CN117393723A - Carbon-coated pre-lithiated silicon-based composite material, and preparation method and application thereof - Google Patents
Carbon-coated pre-lithiated silicon-based composite material, and preparation method and application thereof Download PDFInfo
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 169
- 239000010703 silicon Substances 0.000 title claims abstract description 169
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 165
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 136
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 130
- 239000002131 composite material Substances 0.000 title claims abstract description 70
- 238000002360 preparation method Methods 0.000 title claims abstract description 16
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 149
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 146
- 230000008021 deposition Effects 0.000 claims abstract description 52
- 239000002245 particle Substances 0.000 claims abstract description 52
- 239000002210 silicon-based material Substances 0.000 claims abstract description 47
- 239000000463 material Substances 0.000 claims abstract description 44
- 239000000758 substrate Substances 0.000 claims abstract description 38
- 239000011248 coating agent Substances 0.000 claims abstract description 31
- 238000000576 coating method Methods 0.000 claims abstract description 31
- 239000011247 coating layer Substances 0.000 claims abstract description 11
- 239000008246 gaseous mixture Substances 0.000 claims abstract description 8
- 239000010410 layer Substances 0.000 claims abstract description 5
- 238000010438 heat treatment Methods 0.000 claims description 114
- 238000000151 deposition Methods 0.000 claims description 50
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 47
- 238000000034 method Methods 0.000 claims description 26
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 19
- 238000002156 mixing Methods 0.000 claims description 16
- 239000000377 silicon dioxide Substances 0.000 claims description 16
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 12
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 10
- 235000012239 silicon dioxide Nutrition 0.000 claims description 9
- 238000007740 vapor deposition Methods 0.000 claims description 9
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 8
- 239000000126 substance Substances 0.000 claims description 8
- 239000012159 carrier gas Substances 0.000 claims description 7
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 claims description 6
- 239000007789 gas Substances 0.000 claims description 6
- 229910000103 lithium hydride Inorganic materials 0.000 claims description 6
- 239000012448 Lithium borohydride Substances 0.000 claims description 5
- -1 ethylene, propylene, benzene Chemical class 0.000 claims description 5
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 5
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 229910052786 argon Inorganic materials 0.000 claims description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 4
- 238000009834 vaporization Methods 0.000 claims description 4
- 230000008016 vaporization Effects 0.000 claims description 4
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 claims description 3
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 238000001771 vacuum deposition Methods 0.000 claims description 2
- 239000011149 active material Substances 0.000 claims 2
- 238000011049 filling Methods 0.000 claims 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 16
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 9
- 230000000694 effects Effects 0.000 abstract description 8
- UHZZMRAGKVHANO-UHFFFAOYSA-M chlormequat chloride Chemical compound [Cl-].C[N+](C)(C)CCCl UHZZMRAGKVHANO-UHFFFAOYSA-M 0.000 abstract description 5
- 239000007773 negative electrode material Substances 0.000 abstract description 5
- 239000010406 cathode material Substances 0.000 abstract description 3
- 238000010298 pulverizing process Methods 0.000 abstract 1
- 238000007086 side reaction Methods 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 13
- 239000005543 nano-size silicon particle Substances 0.000 description 12
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- 230000009286 beneficial effect Effects 0.000 description 9
- 230000001276 controlling effect Effects 0.000 description 9
- 238000002309 gasification Methods 0.000 description 7
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 7
- 229910010271 silicon carbide Inorganic materials 0.000 description 7
- 238000012360 testing method Methods 0.000 description 7
- 229910002804 graphite Inorganic materials 0.000 description 6
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- 230000008022 sublimation Effects 0.000 description 5
- 239000010405 anode material Substances 0.000 description 4
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- 125000004122 cyclic group Chemical group 0.000 description 3
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- 208000019901 Anxiety disease Diseases 0.000 description 2
- PNUGDRJNKILROY-UHFFFAOYSA-N [C].[Si].[Li] Chemical compound [C].[Si].[Li] PNUGDRJNKILROY-UHFFFAOYSA-N 0.000 description 2
- OBNDGIHQAIXEAO-UHFFFAOYSA-N [O].[Si] Chemical compound [O].[Si] OBNDGIHQAIXEAO-UHFFFAOYSA-N 0.000 description 2
- 239000006183 anode active material Substances 0.000 description 2
- 230000036506 anxiety Effects 0.000 description 2
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- 238000007599 discharging Methods 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- PAZHGORSDKKUPI-UHFFFAOYSA-N lithium metasilicate Chemical compound [Li+].[Li+].[O-][Si]([O-])=O PAZHGORSDKKUPI-UHFFFAOYSA-N 0.000 description 2
- 229910052912 lithium silicate Inorganic materials 0.000 description 2
- 239000002905 metal composite material Substances 0.000 description 2
- YQCIWBXEVYWRCW-UHFFFAOYSA-N methane;sulfane Chemical compound C.S YQCIWBXEVYWRCW-UHFFFAOYSA-N 0.000 description 2
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- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910001290 LiPF6 Inorganic materials 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 239000004743 Polypropylene Substances 0.000 description 1
- 229910004283 SiO 4 Inorganic materials 0.000 description 1
- 239000002174 Styrene-butadiene Substances 0.000 description 1
- 238000003917 TEM image Methods 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 1
- 239000013543 active substance Substances 0.000 description 1
- 229910003481 amorphous carbon Inorganic materials 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
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- 238000009830 intercalation Methods 0.000 description 1
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- 239000011159 matrix material Substances 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
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- 239000000843 powder Substances 0.000 description 1
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- 238000005096 rolling process Methods 0.000 description 1
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical compound [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 description 1
- 229920001027 sodium carboxymethylcellulose Polymers 0.000 description 1
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- 230000002195 synergetic effect Effects 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
Classifications
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- 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
- H01M4/362—Composites
- H01M4/366—Composites as layered products
-
- 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
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
-
- 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
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- 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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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Composite Materials (AREA)
- Materials Engineering (AREA)
- Inorganic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Crystallography & Structural Chemistry (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention relates to the technical field of lithium ion battery cathode materials, and particularly discloses a carbon-coated pre-lithiated silicon-based composite material, and a preparation method and application thereof. The composite material is a submicron material with pre-lithiated silicon-based deposited particles as an inner core and a carbon coating layer as an outer layer, wherein the particle size of the pre-lithiated silicon-based deposited particles is 0.05-500 mu m, and the thickness of the carbon coating layer is 5-100nm. During preparation, a silicon source and a lithium source are respectively heated under vacuum to generate a gaseous silicon-based material and a gaseous lithium material; introducing a gaseous silicon-based material and a gaseous lithium material into the pre-mix zone; introducing the gaseous mixture in the premixing zone into a deposition zone in which a carbon substrate is placed for deposition; and (3) carbon coating. The invention realizes uniform bulk phase lithium doping and uniform and compact carbon coating of the silicon-based material, effectively solves the problems of expansion pulverization, poor conductivity and lithium consumption caused by interface side reaction of the silicon-based negative electrode material, and remarkably improves the first effect and the cycle performance of the silicon-based negative electrode material.
