CN111864206B - Hard carbon negative electrode material, preparation method thereof, pole piece containing hard carbon negative electrode material and lithium ion battery - Google Patents

Hard carbon negative electrode material, preparation method thereof, pole piece containing hard carbon negative electrode material and lithium ion battery Download PDF

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CN111864206B
CN111864206B CN201910364006.XA CN201910364006A CN111864206B CN 111864206 B CN111864206 B CN 111864206B CN 201910364006 A CN201910364006 A CN 201910364006A CN 111864206 B CN111864206 B CN 111864206B
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hard carbon
negative electrode
electrode material
hours
carbon negative
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CN111864206A (en
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侯博
汪福明
任建国
岳敏
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Shenzhen Beiteri New Energy Technology Research Institute Co ltd
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BTR New Material Group Co Ltd
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    • 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
    • H01M4/624Electric conductive fillers
    • H01M4/625Carbon or graphite
    • 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
    • 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • 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

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Abstract

The invention provides a hard carbon negative electrode material, a preparation method thereof, a pole piece containing the hard carbon negative electrode material and a lithium ion battery. The hard carbon negative electrode material comprises an inner main body and an outer layer which is coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, and the inner main body and the outer layer both comprise hard carbon. The preparation method comprises the following steps: 1) Mixing the first hard carbon precursor, the additive and molten salt, and then carrying out catalytic reaction to obtain a second hard carbon precursor; 2) And purifying the second hard carbon precursor, and sintering to obtain the hard carbon anode material. The hard carbon negative electrode material provided by the invention has the advantages of capacity improvement, adsorptivity reduction and good cycle performance. The preparation method provided by the invention starts from the structure of the hard carbon material, and prepares the hard carbon negative electrode material with high capacity and low adsorptivity through a fused salt auxiliary process and the use of additives.

Description

Hard carbon negative electrode material, preparation method thereof, pole piece containing hard carbon negative electrode material and lithium ion battery
Technical Field
The invention belongs to the technical field of energy storage materials, relates to a negative electrode material, and in particular relates to a hard carbon negative electrode material, a preparation method thereof, a pole piece containing the hard carbon negative electrode material and a lithium ion battery.
Background
The research of carbon materials as electrochemical lithium intercalation host materials has been the focus of the research of lithium ion battery anode materials. The graphite-type carbon negative electrode material has low electrode potential<1.0V vs.Li/Li + ) The lithium ion battery has the advantages of long cycle life, good safety, low price and the like, and becomes a main negative electrode material of the current commercial lithium ion battery. However, graphite negative electrode materials have a layered structure, so that the compatibility with electrolyte is poor, and the co-intercalation phenomenon of solvent ions easily occurs in the process of charging and discharging to cause structural damage, thereby influencing the stoneThe cycling stability and coulombic efficiency of the ink negative electrode material. Meanwhile, due to the anisotropic structure characteristic of graphite, free diffusion of lithium ions in a graphite structure is limited, exertion of electrochemical capacity of a graphite negative electrode is restricted, and particularly the rate capability of the graphite negative electrode material is influenced. These problems make it difficult for simple carbon negative electrode materials to meet the requirements of increasingly developed electronic devices, electric vehicles, and the like for high-performance lithium ion batteries.
Compared with graphite, the hard carbon has the isotropic structural characteristics, larger interlayer spacing and the characteristics of accelerating lithium ion diffusion, and meanwhile, the hard carbon material has the characteristics of good cycle performance and multiplying power performance, low cost and the like, so that the hard carbon is paid attention to the aspect of power lithium ion batteries. However, as the hard carbon material has more surface defects and larger specific surface area, the adsorption is very strong, and part of water can be adsorbed in the air to form bonding effect, the hard carbon material can not be separated even through the vacuum drying treatment at 120 ℃, the capacity and the first effect of the hard carbon material can be greatly reduced after the hard carbon material is placed in the air for a period of time, the practical application of the hard carbon material is limited, and therefore, the process optimization is needed to improve the problem of high adsorption of the hard carbon material. The existing technology can only realize optimization of the properties (such as capacity, initial effect, high-temperature performance or rate capability) of the hard carbon part through doping or surface modification technology, and can not realize the effect of improving the capacity and reducing the adsorptivity on the hard carbon material.
CN 102820455a discloses a preparation method of hard carbon negative electrode material of lithium ion battery, which is technically characterized in that the hard carbon negative electrode material is prepared by mixing carbon source, silicon and phosphorus additive according to a certain proportion and sintering at high temperature. The process mainly improves the first discharge capacity of the anode material. However, the hard carbon material prepared by the method has a plurality of surface defects, and the initial coulomb efficiency is low, so that the practical application of the material is affected.
CN101901891a discloses an electrode material, which comprises an electrode material, a binder and a hydrogen storage alloy, wherein hydrogen generated in the charge and discharge process of a lithium battery material is adsorbed by the hydrogen storage alloy, so that the problem of air expansion of a water-absorbent negative electrode material containing lithium titanate, hard carbon, soft carbon and the like in a lithium battery can be solved. However, the hard carbon material can sacrifice part of energy density by adding the adsorptive material after absorbing water, and meanwhile, adsorbed water can be rapidly decomposed in the high-rate charge and discharge process, so that the battery cell rapidly swells, and huge potential safety hazards exist.
CN106629665a discloses a sulfur-doped hard carbon nano-sheet prepared by molten salt method and its application in sodium ion battery, comprising: grinding 0.1-0.2g glucose, 0.1-0.2g sulfur powder and 2-4g fused salt (weight ratio LiCl/KCl=40-50/50-60) fully, then placing the evenly mixed reactants into a corundum boat, and placing the corundum boat into a tube furnace. Calcining at 300-400 ℃ for 1-3h and then at 550-750 ℃ for 4-6h in argon atmosphere, cooling to room temperature, taking out the sample, washing and collecting. However, the hard carbon nano-sheet prepared by the method has strong adsorptivity, and the performance of the hard carbon nano-sheet is greatly reduced due to the fact that the hard carbon nano-sheet is partially adsorbed by water after being placed in the air for a period of time.
Therefore, developing a high-capacity low-adsorptivity hard carbon negative electrode material is a technical problem in the field of lithium ion batteries.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a hard carbon anode material, a preparation method thereof, a pole piece containing the hard carbon anode material and a lithium ion battery. The hard carbon negative electrode material provided by the invention has high capacity and low adsorptivity, can greatly reduce the performance attenuation generated after the hard carbon material is placed in the air, and obviously improves the circulation stability.
To achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a hard carbon anode material, the hard carbon anode material comprising an inner body and an outer layer coated on the inner body, wherein the disorder degree of the outer layer is lower than that of the inner body, and both the inner body and the outer layer comprise hard carbon.
The hard carbon negative electrode material provided by the invention is a high-capacity low-adsorptivity hard carbon negative electrode material. The hard carbon negative electrode material structurally comprises an inner main body and an outer layer, wherein the disorder degree of the outer layer is lower than that of the inner main body, namely, the surface microcrystalline structure of the hard carbon negative electrode material provided by the invention tends to be regular, so that the porosity is reduced, the hydrophobicity is improved, and the aim of reducing the adsorptivity of the hard carbon is fulfilled. In the present invention, the disorder refers to disorder of the arrangement of carbon atoms.
The inner main body and the outer layer of the hard carbon negative electrode material are structures formed by reducing the disorder degree of the hard carbon surface layer, wherein the part with the disorder degree reduced is the outer layer, and the part with the disorder degree unchanged is the inner main body.
The following preferred technical solutions are used as the present invention, but not as limitations on the technical solutions provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solutions.
In a preferred embodiment of the present invention, the ratio of the intensities of the D peak and the G peak in the raman spectrum of the outer layer is 0.2 to 0.7, for example, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.7, etc., but the present invention is not limited to the recited values, and other non-recited values within the range of the values are equally applicable.
