon content, and the hard carbon negative electrode material prepared in this example had a specific surface area of 4 m 2 The porosity per gram is 14%, the particle diameter D50 is about 8 mu m, and the carbon content is 95 wt%. As shown in the SEM diagram of FIG. 1, the hard carbon negative electrode material has a spherical structure with complete granularity.
The hard carbon anode material prepared by the embodiment is used for preparing anode pieces and sodium ion batteries, and specifically comprises the following steps:
preparing a negative electrode plate: 94.5 parts of hard carbon cathode material, 1.0 part of conductive material (obtained by mixing conductive carbon black and carbon nano tubes according to the mass ratio of 19:1) and 1.75 parts of bonding substance (obtained by mixing sodium carboxymethylcellulose and polyacrylic acid according to the mass ratio of 1:2) are placed in a stirring pot of a stirrer, and dry-mixed and stirred for 100 min at the rotating speed of 1500 r/min to obtain a primary mixture;
Adding 1.0 part of the conductive material, 1.75 parts of the bonding material and water into the primary mixture, stirring for 2 h at the rotating speed of 2500 r/min, adding water until the content of solid matters in a stirring pot is 50%, and adjusting the viscosity to 3.0 Pa.s to obtain a secondary mixture;
coating the secondary mixture on a carbon-coated aluminum foil negative electrode current collector, drying, cold pressing and cutting to obtain a negative electrode plate with the surface density of 0.008 g/cm 2 ；
Preparing a positive electrode plate: the positive electrode active material (sodium nickel manganese ferrite NaNi 0.5 Mn 0.45 Fe 0.05 O 2 ) Conductive agent (single-walled carbon nanotube 4wt% + conductive carbon black 96 wt%) and binder (polyvinylidene fluoride) according to a mass ratio of 97.5:1.5:1.0 preparing positive electrode slurry, coating on a positive electrode current collector aluminum foil, drying, rolling, cutting, slitting, and preparing into positive electrode plate with surface density of 0.017 g/cm 2 。
Preparation of electrolyte: in a glove box, ethylene carbonate, propylene carbonate, methyl acetic acidThe volume ratio of the ester is 1:1:1 preparing a basic solvent, and then adding sodium salt NaPF 6 Adding 4.5wt% of additive vinylene carbonate and fluoroethylene carbonate to the concentration of 1.0 mol/L;
preparation of sodium ion battery: and winding the positive electrode plate, the diaphragm and the negative electrode plate into a bare cell, putting the bare cell into a battery shell, drying at 180 ℃ to remove moisture, injecting electrolyte into the battery shell, and packaging to obtain the secondary battery.
Example 2
The embodiment relates to a preparation method of a hard carbon anode material and a secondary battery, which comprises the following specific preparation processes:
(1) Adding 35 parts of corn starch and 0.5 part of sodium tripolyphosphate into water according to parts by weight, stirring uniformly at 45 ℃ to obtain a solution with uniformly dispersed starch, and adding 7.5 parts of CH 3 Stirring COONa to obtain a mixed solution, reacting 4 h, carrying out suction filtration to obtain a filter cake, washing with water, carrying out suction filtration, and drying to obtain a carbon precursor;
(2) Delivering the carbon precursor into a carbonization furnace, heating to 240 ℃ at a heating rate of 2 ℃ per min under inert gas, staying at 2 h, dehydrating, heating to 1350 ℃ at a heating rate of 5 ℃ per min, staying at 5 h, cooling, and crushing to obtain a hard carbon substrate material;
(3) Dispersing sodium fluorophosphate into ethanol to prepare an ethanol solution of 0.6 wt% sodium fluorophosphate, stirring and mixing 100 parts of hard carbon substrate and 3 parts of the ethanol solution containing sodium fluorophosphate, and vacuum drying at 55 ℃ to obtain a sodium fluorophosphate modified hard carbon substrate;
(4) Placing the hard carbon substrate material prepared in the step (3) in a heating furnace of a fluidized bed, and under inert gas argon: hydrocarbon methane = 10: and 5 (air flow ratio) is carried out at 550 ℃ for 20 min in an atmosphere, surface carbon filling (hydrocarbon cracking, surface defect filling and carbon molecule solidification) is carried out, the heating rate is 5 ℃/min, and then the temperature is reduced, so that the hard carbon anode material is obtained.