Description
Technical Field
The invention relates to the technical field of lithium ion battery cathode materials, in particular to a carbon-coated pre-lithiated silicon-based composite material, a preparation method and application thereof.
Background
Along with the innovation of the energy industry, new energy automobiles using lithium ion batteries as power sources are rapidly developed, and meanwhile, the anxiety of the mileage of the new energy automobiles becomes one of pain points of the new energy automobiles.
At present, carbon materials such as amorphous carbon and graphite are widely adopted as cathode materials of lithium ion batteries used for new energy vehicles, the theoretical gram capacity of the lithium ion batteries is 372mAh/g, and the commercial gram capacity of a high-end graphite cathode reaches 360-365mAh/g and is quite close to the theoretical value, so that the problem of mileage anxiety of the new energy vehicles is solved, and a novel cathode product with high gram capacity must be developed. The silicon-based material has higher theoretical gram capacity (1700-4200 mAh/g) and lower electrochemical lithium intercalation potential (about 0.4V vs. Li/Li+), and is rich in reserves, so that the silicon-based material is considered to be the most potential new negative electrode product of the next generation. However, the low intrinsic conductivity and high expansion rate of silicon-based materials can create problems such as capacity fade, reduced cycle life, and the like, particularly high expansion rates, severely limiting their use. For this reason, researchers have made extensive modification studies on silicon-based materials.
Some researchers have attempted to nanocrystallize silicon-based materials to address the high expansion rate problem, such as: the Chinese patent No. 110544766A discloses an expanded graphite nano-silicon composite anode material and a preparation method thereof, wherein the expanded graphite nano-silicon composite anode material is prepared from nano-silicon suspension, expanded graphite and a coated carbon source, the nano-silicon suspension is prepared by mixing nano-silicon and dispersion liquid, and potential safety hazards and service life problems caused by expansion can be avoided to a certain extent by adopting the nano-silicon and the expanded graphite with high expansion rate and conductivity, but the preparation of the nano-silicon is complicated, the floor production is not facilitated, and the commercialized popularization of the nano-silicon composite anode material is limited.
Other researchers modify silicon-based materials by coating metal composite shells on the surfaces of the silicon-based materials, such as: chinese patent No. CN 114927675A discloses a composite metal coated silicon carbide based negative electrode material, and preparation method and application thereof, the composite metal coated silicon carbide based negative electrode material comprises modified nano silicon carbide and composite metal coated on the surface of the modified nano silicon carbide; the particle size of the modified nano silicon carbide is 20-80nm; the particle size of the composite metal is 50-200nm; the particle size of the composite metal is larger than that of the modified nano silicon carbide. The anode material obtained by the invention has high specific capacity, reliable circularity, good conductivity and long service life, and compared with uncoated silicon carbide, the expansion effect is relieved to a certain extent. However, the swelling effect is relieved, but not fundamentally solved, by the accumulation of stress in the silicon-based material and the brittleness of the metal composite shell.
Still other researchers have prepared SiOx for relieving stress build-up during charge and discharge, as disclosed in chinese patent application CN 111717921a for SiOx nanowires with an atomic ratio of O to Si between (0, 2); silicon is used as an active substance, plays a role in storing lithium, and a silicon oxygen compound is used as a matrix to play a role in buffering; the SiOx nanowire is used as a negative electrode material of a lithium ion battery, can effectively inhibit volume expansion and improve electrode conductivity, but has poor initial performance.
Until researchers have found a prelithiation technique essentially of utilizing active lithium to react with active oxygen in a silicon oxygen material in advance to form lithium silicate (Li 4 SiO 4 /Li 2 SiO 3 /Li 2 Si 2 O 5 ) The generation of lithium silicate not only stabilizes the overall structure, but also avoids consuming active lithium provided by the anode in the battery, and the pre-entered Li source supplements the lithium source consumed in SEI formation, thereby improving the initial performance. The prelithiation technique is considered to be the optimal method for improving the first time efficiency of silicone materials.
However, no matter a liquid pre-lithium agent or a solid pre-lithium agent is adopted, the pre-lithium gradient problem exists in the pre-lithium process, such as: chinese patent No. CN 112701267A discloses a pre-lithiated silica composite material, a negative electrode sheet, a lithium battery and a preparation method thereof, the preparation method of the pre-lithiated silica composite material comprises the following steps: the method comprises the steps of (1) carrying out chemical reaction on lithium ions on the surface of SiOx-Li core in SiOx-Li@C and a hydroxyl compound to obtain SiOx-Li' @C, and carrying out heat treatment to obtain the pre-lithiated silica composite material; the SiOx-Li@C comprises a SiOx-Li core and a carbon layer, wherein lithium ions in the SiOx-Li core are distributed in the interior and the surface of the silicon oxide material; the content of the SiOx-Li' core decreases from the inside to the surface. Although the pre-lithiated silica composite material can achieve higher first coulombic efficiency, the existence of the pre-lithium gradient can cause uneven distribution of compressive stress and tensile stress in the expansion process, thereby causing the problems of cracking of the silicon-based material, reduced cycle performance and the like. Therefore, how to solve the problem of the pre-lithiation gradient is the first factor to be considered in solving the problem of high expansion rate by adopting the pre-lithiation technology at present. In addition, aiming at the defect of low intrinsic conductivity of the silicon-based material, the prior art mostly adopts the carbon material to coat the silicon-based material, and although the carbon material coating can obviously improve the conductivity, how to make the coating layer more uniform and compact so as to avoid the influence of the dew point of the material on the cycling stability of the material is not easy.