Preferably, the ratio of the intensities of the D peak and the G peak in the raman spectrum of the internal body is 0.7 to 1.5, for example, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5, etc., but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.
In the invention, the intensity ratio of the D peak to the G peak in the Raman spectrum is used for measuring the disorder degree of carbon, and the smaller the intensity ratio is, the smaller the disorder degree is.
Preferably, the thickness of the outer layer is 0 to 1 μm and does not comprise 0, e.g. 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm etc. Here, if the outer layer thickness is too thick, the rate performance of the hard carbon anode material is lowered; if the outer layer thickness is too thin, the hydrophobicity is lowered, and the effect of lowering the hard carbon adsorptivity cannot be achieved.
As a preferable technical scheme of the invention, the specific surface area of the hard carbon anode material is 1-20 m 2 /g, e.g. 1m 2 /g、5m 2 /g、10m 2 /g、15m 2 /g or 20m 2 /g, etc., but are not limited to the recited values,other non-enumerated values within this range are equally applicable, preferably 1.5-15 m 2 /g。
The hard carbon negative electrode material preferably has a median particle diameter of 4.0 to 30.0 μm, for example, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, 15.0 μm, 20.0 μm, 25.0 μm or 30.0 μm, etc., but is not limited to the recited values, and other non-recited values within the range are equally applicable, preferably 5.0 to 20.0 μm, further preferably 6.0 to 15.0 μm.
Preferably, the inner body and the outer layer of the hard carbon negative electrode material each include hard carbon and a doping element doped in the hard carbon. The doping element can improve the capacity and first effect of the hard carbon.
Preferably, in the hard carbon anode material, the doping element includes phosphorus and/or nitrogen.
Preferably, in the hard carbon anode material, the mass fraction of the doping element is 0.3-5 wt% based on 100% of the total mass of the hard carbon anode material. Here, if the mass fraction of the doping element is too large, the cycle performance of the hard carbon anode material is reduced; if the mass fraction of the doping element is too small, the capacity and the first effect of the hard carbon material are not obviously improved.
In a second aspect, the present invention provides a method for preparing the hard carbon anode material according to the first aspect, the method comprising the steps of:
(1) Mixing the first hard carbon precursor, the additive and molten salt, and then carrying out catalytic reaction to obtain a second hard carbon precursor;
(2) And (3) purifying the second hard carbon precursor in the step (1), and sintering to obtain the hard carbon anode material.
In the preparation method provided by the invention, the low-temperature catalytic modification is realized by adding the additive by means of a low-temperature blending molten salt auxiliary process, so that the high-capacity low-adsorptivity hard carbon anode material is prepared. Specifically, by adding an additive into the low-temperature molten salt, metal cations in the additive and carbon elements on the surface of the hard carbon are melted to form a compound (such as a ferro-carbon compound), and when the temperature is further increased, the compound is decomposed to enable carbon atoms to be rearranged, the microcrystalline structure on the surface of the hard carbon tends to be regular, the porosity is reduced, the hydrophobicity is improved, and therefore the aim of reducing the adsorptivity of the hard carbon is fulfilled. The process has the characteristics of simple process, remarkable effect, strong pertinence and convenience for industrial production.
As a preferred technical solution of the present invention, in step (1), the preparation method of the first hard carbon precursor includes: carbonizing a hard carbon raw material, and then crushing to obtain a first hard carbon precursor.
Preferably, the hard char feedstock comprises a biomass-based feedstock and/or a thermoplastic resin-based feedstock.
Preferably, the biomass-based raw material comprises any one or a combination of at least two of coconut shells, apricot shells, walnut shells or oil palm shells.
Preferably, the thermoplastic resin raw material comprises any one or a combination of at least two of epoxy resin, phenolic resin, carboxymethyl cellulose, ethyl methyl carbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate or polytetrafluoroethylene.
Preferably, the carbonization is performed under a protective atmosphere.
Preferably, the protective atmosphere is any one or a combination of at least two of nitrogen, helium, neon, argon, krypton or xenon.
The carbonization temperature is preferably 400 to 800 ℃, for example 400 ℃, 500 ℃, 600 ℃, 700 ℃, 800 ℃, or the like, but is not limited to the recited values, and other values not recited in the range of values are equally applicable.
Preferably, the carbonization time is 1 to 8 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc., but is not limited to the recited values, and other non-recited values within the range are equally applicable.
Preferably, the temperature rise rate of the carbonization is 0.5 to 5 ℃ per minute, for example, 0.5 ℃ per minute, 1 ℃ per minute, 2 ℃ per minute, 3 ℃ per minute, 4 ℃ per minute, 5 ℃ per minute, or the like, but is not limited to the values listed, and other values not listed in the range are applicable, and preferably 1 to 3 ℃ per minute.
Preferably, the mixture is carbonized, cooled to 20-30 ℃ and then crushed. I.e. cooled to room temperature and then crushed.
Preferably, the carbonization is performed in any one of a vacuum furnace, a box furnace, a rotary furnace, a roller kiln, a pusher kiln, or a tube furnace.
Preferably, the apparatus for carrying out the comminution comprises a crusher and/or an air mill, preferably a combination of a crusher and a crusher.
Preferably, the crusher comprises any one or a combination of at least two of a jaw crusher, a cone crusher, an impact crusher, a counter-impact crusher or a hammer crusher.
Preferably, the pulverizer comprises any one or a combination of at least two of a flat jet mill, a fluidized bed jet mill, a circulating tube jet mill, a jet mill or a target jet mill.
Preferably, when the apparatus for carrying out the comminution is a combination of a crusher and a crusher, the crusher is used first and then the crusher is used, and the crusher crushes the material to a median particle size of 10 to 4000 μm, for example 10 μm, 100 μm, 500 μm, 1000 μm, 2000 μm, 3000 μm or 4000 μm, etc., but is not limited to the recited values, and other non-recited values within the range of values are equally applicable, for example, preferably 200 to 2000 μm.
Preferably, in the step (1), the first hard carbon precursor is pulverized by a pulverizer to have a median particle diameter of 4.0 to 30.0 μm, for example, 4.0 μm, 5.0 μm, 10.0 μm, 15.0 μm, 20.0 μm, 25.0 μm or 30.0 μm, etc., but not limited to the above-mentioned values, and other non-mentioned values within the above-mentioned value range are equally applicable, preferably 5.0 to 20.0 μm, and further preferably 6.0 to 15.0 μm.
In a preferred embodiment of the present invention, in step (1), the additive contains a metal cation.
Preferably, the additive comprises any one or a combination of at least two of a salt compound of iron, a salt compound of cobalt or a salt compound of nickel.
Preferably, the additive comprises nitrate and/or phosphate in addition to the metal cations. In the invention, when the additive contains both metal cations and nitrate and/or phosphate, the doping and catalysis can be synchronously carried out, the metal cations in the additive can play a role in catalysis, nonmetallic elements in the additive can be fully doped into the hard carbon material, and the capacity and first effect of the hard carbon material can be improved.
Preferably, the additive comprises any one or a combination of at least two of iron phosphate, cobalt phosphate, nickel phosphate, iron nitrate, cobalt nitrate or nickel nitrate, typically but not limited to: a combination of iron phosphate and cobalt phosphate, a combination of nickel phosphate and iron nitrate, a combination of cobalt nitrate and nickel nitrate, and the like.
Preferably, the additive comprises a nitrate-or phosphate-free metal salt comprising any one or a combination of at least two of iron acetate, iron chloride, cobalt acetate, cobalt chloride, nickel acetate or nickel chloride, and a nitrate-or phosphate-containing substance.