The specific surface area, the porosity, the particle size and the carbon content of the prepared hard carbon negative electrode material are tested, and the specific surface area of the hard carbon negative electrode material prepared in the embodimentProduct 9 m 2 Per g, the porosity is 12%, the particle diameter D50 is about 6 μm, and the carbon content is 95 wt%.
The hard carbon anode material prepared by the embodiment is used for preparing anode pieces and sodium ion batteries, and specifically comprises the following steps:
preparing a negative electrode plate: 94.5 parts of hard carbon cathode material, 1.0 part of conductive material (obtained by mixing conductive carbon black and carbon nano tubes according to the mass ratio of 19:1) and 1.75 parts of bonding substance (obtained by mixing sodium carboxymethylcellulose and polyacrylic acid according to the mass ratio of 1:2) are placed in a stirring pot of a stirrer, and dry-mixed and stirred for 100 min at the rotating speed of 1500 r/min to obtain a primary mixture;
adding 1.0 part of the conductive material, 1.75 parts of the bonding material and water into the primary mixture, stirring for 2 h at the rotating speed of 2500 r/min, adding water until the content of solid matters in a stirring pot is 49%, and adjusting the viscosity to 3.1 Pa.s to obtain a secondary mixture;
coating the secondary mixture on a carbon-coated aluminum foil negative electrode current collector, drying, cold pressing and cutting to obtain a negative electrode plate with the surface density of 0.008 g/cm 2 ；
Preparing a positive electrode plate: the positive electrode active material (sodium nickel manganese ferrite NaNi 0.5 Mn 0.45 Fe 0.05 O 2 ) Conductive agent (single-walled carbon nanotube 4wt% + conductive carbon black 96 wt%) and binder (polyvinylidene fluoride) according to a mass ratio of 97.5:1.5:1.0 preparing positive electrode slurry, coating on a positive electrode current collector aluminum foil, drying, rolling, cutting, slitting, and preparing into positive electrode plate with surface density of 0.017 g/cm 2 。
Preparation of electrolyte: in a glove box, ethylene carbonate, propylene carbonate and methyl acetate are mixed according to a volume ratio of 1:1:1 preparing a basic solvent, and then adding sodium salt NaPF 6 Adding 4.5wt% of additive vinylene carbonate and fluoroethylene carbonate to the concentration of 1.0 mol/L;
preparation of sodium ion battery: and winding the positive electrode plate, the diaphragm and the negative electrode plate into a bare cell, putting the bare cell into a battery shell, drying at 180 ℃ to remove moisture, injecting electrolyte into the battery shell, and packaging to obtain the secondary battery.
Example 3
The embodiment relates to a preparation method of a hard carbon anode material and a secondary battery, which comprises the following specific preparation processes:
(1) Adding 35 parts of corn starch and 0.5 part of sodium tripolyphosphate into water according to parts by weight, stirring uniformly at 45 ℃ to obtain a solution with uniformly dispersed starch, and adding 9 parts of CH 3 Stirring COONa to obtain a mixed solution, reacting 4 h, carrying out suction filtration to obtain a filter cake, washing with water, carrying out suction filtration, and drying to obtain a carbon precursor;
(2) Delivering the carbon precursor into a carbonization furnace, heating to 240 ℃ at a heating rate of 5 ℃ per min under inert gas, staying at 2 h, carrying out dehydration treatment, heating to 1400 ℃ at a heating rate of 4 ℃ per min, staying at 5 h, cooling, and crushing to obtain a hard carbon substrate material;
(3) Dispersing sodium fluorophosphate into ethanol to prepare an ethanol solution of 0.6 wt% sodium fluorophosphate, stirring and mixing 100 parts of hard carbon substrate and 3 parts of the ethanol solution containing sodium fluorophosphate, and vacuum drying at 55 ℃ to obtain a sodium fluorophosphate modified hard carbon substrate;
(4) Placing the hard carbon substrate material prepared in the step (3) in a heating furnace of a fluidized bed, and under inert gas argon: hydrocarbon methane = 10: and 5 (air flow ratio) is carried out at 550 ℃ for 20 min in an atmosphere, surface carbon filling (hydrocarbon cracking, surface defect filling and carbon molecule solidification) is carried out, the heating rate is 5 ℃/min, and then the temperature is reduced, so that the hard carbon anode material is obtained.
