CN116759563A - Porous lithium battery composite anode material, preparation method thereof and lithium battery - Google Patents
Porous lithium battery composite anode material, preparation method thereof and lithium battery Download PDFInfo
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- CN116759563A CN116759563A CN202311054498.5A CN202311054498A CN116759563A CN 116759563 A CN116759563 A CN 116759563A CN 202311054498 A CN202311054498 A CN 202311054498A CN 116759563 A CN116759563 A CN 116759563A
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- lithium battery
- porous
- silicon
- porous graphite
- graphite
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 94
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 94
- 239000010405 anode material Substances 0.000 title claims abstract description 52
- 239000002131 composite material Substances 0.000 title claims abstract description 52
- 238000002360 preparation method Methods 0.000 title claims abstract description 32
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 265
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 192
- 239000010439 graphite Substances 0.000 claims abstract description 183
- 239000007771 core particle Substances 0.000 claims abstract description 80
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 73
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 71
- 239000011148 porous material Substances 0.000 claims abstract description 53
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 52
- 239000010703 silicon Substances 0.000 claims abstract description 52
- 238000002156 mixing Methods 0.000 claims abstract description 47
- 239000011259 mixed solution Substances 0.000 claims abstract description 32
- 238000005245 sintering Methods 0.000 claims abstract description 31
- 239000006185 dispersion Substances 0.000 claims abstract description 24
- 239000007788 liquid Substances 0.000 claims abstract description 24
- 239000006255 coating slurry Substances 0.000 claims abstract description 21
- 239000013067 intermediate product Substances 0.000 claims abstract description 21
- 229920000609 methyl cellulose Polymers 0.000 claims abstract description 21
- 239000001923 methylcellulose Substances 0.000 claims abstract description 21
- 229910000314 transition metal oxide Inorganic materials 0.000 claims abstract description 20
- 238000005469 granulation Methods 0.000 claims abstract description 19
- 230000003179 granulation Effects 0.000 claims abstract description 19
- 239000007921 spray Substances 0.000 claims abstract description 19
- 239000007773 negative electrode material Substances 0.000 claims abstract description 16
- 238000000498 ball milling Methods 0.000 claims abstract description 15
- 239000002904 solvent Substances 0.000 claims abstract description 11
- -1 and simultaneously Substances 0.000 claims abstract description 9
- 239000011230 binding agent Substances 0.000 claims abstract description 9
- 239000002270 dispersing agent Substances 0.000 claims abstract description 8
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- 238000000034 method Methods 0.000 claims description 52
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- 239000011247 coating layer Substances 0.000 claims description 41
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- 235000010981 methylcellulose Nutrition 0.000 claims description 20
- 238000010438 heat treatment Methods 0.000 claims description 19
- 239000007800 oxidant agent Substances 0.000 claims description 19
- 230000001590 oxidative effect Effects 0.000 claims description 17
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- QAOWNCQODCNURD-UHFFFAOYSA-N sulfuric acid Substances OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 11
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 9
- 239000007770 graphite material Substances 0.000 claims description 9
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 8
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 8
- 238000001816 cooling Methods 0.000 claims description 8
- 239000000138 intercalating agent Substances 0.000 claims description 8
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 claims description 7
- 238000001035 drying Methods 0.000 claims description 7
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- 229920002401 polyacrylamide Polymers 0.000 claims description 7
- 239000012286 potassium permanganate Substances 0.000 claims description 7
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 6
- 239000004698 Polyethylene Substances 0.000 claims description 6
- 239000002202 Polyethylene glycol Substances 0.000 claims description 6
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 6
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- 229920000647 polyepoxide Polymers 0.000 claims description 6
- 229920001223 polyethylene glycol Polymers 0.000 claims description 6
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 6
- 229920002134 Carboxymethyl cellulose Polymers 0.000 claims description 5
- 239000002033 PVDF binder Substances 0.000 claims description 5
- 229920002125 Sokalan® Polymers 0.000 claims description 5
- WQZGKKKJIJFFOK-VFUOTHLCSA-N beta-D-glucose Chemical compound OC[C@H]1O[C@@H](O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-VFUOTHLCSA-N 0.000 claims description 5
- 239000001768 carboxy methyl cellulose Substances 0.000 claims description 5
- 235000010948 carboxy methyl cellulose Nutrition 0.000 claims description 5
- 239000008112 carboxymethyl-cellulose Substances 0.000 claims description 5
- 239000004584 polyacrylic acid Substances 0.000 claims description 5
- 229920002239 polyacrylonitrile Polymers 0.000 claims description 5
- 229920000573 polyethylene Polymers 0.000 claims description 5
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims description 5
- 239000001866 hydroxypropyl methyl cellulose Substances 0.000 claims description 4
- 229920003088 hydroxypropyl methyl cellulose Polymers 0.000 claims description 4
- 235000010979 hydroxypropyl methyl cellulose Nutrition 0.000 claims description 4
- UFVKGYZPFZQRLF-UHFFFAOYSA-N hydroxypropyl methyl cellulose Chemical compound OC1C(O)C(OC)OC(CO)C1OC1C(O)C(O)C(OC2C(C(O)C(OC3C(C(O)C(O)C(CO)O3)O)C(CO)O2)O)C(CO)O1 UFVKGYZPFZQRLF-UHFFFAOYSA-N 0.000 claims description 4
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 4
- 238000004321 preservation Methods 0.000 claims description 4
- 229910000428 cobalt oxide Inorganic materials 0.000 claims description 3
- IVMYJDGYRUAWML-UHFFFAOYSA-N cobalt(ii) oxide Chemical compound [Co]=O IVMYJDGYRUAWML-UHFFFAOYSA-N 0.000 claims description 3
- 239000008367 deionised water Substances 0.000 claims description 3