Preferably, in step (1), the molten salt comprises any one or a combination of at least two of potassium chloride, sodium chloride, lithium chloride, magnesium chloride or calcium chloride, typically but not limited to: a combination of potassium chloride and sodium chloride, a combination of sodium chloride and lithium chloride, a combination of lithium chloride and magnesium chloride, a combination of lithium chloride, magnesium chloride and calcium chloride, and the like.
Preferably, in step (1), the mixing is performed in a mixing device.
Preferably, the mixing device comprises any one of a VC mixer, a ball mill or a double cone mixer.
Preferably, in the step (1), the mass ratio of the first hard carbon precursor, the molten salt and the additive is 1 (2-10): (0.01-0.5), for example, 1:2:0.01, 1:3:0.08, 1:4:0.1, 1:6:0.2, 1:8:0.4 or 1:10:0.5, but not limited to the recited values, other non-recited values within the range of values are equally applicable, preferably 1 (3-8): (0.03-0.3).
Preferably, the catalytic reaction of step (1) is carried out under a protective atmosphere.
Preferably, the protective atmosphere is any one or a combination of at least two of nitrogen, helium, neon, argon, krypton or xenon.
Preferably, the catalytic reaction is carried out in any one of a vacuum furnace, a box furnace, a rotary furnace, a roller kiln, a pusher kiln or a tube furnace.
Preferably, the reaction temperature of the catalytic reaction is 500 ℃ to 1000 ℃.
Preferably, the reaction time of the catalytic reaction is 0.5 to 8 hours, for example, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, etc., but is not limited to the recited values, and other non-recited values within the range of the recited values are equally applicable, preferably 1 to 6 hours. The thickness of the outer layer of the hard carbon material provided by the invention can be controlled through the time of catalytic reaction, and the longer the time of catalytic reaction is, the more complete the rearrangement of the carbon skeleton is, and the thicker the thickness of the outer layer with low disorder degree is.
The temperature rise rate of the catalyst reaction is preferably 0.5 to 10℃per minute, for example, 0.5℃per minute, 1℃per minute, 2℃per minute, 4℃per minute, 6℃per minute, 8℃per minute or 10℃per minute, etc., but is not limited to the values listed, and other values not listed in the range of the values are applicable, and preferably 1 to 6℃per minute, and more preferably 2 to 4℃per minute.
As a preferred embodiment of the present invention, in the step (2), the purifying method includes: and (3) mixing the second hard carbon precursor in the step (1), acid and water, soaking, centrifugally washing, and drying the obtained solid substance.
Preferably, the acid comprises any one or a combination of at least two of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid or hydrofluoric acid.
Preferably, the mass ratio of the second hard carbon precursor, the acid and the water is 1 (0.5-5): (2-20), such as 1:0.5:2, 1:1:5, 1:1.5:10, 1:2:15, 1:0.8:18, or 1:5:20, etc., but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.
Preferably, the soaking time is 1 to 10 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, etc., but is not limited to the recited values, and other non-recited values within the range are equally applicable, preferably 1 to 4 hours.
Preferably, the time of the centrifugal washing is 0.5 to 6 hours, for example, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours, etc., but is not limited to the exemplified values, and other non-exemplified values within the range are equally applicable, preferably 1 to 4 hours, and more preferably 1.5 to 3 hours.
Preferably, the drying is performed in any one of a vacuum drying oven, a forced air drying oven, a box-type oven, a rotary kiln, or a double cone dryer.
The temperature of the drying is preferably 60 to 200 ℃, for example 60 ℃, 80 ℃, 100 ℃, 120 ℃, 140 ℃, 160 ℃, 180 ℃, 200 ℃, or the like, but is not limited to the values listed, and other values not listed in the range are applicable, and preferably 80 to 150 ℃.
Preferably, the drying time is 6 to 48 hours, for example, 6 hours, 12 hours, 18 hours, 24 hours, 30 hours, 36 hours, 42 hours, 48 hours, etc., but not limited to the recited values, and other non-recited values within the range are equally applicable.
Preferably, in step (2), the sintering is performed under a protective atmosphere.
Preferably, the protective atmosphere is any one or a combination of at least two of nitrogen, helium, neon, argon, krypton or xenon.
Preferably, the sintering is performed in any one of a vacuum furnace, a box furnace, a rotary furnace, a roller kiln, a pusher kiln, or a tube furnace.
Preferably, the sintering temperature is 900 to 1400 ℃, for example 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃ or the like, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.
Preferably, the sintering time is 2 to 8 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or the like, but is not limited to the recited values, and other non-recited values within the range are equally applicable, preferably 3 to 6 hours.
Preferably, the temperature rise rate of the sintering is 0.5 to 10 ℃ per minute, for example, 1 ℃ per minute, 2 ℃ per minute, 4 ℃ per minute, 6 ℃ per minute, 8 ℃ per minute, 10 ℃ per minute, or the like, but not limited to the values recited, and other values not recited in the range are applicable, and preferably 1 to 6 ℃ per minute.
Preferably, the preparation method further comprises: refining the hard carbon anode material obtained in the step (2);
preferably, the refining includes demagnetizing and sieving.
As a further preferred technical solution of the preparation method according to the invention, the method comprises the following steps:
(1) Heating the hard carbon raw material to 400-800 ℃ at a heating rate of 1-3 ℃/min under a protective atmosphere, carbonizing for 1-8 h, cooling to 20-30 ℃, crushing, and crushing the median particle size of the material to 6.0-15.0 mu m to obtain a first hard carbon precursor;
(2) Mixing a first hard carbon precursor, an additive and molten salt, wherein the mass ratio of the first hard carbon precursor to the molten salt to the additive is 1 (2-10) (0.01-0.5), heating to 500-1000 ℃ at a heating rate of 2-4 ℃/min under protective atmosphere after mixing, and carrying out doping and catalytic reaction for 1-6 h to obtain a second hard carbon precursor;
Wherein the additive comprises any one or a combination of at least two of an iron salt compound, a cobalt salt compound or a nickel salt compound; and the additive comprises nitrate radical and/or phosphate radical besides metal cation; the molten salt comprises any one or a combination of at least two of potassium chloride, sodium chloride, lithium chloride, magnesium chloride or calcium chloride;
(3) Mixing the second hard carbon precursor obtained in the step (2), acid and water, wherein the mass ratio of the second hard carbon precursor to the acid to the water is 1 (0.5-5) (2-20), soaking for 1-4 h after mixing, centrifugally washing for 1.5-3 h, drying for 6-48 h at 80-150 ℃, then heating to 900-1400 ℃ at a heating rate of 3-5 ℃/min under a protective atmosphere, sintering for 3-6 h, and carrying out demagnetizing and screening on the obtained product after sintering to obtain the hard carbon negative electrode material.
The further preferable technical scheme adopts a low-temperature blending molten salt auxiliary process, and the purposes of surface catalytic modification and doping modification are achieved by adding specific additives into molten salt. The high-capacity low-adsorptivity hard carbon negative electrode material is prepared by uniformly mixing a carbon source, an additive and molten salt according to a certain proportion, pretreating at a low temperature, adding acid for purification and impurity removal, drying, and burning to a high temperature.
In a third aspect, the present invention provides a pole piece comprising a hard carbon negative electrode material as described in the first aspect.
In a fourth aspect, the present invention provides a lithium ion battery comprising a hard carbon negative electrode material as described in the first aspect.
Compared with the prior art, the invention has the following beneficial effects:
(1) The hard carbon negative electrode material provided by the invention has the advantages that the capacity is improved, the adsorptivity is reduced, the cycle performance is good, the first lithium removal capacity can reach 499.4mAh/g, the first coulomb efficiency can reach 85.2%, the 1000-cycle capacity retention rate can reach 92.5%, the reversible capacity after being placed in air for 30 days can reach 490.6mAh/g, and the first coulomb efficiency after being placed in air for 30 days can reach 84.7%.