The prepared hard carbon negative electrode material was tested for specific surface area, porosity, particle diameter and carbon content, and the hard carbon negative electrode material prepared in this example had a specific surface area of 4 m 2 Per g, the porosity is 12%, the particle diameter D50 is about 8 μm, and the carbon content is 95 wt%.
The hard carbon anode material prepared by the embodiment is used for preparing anode pieces and sodium ion batteries, and specifically comprises the following steps:
preparing a negative electrode plate: 94.5 parts of hard carbon cathode material, 1.0 part of conductive material (obtained by mixing conductive carbon black and carbon nano tubes according to the mass ratio of 19:1) and 1.75 parts of bonding substance (obtained by mixing sodium carboxymethylcellulose and polyacrylic acid according to the mass ratio of 1:2) are placed in a stirring pot of a stirrer, and dry-mixed and stirred for 100 min at the rotating speed of 1500 r/min to obtain a primary mixture;
adding 1.0 part of the conductive material, 1.75 parts of the bonding material and water into the primary mixture, stirring for 2 h at the rotating speed of 2500 r/min, adding water until the content of solid matters in a stirring pot is 49%, and adjusting the viscosity to 2.8 Pa.s to obtain a secondary mixture;
coating the secondary mixture on a carbon-coated aluminum foil negative electrode current collector, drying, cold pressing and cutting to obtain a negative electrode plate with the surface density of 0.008 g/cm 2 ；
Preparing a positive electrode plate: the positive electrode active material (sodium nickel manganese ferrite NaNi 0.5 Mn 0.45 Fe 0.05 O 2 ) Conductive agent (single-walled carbon nanotube 4wt% + conductive carbon black 96 wt%) and binder (polyvinylidene fluoride) according to a mass ratio of 97.5:1.5:1.0 preparing positive electrode slurry, coating on a positive electrode current collector aluminum foil, drying, rolling, cutting, slitting, and preparing into positive electrode plate with surface density of 0.017 g/cm 2 。
Preparation of electrolyte: in a glove box, ethylene carbonate, propylene carbonate and methyl acetate are mixed according to a volume ratio of 1:1:1 preparing a basic solvent, and then adding sodium salt NaPF 6 Adding 4.5wt% of additive vinylene carbonate and fluoroethylene carbonate to the concentration of 1.0 mol/L;
preparation of sodium ion battery: and winding the positive electrode plate, the diaphragm and the negative electrode plate into a bare cell, putting the bare cell into a battery shell, drying at 180 ℃ to remove moisture, injecting electrolyte into the battery shell, and packaging to obtain the secondary battery.
Example 4
The embodiment relates to a preparation method of a hard carbon anode material and a secondary battery, which comprises the following specific preparation processes:
(1) Adding 42 parts of corn starch and 0.6 part of sodium tripolyphosphate into water according to parts by weight, stirring uniformly at 45 ℃ to obtain a solution with uniformly dispersed starch, and adding 6 parts of CH 3 Stirring COONa to obtain a mixed solution, reacting 4 h, carrying out suction filtration to obtain a filter cake, washing with water, carrying out suction filtration, and drying to obtain a carbon precursor;
(2) Delivering the carbon precursor into a carbonization furnace, heating to 280 ℃ at a heating rate of 2 ℃ per min under inert gas, staying at 2 h, dehydrating, heating to 1300 ℃ at a heating rate of 5 ℃ per min, staying at 5 h, cooling, and crushing to obtain a hard carbon substrate material;
(3) Dispersing sodium fluoride into ethanol to prepare an ethanol solution of 1.5 wt% sodium fluoride, stirring and mixing 100 parts of hard carbon substrate and 5 parts of the ethanol solution containing sodium fluoride, and vacuum drying at 55 ℃ to obtain a sodium fluoride modified hard carbon substrate;
(4) Placing the hard carbon substrate material prepared in the step (3) in a heating furnace of a fluidized bed, and under inert gas argon: hydrocarbon acetylene = 10:2 (air flow ratio) is carried out at 600 ℃ for 15 min in an atmosphere, surface carbon filling (hydrocarbon cracking, surface defect filling and carbon molecule solidification) is carried out, the heating rate is 5 ℃/min, and then the temperature is reduced, so that the hard carbon anode material is obtained.