- 229910021641 deionized water Inorganic materials 0.000 claims description 3
- SZVJSHCCFOBDDC-UHFFFAOYSA-N ferrosoferric oxide Chemical compound O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 claims description 3
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- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 claims description 3
- 239000004408 titanium dioxide Substances 0.000 claims description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 3
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- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical compound [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 claims description 2
- 229920000178 Acrylic resin Polymers 0.000 claims description 2
- 239000004925 Acrylic resin Substances 0.000 claims description 2
- CZMRCDWAGMRECN-UGDNZRGBSA-N Sucrose Chemical compound O[C@H]1[C@H](O)[C@@H](CO)O[C@@]1(CO)O[C@@H]1[C@H](O)[C@@H](O)[C@H](O)[C@@H](CO)O1 CZMRCDWAGMRECN-UGDNZRGBSA-N 0.000 claims description 2
- 229930006000 Sucrose Natural products 0.000 claims description 2
- 229920005546 furfural resin Polymers 0.000 claims description 2
- 238000010030 laminating Methods 0.000 claims description 2
- 229910000480 nickel oxide Inorganic materials 0.000 claims description 2
- NDLPOXTZKUMGOV-UHFFFAOYSA-N oxo(oxoferriooxy)iron hydrate Chemical compound O.O=[Fe]O[Fe]=O NDLPOXTZKUMGOV-UHFFFAOYSA-N 0.000 claims description 2
- GNRSAWUEBMWBQH-UHFFFAOYSA-N oxonickel Chemical compound [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 claims description 2
- 229920001568 phenolic resin Polymers 0.000 claims description 2
- 239000005011 phenolic resin Substances 0.000 claims description 2
- 229920000767 polyaniline Polymers 0.000 claims description 2
- 229920000915 polyvinyl chloride Polymers 0.000 claims description 2
- 239000004800 polyvinyl chloride Substances 0.000 claims description 2
- 239000005720 sucrose Substances 0.000 claims description 2
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 claims 1
- 229910001928 zirconium oxide Inorganic materials 0.000 claims 1
- 238000006243 chemical reaction Methods 0.000 description 19
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- 125000004122 cyclic group Chemical group 0.000 description 13
- 239000012299 nitrogen atmosphere Substances 0.000 description 12
- 239000011229 interlayer Substances 0.000 description 11
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 10
- 229910001416 lithium ion Inorganic materials 0.000 description 10
- 239000000463 material Substances 0.000 description 10
- 230000000694 effects Effects 0.000 description 8
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- 230000009286 beneficial effect Effects 0.000 description 4
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- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 3
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 3
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- LNAZSHAWQACDHT-XIYTZBAFSA-N (2r,3r,4s,5r,6s)-4,5-dimethoxy-2-(methoxymethyl)-3-[(2s,3r,4s,5r,6r)-3,4,5-trimethoxy-6-(methoxymethyl)oxan-2-yl]oxy-6-[(2r,3r,4s,5r,6r)-4,5,6-trimethoxy-2-(methoxymethyl)oxan-3-yl]oxyoxane Chemical compound CO[C@@H]1[C@@H](OC)[C@H](OC)[C@@H](COC)O[C@H]1O[C@H]1[C@H](OC)[C@@H](OC)[C@H](O[C@H]2[C@@H]([C@@H](OC)[C@H](OC)O[C@@H]2COC)OC)O[C@@H]1COC LNAZSHAWQACDHT-XIYTZBAFSA-N 0.000 description 2
- 229910003481 amorphous carbon Inorganic materials 0.000 description 2
- 239000006183 anode active material Substances 0.000 description 2
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- BYHQTRFJOGIQAO-GOSISDBHSA-N 3-(4-bromophenyl)-8-[(2R)-2-hydroxypropyl]-1-[(3-methoxyphenyl)methyl]-1,3,8-triazaspiro[4.5]decan-2-one Chemical compound C[C@H](CN1CCC2(CC1)CN(C(=O)N2CC3=CC(=CC=C3)OC)C4=CC=C(C=C4)Br)O BYHQTRFJOGIQAO-GOSISDBHSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910013716 LiNi Inorganic materials 0.000 description 1
- 229910001290 LiPF6 Inorganic materials 0.000 description 1
- 229910000676 Si alloy Inorganic materials 0.000 description 1
- 238000005411 Van der Waals force Methods 0.000 description 1
- HFCVPDYCRZVZDF-UHFFFAOYSA-N [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O Chemical compound [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O HFCVPDYCRZVZDF-UHFFFAOYSA-N 0.000 description 1
- ZVLDJSZFKQJMKD-UHFFFAOYSA-N [Li].[Si] Chemical compound [Li].[Si] ZVLDJSZFKQJMKD-UHFFFAOYSA-N 0.000 description 1
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- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 125000004432 carbon atom Chemical group C* 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 239000002041 carbon nanotube Substances 0.000 description 1
- 229910021393 carbon nanotube Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
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- 125000002791 glucosyl group Chemical group C1([C@H](O)[C@@H](O)[C@H](O)[C@H](O1)CO)* 0.000 description 1
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- 150000003624 transition metals Chemical class 0.000 description 1
Classifications
-
- 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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
-
- 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
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
-
- 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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
-
- 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
Abstract
The invention provides a porous lithium battery composite anode material, a preparation method thereof and a lithium battery, wherein the preparation method comprises the following steps: mixing a silicon source, a carbon source, methylcellulose and a dispersing agent to obtain a dispersion liquid, mixing the dispersion liquid with porous graphite to obtain a mixed solution, and then carrying out spray granulation to fill the silicon source and the carbon source into pore channels of the porous graphite, and simultaneously, coating the superfluous carbon source on the outer surface of the porous graphite to finally form core particles; mixing transition metal oxide, a binder and a solvent to obtain coating slurry, and mixing and ball-milling the coating slurry and core particles to obtain an intermediate product; and (III) sintering the intermediate product in a protective atmosphere to obtain the lithium battery composite anode material with the porous structure. The lithium battery prepared from the negative electrode material prepared by the invention has excellent charge-discharge cycle performance and rate capability, and high first coulombic efficiency.