(2) The preparation method provided by the invention starts with the structure of the hard carbon material, and carries out structural optimization design, the hard carbon negative electrode material with high capacity and low adsorptivity is prepared by a molten salt auxiliary process one-step method, the capacity and first effect of the hard carbon can be improved by doping nonmetallic elements, and the carbon skeleton is rearranged by decomposing carbide generated by metal cations in the additive and the carbon material, so that the purposes of reducing the specific surface area and the porosity of the hard carbon material are achieved, and the adsorptivity of the hard carbon material is improved. In addition, the preparation method provided by the invention has the characteristics of simple process, remarkable effect, strong pertinence and convenience in industrial production.
Drawings
FIG. 1 is a scanning electron microscope picture of a hard carbon anode material prepared in example 1 of the present invention;
FIG. 2 is a Raman spectrum of the hard carbon anode material prepared in example 1 of the present invention;
FIG. 3 is a graph showing the first charge and discharge curves of the hard carbon negative electrode material prepared in example 1 of the present invention;
fig. 4 is a cycle performance curve of the hard carbon negative electrode material prepared in example 1 of the present invention.
Detailed Description
For better illustrating the present invention, the technical scheme of the present invention is convenient to understand, and the present invention is further described in detail below. The following examples are merely illustrative of the present invention and are not intended to represent or limit the scope of the invention as defined in the claims.
The following are exemplary but non-limiting examples of the invention:
example 1
The hard carbon negative electrode material is prepared according to the following method:
(1) Heating 600g of apricot shells to 600 ℃ at a heating rate of 2 ℃/min in a box furnace under nitrogen atmosphere, carbonizing for 3h, cooling to 25 ℃ to obtain 170g of carbonized material, crushing the carbonized material by using a ball mill, and crushing the medium particle size of the material to 10.0 mu m to obtain a first hard carbon precursor;
(2) Mixing 100g of a first hard carbon precursor, 350g of potassium chloride, 300g of lithium chloride and 15g of ferric phosphate in a VC mixer, uniformly mixing, filling into a graphite crucible, placing in a box furnace, heating to 800 ℃ at a heating rate of 3 ℃/min under nitrogen atmosphere, carrying out doping and catalytic reaction, and cooling to 25 ℃ for 4 hours to obtain a second hard carbon precursor;
(3) Mixing the second hard carbon precursor, hydrochloric acid and water in the step (2), wherein the mass ratio of the second hard carbon precursor to the hydrochloric acid to the water is 1:2:10, soaking for 3 hours after mixing, centrifugally washing for 2.5 hours, drying at 110 ℃ for 24 hours, placing 50g of the dried material into a crucible, placing into a tube furnace, heating to 1100 ℃ at a heating rate of 4 ℃/min under nitrogen atmosphere, sintering for 3 hours, naturally cooling after sintering, and carrying out demagnetizing and screening on the obtained product to obtain the hard carbon negative electrode material.
The hard carbon negative electrode material prepared in this example was subjected to structural test by the following method:
the specific surface area of the material was tested using a Tristar3000 fully automatic specific surface area and porosity analyzer from american microphone instruments.
The material particle size range and the average particle size of the raw material particles were tested using a malvern laser particle size tester MS 2000.
The material was tested for carbon layer disorder using a Raman spectrometer xplor.
The surface morphology, particle size, etc. of the sample were observed using a Hitachi S4800 scanning electron microscope.
The hard carbon anode material prepared by the embodiment comprises an inner main body and an outer layer coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, and the inner main body and the outer layer both comprise hard carbon and doping elements doped in the hard carbon. The intensity ratio of the D peak to the G peak in the Raman spectrum of the whole hard carbon anode material is 0.77, the intensity ratio of the D peak to the G peak in the Raman spectrum of the outer layer is 0.31, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the inner main body is 1.04; the thickness of the outer layer is 0.5 μm; the specific surface area of the hard carbon anode material is 2.853m 2 /g; the doping element is phosphorus, and the mass fraction of the doping element in the hard carbon negative electrode material is 1.836wt% based on 100% of the total mass of the hard carbon negative electrode material.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the example are shown in table 1.
Fig. 1 is a scanning electron microscope picture of the hard carbon negative electrode material prepared in the embodiment, and it can be seen from the picture that the surface of the hard carbon negative electrode material is smoother, irregular holes are distributed on the surface of particles, meanwhile, the particle size distribution is generally 2-8 μm, the individual small particle size is smaller than 1 μm, and the overall particle size distribution is more uniform.
FIG. 2 is a Raman spectrum of the hard carbon anode material prepared in the present example, from which it can be seen that the D peak and the G peak are located at 1360cm, respectively -1 And 1580cm -1 The whole Raman light of the material is shown in the figureThe spectrum, the D peak and G peak intensity ratio was 0.77. The larger the intensity ratio is, the larger the disorder degree of the material is, the larger the ratio is, generally, the larger the conventional hard carbon is, the surface carbon layer arrangement of the material prepared by the embodiment becomes more regular under the catalysis of the additive, the disorder degree is reduced, and therefore the intensity ratio of the D peak to the G peak in the Raman spectrum is reduced.
Fig. 3 is a first charge-discharge curve of the hard carbon negative electrode material prepared in this embodiment, and it can be seen from the graph that the discharge capacity of the hard carbon material is 586.2mAh/g, the delithiation capacity is 499.4mAh/g, and the first coulomb efficiency reaches 85.2%, and meanwhile, it can be seen that the discharge curve of the material has a large capacity at the position close to 0V on the voltage platform, which is typical of the hard carbon charge-discharge characteristics.
Fig. 4 is a graph showing the cycle performance of the hard carbon negative electrode material prepared in this example, wherein the cycle performance is the capacity retention rate of the cylindrical full battery after charging and discharging for 1000 weeks at a current density of 3C multiplying power, and it can be seen from the graph that the material has excellent cycle stability, gradually decreases the capacity retention rate, and finally reaches 92.5% after 1000 cycles. In the figure, a certain fluctuation exists in the middle of the circulation curve, which is caused by capacity fluctuation caused by the change of the test environment temperature in the 1000-week circulation process, and belongs to a normal phenomenon.
Example 2
The hard carbon negative electrode material is prepared according to the following method:
(1) 4.5kg of coconut shells are placed in a pushed slab kiln under nitrogen atmosphere, heated to 500 ℃ at a heating rate of 2 ℃/min, carbonized for 4 hours, cooled to 25 ℃ to obtain 1.5kg of carbonized material, crushed, and the median particle size of the material is crushed to 6 mu m to obtain a first hard carbon precursor;
(2) Mixing 1.0kg of a first hard carbon precursor, 2kg of sodium chloride, 3kg of lithium chloride, 40g of nickel chloride and 40g of phosphoric acid in a VC mixer, uniformly mixing, filling into a graphite crucible, placing in a box furnace, heating to 750 ℃ at a heating rate of 3 ℃/min under nitrogen atmosphere, carrying out doping and catalytic reaction, reacting for 3h, and cooling to 25 ℃ to obtain a second hard carbon precursor;
(3) Mixing the second hard carbon precursor, hydrochloric acid and water in the step (2), wherein the mass ratio of the second hard carbon precursor to the hydrochloric acid to the water is 1:1:10, soaking for 2 hours after mixing, centrifugally washing for 2 hours, drying at 100 ℃ for 28 hours, placing 500g of the dried material into a crucible, placing the crucible into a roller kiln, heating to 1200 ℃ at a heating rate of 4 ℃/min under nitrogen atmosphere, sintering for 3 hours, naturally cooling after sintering, and carrying out demagnetizing and screening on the obtained product to obtain the hard carbon anode material.
The hard carbon negative electrode material prepared in this example was subjected to structural test by the method of example 1.