For this purpose, the present application is presented.
Disclosure of Invention
Aiming at the problems in the prior art, the invention discloses a carbon-coated pre-lithiated silicon-based composite material, a preparation method and application thereof, and aims to solve the problems that the existing pre-lithiation technology causes uneven distribution of compressive stress and tensile stress in the expansion process due to the existence of pre-lithiation gradient, and then causes cracking of the silicon-based material, cycle performance reduction and the like, and further solves the problem that the cycling stability is affected by the material dew point caused by uneven and non-compact carbon coating.
The invention is realized by the following technical scheme:
in one aspect, the invention provides a preparation method of a carbon-coated pre-lithiated silicon-based composite material, comprising the following operation steps:
s1, respectively heating a silicon source and a lithium source under vacuum to generate a gaseous silicon-based material and a gaseous lithium material;
s2, introducing a gaseous silicon-based material and a gaseous lithium material into a vacuum premixing zone;
s3, introducing the uniformly mixed gaseous mixture in the pre-mixing zone into a vacuum deposition zone in which a carbon substrate is placed, and obtaining pre-lithiated silicon-based deposition particles after deposition;
and S4, carrying out carbon coating on the pre-lithiated silicon-based deposited particles to obtain the carbon-coated pre-lithiated silicon-based composite material.
The inventor of the application finds that in the research of the existing pre-lithiation technology, a silicon source and a lithium source are generally placed in the same temperature area and heated under the same temperature condition, and because the gasification temperatures of the silicon source and the lithium source are greatly different, the heating under the same temperature condition can cause the difference of sublimation time due to different gasification points of the silicon source and the lithium source, then the uneven doping of lithium element in a silicon-based material is caused, a pre-lithium gradient is generated, the pre-lithium gradient can cause uneven distribution of compressive stress and tensile stress in the expansion process, and further the problems of cracking, cycle performance reduction and the like of the silicon-based material are caused.
Therefore, the silicon source and the lithium source are arranged in the two temperature areas, and the silicon source and the lithium source are heated by adopting proper temperatures respectively, so that the gasification points of the silicon source and the lithium source are balanced, the sublimation time difference between the silicon source and the lithium source caused by heating in a single temperature area is avoided, and the uniform doping of lithium element in the silicon-based material is facilitated; on the basis of the method, the vacuum premixing zone is also arranged, the premixing zone is beneficial to uniformly mixing the gaseous silicon substrate and the gaseous lithium material before deposition and does not precipitate, the uniformly doped and accurate ratio of the silicon substrate material to the lithium material in the gaseous mixture material is further ensured, and the aim of accurately regulating and controlling the pre-lithium amount is finally achieved. In addition, the pre-lithiated silicon-based deposition particles are deposited on the carbon base and are coated by carbon after deposition, so that a conductive network of the silicon-based material is effectively constructed, the conductive performance of the silicon-based material is remarkably improved, the lithium-carbon-silicon composite structure is stabilized, the problem of high expansibility of the silicon-based material is solved, the problem of poor intrinsic conductivity of the silicon-based material is solved, and the first effect and the cycle performance are enhanced.
It should be noted that:
1. the above-mentioned S1, S2 and S3 are all carried out under vacuum conditions, and the vacuum degree is preferably not higher than 1Pa.
2. In S2, in order to further improve the uniformity of mixing, the gaseous silicon-based material and the gaseous lithium material are preferably synchronously introduced into a vacuum premixing zone;
3. the temperature of the deposition area and the temperature during carbon coating are both preferably adopted by a temperature programming method, and the deposition and the carbon coating are respectively carried out after the temperature programming is carried out to the target temperature and the constant temperature is maintained for a certain time; the temperature increase rate at the time of temperature programming is preferably increased to the target temperature simultaneously or nearly simultaneously in the two temperature zones, the pre-mixing zone and the deposition zone, as the case may be.
Preferably, the heating temperature of the silicon source is T A The heating temperature of the lithium source is T B The temperature of the premixing zone is T C The temperature of the deposition area is T D ，T A Above the vaporization temperature of the silicon source, T B Above the vaporization temperature of the lithium source, T D <T B <T A <T C By controlling T A And T is B Controlling the pre-lithium amount and uniformity of the pre-lithiated silicon-based deposited particles by controlling T D And T is B And controlling the particle size of the prelithiated silica-based deposit particles.
T A Is higher than the gasification temperature of the silicon source to ensure the high-efficiency gasification of the silicon source. T (T) B And the gasification temperature of the lithium source is higher than that of the lithium source so as to ensure the efficient gasification of the lithium source. T (T) C Above T A To ensure that the substances in the gaseous mixture do not deposit within the pre-mix zone. T (T) A And T is B A constant temperature difference exists between the silicon source and the lithium source, and the sublimation rate of the silicon source and the lithium source is indirectly controlled through regulating and controlling the constant temperature difference, so that the ordered deposition of the gaseous mixture material on the carbon base is realized, on one hand, the pre-lithium amount of the pre-lithiated silicon-based deposition particles can be controlled, and on the other hand, the uniform lithium element in the silicon-based material can be realizedAnd (5) uniformly doping. T (T) D And T is B The temperature difference of (2) is used for providing supercooling degree so as to ensure uniform and rapid deposition of the gaseous mixture and simultaneously avoid deposition of lithium materials in preference to silicon-based materials, and the larger the supercooling degree is, the smaller the particle size of the obtained pre-lithiated silicon-based deposition particles is, therefore, the T can be regulated D And T is B And controlling the particle size of the prelithiated silica-based deposit particles.
Further preferably, in S1, the silicon source includes at least one of elemental silicon, silicon dioxide, and silicon oxide, and when the silicon source is a mixture of two or more kinds, the silicon source is uniformly mixed before heating; the lithium source is one of simple substance lithium, lithium carbonate, lithium hydroxide, lithium hydride and lithium borohydride.