Description
Technical Field
The invention belongs to the technical field of battery materials, and relates to a lithium battery composite anode material with a porous structure, a preparation method thereof and a lithium battery.
Background
Lithium batteries are secondary battery systems in which two different lithium intercalation compounds capable of reversibly intercalating and deintercalating lithium ions are used as positive electrode sheets and negative electrodes, respectively. During charging, lithium ions are released from the positive electrode and are inserted into the negative electrode through the electrolyte and the diaphragm; in contrast, lithium ions are released from the negative electrode during discharge, and are inserted into the positive electrode through the electrolyte and the separator.
The lithium battery has excellent performances such as high working voltage, high energy density, long service life, wide application temperature range, no memory and the like, and is widely applied to fields such as new energy automobiles and the like. However, as the requirements of consumers on longer endurance and the like of battery products are continuously improved, the development of battery products with larger specific capacity and higher energy density becomes an important current exploration direction. Currently, the main factors limiting the further improvement of the capacity and energy of lithium batteries are: the capacity of the graphite-based negative electrode material which is currently mainstream is brought into play and is close to the theoretical gram capacity of 372mAh/g, and the gram capacity of the material is difficult to further improve. Therefore, the search for higher gram capacity lithium ion negative electrode tab materials is critical to develop higher specific capacity, higher energy density battery products.
Silicon has 4200mAh/g theoretical lithium storage capacity, low lithium removal/intercalation potential, rich storage and low cost, and thus, the silicon has gained important attention of a large number of researchers. However, silicon is not currently used on a large scale on lithium ion negative electrode sheets, mainly because of the severe volume changes of silicon during the lithium removal/intercalation process. The characteristic causes the battery capacity attenuation and the cycle performance deterioration in two aspects when the material is used for the negative electrode material, on one hand, the damage of the material structure and the mechanical pulverization cause the negative electrode material to be separated from a current collector, so that the battery capacity and the cycle performance are physically reduced; on the other hand, the volume expansion and contraction cause continuous rupture and reconstruction of the SEI film, continuously consume active materials, and cause adverse effects such as battery capacity attenuation and cycle performance deterioration. Therefore, silicon has not been used as a negative electrode material for large-scale applications. And the silicon/carbon composite material is favored by a plurality of researchers by combining comprehensive technical researches on graphite cathode materials and the characteristic of high lithium storage capacity of silicon.
Graphite is a main commercial lithium ion negative electrode plate material at present because of the advantages of high electronic conductivity, large lithium ion diffusion coefficient, small volume change of a layered structure before and after lithium intercalation, high lithium intercalation capacity, low lithium intercalation potential and the like. However, the theoretical gram capacity of graphite is about 375mAh/g, the requirement of the market on the high energy density of lithium batteries can not be met, and the research of high-capacity silicon-carbon composite materials is focused widely.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a lithium battery composite anode material with a porous structure, a preparation method thereof and a lithium battery. The lithium battery prepared from the negative electrode material prepared by the invention has excellent charge-discharge cycle performance and rate capability, and high first coulombic efficiency.
To achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a porous lithium battery composite anode material, where the preparation method includes:
mixing a silicon source, a carbon source, methylcellulose and a dispersing agent to obtain a dispersion liquid, mixing the dispersion liquid with porous graphite to obtain a mixed solution, and then carrying out spray granulation to fill the silicon source and the carbon source into pore channels of the porous graphite, and simultaneously, coating the superfluous carbon source on the outer surface of the porous graphite to finally form core particles;
Mixing transition metal oxide, a binder and a solvent to obtain coating slurry, and mixing and ball-milling the coating slurry and core particles to obtain an intermediate product;
and (III) sintering the intermediate product in a protective atmosphere to obtain the lithium battery composite anode material with the porous structure.
The lithium battery composite anode material with the core-shell structure is prepared by adopting the preparation method provided by the invention, and the coating layer is transition metal oxide, so that the volume expansion of the silicon-carbon composite material in the cyclic charge and discharge process can be effectively relieved, and the interface reaction between the silicon-carbon composite material and electrolyte can be improved. The inner core particles are of an embedded composite porous structure and comprise porous graphite and silicon-carbon composite materials embedded in porous graphite pore channels, ordered and mutually communicated pore channels are formed between sheets of the porous graphite, so that the storage of ions and the infiltration of electrolyte are facilitated, the silicon-carbon composite materials are in better contact with the electrolyte, and the contact surface of the silicon-carbon composite materials and the inner walls of the pore channels provides effective conductive channels for the transmission of electrons and lithium ions. The lithium battery prepared from the negative electrode material prepared by the invention has excellent charge-discharge cycle performance and rate capability.
According to the invention, the silicon source, the carbon source and the porous graphite are mixed, so that the silicon-carbon composite material is distributed in the pore canal structure of the porous graphite, the silicon-carbon composite material can effectively support the pore canal structure, the collapse and the re-stacking of the pore canal of the porous graphite are prevented, and the good flexible structure of the core particles can be maintained. The porous graphite with the pore canal structure reserves space for the volume expansion of the silicon-carbon composite material in the charge-discharge process, thereby improving the first efficiency and the cycle performance of the silicon-based negative electrode material.