The hard carbon cathode material prepared by the embodiment mainly comprises an inner main body and an outer layer coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, and the inner main body and the outer layer both comprise hard carbon and doping elements doped in the hard carbon. The intensity ratio of the D peak to the G peak in the Raman spectrum of the whole hard carbon anode material is 0.892, the intensity ratio of the D peak to the G peak in the Raman spectrum of the outer layer is 0.618, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the inner main body is 1.24; the thickness of the outer layer is 0.1 μm; the specific surface area of the hard carbon anode material is 2.15m 2 /g; the doping element is phosphorus, and the mass fraction of the doping element in the hard carbon negative electrode material is 0.32wt% based on 100% of the mass of the hard carbon.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the example are shown in table 1.
Example 3
The hard carbon negative electrode material is prepared according to the following method:
(1) Placing walnut shells in a box furnace under nitrogen atmosphere, heating to 400 ℃ at a heating rate of 1 ℃/min, carbonizing for 8 hours, cooling to 20 ℃ to obtain carbonized materials, crushing the materials to a median particle size of 200 mu m by using a cone crusher, and crushing the median particle size of the materials to 8.0 mu m by using a fluidized bed counter jet mill to obtain a first hard carbon precursor;
(2) Mixing a first hard carbon precursor, molten salt (sodium chloride) and an additive (cobalt phosphate) together in a ball mill according to the mass ratio of 1:8:0.20, uniformly mixing, filling into a graphite crucible, placing into a box furnace, heating to 850 ℃ at the heating rate of 2 ℃/min under nitrogen atmosphere for doping and catalytic reaction, wherein the reaction time is 6h, and cooling to 20 ℃ to obtain a second hard carbon precursor;
(3) Mixing the second hard carbon precursor obtained in the step (2), sulfuric acid and water, wherein the mass ratio of the second hard carbon precursor to the hydrochloric acid to the water is 1:3:15, soaking for 1h after mixing, centrifugally washing for 1.5h, drying at 80 ℃ for 48h, placing the dried material into a crucible, placing the crucible into a tube furnace, heating to 1000 ℃ at a heating rate of 3 ℃/min under nitrogen atmosphere, sintering for 4h, naturally cooling after sintering, and carrying out demagnetizing and screening on the obtained product to obtain the hard carbon anode material.
The hard carbon negative electrode material prepared in this example was subjected to structural test by the method of example 1.
The hard carbon anode material prepared by the embodiment comprises an inner main body and an outer layer coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, and the inner main body and the outer layer both comprise hard carbon and doping elements doped in the hard carbon. The intensity ratio of the D peak to the G peak in the Raman spectrum of the outer layer is 0.26, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the inner body is 1.15; the thickness of the outer layer is 0.7 μm; the specific surface area of the hard carbon anode material is 3.56m 2 /g; the doping element is phosphorus, and the mass fraction of the doping element in the hard carbon negative electrode material is 2.13wt% based on 100% of the mass of the hard carbon.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the example are shown in table 1.
Example 4
The hard carbon negative electrode material is prepared according to the following method:
(1) Placing oil palm shells in a box furnace under nitrogen atmosphere, heating to 800 ℃ at a heating rate of 3 ℃/min, carbonizing for 1h, cooling to 30 ℃ to obtain carbonized materials, crushing the materials to a median particle size of 2000 mu m by using a cone crusher, and crushing the median particle size of the materials to 15.0 mu m by using a fluidized bed counter jet mill to obtain a first hard carbon precursor;
(2) Mixing a first hard carbon precursor, molten salt (sodium chloride and lithium chloride) and an additive (nickel phosphate) together in a ball mill according to a mass ratio of 1:4:0.10, uniformly mixing, filling into a graphite crucible, placing into a box furnace, heating to 700 ℃ at a heating rate of 4 ℃/min under nitrogen atmosphere, carrying out doping and catalytic reaction, reacting for 2h, and cooling to 30 ℃ to obtain a second hard carbon precursor;
(3) Mixing the second hard carbon precursor obtained in the step (2), sulfuric acid and water, wherein the mass ratio of the second hard carbon precursor to the hydrochloric acid to the water is 1:5:20, soaking for 4 hours after mixing, centrifugally washing for 3 hours, drying at 150 ℃ for 6 hours, placing the dried materials into a crucible, placing the crucible into a tubular furnace, heating to 900 ℃ at a heating rate of 5 ℃/min under nitrogen atmosphere, sintering for 6 hours, naturally cooling after sintering, and performing demagnetization and screening on the obtained product to obtain the hard carbon anode material.
The hard carbon negative electrode material prepared in this example was subjected to structural test by the method of example 1.
The hard carbon cathode material prepared by the embodiment mainly comprises an inner main body and an outer layer coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, and the inner main body and the outer layer both comprise hard carbon and doping elements doped in the hard carbon. The intensity ratio of the D peak to the G peak in the Raman spectrum of the outer layer is 0.54, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the inner body is 1.39; the thickness of the outer layer is 0.4 μm; the specific surface area of the hard carbon anode material is 2.799m 2 /g; the doping element is phosphorus, and the mass fraction of the doping element in the hard carbon negative electrode material is 1.06wt% based on 100% of the mass of the hard carbon.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the example are shown in table 1.
Example 5
The hard carbon negative electrode material is prepared according to the following method:
(1) Placing epoxy resin in a box furnace under argon atmosphere, heating to 600 ℃ at a heating rate of 0.5 ℃/min, carbonizing for 5 hours, cooling to 25 ℃ to obtain carbonized material, crushing the material to a median particle size of 4000 mu m by using an impact crusher, and crushing the median particle size of the material to 20.0 mu m by using a flat jet mill to obtain a first hard carbon precursor;
(2) Mixing a first hard carbon precursor, molten salt (magnesium chloride and calcium chloride with the mass ratio of 1:1) and an additive (nickel phosphate and ferric chloride with the mass ratio of 1:1) together in a double-cone mixer according to the mass ratio of 1:4:0.5, uniformly mixing, filling into a graphite crucible, placing into a box furnace, heating to 800 ℃ at the heating rate of 1 ℃/min under argon atmosphere, carrying out doping and catalytic reaction, and cooling to 25 ℃ for 8 hours to obtain a second hard carbon precursor;
(3) Mixing the second hard carbon precursor, sulfuric acid and water in the step (2), wherein the mass ratio of the second hard carbon precursor to the sulfuric acid to the water is 1:2:10, soaking for 1h after mixing, centrifugally washing for 1h, drying at 60 ℃ for 48h, placing the dried material into a crucible, placing the crucible into a tubular furnace, heating to 1400 ℃ at a heating rate of 2 ℃/min under argon atmosphere, sintering for 2h, naturally cooling after sintering, and performing demagnetization and screening on the obtained product to obtain the hard carbon anode material.
The hard carbon negative electrode material prepared in this example was subjected to structural test by the method of example 1.
The hard carbon anode material prepared by the embodiment comprises an inner main body and an outer layer coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, and the inner main body and the outer layer both comprise hard carbon and doping elements doped in the hard carbon. The intensity ratio of the D peak to the G peak in the Raman spectrum of the outer layer is 0.337, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the inner body is 1.217; the thickness of the outer layer is 0.8 μm; the specific surface area of the hard carbon anode material is 5.451m 2 /g; the doping element is phosphorus, and the mass of the doping element is calculated by taking the total mass of the hard carbon anode material as 100 percent in the hard carbon anode material The fraction was 4.572wt%.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the example are shown in table 1.