It should be noted that: when the silicon source is a mixture of two or more silicon sources, the silicon source is uniformly mixed before heating, and a double-cone mixer with the rotating speed of 0.1-50r/min is preferably used for mixing for 0.5-10h. Of course, other blendors that can achieve the purpose of uniformly mixing various materials in the silicon source are also possible, and the invention is not limited.
Further preferably, in S2, the mass ratio of the lithium source to the silicon source is 1: (4-20), in order to precisely meter and avoid unnecessary errors, the silicon source and the lithium source need to be dried under vacuum before use.
The application finds that the pre-lithium amount is not only related to the materials and the proportion adopted by the silicon source and the lithium source, but also related to the specific surface area of the carbon base and the heating temperature T of the silicon source A Heating temperature T of lithium source B Temperature T of the premixing zone C Temperature T of deposition zone D And the like. Through the inventive effort, the present application confirms:
(1) The following technical scheme is adopted to help obtain the carbon-coated pre-lithiated silicon-based composite material with higher pre-lithium amount: the silicon source is silicon oxide, the lithium source is lithium simple substance or lithium hydride, and the specific surface area of the carbon substrate is 1000-2000cm 2 /g，T A 、T B 、T C 、T D The method meets the following conditions: t (T) A Is at a temperature of 1000-1800 ℃ and a temperature of 800 ℃ or less than T B ≤T A -200℃，T A +100℃≤T C ≤1900℃，0℃≤T D ≤T B -700 ℃; the lithium element in the obtained composite material accounts for 10-20% of the total mass fraction of the composite material. Further, in preparing a carbon-coated pre-lithiated silicon-based composite material of higher pre-lithium amount, the preferred mass ratio of lithium source to silicon source is 1:5.
(2) The following technical scheme is adopted to help obtain the carbon-coated pre-lithiated silicon-based composite material with the intermediate pre-lithium amount: the silicon source is a mixture of silicon and silicon dioxide or silicon oxide, the lithium source is lithium carbonate or lithium hydroxide, and the specific surface area of the carbon substrate is 500-900cm 2 /g，T A 、T B 、T C 、T D The method meets the following conditions: t (T) A Is at a temperature of 1000-1800 ℃ and a temperature of 600 ℃ to less than or equal to T B ≤T A -200℃，T A +100℃≤T C ≤2000℃，100℃≤T D ≤T B -500 ℃; the lithium element in the obtained composite material accounts for 5-10% of the total mass fraction of the composite material; further, in preparing a medium pre-lithium amount of carbon-coated pre-lithiated silicon-based composite material, the preferred mass ratio of lithium source to silicon source is 1:8.
(3) The following technical scheme is adopted to help obtain the carbon-coated pre-lithiated silicon-based composite material with lower pre-lithium amount: the silicon source is silicon and/or silicon dioxide, the lithium source is lithium borohydride, and the specific surface area of the carbon substrate is 100-400cm 2 /g，T A 、T B 、T C 、T D The method meets the following conditions: t (T) A Is 1200-1400 ℃, and the temperature is 200 ℃ to less than or equal to T B ≤T A -1000℃，T A +200℃≤T C ≤1600℃，0℃≤T D ≤T B -100 ℃; the lithium element in the obtained composite material accounts for 0.1-5% of the total mass fraction of the composite material. Further, in preparing a carbon-coated pre-lithiated silicon-based composite material of lower pre-lithium amount, the preferred mass ratio of lithium source to silicon source is 1:15.
further preferably, in S4, the pre-lithiated silicon-based deposition particles are loaded into a fluidized bed reactor, the temperature is raised to a thermal replacement temperature under an inert atmosphere, the temperature is raised to a vapor deposition temperature after thermal replacement, carbon source gas and carrier gas are respectively introduced at a constant temperature for vapor deposition, and uniform carbon coating on the outer surfaces of the pre-lithiated silicon-based deposition particles is realized by utilizing efficient two-phase turbulence of the fluidized bed.
The application surprisingly found that the coating is carried out according to the following technical parameters: heating to a thermal replacement temperature at a speed of 1-20 ℃/min under an inert atmosphere, wherein the thermal replacement temperature is 100-300 ℃; after heat replacement for 1-30min, continuously heating to a vapor deposition temperature at a speed of 1-20 ℃/min, wherein the vapor deposition temperature is 700-1200 ℃; the obtained carbon coating layer fully covers the outer surface of the pre-lithiated silicon-based deposited particles, is uniform and compact, can effectively avoid the problem of dew point of the material while obviously improving the conductivity, is beneficial to improving the cycling stability of the material and prolonging the service life of the material.
The inert atmosphere in S4 is provided by at least one of nitrogen and argon, the carbon source gas is at least one of methane, acetylene, ethylene, propylene, benzene and toluene, and the carrier gas is at least one of nitrogen and argon.
On the other hand, the invention also provides a carbon-coated pre-lithiated silicon-based composite material, which is prepared by adopting the preparation method shown above. The carbon-coated pre-lithiated silicon-based composite material uses the pre-lithiated silicon-based deposition particles as an inner core and uses a carbon coating layer as an outer layer of a submicron material, wherein the particle size of the pre-lithiated silicon-based deposition particles is 0.05-500 mu m, and the thickness of the carbon coating layer is 5-100nm.
Still further, in the carbon-coated pre-lithiated silicon-based composite material, the mass percentages of the silicon-based material, the metallic lithium, the carbon substrate and the carbon coating layer are respectively as follows: 62% -98.8%, 0.1% -20%, 0.1% -10% and 1% -8%.
In addition, the invention also provides application of the carbon-coated pre-lithiated silicon-based composite material, which can be coated on a negative current collector to be used as a negative electrode plate of a lithium battery.