In the spray granulation process, the amorphous carbon is uniformly coated on the surface of the porous graphite by the carbon source to form a coated carbon layer, the volume expansion effect of the silicon-carbon composite material in the charge and discharge process can be effectively limited by the coated carbon layer and the porous graphite with a three-dimensional structure, so that the lithium battery can maintain higher specific capacity, and the coated carbon layer and the porous graphite have better conductivity, thereby being beneficial to improving the conductivity of the cathode material.
In the preferred embodiment of the present invention, in the step (i), the mass ratio of the silicon source, the carbon source and the methylcellulose is (0.7-0.8): 1.6-2.3): 1, for example, but not limited to, 0.7:1.6:1, 0.71:1.7:1, 0.72:1.8:1, 0.73:1.9:1, 0.74:2.0:1, 0.75:2.1:1, 0.76:2.2:1, 0.77:2.3:1, 0.78:1.8:1, 0.79:2.0:1 or 0.8:2.2:1, other non-enumerated values within the numerical range are equally applicable.
The three-dimensional network structure formed by the methylcellulose has certain elasticity and stress dispersion characteristics, and after the silicon-carbon composite material is embedded into the three-dimensional network structure, the material fragmentation caused by volume expansion can be effectively avoided, the loss of the silicon-carbon composite material is reduced, the occurrence probability of side reaction is reduced, the consumption of active lithium ions in the electrolyte is reduced, and the cycle life of the cathode material is further improved.
The invention is particularly limited that the mass ratio of the silicon source to the carbon source to the methylcellulose is (0.7-0.8): (1.6-2.3): 1. When the dosage of the silicon source in the reaction system is increased, the surface area of the carbon source required for accommodating the adhesion of the silicon source is correspondingly increased, however, the carbon source content in the reaction system is certain, and when the silicon source is excessive, on one hand, the silicon source adhered to the surface of the carbon source is increased, so that the thickness of the silicon layer coated on the surface of the carbon source is increased, the interface bonding strength between the silicon layer and the surface of the carbon source is reduced, and the silicon layer is easy to fall off; on the other hand, the silicon source which is not attached to the surface of the carbon source exists in the reaction system in a dispersed or self-polymerized form, so that the volume expansion effect of the silicon source is aggravated by the fact that the silicon source cannot be released, and the structure of the silicon-carbon composite material is damaged. Therefore, although increasing the silicon source content in the silicon-carbon composite material contributes to the improvement of the specific capacity of the negative electrode material, it is extremely likely to cause capacity degradation in a lithium battery during long cycles and deterioration in cycle stability.
When the silicon source, the carbon source, the methylcellulose and the dispersing agent are mixed, a part of the methylcellulose in a powder state is added into the silicon source in a powder state and the carbon source in a powder state to form mixed powder, and the methylcellulose is fully stirred and impacted with the silicon source and the carbon source in any mixing mode such as mechanical stirring, magnetic stirring or ball milling to achieve the macro-dispersion effect. And then mixing the rest methyl cellulose with a dispersing agent to form a mixed solution, spraying the mixed solution into the mixed powder in a spraying mode, and continuously stirring and dispersing the mixed powder to transition the mixed powder from a dry powder state to a wet state, wherein in the process, stirring, friction, shearing and kneading are continuously carried out between the powder materials, and finally, the micro-dispersion effect is achieved.
The silicon source comprises silicon powder.
The carbon source comprises any one or a combination of at least two of sucrose, glucose, polyacrylic acid, polyacrylonitrile, polyethylene, polyvinyl chloride, polyethylene glycol, polyvinyl alcohol, polyaniline, epoxy resin, phenolic resin, furfural resin or acrylic resin.
The methylcellulose comprises carboxymethyl cellulose or hydroxypropyl methylcellulose.
The dispersant comprises polyacrylamide.
In a preferred embodiment of the present invention, in the step (i), the mass ratio of the total mass of the silicon source and the carbon source to the porous graphite is (0.05-0.1): 1, for example, 0.05:1, 0.055:1, 0.06:1, 0.065:1, 0.07:1, 0.075:1, 0.08:1, 0.085:1, 0.09:1, 0.095:1 or 0.1:1, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.
The inlet air temperature of the spray granulation may be 180 to 200 ℃, for example, 180 ℃, 182 ℃, 184 ℃, 186 ℃, 188 ℃, 190 ℃, 192 ℃, 194 ℃, 196 ℃, 198 ℃, or 200 ℃, but is not limited to the values listed, and other values not listed in the range are equally applicable.
The outlet temperature of the spray granulation may be 140 to 150 ℃, for example 140 ℃, 141 ℃, 142 ℃, 143 ℃, 144 ℃, 145 ℃, 146 ℃, 147 ℃, 148 ℃, 149 ℃, or 150 ℃, but is not limited to the values listed, and other values not listed in the range are equally applicable.
As a preferable technical scheme of the invention, in the step (I), the porous graphite is prepared by adopting the following method:
Mixing natural crystalline flake graphite, an intercalation agent and an oxidant to be in a viscous state at low temperature, drying the mixed solution, and calcining to obtain the porous graphite.
Firstly, adjusting an intercalation agent to a low-temperature environment, then adding natural crystalline flake graphite, and continuously stirring until the mixture is uniformly mixed to form slurry suspension; and then adding an oxidant, wherein the oxidant is preferably added in batches, so that the excessive oxidation of natural crystalline flake graphite caused by the excessive concentration of the local oxidant in a reaction system due to one-time addition is prevented, and the layered structure of the natural crystalline flake graphite is damaged.