Example 6
The hard carbon negative electrode material is prepared according to the following method:
(1) Placing epoxy resin in a box furnace under argon atmosphere, heating to 600 ℃ at a heating rate of 5 ℃/min, carbonizing for 5 hours, cooling to 25 ℃ to obtain carbonized material, crushing the material to a median particle size of 10 mu m by using an impact crusher, and crushing the median particle size of the material to 5.0 mu m by using a flat jet mill to obtain a first hard carbon precursor;
(2) Mixing a first hard carbon precursor, molten salt (magnesium chloride and calcium chloride with the mass ratio of 1:1) and additives (metaphosphoric acid and ferric nitrate with the mass ratio of 1:1) together in a double-cone mixer according to the mass ratio of 1:3:0.3, placing the mixture into a graphite crucible, placing the graphite crucible in a box furnace, heating to 500 ℃ at the heating rate of 1 ℃/min under argon atmosphere, carrying out doping and catalytic reaction, and cooling to 25 ℃ for 0.5h to obtain a second hard carbon precursor;
(3) Mixing the second hard carbon precursor, sulfuric acid and water in the step (2), wherein the mass ratio of the second hard carbon precursor to the sulfuric acid to the water is 1:2:10, soaking for 10 hours after mixing, centrifugally washing for 4 hours, drying at 200 ℃ for 12 hours, placing the dried materials into a crucible, placing the crucible into a tubular furnace, heating to 1400 ℃ at a heating rate of 8 ℃/min under argon atmosphere, sintering for 2 hours, naturally cooling after sintering, and performing demagnetization and screening on the obtained product to obtain the hard carbon anode material.
The hard carbon negative electrode material prepared in this example was subjected to structural test by the method of example 1.
The hard carbon anode material prepared by the embodiment comprises an inner main body and an outer layer coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, and the inner main body and the outer layer both comprise hard carbon and doping elements doped in the hard carbon. D and G peaks in the Raman spectrum of the outer layerThe intensity ratio is 0.693, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the internal body is 1.237; the thickness of the outer layer is 0.6 μm; the specific surface area of the hard carbon anode material is 4.571m 2 /g; the doping elements are nitrogen and chlorine, and the mass fraction of the doping elements in the hard carbon negative electrode material is 2.679wt% based on 100% of the total mass of the hard carbon negative electrode material.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the example are shown in table 1.
Example 7
The specific method for preparing the hard carbon cathode material in this example is described with reference to example 1, except that in step (1), the median particle diameter of the material is 6 μm; in the step (2), the mass ratio of the first hard carbon precursor, the molten salt (potassium chloride and lithium chloride with the mass ratio of 1:1) and the additive (ferric phosphate) is 1:2:0.01, and the heating rate is 0.5 ℃/min; in the step (3), the centrifugal washing time is 6 hours, and the heating rate is 1 ℃/min.
The hard carbon negative electrode material prepared in this example was subjected to structural test by the method of example 1.
The hard carbon anode material prepared by the embodiment comprises an inner main body and an outer layer coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, and the inner main body and the outer layer both comprise hard carbon and doping elements doped in the hard carbon. The intensity ratio of the D peak to the G peak in the Raman spectrum of the outer layer is 0.527, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the inner body is 1.225; the thickness of the outer layer is 0.2 μm; the specific surface area of the hard carbon anode material is 4.596m 2 /g; the doping element is phosphorus, and the mass fraction of the doping element in the hard carbon anode material is 0.334wt% based on 100% of the total mass of the anode material.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the example are shown in table 1.
Example 8
The specific method for preparing the hard carbon anode material in this example is described with reference to example 1, except that in step (1), the median particle diameter of the material is 13.0 μm; in the step (2), the mass ratio of the first hard carbon precursor, the molten salt (potassium chloride and lithium chloride with the mass ratio of 1:1) and the additive (ferric phosphate) is 1:2:0.03, and the heating rate is 10 ℃/min; in the step (3), the centrifugal washing time is 0.5h, and the heating rate is 10 ℃/min.
The hard carbon negative electrode material prepared in this example was subjected to structural test by the method of example 1.
The hard carbon anode material prepared by the embodiment comprises an inner main body and an outer layer coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, and the inner main body and the outer layer both comprise hard carbon and doping elements doped in the hard carbon. The intensity ratio of the D peak to the G peak in the Raman spectrum of the outer layer is 0.416, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the inner body is 1.241; the thickness of the outer layer is 0.3 μm; the specific surface area of the hard carbon anode material is 2.124m 2 /g; the doping elements are phosphorus and chlorine, and in the hard carbon negative electrode material, the mass fraction of the doping elements is 0.782wt% based on 100% of the total mass of the hard carbon negative electrode material.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the example are shown in table 1.
Example 9
The specific method for preparing the hard carbon anode material of this example refers to example 1, except that the iron phosphate described in step (2) is replaced with an equal mass of ferric chloride.
The hard carbon negative electrode material prepared in this example was subjected to structural test by the method of example 1.
The hard carbon negative electrode material prepared by the embodiment comprises an inner main body and an outer layer coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, and the inner main body and the outer layer both comprise hard carbon. The intensity ratio of the D peak to the G peak in the Raman spectrum of the whole hard carbon anode material is 0.75, the intensity ratio of the D peak to the G peak in the Raman spectrum of the outer layer is 0.28, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the inner main body is 1.05; the outer layer is provided withThickness is 0.55 μm; the specific surface area of the hard carbon anode material is 2.135m 2 And/g. The hard carbon anode material provided in this embodiment does not contain doping elements.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the example are shown in table 1.
Comparative example 1
The specific preparation method of this comparative example was as described in example 1, except that the operation of step (2) was not performed, i.e., the doping and catalytic reaction was not performed.
The hard carbon negative electrode material prepared in this comparative example does not contain doping elements, and the negative electrode material does not exhibit an outer layer and an inner body having different disorder degrees, and the disorder degrees are uniform.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the comparative example are shown in table 1.
Comparative example 2
The specific preparation method of this comparative example was as described in example 1, except that no additive iron phosphate was added in step (2).
The hard carbon negative electrode material prepared in this comparative example does not contain doping elements, and the negative electrode material does not exhibit an outer layer and an inner body having different disorder degrees, and the disorder degrees are uniform.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the comparative example are shown in table 1.
Comparative example 3
The specific preparation method of this comparative example was as described in example 1, except that the molten salt potassium chloride and lithium chloride were not added in step (2), i.e., the molten salt system was not used.
The hard carbon cathode material of the comparative example does not show an outer layer and an inner main body with different disorder degrees, the disorder degrees are uniform, and the material contains a certain amount of doping elements.
The results of the electrochemical test and the adsorption performance decay test of the hard carbon anode material prepared in the comparative example are shown in table 1.
Electrochemical test and adsorption performance decay test method:
the hard carbon anode materials obtained in the above examples and comparative examples were prepared into batteries, and then subjected to electrochemical performance test and adsorption performance decay test.
Specific button cell preparations were made using methods well known in the art: the preparation method comprises the steps of (1) adjusting a cathode material, a conductive agent and a binder to be 50% by mass with distilled water according to the mass percentage of 91:3:6, uniformly mixing, coating the mixture on a copper foil current collector, and carrying out vacuum drying to obtain a cathode pole piece; lithium sheets are used as counter electrodes, 1mol/L of LiPF6/EC+DMC+EMC (v/v=1:1:1) is used as electrolyte, celgrad2400 is used as a diaphragm, and 2016 button cell casing is used as a casing.
The preparation method of the cylindrical battery comprises the following steps: dispersing a negative electrode material, a conductive agent and a binder in a solvent according to a mass ratio of 94:1:5, uniformly mixing, controlling the solid content to be 50%, coating the mixture on a copper foil current collector, and vacuum drying to obtain a negative electrode plate; and then assembling 18650 cylindrical single batteries by using a conventional production process on the lithium cobaltate positive electrode plate prepared by the conventional mature process, 1mol/L LiPF6/EC+DMC+EMC (v/v=1:1:1) electrolyte, celgard2400 diaphragm and a shell.