The invention has the characteristics and beneficial effects that:
(1) The silicon source and the lithium source are arranged in two temperature areas, the silicon source and the lithium source are heated by adopting proper temperatures respectively, the sublimation time difference between the silicon source and the lithium source caused by heating in a single temperature area is avoided, and the uniform doping of lithium element in the silicon-based material rather than gradient doping is facilitated;
(2) On the basis of two temperature areas, a vacuum premixing area is additionally arranged, and the premixing area is beneficial to uniformly mixing gaseous silicon substrate and gaseous lithium material before deposition and does not precipitate, so that uniform doping is further ensured, and the proportion of the silicon substrate material and the lithium material in the gaseous mixture material is accurately controlled;
(3) The pre-lithiated silicon-based deposition particles are deposited on a carbon base and are subjected to carbon coating after deposition, and a conductive network of the silicon-based material is effectively constructed by the coordination of the pre-lithiated silicon-based deposition particles and the carbon coating, so that the conductive performance of the silicon-based material can be remarkably improved, the lithium-carbon-silicon composite structure is stabilized, the problem of high expansibility of the silicon-based material is solved, the problem of poor intrinsic conductivity of the silicon-based material is solved, and the first effect and the cycle performance are enhanced;
(4) The specific technical parameters are adopted to carry out carbon coating by using a fluidized bed technology, and the obtained carbon coating fully covers the outer surface of the pre-lithiated silicon-based deposited particles, is uniform and compact, is beneficial to improving the circulation stability of the material and prolonging the service life of the material;
(5) The pre-lithium quantity and uniformity of the pre-lithiated silicon-based deposited particles are controllable by regulating and controlling the temperature difference between the heating temperature of the silicon source and the heating temperature of the lithium source; the particle size of the pre-lithiated silicon-based deposition particles is controllable by regulating and controlling the temperature difference between the deposition temperature and the heating temperature of a lithium source; both modes can effectively reduce the preparation cost of the composite material.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is an SEM image of a carbon-coated pre-lithiated silicon-based composite material prepared in example 1 of the present invention;
FIG. 2 is a TEM image of a carbon-coated pre-lithiated silicon-based composite material prepared in example 1 of the present invention;
fig. 3 is an SEM image of the carbon-coated pre-lithiated silicon-based composite material prepared in example 1 of the present invention.
Detailed Description
The present invention will be described more fully hereinafter with reference to the following examples, which are given to illustrate the present invention and are not to be construed as limiting the scope of the present invention, in order to facilitate the understanding of the present invention.
Example 1
Silicon oxide with the particle size of 3-5 mu m is taken as a silicon source (before the silicon oxide is used, the silicon oxide needs to be dried for 12 hours at the temperature of 100 ℃ in vacuum), lithium hydride is taken as a lithium source, and the mass ratio of the lithium source to the silicon source is 1:5, adopting specific surface area 1000cm during deposition 2 And (3) carrying out temperature programming on the silicon source heating zone, the lithium source heating zone, the premixing zone and the deposition zone according to the following technical parameters, wherein each zone is vacuumized to 1Pa before the temperature programming: heating a silicon source heating zone to 1100 ℃ at a heating rate of 10 ℃/min, heating a lithium source heating zone to 800 ℃ at a heating rate of 7 ℃/min, heating a premixing zone to 1300 ℃ at a heating rate of 10 ℃/min, heating a deposition zone to 100 ℃ at a heating rate of 1 ℃/min, keeping constant temperature for 6 hours after the heating program is executed to ensure that the silicon source and the lithium source are completely gasified, synchronously introducing the two materials into the premixing zone, uniformly mixing the materials through the premixing zone, introducing the materials into the deposition zone, naturally cooling to room temperature after the deposition is finished, and discharging the materials to obtain the pre-lithiated silicon-based deposition particles; and loading the pre-lithiated silicon-based deposited particles into a fluidized bed reactor, introducing carrier gas nitrogen, heating to 300 ℃ at the same time, performing thermal displacement reaction for 20min, then heating to 850 ℃ at a heating rate of 10 ℃/min, increasing the carrier gas flow rate to 12L/min to ensure the fluidization state of powder in the fluidized bed reactor, simultaneously opening carbon source gas acetylene for vapor deposition, closing the carbon source gas and the carrier gas after 60min to obtain the carbon-coated pre-lithiated silicon-based composite material.
SEM testing of the product of example 1 was performed using a HITACHI, SU8100 cold field emission scanning electron microscope; the product of example 1 was subjected to TEM testing using a japanese JEOL field emission transmission electron microscope. The carbon substrate and carbon coating in the product of example 1 were tested using a Sichuan Saensi HCS series infrared carbon sulfur analyzer (pressure reduction gauge 0.5MPa, panel pressure gauge 0.06-0.08MPa, oscilloscope peak to trough difference < 0.003, initial voltage: 0.5-1.5V). As shown in fig. 1, 2 and 3 together: the product particle size was 5.1. Mu.m. The method is characterized by comprising the following steps of testing and analyzing by a carbon-sulfur analyzer and an inductive coupling plasma spectrometer: the silicon-based material accounts for 81.33% of the whole mass; the lithium metal element accounts for 14.60% of the total mass; the carbon substrate accounts for 1.07% of the total mass; the carbon coating accounts for 3.00% of the total mass.
Example 2
In comparison with example 1, the specific operation of heating each zone programmed consisted of "heating the silicon source heating zone to 1100 ℃ at a heating rate of 10 ℃/min, heating the lithium source heating zone to 800 ℃ at a heating rate of 7 ℃/min, heating the pre-mix zone to 1300 ℃ at a heating rate of 10 ℃/min, heating the deposition zone to 100 ℃ at a heating rate of 1 ℃/min," changing "heating the silicon source heating zone to 1700 ℃ at a heating rate of 16 ℃/min, heating the lithium source heating zone to 1300 ℃ at a heating rate of 12 ℃/min, heating the pre-mix zone to 1900 ℃ at a heating rate of 18 ℃/min, and heating the deposition zone to 1000 ℃ at a heating rate of 10 ℃/min"; the specific surface area of the carbon substrate used in the deposition is changed from 1000cm 2 The/g "change to" 1500cm 2 /g ", the remainder being the same as in example 1.