The mass ratio of the natural crystalline flake graphite, the intercalating agent and the oxidizing agent is (1-5): (10-40): 1, for example, may be 1:10:1, 1:15:1, 1.5:20:1, 2:25:1, 2.5:30:1, 3:35:1, 3.5:40:1, 4:20:1, 4.5:30:1 or 5:40:1, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.
The intercalating agent comprises concentrated sulfuric acid or concentrated hydrochloric acid.
The oxidant comprises potassium permanganate or hydrogen peroxide.
The invention adopts potassium permanganate or hydrogen peroxide as oxidant, and has the function of destroying the edges of the natural crystalline flake graphite, so that carbon atoms on adjacent layers of the crystalline flake edges of the natural crystalline flake graphite are mutually repelled, the spacing between the layers is increased, the activation energy of intercalation reaction is reduced, and conditions are created for the intercalation agent to smoothly enter the layers of the natural crystalline flake graphite. The invention particularly limits the mass ratio range of the natural crystalline flake graphite to the oxidant, and in the range, the volume expansion rate of the natural crystalline flake graphite is improved along with the increase of the consumption of the oxidant. When the consumption of the oxidant is small, the oxidation process of the natural crystalline flake graphite is incomplete, part of crystalline flake edges of the natural crystalline flake graphite are not opened or are opened to a lower degree, and the intercalation agent entering the interlayer of the flake is less, so that the volume expansion rate of the natural crystalline flake graphite is lower, and a sufficient pore channel structure cannot be formed.
On the contrary, when the consumption of the oxidant is excessive, the lamellar structure of the natural crystalline flake graphite is excessively opened, so that the lamellar structure of the natural crystalline flake graphite is completely destroyed on one hand, and the intercalation agent originally entering the lamellar layer is escaped on the other hand, thereby reducing the volume expansion rate of the natural crystalline flake graphite. Secondly, when the consumption of the oxidant is too large, the intercalation is too strong, the intercalation is greatly consumed in a short time, the lamellar structure of most of natural crystalline flake graphite is destroyed, and the natural crystalline flake graphite becomes finer graphite particles, so that the viscosity of a reaction system is increased, and stirring is difficult. And when the consumption of the oxidant exceeds the numerical range defined by the invention, the intercalation reaction is exothermic, so that the intercalation reaction is aggravated along with the increase of the concentration of the oxidant, the temperature of a reaction system is gradually increased, and a large amount of reaction heat can cause the primary expansion of the natural crystalline graphite, so that the volume expansion rate of the natural crystalline graphite is reduced.
The intercalation degree of the intercalation agent directly relates to the volume expansion rate of the natural crystalline flake graphite, so the invention particularly limits the mass ratio range of the intercalation agent and the natural crystalline flake graphite, and when the mass ratio of the intercalation agent to the natural crystalline flake graphite is within the mass ratio range defined by the invention, the volume expansion rate of the natural crystalline flake graphite is increased along with the increase of the dosage of the intercalation agent. With the increase of the dosage of the intercalation agent, the more complete the intercalation reaction, the higher the volume expansion rate, and the more complete the pore diameter development of the pore channel structure. When the dosage of the intercalation agent is excessive, the intercalation reaction is excessive, and the lamellar structure of part of natural crystalline flake graphite is damaged; in addition, the excessive amount of the intercalating agent causes the relative decrease of the concentration of the oxidizing agent, so that the oxidation of the natural crystalline flake graphite is incomplete, the interlayer structure is difficult to open, the intercalating agent is difficult to infiltrate into the lamellar layers of the natural crystalline flake graphite, and finally the volume expansion rate of the natural crystalline flake graphite is reduced.
The temperature of the mixture is 0 to 10 ℃, and may be, for example, 0 ℃, 1 ℃, 2 ℃, 3 ℃, 4 ℃, 5 ℃, 6 ℃, 7 ℃, 8 ℃, 9 ℃, or 10 ℃, but is not limited to the values recited, and other values not recited in the range are equally applicable.
The temperature of the drying is 90 to 100 ℃, and may be 90 ℃, 91 ℃, 92 ℃, 93 ℃, 94 ℃, 95 ℃, 96 ℃, 97 ℃, 98 ℃, 99 ℃ or 100 ℃, for example, but is not limited to the values listed, and other values not listed in the range are equally applicable.
The calcination temperature may be 430 to 520 ℃, for example, 430 ℃, 440 ℃, 450 ℃, 460 ℃, 470 ℃, 480 ℃, 490 ℃, 500 ℃, 510 ℃, or 520 ℃, but is not limited to the recited values, and other values not recited in the range of values are equally applicable.
The invention is particularly limited to the calcination temperature of 430-520 ℃, and the natural crystalline flake graphite can be puffed within the temperature range. When the calcination temperature is lower than 430 ℃, the decomposition rate of the interlayer compound of the natural crystalline flake graphite is too low, the calcination is incomplete, the generated driving force is smaller, the interlayer spacing of the natural crystalline flake graphite cannot be completely opened, the interlayer spacing of the natural crystalline flake graphite cannot reach an ideal state, and a pore channel structure with the required pore size cannot be formed. When the calcining temperature is 430-520 ℃, the decomposition speed of the interlayer compound of the natural crystalline flake graphite is greatly improved along with the increasing of the calcining temperature, and the volume expansion rate of the natural crystalline flake graphite is gradually increased, so that a pore canal structure with the required pore size is formed. When the calcination temperature is higher than 520 ℃, the natural crystalline flake graphite is oxidized at high temperature, so that the volume expansion rate of the natural crystalline flake graphite is reduced.
The calcination time is 10 to 15 hours, and may be, for example, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the recited values, and other non-recited values within the range are equally applicable.