The prepared hard carbon negative electrode material was tested for specific surface area, porosity, particle diameter and carbon content, and the hard carbon negative electrode material prepared in this example had a specific surface area of 4 m 2 Per g, the porosity is 13%, the particle diameter D50 is about 8 μm, and the carbon content is 97 wt%.
The hard carbon anode material prepared by the embodiment is used for preparing anode pieces and sodium ion batteries, and specifically comprises the following steps:
preparing a negative electrode plate: 95 parts of hard carbon cathode material, 0.875 part of conductive material (obtained by mixing conductive carbon black and carbon nano tubes according to the mass ratio of 19:1) and 1.625 parts of bonding substance (obtained by mixing sodium carboxymethylcellulose and polyacrylic acid according to the mass ratio of 1:2) are placed in a stirring pot of a stirrer, and dry-mixed and stirred for 100 min at the rotating speed of 1500 r/min to obtain a primary mixture;
Adding 0.875 parts of the conductive material, 1.625 parts of the bonding material and water into the primary mixture, stirring for 90 min at the rotating speed of 3000 r/min, adding water until the content of solid matters in a stirring pot is 51%, and adjusting the viscosity to 3.7 Pa.s to obtain a secondary mixture;
coating the secondary mixture on a carbon-coated aluminum foil negative electrode current collector, drying, cold pressing and cutting to obtain a negative electrode plate with the surface density of 0.008 g/cm 2 ；
Preparing a positive electrode plate: the positive electrode active material (sodium nickel manganese ferrite NaNi 0.5 Mn 0.45 Fe 0.05 O 2 ) Conductive agent (single-walled carbon nanotube 4wt% + conductive carbon black 96 wt%) and binder (polyvinylidene fluoride) according to a mass ratio of 97.5:1.5:1.0 preparing positive electrode slurry, coating on a positive electrode current collector aluminum foil, drying, rolling, cutting, slitting, and preparing into positive electrode plate with surface density of 0.017 g/cm 2 。
Preparation of electrolyte: in a glove box, ethylene carbonate, propylene carbonate and methyl acetate are mixed according to a volume ratio of 1:1:1 preparing a basic solvent, and then adding sodium salt NaPF 6 Adding 4.5wt% of additive vinylene carbonate and fluoroethylene carbonate to the concentration of 1.0 mol/L;
preparation of sodium ion battery: and winding the positive electrode plate, the diaphragm and the negative electrode plate into a bare cell, putting the bare cell into a battery shell, drying at 160 ℃ to remove moisture, injecting electrolyte into the battery shell, and packaging to obtain the secondary battery.
Example 5
The embodiment relates to a preparation method of a hard carbon anode material and a secondary battery, which comprises the following specific preparation processes:
(1) Adding 42 parts of corn starch and 0.6 part of sodium tripolyphosphate into water according to parts by weight, stirring uniformly at 45 ℃ to obtain a solution with uniformly dispersed starch, and adding 7.5 parts of CH 3 Stirring COONa to obtain a mixed solution, reacting 4 h, carrying out suction filtration to obtain a filter cake, washing with water, carrying out suction filtration, and drying to obtain a carbon precursor;
(2) Delivering the carbon precursor into a carbonization furnace, heating to 280 ℃ at a heating rate of 2 ℃ per min under inert gas, staying at 2 h, dehydrating, heating to 1350 ℃ at a heating rate of 5 ℃ per min, staying at 5 h, cooling, and crushing to obtain a hard carbon substrate material;
(3) Dispersing sodium fluoride into ethanol to prepare an ethanol solution of 1.5 wt% sodium fluoride, stirring and mixing 100 parts of hard carbon substrate and 5 parts of the ethanol solution containing sodium fluoride, and vacuum drying at 55 ℃ to obtain a sodium fluoride modified hard carbon substrate;
(4) Placing the hard carbon substrate material prepared in the step (3) in a heating furnace of a fluidized bed, and under inert gas argon: hydrocarbon acetylene = 10:2 (air flow ratio) is carried out at 600 ℃ for 15 min in an atmosphere, surface carbon filling (hydrocarbon cracking, surface defect filling and carbon molecule solidification) is carried out, the heating rate is 5 ℃/min, and then the temperature is reduced, so that the hard carbon anode material is obtained.