The measurement is as follows: the particle size of the obtained carbon-coated pre-lithiated silicon-based composite material is 5.05 mu m, and the silicon-based material accounts for 83.39% of the whole mass; the lithium metal element accounts for 11.40% of the total mass; the carbon substrate accounts for 1.41% of the total mass; the carbon coating accounts for 3.8% of the total mass.
Example 3
Compared with the example 1, the temperature-raising program is changed from ' constant temperature 6h ' to ' constant temperature 4h ', and the specific surface area of the carbon substrate used in deposition is changed from ' 1000cm 2 The/g "change to" 2000cm 2 /g ", the remainder being the same as in example 1.
The measurement is as follows: the particle size of the obtained carbon-coated pre-lithiated silicon-based composite material is 5.01 mu m, and the silicon-based material accounts for 84.11% of the whole mass; the lithium metal element accounts for 10.3% of the total mass; the carbon substrate accounts for 1.49% of the total mass; the carbon coating accounts for 4.10% of the total mass.
The specific selection and mass ratio of the lithium source to the silicon source, the temperature range of each region, the specific surface area of the carbon substrate and other conditions in examples 1-3 are all in accordance with the preparation of the carbon-coated pre-lithiated silicon-based composite material with higher pre-lithium amount, and the above measurement data prove that: examples 1-3 did produce carbon-coated pre-lithiated silicon-based composites with higher pre-lithium amounts.
Example 4
Compared to example 1, the silicon source is changed to a silicon to silicon dioxide mass ratio of 1:1, a mixture of two or more of the above-mentioned materials; the lithium source is changed into lithium carbonate; the mass ratio of the lithium source to the silicon source is changed to 1:8, 8; the temperature rise is specifically changed into: heating the silicon source heating zone to 1300 ℃ at a heating rate of 13 ℃/min, heating the lithium source heating zone to 1100 ℃ at a heating rate of 11 ℃/min, heating the premixing zone to 1400 ℃ at a heating rate of 13 ℃/min, and heating the deposition zone to 300 ℃ at a heating rate of 3 ℃/min; the specific surface area of the carbon substrate used in deposition is changed to 500cm 2 /g。
The measurement is as follows: the particle size of the obtained carbon-coated pre-lithiated silicon-based composite material is 4.97 mu m, and the silicon-based material accounts for 86.22% of the whole mass; the lithium metal element accounts for 8.70% of the total mass; the carbon substrate accounts for 1.38% of the total mass; the carbon coating accounts for 3.70% of the total mass.
Example 5
Compared with example 4, the temperature programming is specifically changed to: heating the silicon source heating zone to 1500 ℃ at a heating rate of 14 ℃/min, heating the lithium source heating zone to 1300 ℃ at a heating rate of 12 ℃/min, heating the premixing zone to 1600 ℃ at a heating rate of 15 ℃/min, and heating the deposition zone to 700 ℃ at a heating rate of 6 ℃/min; the specific surface area of the carbon substrate used in the deposition is changed to 700cm 2 /g。
The measurement is as follows: the particle size of the obtained carbon-coated pre-lithiated silicon-based composite material is 4.76 mu m, and the silicon-based material accounts for 88.68% of the whole mass; the lithium metal element accounts for 6.40% of the total mass; the carbon substrate accounts for 1.32% of the total mass; the carbon coating accounts for 3.60% of the total mass.
Example 6
Compared with example 4, the silicon source is changed to silicon oxide, and the specific surface area of the carbon substrate used in deposition is changed to 500cm 2 /g。
The measurement is as follows: the particle size of the obtained carbon-coated pre-lithiated silicon-based composite material is 4.49 mu m, and the silicon-based material accounts for 88.77% of the whole mass; the lithium metal element accounts for 6.10% of the total mass; the carbon substrate accounts for 1.23% of the total mass; the carbon coating layer accounts for 3.90% of the total mass.
The specific selection and mass ratio of the lithium source to the silicon source, the temperature range of each zone, the specific surface area of the carbon substrate and other conditions in examples 4-6 all meet the requirements of preparing the carbon-coated pre-lithiated silicon-based composite material with medium pre-lithium amount, and the above measurement data prove that: examples 4-6 did produce carbon-coated pre-lithiated silicon-based composites with moderate pre-lithium amounts.
Example 7
Compared with example 1, the silicon source is changed from ' silicon oxide ' to ' silicon to silicon dioxide mass ratio 1:1, changing a lithium source from lithium hydride to lithium borohydride, and changing the mass ratio of the lithium source to the silicon source into 1:5 "change to" lithium source to silicon source mass ratio of 1:15", the specific operation of programming the temperature of each zone is changed from heating the silicon source heating zone to 1100 ℃ at a heating rate of 10 ℃/min, heating the lithium source heating zone to 800 ℃ at a heating rate of 7 ℃/min, heating the pre-mixed zone to 1300 ℃ at a heating rate of 10 ℃/min, heating the deposition zone to 100 ℃ at a heating rate of 1 ℃/min, heating the silicon source heating zone to 1300 ℃ at a heating rate of 13 ℃/min, heating the lithium source heating zone to 300 ℃ at a heating rate of 3 ℃/min, heating the pre-mixed zone to 1500 ℃ at a heating rate of 15 ℃/min, and heating the deposition zone to 200 ℃ at a heating rate of 2 ℃/min; the specific surface area of the carbon substrate used in the deposition is changed from 1000cm 2 The/g "change to" 400cm 2 /g ", the remainder being the same as in example 1.
The measurement is as follows: the particle size of the obtained carbon-coated pre-lithiated silicon-based composite material is 4.81 mu m, and the silicon-based material accounts for 91.70% of the whole mass; the lithium metal element accounts for 3.10% of the total mass; the carbon substrate accounts for 2.10% of the total mass; the carbon coating accounts for 3.10% of the total mass.
Example 8
Compared with the embodiment 7, the silicon source is changed into simple substance Si, and the specific operation of temperature programming is changed into: "heating the silicon source heating zone to 1200 ℃ at a heating rate of 12 ℃/min, heating the lithium source heating zone to 200 ℃ at a heating rate of 2 ℃/min, heating the premixing zone to 1400 ℃ at a heating rate of 14 ℃/min, and heating the deposition zone to 100 ℃ at a heating rate of 1 ℃/min"; the specific surface area of the carbon substrate used in the deposition is changed to 300cm 2 /g ", the remainder being the same as in example 1.