The invention is particularly limited to 10-15h of calcination time, and when the calcination time is lower than 10h, the puffing process of the natural crystalline flake graphite is incomplete; when the calcination time is higher than 15 hours, the natural crystalline flake graphite can be oxidized at high temperature, so that the volume expansion rate of the natural crystalline flake graphite is reduced.
As a preferred embodiment of the present invention, in the step (II), the mass ratio of the transition metal oxide, the binder and the solvent is 1 (0.4-0.5): (1.1-1.2), for example, but not limited to, 1:0.4:1.1, 1:0.41:1.11, 1:0.42:1.12, 1:0.43:1.13, 1:0.44:1.14, 1:0.45:1.15, 1:0.46:1.16, 1:0.47:1.17, 1:0.48:1.18, 1:0.49:1.19 or 1:0.5:1.2, and other non-enumerated values within the numerical range are equally applicable.
The transition metal oxide includes any one or a combination of at least two of zirconia, nickel oxide, iron oxide, ferroferric oxide, cobalt oxide or titanium dioxide.
The binder comprises any one or a combination of at least two of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile or polyacrylate.
The solvent comprises any one or a combination of at least two of deionized water, N-methyl pyrrolidone, tetrahydrofuran, methanol or ethanol.
According to the invention, the surface of the core particle is coated with the transition metal oxide, and the transition metal oxide can form an ion conductive network structure with high ion conductivity with the coated carbon layer formed on the surface of the core particle, so that the impedance of the anode material is effectively reduced, and the ion conductivity of the anode material is improved; meanwhile, the volume expansion of the silicon-carbon composite material in the cyclic charge and discharge process can be relieved, the interface reaction between the silicon-carbon composite material and the electrolyte is changed, and the cyclic stability and the cyclic efficiency of the cathode material are improved.
As a preferred embodiment of the present invention, in the step (II), the ball milling process is performed in a protective atmosphere.
The rotation speed of the ball mill is 700 to 800rpm, and for example, 700rpm, 710rpm, 720rpm, 730rpm, 740rpm, 750rpm, 760rpm, 770rpm, 780rpm, 790rpm or 800rpm may be used, but the rotation speed is not limited to the recited values, and other non-recited values within the range of the recited values are equally applicable.
The ball milling time is 10-12h, for example, 10.0h, 10.2h, 10.4h, 10.6h, 10.8h, 11.0h, 11.2h, 11.4h, 11.6h, 11.8h or 12.0h, but is not limited to the recited values, and other non-recited values within the range are equally applicable.
As a preferred embodiment of the present invention, in the step (iii), the sintering process includes:
heating the intermediate product to a first sintering temperature in a protective atmosphere, and preserving heat at the first sintering temperature for a period of time; then, continuously heating to a second sintering temperature, and preserving heat for a period of time at the second sintering temperature; finally, cooling to room temperature with the furnace.
The first sintering temperature is 800-1000 ℃, and can be 800 ℃, 820 ℃, 840 ℃, 860 ℃, 880 ℃, 900 ℃, 920 ℃, 940 ℃, 960 ℃, 980 ℃ or 1000 ℃ for example; the heat preservation at the first sintering temperature may be, for example, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the recited values, and other non-recited values within the range are equally applicable.
The heating rate is 3 to 5 ℃ per minute, and may be, for example, 3.0 ℃ per minute, 3.2 ℃ per minute, 3.4 ℃ per minute, 3.6 ℃ per minute, 3.8 ℃ per minute, 4.0 ℃ per minute, 4.2 ℃ per minute, 4.4 ℃ per minute, 4.6 ℃ per minute, 4.8 ℃ per minute, or 5.0 ℃ per minute, but is not limited to the recited values, and other values not recited in the range of values are equally applicable.
The second sintering temperature is 1100-1200deg.C, such as 1100 deg.C, 1110 deg.C, 1120 deg.C, 1130 deg.C, 1140 deg.C, 1150 deg.C, 1160 deg.C, 1170 deg.C, 1180 deg.C, 1190deg.C or 1200deg.C; the heat preservation at the first sintering temperature may be performed for 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours or 3.0 hours, but is not limited to the recited values, and other non-recited values within the range are equally applicable.
The invention adopts twice sintering, and can realize the in-situ compounding of the silicon-carbon composite material and the formation of the transition metal oxide coating layer.
The first sintering aims at forming a silicon-carbon composite material, and the silicon source, the carbon source and the methyl cellulose are mixed, so that the silicon source and the carbon source are embedded into a three-dimensional network structure formed by the methyl cellulose to form a silicon-carbon composite precursor, and a composite anode active material taking the methyl cellulose as a framework structure and the silicon-carbon composite material as a disperse phase is formed in the subsequent sintering process. In the first sintering process, the carbon source is softened and converted into soft carbon, the silicon source is limited by a carbon skeleton formed by the soft carbon and a three-dimensional network structure formed by the methylcellulose, and the volume expansion of the silicon in the charging and discharging process is limited by the synergistic effect of the carbon source and the methylcellulose, so that the cycle performance of the anode material is improved.
The surface defect exists in the core particles formed after the first sintering, so that the specific surface area of the core particles is overlarge, the transition metal oxide coating is carried out through the second sintering, the surfaces of the core particles are filled and coated through the transition metal oxide, and the specific surface area of the core particles is reduced. In the second sintering process, the transition metal oxide is melted by increasing the temperature to form a melt which is coated on the surfaces of the inner shell particles, and the melt is cooled to form a coating layer, so that the reduction of the specific surface area of the inner core particles can reduce the active sites on the surfaces of the porous graphite, thereby reducing the side reaction between the porous graphite and the electrolyte and improving the circulation stability.