The prepared hard carbon negative electrode material was tested for specific surface area, porosity, particle diameter and carbon content, and the hard carbon negative electrode material prepared in this example had a specific surface area of 4 m 2 Per g, the porosity is 15%, the particle diameter D50 is about 7 μm, and the carbon content is 96 wt%.
The hard carbon anode material prepared by the embodiment is used for preparing anode pieces and sodium ion batteries, and specifically comprises the following steps:
preparing a negative electrode plate: 95 parts of hard carbon cathode material, 0.875 part of conductive material (obtained by mixing conductive carbon black and carbon nano tubes according to the mass ratio of 19:1) and 1.625 parts of bonding substance (obtained by mixing sodium carboxymethylcellulose and polyacrylic acid according to the mass ratio of 1:2) are placed in a stirring pot of a stirrer, and dry-mixed and stirred for 90 min at the rotating speed of 1500 r/min to obtain a primary mixture;
adding 0.875 parts of the conductive material, 1.625 parts of the bonding material and water into the primary mixture, stirring for 100 min at the rotating speed of 3000 r/min, adding water until the content of solid matters in a stirring pot is 51%, and adjusting the viscosity to 3.9 Pa.s to obtain a secondary mixture;
coating the secondary mixture on a carbon-coated aluminum foil negative electrode current collector, drying, cold pressing and cutting to obtain a negative electrode plate with the surface density of 0.008 g/cm 2 ；
Preparing a positive electrode plate: the positive electrode active material (sodium nickel manganese ferrite NaNi 0.5 Mn 0.45 Fe 0.05 O 2 ) Conductive agent (single-walled carbon nanotube 4wt% + conductive carbon black 96 wt%) and binder (polyvinylidene fluoride) according to a mass ratio of 97.5:1.5:1.0 preparing positive electrode slurry, coating on a positive electrode current collector aluminum foil, drying, rolling, cutting, slitting, and preparing into positive electrode plate with surface density of 0.017 g/cm 2 。
Preparation of electrolyte: in a glove box, ethylene carbonate, propylene carbonate and methyl acetate are mixed according to a volume ratio of 1:1:1 preparing a basic solvent, and then adding sodium salt NaPF 6 Adding 4.5wt% of additive vinylene carbonate and fluoroethylene carbonate to the concentration of 1.0 mol/L;
preparation of sodium ion battery: and winding the positive electrode plate, the diaphragm and the negative electrode plate into a bare cell, putting the bare cell into a battery shell, drying at 160 ℃ to remove moisture, injecting electrolyte into the battery shell, and packaging to obtain the secondary battery.
Example 6
The embodiment relates to a preparation method of a hard carbon anode material and a secondary battery, which comprises the following specific preparation processes:
(1) Adding 42 parts of corn starch and 0.6 part of sodium tripolyphosphate into water according to parts by weight, stirring uniformly at 45 ℃ to obtain a solution with uniformly dispersed starch, and adding 7.5 parts of CH 3 Stirring COONa to obtain a mixed solution, reacting 4 h, carrying out suction filtration to obtain a filter cake, washing with water, carrying out suction filtration, and drying to obtain a carbon precursor;
(2) Delivering the carbon precursor into a carbonization furnace, heating to 280 ℃ at a heating rate of 2 ℃ per min under inert gas, staying at 2 h, dehydrating, heating to 1400 ℃ at a heating rate of 5 ℃ per min, staying at 5 h, cooling, and crushing to obtain a hard carbon substrate material;
(3) Dispersing sodium fluoride into ethanol to prepare an ethanol solution of 1.5 wt% sodium fluoride, stirring and mixing 100 parts of hard carbon substrate and 5 parts of the ethanol solution containing sodium fluoride, and vacuum drying at 55 ℃ to obtain a sodium fluoride modified hard carbon substrate;
(4) Placing the hard carbon substrate material prepared in the step (3) in a heating furnace of a fluidized bed, and under inert gas argon: hydrocarbon acetylene = 10:2 (air flow ratio) is carried out at 600 ℃ for 15 min in an atmosphere, surface carbon filling (hydrocarbon cracking, surface defect filling and carbon molecule solidification) is carried out, the heating rate is 5 ℃/min, and then the temperature is reduced, so that the hard carbon anode material is obtained.
The prepared hard carbon negative electrode material was tested for specific surface area, porosity, particle diameter and carbon content, and the hard carbon negative electrode material prepared in this example had a specific surface area of 4 m 2 Per g, the porosity is 13%, the particle diameter D50 is about 7 μm, and the carbon content is 96 wt%.