The hard carbon negative electrode materials prepared in each example and comparative example were tested for first reversible capacity and first coulombic efficiency using button cells under the following specific test conditions: the test was performed on a LAND battery test system from Wohanno electronics, inc., with a 0.1C discharge, a cut-off voltage of 1mV, then a 0.1C charge, and a cut-off voltage of 1.5V.
The adsorption performance attenuation test is to prepare button cells by the method after placing the hard carbon cathode materials obtained in each example and comparative example in air for 30 days, and test according to the conditions of the first reversible capacity and the first coulombic efficiency.
The 1C@1000 cycle performance of the hard carbon negative electrode materials of each example and comparative example was tested by using a cylindrical battery, and specific test conditions thereof were: the test is carried out on a LAND battery test system of the Wuhan Jinno electronic company, namely, the battery is activated for 2 weeks by charging and discharging at 0.1C, 0.2C and 0.5C multiplying power in sequence, then the charging and discharging multiplying power is increased to 1C, and the cycle performance is carried out under the normal temperature condition.
The results of the above test are shown in Table 1.
TABLE 1
From the above examples and comparative examples, it is understood that the hard carbon anode materials provided in examples 1 to 8 of the present invention have extremely excellent electrochemical properties in terms of the first reversible capacity, the first coulombic efficiency, the cyclic capacity retention rate, etc., because they have both doping elements and a low disorder degree of the outer layer, and the degree of decay of the properties after being placed in air is greatly reduced.
The hard carbon anode material provided in example 9 has no doping element, so that the capacity, the first effect and other electrochemical properties cannot be improved by doping nitrogen and phosphorus, and the product of example 9 is inferior to that of example 1 in terms of capacity and first effect.
Comparative example 1 was inferior to example 1 in terms of the first reversible capacity, the first coulombic efficiency, the 1000 cycle capacity retention, the reversible capacity after 30 days of standing, and the first coulombic efficiency of the material after 30 days of standing, probably because the product of comparative example 1 was neither doped nor catalyzed, and thus the product of comparative example 1 was not subjected to the process of re-decomposition of metal cations and carbon material to form carbides to rearrange the carbon skeleton, nor doping of nonmetallic elements, and therefore it was inferior to the product of example 1 in terms of various properties tested.
Comparative example 2 was inferior to example 1 in terms of the first reversible capacity, the first coulombic efficiency, the 1000 cycle capacity retention, the reversible capacity after 30 days of standing, and the first coulombic efficiency of the material after 30 days of standing, probably because comparative example 2 was free of additives, which are critical for allowing catalytic reaction and doping to proceed although comparative example 2 was heat-treated under a molten salt system, metal cations in the additives acted as catalysts, nonmetallic elements acted as doping, and comparative example 2 was not added with additives, and the product did not undergo catalytic modification and doping, so it was inferior to the product of example 1 in terms of various properties tested.
Comparative example 3 is inferior to example 1 in terms of first reversible capacity, first coulombic efficiency, 1000 cycle capacity retention, reversible capacity after 30 days of standing, and first coulombic efficiency of the material after 30 days of standing, probably because no molten salt system was added to comparative example 3, and the additive eventually had catalytic and doping effects with the aid of molten salt, and comparative example 3 was not added to the molten salt system, and although the additive had some doping effect, catalytic modification effect was limited, and thus the product of example 1 was inferior in various properties to be tested.
The applicant states that the detailed process equipment and process flows of the present invention are described by the above examples, but the present invention is not limited to, i.e., does not mean that the present invention must be practiced in dependence upon, the above detailed process equipment and process flows. It should be apparent to those skilled in the art that any modification of the present invention, equivalent substitution of raw materials for the product of the present invention, addition of auxiliary components, selection of specific modes, etc., falls within the scope of the present invention and the scope of disclosure.

Claims (75)

1. The hard carbon anode material is characterized by comprising an inner main body and an outer layer coated on the inner main body, wherein the disorder degree of the outer layer is lower than that of the inner main body, the inner main body and the outer layer both comprise hard carbon and doping elements doped in the hard carbon, and the doping elements comprise phosphorus;
the intensity ratio of the D peak to the G peak in the Raman spectrum of the outer layer is 0.2-0.7;
the ratio of D peak to G peak in the Raman spectrum of the inner body is 0.7-1.5.
2. The hard carbon negative electrode material according to claim 1, wherein the thickness of the outer layer is 0 to 1 μm and does not contain 0.
3. The hard carbon negative electrode material according to claim 1, wherein the specific surface area of the hard carbon negative electrode material is 1 to 20m 2 /g。
4. The hard carbon negative electrode material according to claim 1, wherein the specific surface area of the hard carbon negative electrode material is 1.5 to 15m 2 /g。
5. The hard carbon negative electrode material according to claim 1, wherein the hard carbon negative electrode material has a median particle diameter of 4.0 to 30.0 μm.
6. The hard carbon negative electrode material according to claim 1, wherein the hard carbon negative electrode material has a median particle diameter of 5.0 to 20.0 μm.
7. The hard carbon negative electrode material according to claim 1, wherein the hard carbon negative electrode material has a median particle diameter of 6.0 to 15.0 μm.
8. The hard carbon negative electrode material according to claim 1, wherein the doping element further comprises nitrogen in the hard carbon negative electrode material.
9. The hard carbon negative electrode material according to claim 1, wherein the mass fraction of the doping element in the hard carbon negative electrode material is 0.3 to 5wt% based on 100% of the total mass of the hard carbon negative electrode material.
10. A method for preparing a hard carbon anode material according to any one of claims 1 to 9, comprising the steps of:
(1) Mixing the first hard carbon precursor, the additive and molten salt, and then carrying out catalytic reaction to obtain a second hard carbon precursor;
(2) Purifying the second hard carbon precursor in the step (1), and sintering to obtain the hard carbon anode material;
in the step (1), the additive contains metal cations;
the additive contains phosphate in addition to metal cations.
11. The method of claim 10, wherein in step (1), the method of preparing the first hard carbon precursor comprises: carbonizing a hard carbon raw material, and then crushing to obtain a first hard carbon precursor.
12. The method of claim 11, wherein the hard char feedstock comprises a biomass-based feedstock and/or a thermoplastic resin-based feedstock.
13. The method of claim 12, wherein the biomass-based feedstock comprises any one or a combination of at least two of coconut shells, apricot shells, walnut shells, or oil palm shells.
14. The method according to claim 12, wherein the thermoplastic resin-based raw material comprises any one or a combination of at least two of epoxy resin, phenolic resin, carboxymethyl cellulose, ethyl methyl carbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, and polytetrafluoroethylene.
15. The method of claim 11, wherein the carbonization is performed under a protective atmosphere.
16. The method of claim 15, wherein the protective atmosphere is any one or a combination of at least two of nitrogen, helium, neon, argon, krypton, or xenon.
17. The method of claim 11, wherein the carbonization temperature is 400-800 ℃.
18. The method of claim 11, wherein the carbonization time is 1 to 8 hours.
19. The method according to claim 11, wherein the carbonization has a temperature rise rate of 0.5 to 5 ℃/min.
20. The method according to claim 11, wherein the carbonization has a temperature rise rate of 1 to 3 ℃/min.
21. The method according to claim 11, wherein the carbonized material is cooled to 20 to 30 ℃ and then crushed.
22. The production method according to claim 11, wherein the carbonization is performed in any one of a vacuum furnace, a box furnace, a rotary furnace, a roller kiln, a pusher kiln, or a tube furnace.
23. The method of preparation according to claim 11, characterized in that the equipment for carrying out the comminution comprises a crusher and/or an air mill.
24. The method of claim 11, wherein the apparatus for performing the comminution is a combination of a crusher and a pulverizer.