In a second aspect, the invention provides a lithium battery composite anode material with a porous structure, wherein the lithium battery composite anode material with the porous structure is prepared by adopting the preparation method in the first aspect;
the lithium battery composite anode material with the porous structure comprises core particles and a coating layer coated on the surfaces of the core particles, wherein the core particles comprise porous graphite and a carbon coating layer formed on the outer surface of the porous graphite, and silicon-carbon composite materials are filled and dispersed in pore channels of the porous graphite.
In a preferred embodiment of the present invention, the average particle diameter of the porous graphite is 5 to 6. Mu.m, for example, 5.0. Mu.m, 5.1. Mu.m, 5.2. Mu.m, 5.3. Mu.m, 5.4. Mu.m, 5.5. Mu.m, 5.6. Mu.m, 5.7. Mu.m, 5.8. Mu.m, 5.9. Mu.m, or 6.0. Mu.m, but the present invention is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned value range are applicable.
The average pore diameter of the porous graphite is 5 to 15nm, and may be, for example, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm or 15nm, but is not limited to the recited values, and other values not recited in the range of the recited values are equally applicable.
The silicon carbon composite material may be filled in an amount of 2 to 5wt% based on the total mass of the core particles, for example, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt% or 5.0wt%, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable.
The thickness of the carbon-coated layer is 1 to 5nm, and may be, for example, 1.0nm, 1.5nm, 2.0nm, 2.5nm, 3.0nm, 3.5nm, 4.0nm, 4.5nm or 5.0nm, but is not limited to the values recited, and other values not recited in the range are equally applicable.
Graphite is widely used as a negative electrode material of a lithium battery, but the activity at the edge is larger due to the anisotropy of the height of graphite crystal and weak van der Waals force between layers, so that an SEI film formed on the surface of the graphite has non-uniformity and brittleness, the compatibility of the graphite and electrolyte is poor, the overcharge and overdischarge resistance is poor, the graphite layer is easily stripped in the lithium intercalation process, the circulation performance is poor, lithium dendrites are generated in the circulation process, and great hidden danger is brought to the safety of the battery. According to the invention, the carbon layer is coated on the surface of the porous graphite as an auxiliary interface layer, and the silicon-carbon composite material in the pore channel structure of the porous graphite is decomposed to generate the lithium-silicon alloy with high ionic conductivity and low electric conductivity after lithium intercalation, so that a three-dimensional ionic conduction path is formed, the growth of lithium dendrites is effectively inhibited, and the peeling of the graphite layer is prevented.
The thickness of the coating layer is 10 to 50nm, and may be, for example, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 50nm, but is not limited to the values recited, and other values not recited in the range are equally applicable.
According to the invention, the mass ratio of the coating slurry to the core particles is regulated, so that a coating layer with the thickness of 10-50nm is formed on the surfaces of the core particles, the first charge and discharge efficiency of the lithium battery is improved along with the increase of the thickness of the coating layer, when the thickness of the coating layer is 10-50nm, the first charge and discharge efficiency of the lithium battery is at a higher level, and the first charge and discharge efficiency of the lithium battery is reduced due to the continuous increase of the thickness of the coating layer.
When the thickness of the coating layer is lower than 10nm, the first charge and discharge efficiency of the lithium battery is lower, because when the thickness of the coating layer is lower, the surface of the inner core particle still has partially exposed porous graphite, and in the charge and discharge process, the porous graphite can generate side reaction with a solvent in the electrolyte, so the first charge and discharge efficiency is lower; when the thickness of the coating layer is higher than 50nm, although the probability of side reaction between the porous graphite and the solvent in the electrolyte is reduced, the irreversible capacity of the lithium battery is increased due to the excessively high mass fraction of the transition metal oxide in the anode material, so that the first charge and discharge efficiency of the lithium battery is reduced again.
The thickness of the coating layer can just cover the surface of the kernel particle completely when the thickness is within the range of 10-50nm, and a thinner uniform transition metal coating layer is formed on the surface of the porous graphite, so that the porous graphite is effectively prevented from directly contacting and reacting with electrolyte, the irreversible capacity caused in the SEI film forming process is reduced, and the first charge and discharge efficiency of the anode material is improved.
The invention provides a preparation method of a lithium battery composite anode material with a porous structure, which specifically comprises the following steps:
(1) Mixing natural crystalline flake graphite, an intercalator and an oxidant in a mass ratio of (1-5): 10-40): 1 to a viscous state at a temperature of 0-10 ℃; subsequently, the mixed solution is placed in an environment with the temperature of 90-100 ℃ for drying; finally, calcining for 10-15h at 430-520 ℃ to obtain porous graphite with an average particle size of 5-6 mu m, wherein the average pore diameter of the porous graphite is 5-15nm;
(2) Adding a silicon source, a carbon source and methylcellulose into a dispersing agent according to the mass ratio of (0.7-0.8) (1.6-2.3) to obtain a dispersing liquid, and uniformly mixing the dispersing liquid with the porous graphite obtained in the step (1) to obtain a mixed solution, wherein the mass ratio of the total mass of the silicon source and the carbon source in the dispersing liquid to the porous graphite is (0.05-0.1) to 1;
(3) Spraying and granulating the mixed solution obtained in the step (2) to obtain core particles, wherein the air inlet temperature of the spraying and granulating is 180-200 ℃, and the air outlet temperature is 140-150 ℃; the silicon source and the carbon source in the mixed solution form a silicon-carbon composite material and are filled into the pore canal structure of the porous graphite, and the filling amount of the silicon-carbon composite material is 2-5wt% of the total mass of the core particles; meanwhile, redundant carbon sources form a coated carbon layer with the thickness of 1-5nm on the outer surface of the porous graphite;
(4) Uniformly mixing transition metal oxide, a binder and a solvent according to the mass ratio of (0.4-0.5) (1.1-1.2) to obtain coating slurry, putting the coating slurry and the core particles obtained in the step (3) into a planetary ball mill, and mixing and ball milling for 10-12 hours at the rotating speed of 700-800rpm in a nitrogen atmosphere to obtain an intermediate product;
(5) Heating the intermediate product obtained in the step (4) to 800-1000 ℃ in nitrogen atmosphere, and preserving heat for 1-2h in the temperature environment; then, continuously heating to 1100-1200 ℃ at a heating rate of 3-5 ℃/min, and keeping the temperature for 2-3h; and finally, cooling to room temperature along with the furnace, so that a coating layer with the thickness of 10-50nm is formed on the surface of the core particle, and the lithium battery composite anode material with the porous structure is obtained.