The hard carbon anode material prepared by the embodiment is used for preparing anode pieces and sodium ion batteries, and specifically comprises the following steps:
preparing a negative electrode plate: 95 parts of hard carbon cathode material, 0.875 part of conductive material (obtained by mixing conductive carbon black and carbon nano tubes according to the mass ratio of 19:1) and 1.625 parts of bonding substance (obtained by mixing sodium carboxymethylcellulose and polyacrylic acid according to the mass ratio of 1:2) are placed in a stirring pot of a stirrer, and dry-mixed and stirred for 90 min at the rotating speed of 1500 r/min to obtain a primary mixture;
adding 0.875 parts of the conductive material, 1.625 parts of the bonding material and water into the primary mixture, stirring for 100 min at the rotating speed of 3000 r/min, adding water until the content of solid matters in a stirring pot is 52%, and adjusting the viscosity to be 4.4 Pa.s to obtain a secondary mixture;
coating the secondary mixture on a carbon-coated aluminum foil negative electrode current collector, drying, cold pressing and cutting to obtain a negative electrode plate with the surface density of 0.008 g/cm 2 ；
Preparing a positive electrode plate: the positive electrode active material (sodium nickel manganese ferrite NaNi 0.5 Mn 0.45 Fe 0.05 O 2 ) Conductive agent (single-walled carbon nanotube 4wt% + conductive carbon black 96 wt%) and binder (polyvinylidene fluoride) according to a mass ratio of 97.5:1.5:1.0 preparing positive electrode slurry, coating on a positive electrode current collector aluminum foil, drying, rolling, cutting, slitting, and preparing into positive electrode plate with surface density of 0.017 g/cm 2 。
Preparation of electrolyte: in a glove box, ethylene carbonate, propyleneCarbonate and methyl acetate according to the volume ratio of 1:1:1 preparing a basic solvent, and then adding sodium salt NaPF 6 Adding 4.5wt% of additive vinylene carbonate and fluoroethylene carbonate to the concentration of 1.0 mol/L;
preparation of sodium ion battery: and winding the positive electrode plate, the diaphragm and the negative electrode plate into a bare cell, putting the bare cell into a battery shell, drying at 160 ℃ to remove moisture, injecting electrolyte into the battery shell, and packaging to obtain the secondary battery.
Comparative example 1
This comparative example relates to the preparation of a hard carbon negative electrode material and a secondary battery, and differs from example 1 only in that: no modifier CH is added in the preparation of the hard carbon anode material 3 COONa, the rest of the procedure was identical.
Comparative example 2
This comparative example relates to the preparation of a hard carbon negative electrode material and a secondary battery, and differs from example 1 only in that: the preparation of the hard carbon anode material does not comprise the step (3), the interfacial active layer is not introduced, and the rest operations are the same.
An SEM image of the hard carbon anode material prepared in this comparative example is shown in fig. 2, and a broken structure can be observed; as can be seen from fig. 1 and 2, the present invention can effectively prevent the collapse of the structure of the starch granules during the dehydration and carbonization process by modifying the surface of the starch granules before carbonization.
Comparative example 3
This comparative example relates to the preparation of a hard carbon negative electrode material and a secondary battery, and differs from example 1 only in that: the preparation of the hard carbon anode material does not comprise the step (4), the surface carbon filling is not carried out, and the rest operations are the same.
Comparative example 4
This comparative example relates to the preparation of a hard carbon negative electrode material and a secondary battery, which differ from example 1 only in step (4), and is specifically conducted as follows:
and (3) mixing the sodium fluorophosphate modified hard carbon substrate prepared in the step (3) of the example 1 with asphalt in a mass ratio of 98.5:1.5, uniformly mixing, and then treating at a high temperature of 1100 ℃ for 2 h to prepare the hard carbon anode material, wherein the rest operations are the same.