25. The method of making according to claim 23, wherein the crusher comprises any one or a combination of at least two of a jaw crusher, a cone crusher, an impact crusher, a counter-impact crusher, or a hammer crusher.
26. The method of claim 24, wherein the pulverizer comprises any one or a combination of at least two of a flat jet mill, a fluidized bed jet mill, a circulating tube jet mill, a jet mill, or a target jet mill.
27. The method of claim 24, wherein when the apparatus for performing the pulverization is a combination of a crusher and a pulverizer, the crusher is used first and then the pulverizer is used, and the crusher crushes the material to a median particle diameter of 10 to 4000 μm.
28. The method of claim 27, wherein the crusher crushes the material to a median particle size of 200 to 2000 μm.
29. The method of claim 10, wherein in step (1), the first hard carbon precursor has a median particle diameter of 4.0 to 30.0 μm.
30. The method of claim 10, wherein in step (1), the first hard carbon precursor has a median particle diameter of 5.0 to 20.0 μm.
31. The method of claim 10, wherein in step (1), the first hard carbon precursor has a median particle diameter of 6.0 to 15.0 μm.
32. The method according to claim 10, wherein the additive comprises any one or a combination of at least two of a salt compound of iron, a salt compound of cobalt, and a salt compound of nickel.
33. The method of claim 10, wherein the additive comprises nitrate in addition to the metal cations.
34. The method of claim 10, wherein the additive comprises any one or a combination of at least two of iron phosphate, cobalt phosphate, nickel phosphate, iron nitrate, cobalt nitrate, or nickel nitrate.
35. The method of claim 10, wherein the additive comprises a nitrate-or phosphate-free metal salt and a nitrate-or phosphate-containing substance.
36. The method of producing according to claim 35, wherein the nitrate-or phosphate-free metal salt includes any one or a combination of at least two of iron acetate, iron chloride, cobalt acetate, cobalt chloride, nickel acetate, and nickel chloride.
37. The method of claim 10, wherein in step (1), the molten salt comprises any one or a combination of at least two of potassium chloride, sodium chloride, lithium chloride, magnesium chloride, or calcium chloride.
38. The method of claim 10, wherein in step (1), the mixing is performed in a mixing device.
39. The method of claim 38, wherein the mixing device comprises any one of a VC mixer, a ball mill, or a double cone mixer.
40. The method according to claim 10, wherein in the step (1), the mass ratio of the first hard carbon precursor, the molten salt and the additive is 1 (2-10): 0.01-0.5.
41. The method according to claim 10, wherein in the step (1), the mass ratio of the first hard carbon precursor, the molten salt and the additive is 1 (3-8): 0.03-0.3.
42. The method of claim 10, wherein the catalytic reaction of step (1) is carried out in a protective atmosphere.
43. The method of claim 42, wherein the protective atmosphere is any one or a combination of at least two of nitrogen, helium, neon, argon, krypton, or xenon.
44. The method of claim 10, wherein the catalytic reaction is performed in any one of a vacuum furnace, a box furnace, a rotary furnace, a roller kiln, a pusher kiln, or a tube furnace.
45. The method according to claim 10, wherein the reaction temperature of the catalytic reaction is 500 ℃ to 1000 ℃.
46. The method according to claim 10, wherein the reaction time of the catalytic reaction is 0.5 to 8 hours.
47. The method according to claim 10, wherein the reaction time of the catalytic reaction is 1 to 6 hours.
48. The method according to claim 10, wherein the temperature rise rate of the catalytic reaction is 0.5 to 10 ℃/min.
49. The method according to claim 10, wherein the temperature rise rate of the catalytic reaction is 1 to 6 ℃/min.
50. The method according to claim 10, wherein the temperature rise rate of the catalytic reaction is 2 to 4 ℃/min.
51. The method of claim 10, wherein in step (2), the method of purifying comprises: and (3) mixing the second hard carbon precursor in the step (1), acid and water, soaking, centrifugally washing, and drying the obtained solid substance.
52. The method of claim 51, wherein the acid comprises any one or a combination of at least two of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, or hydrofluoric acid.
53. The method according to claim 51, wherein the mass ratio of the second hard carbon precursor, the acid and the water is 1 (0.5-5): 2-20.
54. The method of claim 51, wherein the soaking time is 1 to 10 hours.
55. The method of claim 51, wherein the soaking time is 1-4 hours.
56. The method according to claim 51, wherein the centrifugal washing time is 0.5 to 6 hours.
57. The method according to claim 51, wherein the centrifugal washing time is 1 to 4 hours.
58. The method according to claim 51, wherein the centrifugal washing time is 1.5 to 3 hours.
59. The method of claim 51, wherein the drying is performed in any one of a vacuum drying oven, a forced air drying oven, a box furnace, a rotary kiln, or a twin cone dryer.
60. The process of claim 51 wherein the temperature of the drying is 60-200 ℃.
61. The process of claim 51 wherein the temperature of the drying is 80-150 ℃.
62. The method of claim 51, wherein the drying time is 6 to 48 hours.
63. The method of claim 10, wherein in step (2), the sintering is performed under a protective atmosphere.
64. The method of claim 63, wherein the protective atmosphere is any one or a combination of at least two of nitrogen, helium, neon, argon, krypton, or xenon.
65. The method according to claim 10, wherein the sintering is performed in any one of a vacuum furnace, a box furnace, a rotary furnace, a roller kiln, a pusher kiln, or a tube furnace.
66. The method according to claim 10, wherein the sintering temperature is 900 to 1400 ℃.
67. The method of claim 10, wherein the sintering time is 2 to 8 hours.
68. The method of claim 10, wherein the sintering time is 3 to 6 hours.
69. The method according to claim 10, wherein the temperature rise rate of sintering is 0.5 to 10 ℃/min.
70. The method according to claim 10, wherein the temperature rise rate of the sintering is 1 to 6 ℃/min.
71. The method of manufacturing according to claim 10, further comprising: and (3) refining the hard carbon anode material obtained in the step (2).
72. The method of claim 71, wherein refining comprises demagnetizing and sieving.
73. The method of preparation according to claim 10, characterized in that the method comprises the steps of:
(1) Heating the hard carbon raw material to 400-800 ℃ at a heating rate of 1-3 ℃/min under a protective atmosphere, carbonizing for 1-8 h, cooling to 20-30 ℃, crushing, and crushing the median particle size of the material to 6.0-15.0 mu m to obtain a first hard carbon precursor;
(2) Mixing a first hard carbon precursor, an additive and molten salt, wherein the mass ratio of the first hard carbon precursor to the molten salt to the additive is 1 (3-8): (0.03-0.3), mixing, heating to 500-1000 ℃ at a heating rate of 2-4 ℃/min under protective atmosphere, and carrying out doping and catalytic reaction for 1-6 h to obtain a second hard carbon precursor;
wherein the additive comprises any one or a combination of at least two of an iron salt compound, a cobalt salt compound or a nickel salt compound; and the additive comprises nitrate radical and/or phosphate radical besides metal cation; the molten salt comprises any one or a combination of at least two of potassium chloride, sodium chloride, lithium chloride, magnesium chloride or calcium chloride;
(3) Mixing the second hard carbon precursor in the step (2), acid and water, wherein the mass ratio of the second hard carbon precursor to the acid to the water is 1: (0.5-5): (2-20), mixing, soaking for 1-4 h, centrifugally washing for 1.5-3 h, drying at 80-150 ℃ for 6-48 h, heating to 900-1400 ℃ at a heating rate of 3-5 ℃/min under protective atmosphere, sintering for 3-6 h, and carrying out demagnetization and screening on the obtained product after sintering to obtain the hard carbon anode material.
74. A pole piece, characterized in that it comprises a hard carbon negative electrode material according to any one of claims 1-9.
75. A lithium ion battery comprising a hard carbon negative electrode material according to any one of claims 1-9.
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