The measurement is as follows: the particle size of the obtained carbon-coated pre-lithiated silicon-based composite material is 4.64 mu m, and the silicon-based material accounts for 90.10% of the whole mass; the lithium metal element accounts for 3.80% of the total mass; the carbon substrate accounts for 2.40% of the total mass; the carbon coating accounts for 3.70% of the total mass.
Example 9
Compared with example 8, the silicon source is changed to silicon dioxide, the constant temperature time is changed to 4 hours, and the specific surface area of the carbon substrate used in deposition is changed to 100cm 2 The remainder of the "g" was the same as in example 8.
The measurement is as follows: the particle size of the obtained carbon-coated pre-lithiated silicon-based composite material is 4.64 mu m, and the silicon-based material accounts for 90.10% of the whole mass; the lithium metal element accounts for 3.80% of the total mass; the carbon substrate accounts for 2.40% of the total mass; the carbon coating accounts for 3.70% of the total mass.
The specific selection and mass ratio of the lithium source to the silicon source, the temperature range of each region, the specific surface area of the carbon substrate, and the like in examples 7 to 9 all meet the conditions for preparing the carbon-coated pre-lithiated silicon-based composite material with a lower pre-lithium amount, and the above measurement data prove that: examples 7-9 did produce carbon-coated pre-lithiated silicon-based composites with lower pre-lithium amounts.
Comparative example 1
Compared with the embodiment 4, the lithium source and the silicon source are heated in the same temperature zone at 1300 ℃, and the rest is the same as the embodiment 4;
comparative example 2
In comparison with example 4, no premixing zone was provided, and the rest was the same as in example 4;
comparative example 3
In comparison with example 4, no carbon coating was performed, and the rest was the same as in example 4.
The products obtained in examples 1-9 and comparative examples 1-3 were tested for electrochemical performance using a blue-electric testing system. In the test, the products prepared in each example and comparative example are respectively used as anode active materials, and the anode active materials are mixed with a conductive agent Super P, sodium carboxymethyl cellulose CMC and a binder styrene butadiene rubber SBR (40% SC) according to the mass ratio of 85:10:1.8:3.2, mixing, preparing into slurry (solid content is 30%), coating on copper foil, vacuum drying, rolling and cutting to obtain the negative pole piece. The button half cell is assembled in a glove box, and the specific steps are that a negative electrode shell, a spring piece, a gasket, a negative electrode plate, electrolyte (1M LiPF6 in EC:EMC:DEC =1:1:1, 5% FEC) are sequentially placed, a diaphragm (a single-layer or multi-layer polyethylene or polypropylene diaphragm) is placed, electrolyte is added, a metal lithium piece is placed, a positive electrode shell is placed, and the button half cell is sealed (the pressure value is 5-10 MPa). The initial and cyclic 100-turn capacity retention test was performed according to the following test procedure: (1) placing for 12h; (2) discharging: 0.1 CC to 5mv; standing for 5min;0.05C CC to 5mV; standing for 5min;0.02C CC to 5mV; standing for 5min;0.01CCC to 5mV; standing for 5min; (3) charging: 0.1 CC to 2.0v; standing for 5min; (4) the cycle was 100 cycles. The final test results are shown in table 1 below:
TABLE 1 lithium doping amount and electrochemical properties of examples 1-9 and comparative examples 1-3
As can be seen from table 1: the carbon-coated pre-lithiated silicon-based composite material prepared by the embodiments of the invention can maintain higher capacity after 100 circles of circulation. Moreover, the higher the doping amount of lithium is, the higher the first effect is, which shows that the doping substance improves the electron conduction and effectively prevents dead lithium from being generated; however, as the doping amount of lithium is further increased, the capacity retention rate of the composite material after 100 cycles is reduced, which indicates that the excessively high doping amount is unfavorable for the stability of the internal structure during the charge and discharge process.
From the comparison of example 4 and comparative example 1, it is understood that: under the condition that the mass ratio of the lithium source, the silicon source, the lithium source and the silicon source is completely consistent with other conditions, whether the double-temperature region is adopted for heating the lithium source and the silicon source respectively can cause great difference in lithium doping amount and doping uniformity, the double-temperature region heating lithium doping amount is 8.7% under the same condition, the single-temperature region heating is only 4.16%, and the higher lithium doping amount and the better doping uniformity are beneficial to generating better first effect and 100-circle capacity retention rate.
As can be seen from the comparison of example 4 with comparative example 2: under the condition that the mass ratio of a lithium source, a silicon source, a lithium source and the silicon source are completely consistent with other conditions, whether a pre-mixing region is arranged or not is set while a double-temperature region is arranged for heating the lithium source and the silicon source respectively, so that great difference exists between the doping amount and the doping uniformity of lithium, the doping amount of the lithium in the pre-mixing region is 8.7% under the same condition, the doping uniformity of the lithium in the pre-mixing region is only 3.22% without the pre-mixing region, the higher doping amount of the lithium and the better doping uniformity are beneficial to generating better first effect and capacity retention rate of 100 circles, and the pre-mixing region is not arranged, which is obviously unfavorable to the first effect and the capacity retention rate of 100 circles.
As can be seen from the comparison of example 4 and comparative example 3: carbon coating of the pre-lithiated silicon-based deposited particles can achieve better initial efficiency and 100-turn capacity retention under all other conditions that are fully consistent.
Further, as a result of the test of comparative example 4, comparative example 1, comparative example 2, comparative example 3, we speculate whether the pre-mix zone is provided with a large influence on the lithium doping amount and electrochemical properties of the product and whether the dual temperature zone is provided with a large influence on the lithium doping amount and electrochemical properties of the product and whether the carbon coating is performed.