Performance testing
The initial coulombic efficiency of the anode materials prepared in the above examples and comparative examples and the cycle performance of the prepared sodium secondary battery were examined, and the specific operations were as follows:
initial coulombic efficiency test: cutting the negative electrode plate prepared in each example and comparative example into a circular sheet with the diameter of 12 mm, then conveying the circular sheet into a glove box to assemble a 2032 type button cell, wherein the electrolyte is composed of a solvent EC&NaClO in DMC (volume ratio 1:1) 1M 4 . The polypropylene film is used as a separation film, and the metal sodium sheet is used as a counter electrode. Performing a 0-1.5V discharge/charge test on the constructed button cell, testing the initial charge capacity and initial discharge capacity of the button cell, and calculating initial coulomb efficiency (initial coulomb efficiency=initial charge capacity/initial discharge capacity);
And (3) testing the cycle performance: the secondary batteries prepared in the above examples and comparative examples are firstly formed and fixed in volume, and the ratios of battery formation and first-circle charge and discharge of the fixed volume are recorded; and then 0.2C to 3.9V, 3.9V constant voltage to current to reduce to 0.05C, 0.33C to 2.0V, 0.2C to 3.9V, 3.9V constant voltage to current to reduce to 0.05C, the battery is circularly charged and discharged, the charge and discharge of the battery are recorded at 200 circles of capacity, 500 circles of capacity to initial circle of capacity percentage and corresponding circles of attenuation to 80% of capacity percentage, and the electrochemical performance of the battery is evaluated.
The test results are shown in table 1 below:
TABLE 1
As can be seen from table 1, the secondary batteries prepared in examples 1 to 6 clearly have higher initial coulombic efficiency and better cycle performance than those in comparative examples 1 to 4. As is apparent from examples 1 and comparative examples 1 to 3, the effect of surface modification before carbonization of starch and final carbon filling on cycle performance is more remarkable, for example, the cycle number corresponding to the sodium secondary battery having the hard carbon negative electrode material prepared in example 1 whose capacity was attenuated to 80% was increased by 200 cycles or more as compared with comparative example 3 without carbon filling, which also indicates that carbon filling on the surface of the hard carbon substrate can effectively improve the cycle performance of the battery; compared with example 1, the preparation method of the hard carbon negative electrode material in comparative example 2 has relatively low initial coulombic efficiency and also has a certain influence on the cycle performance of the constructed sodium secondary battery, wherein the hard carbon substrate is not subjected to modification treatment by sodium fluorophosphate before carbon filling, so that an interface active layer is formed.
However, as can be seen from examples 1 and 4, the preparation of the carbon layer on the surface of the hard carbon substrate by using the high-temperature cracking carbide is greatly different from the preparation of the carbon layer by using the mixing and calcining method in comparative example 4 in the improvement of the cycle performance; compared with comparative example 3, the cycle performance of the hard carbon negative electrode material prepared by pitch cladding and calcination is only slightly improved (the cycle number corresponding to the capacity reduced to 80% is only increased by 19), and it was unexpectedly found that the initial coulombic efficiency of the secondary battery constructed in comparative example 4 is rather reduced.
In conclusion, the hard carbon negative electrode material with high initial coulombic efficiency is prepared under the synergistic effect of surface modification before starch carbonization, introduction of the interfacial active layer and filling of small-surface carbon, and the secondary battery containing the hard carbon negative electrode material has good cycle performance.
The above-described embodiments are merely preferred embodiments for fully explaining the present invention, and the scope of the present invention is not limited thereto. Equivalent substitutions and modifications will occur to those skilled in the art based on the present invention, and are intended to be within the scope of the present invention. The protection scope of the invention is subject to the claims.

Claims (10)

1. The preparation method of the hard carbon anode material is characterized by comprising the following steps of:
(1) Mixing starch, a dispersing agent and a modifying agent in water, and drying to obtain a carbon precursor; the modifier is R 1 COOR 2 And/or (R) 1 COO） 2 R 2 Wherein R is 1 Selected from C1-C12 alkyl, C3-C12 cycloalkyl, phenyl, C6-C12 substituted phenylR, R is as follows 1 COOR 2 R in (a) 2 Is CH 3 H, K, na, li or NH 4 ，（R 1 COO） 2 R 2 R in (a) 2 Is Mg or Ca;
(2) Sequentially dehydrating and carbonizing the carbon precursor prepared in the step (1) to obtain a hard carbon substrate;
(3) Mixing the hard carbon substrate prepared in the step (2) with an aqueous solution or an organic solution of a fluorine-containing substance, and drying to obtain a hard carbon substrate with a surface modified with the fluorine-containing substance;
(4) Placing the hard carbon substrate with the surface modified with the fluorine-containing substances prepared in the step (3) under a mixed atmosphere, and sweeping for 10 min-1 h at 300-700 ℃ to fill surface carbon, so as to obtain the hard carbon negative electrode material; the mixed atmosphere is composed of hydrocarbon and inert gas.
2. The preparation method according to claim 1, wherein in the step (1), starch and a dispersing agent are added into water, uniformly stirred at 25-60 ℃, then a modifying agent is added, the stirring reaction is continued for 30 min-12 h, and the carbon precursor is obtained after drying treatment.
3. The method according to claim 1, wherein in step (1), the starch is selected from one or more of wheat starch, corn starch, soybean starch, mung bean starch, pea starch, potato starch, rice starch, millet starch, potato starch, tapioca starch;
the dispersing agent is one or more selected from sodium chloride, dimethylformamide, sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, sodium alkyl sulfonate, sodium stearate, magnesium stearate, calcium stearate and copper stearate;
the modifier is selected from CH 3 COONa and/or CH 3 COONH 4 ；
The mass ratio of the starch to the dispersant to the modifier is 0.1-45:0.05-10:0.05-22.
4. The method according to claim 1, wherein in the step (2), the dehydrating step comprises: heating to 100-400 ℃ at a heating rate of 1-5 ℃/min under inert atmosphere, and preserving heat for 1-8 h;
the carbonization treatment step comprises the following steps: heating to 300-700 ℃ at a heating rate of 2-10 ℃/min, and preserving heat for 2-16 h.
5. The method according to claim 1, wherein in the step (3), the fluorine-containing substance is selected from one or more of sodium fluoride, sodium monofluorophosphate, sodium fluoromettaphosphate;
The mass ratio of the fluorine-containing substances in the aqueous solution or the organic solution of the fluorine-containing substances is 0.05-wt-8 wt%;
the mass ratio of the hard carbon substrate to the aqueous solution or the organic solution of the fluorine-containing substance is 100:0.05-8.
6. The method according to claim 1, wherein in the step (4), the hydrocarbon-containing compound is selected from one or more of methane, ethane, acetylene, butyne, propane, butane;
the inert gas is nitrogen, helium, neon or argon;
the volume ratio of hydrocarbon to inert gas in the mixed atmosphere is 1-8:5-50.
7. A hard carbon anode material, characterized in that the hard carbon anode material is prepared by the preparation method of any one of claims 1 to 6; the hard carbon anode material comprises a hard carbon core, a fluorine-containing interface activation layer and a carbon coating layer which are distributed in sequence from inside to outside.
8. The hard carbon negative electrode material according to claim 7, wherein the carbon coating layer has an oxygen content ratio lower than that of the hard carbon core.
9. A negative electrode sheet comprising the hard carbon negative electrode material of claim 7 or 8.
10. A secondary battery comprising the hard carbon negative electrode material according to claim 7 or 8, or the negative electrode sheet according to claim 9.
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Publication number Priority date Publication date Assignee Title
CN105633380A (en) * 2016-03-04 2016-06-01 中国科学院新疆理化技术研究所 Preparation method for starch-based porous hard carbon negative electrode material of lithium ion battery
CN109921018A (en) * 2017-12-13 2019-06-21 宁波杉杉新材料科技有限公司 The preparation method of sodium-ion battery high capacity biomass hard charcoal negative electrode material
CN114873579A (en) * 2022-05-10 2022-08-09 山东能源集团有限公司 Composite carbon microsphere, preparation method and application thereof
CN115207308A (en) * 2022-06-27 2022-10-18 珠海冠宇电池股份有限公司 Negative electrode material, preparation method thereof and battery

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105633380A (en) * 2016-03-04 2016-06-01 中国科学院新疆理化技术研究所 Preparation method for starch-based porous hard carbon negative electrode material of lithium ion battery
CN109921018A (en) * 2017-12-13 2019-06-21 宁波杉杉新材料科技有限公司 The preparation method of sodium-ion battery high capacity biomass hard charcoal negative electrode material
CN114873579A (en) * 2022-05-10 2022-08-09 山东能源集团有限公司 Composite carbon microsphere, preparation method and application thereof
CN115207308A (en) * 2022-06-27 2022-10-18 珠海冠宇电池股份有限公司 Negative electrode material, preparation method thereof and battery

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