To sum up: the invention is characterized in that: (1) The silicon source and the lithium source are arranged in two temperature areas and heated respectively to avoid the sublimation time difference between the silicon source and the lithium source caused by heating in a single temperature area, thereby being beneficial to the uniform doping of lithium element in the silicon-based material rather than the gradient doping; (2) The premixing area is additionally arranged, so that the gaseous silicon substrate and the gaseous lithium material are uniformly mixed and do not precipitate before deposition, and the uniform doping is further ensured, and the proportion of the silicon substrate material and the lithium material in the gaseous mixed material is accurately controlled; (3) The fluidized bed technology is utilized for carbon coating, and the obtained carbon coating fully covers the outer surface of the pre-lithiated silicon-based deposited particles, is uniform and compact, is beneficial to improving the circulation stability of the material and prolonging the service life of the material; the carbon-coated pre-lithiated silicon-based composite material with uniform lithium doping can be obtained by the synergistic effect of the technical means, the capacity attenuation of the composite material is smaller in the cyclic process, and the volume expansion caused by the deintercalation of lithium can be effectively reduced, so that the electrochemical performance and the cyclic life of the silicon-based material are improved.
It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A preparation method of a carbon-coated pre-lithiated silicon-based composite material is characterized by comprising the following steps: the method comprises the following operation steps:
s1, respectively heating a silicon source and a lithium source under vacuum to generate a gaseous silicon-based material and a gaseous lithium material;
s2, introducing a gaseous silicon-based material and a gaseous lithium material into a vacuum premixing zone;
s3, introducing the uniformly mixed gaseous mixture in the pre-mixing zone into a vacuum deposition zone in which a carbon substrate is placed, and obtaining pre-lithiated silicon-based deposition particles after deposition;
and S4, carrying out carbon coating on the pre-lithiated silicon-based deposited particles to obtain the carbon-coated pre-lithiated silicon-based composite material.
2. The method for preparing a carbon-coated pre-lithiated silicon-based composite material of claim 1, wherein: the heating temperature of the silicon source is T A The heating temperature of the lithium source is T B The temperature of the premixing zone is T C The temperature of the deposition area is T D ，T A Above the vaporization temperature of the silicon source, T B Above the vaporization temperature of the lithium source, T D <T B <T A <T C By controlling T A And T is B Controlling the pre-lithium amount and uniformity of the pre-lithiated silicon-based deposited particles by controlling T D And T is B And controlling the particle size of the prelithiated silica-based deposit particles.
3. The method for preparing a carbon-coated pre-lithiated silicon-based composite material of claim 2, wherein: in the S1, the silicon source comprises at least one of a silicon simple substance, silicon dioxide and silicon oxide, the lithium source is one of a lithium simple substance, lithium carbonate, lithium hydroxide, lithium hydride and lithium borohydride, and the mass ratio of the lithium source to the silicon source is 1: (4-20).
4. The method for preparing a carbon-coated pre-lithiated silicon-based composite material of claim 3, wherein:
the silicon source is silicon oxide, the lithium source is lithium simple substance or lithium hydride, and the specific surface area of the carbon substrate is 1000-2000cm 2 /g，T A 、T B 、T C 、T D The method meets the following conditions: t (T) A Is at a temperature of 1000-1800 ℃ and a temperature of 800 ℃ or less than T B ≤T A -200℃，T A +100℃≤T C ≤1900℃，0℃≤T D ≤T B -700℃；
The silicon source is a mixture of silicon and silicon dioxide or silicon oxide, the lithium source is lithium carbonate or lithium hydroxide, and the specific surface area of the carbon substrate is 500-900cm 2 /g，T A 、T B 、T C 、T D The method meets the following conditions: t (T) A Is at a temperature of 1000-1800 ℃ and a temperature of 600 ℃ to less than or equal to T B ≤T A -200℃，T A +100℃≤T C ≤2000℃，100℃≤T D ≤T B -500℃；
The silicon source is silicon and/or silicon dioxide, the lithium source is lithium borohydride, and the specific surface area of the carbon substrate is 100-400cm 2 /g，T A 、T B 、T C 、T D The method meets the following conditions: t (T) A Is 1200-1400 ℃, and the temperature is 200 ℃ to less than or equal to T B ≤T A -1000℃，T A +200℃≤T C ≤1600℃，0℃≤T D ≤T B -100℃。
5. The method for preparing a carbon-coated pre-lithiated silicon-based composite material of claim 1, wherein: and S4, filling the pre-lithiated silicon-based deposited particles into a fluidized bed reactor, heating to a thermal replacement temperature under inert atmosphere, continuously heating to a vapor deposition temperature after thermal replacement, and respectively introducing carbon source gas and carrier gas at constant temperature to carry out carbon coating through vapor deposition.
6. The method for preparing a carbon-coated pre-lithiated silicon-based composite material of claim 5, wherein: heating to a thermal replacement temperature at a speed of 1-20 ℃/min under an inert atmosphere, wherein the thermal replacement temperature is 100-300 ℃; after heat replacement for 1-30min, continuously heating to a vapor deposition temperature at a speed of 1-20 ℃/min, wherein the vapor deposition temperature is 700-1200 ℃; the inert atmosphere is provided by at least one of nitrogen and argon, the carbon source gas is at least one of methane, acetylene, ethylene, propylene, benzene and toluene, and the carrier gas is at least one of nitrogen and argon.
7. A carbon-coated pre-lithiated silicon-based composite material characterized by: a method of manufacture as claimed in any one of claims 1 to 6.
8. The carbon-coated pre-lithiated silicon-based composite material of claim 7, wherein: the carbon-coated pre-lithiated silicon-based composite material is a submicron material taking the pre-lithiated silicon-based deposited particles as an inner core and a carbon coating layer as an outer layer, wherein the particle size of the pre-lithiated silicon-based deposited particles is 0.05-500 mu m, the thickness of the carbon coating layer is 5-100nm, and the mass percentages of silicon-based materials, metallic lithium, a carbon substrate and the carbon coating layer are respectively as follows in sequence: 62% -98.8%, 0.1% -20%, 0.1% -10% and 1% -8%.
9. The negative pole piece is characterized in that: an active material comprising a negative electrode current collector and coated on the surface of the negative electrode current collector, the active material comprising the carbon-coated pre-lithiated silicon-based composite material of claim 7 or 8.
10. A lithium battery, characterized in that: comprising the negative electrode tab of claim 9.
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