In a third aspect, the present invention provides a lithium battery, including a housing and a cell located in the housing, wherein an electrolyte is injected into the housing; the battery cell is formed by sequentially laminating and winding a positive pole piece, a diaphragm and a negative pole piece;
the negative electrode plate comprises a negative electrode current collector and a negative electrode active layer arranged on the surface of the negative electrode current collector, wherein the negative electrode active layer comprises the lithium battery composite negative electrode material with the porous structure in the second aspect.
Compared with the prior art, the invention has the beneficial effects that:
(1) The lithium battery composite anode material with the core-shell structure is prepared by adopting the preparation method provided by the invention, and the coating layer is transition metal oxide, so that the volume expansion of the silicon-carbon composite material in the cyclic charge and discharge process can be effectively relieved, and the interface reaction between the silicon-carbon composite material and electrolyte can be improved. The inner core particles are of an embedded composite porous structure and comprise porous graphite and silicon-carbon composite materials embedded in porous graphite pore channels, ordered and mutually communicated pore channels are formed between sheets of the porous graphite, so that the storage of ions and the infiltration of electrolyte are facilitated, the silicon-carbon composite materials are in better contact with the electrolyte, and the contact surface of the silicon-carbon composite materials and the inner walls of the pore channels provides effective conductive channels for the transmission of electrons and lithium ions. The lithium battery prepared from the negative electrode material prepared by the invention has excellent charge-discharge cycle performance and rate capability.
(2) According to the invention, the silicon source, the carbon source and the porous graphite are mixed, so that the silicon-carbon composite material is distributed in the pore canal structure of the porous graphite, the silicon-carbon composite material can effectively support the pore canal structure, the collapse and the re-stacking of the pore canal of the porous graphite are prevented, and the good flexible structure of the core particles can be maintained. The porous graphite with the pore canal structure reserves space for the volume expansion of the silicon-carbon composite material in the charge-discharge process, thereby improving the first efficiency and the cycle performance of the silicon-based negative electrode material.
(3) In the spray granulation process, the amorphous carbon is uniformly coated on the surface of the porous graphite by the carbon source to form a coated carbon layer, the volume expansion effect of the silicon-carbon composite material in the charge and discharge process can be effectively limited by the coated carbon layer and the porous graphite with a three-dimensional structure, so that the lithium battery can maintain higher specific capacity, and the coated carbon layer and the porous graphite have better conductivity, thereby being beneficial to improving the conductivity of the cathode material.
(4) According to the invention, the surface of the core particle is coated with the transition metal oxide, and the transition metal oxide can form an ion conductive network structure with high ion conductivity with the coated carbon layer formed on the surface of the core particle, so that the impedance of the anode material is effectively reduced, and the ion conductivity of the anode material is improved; meanwhile, the volume expansion of the silicon-carbon composite material in the cyclic charge and discharge process can be relieved, the interface reaction between the silicon-carbon composite material and the electrolyte is changed, and the cyclic stability and the cyclic efficiency of the cathode material are improved.
Drawings
FIG. 1 is a flow chart of the preparation method provided in examples 1-12 of the present application;
FIG. 2 is an electron micrograph of porous graphite prepared in example 1 of the present application;
FIG. 3 is an electron micrograph of porous graphite prepared in example 6 of the present application;
FIG. 4 is an electron micrograph of porous graphite prepared in example 7 of the present application;
fig. 5 is a cycle chart of a lithium battery prepared in example 1 of the present application.
Detailed Description
The technical scheme of the application is described in detail below with reference to specific embodiments and attached drawings. The examples described herein are specific embodiments of the present application for illustrating the concept of the present application; the description is intended to be illustrative and exemplary in nature and should not be construed as limiting the scope of the application in its aspects. In addition to the embodiments described herein, those skilled in the art can adopt other obvious solutions based on the disclosure of the claims and the specification thereof, including those adopting any obvious substitutions and modifications to the embodiments described herein.
Example 1
The embodiment provides a preparation method of a lithium battery composite anode material with a porous structure, as shown in fig. 1, the preparation method specifically comprises the following steps:
(1) Mixing natural crystalline flake graphite, concentrated sulfuric acid and potassium permanganate to a viscous state at a mass ratio of 1:15:1 at a temperature of 0 ℃; subsequently, the mixed solution is dried in the environment of 90 ℃; finally, calcining for 15 hours at 430 ℃ to obtain porous graphite with an average particle size of 5.18 mu m, wherein the average pore diameter of the porous graphite is 5.2nm;
(2) Adding silicon powder, glucose and carboxymethyl cellulose into polyacrylamide according to the mass ratio of 0.7:1.8:1, uniformly mixing to obtain a dispersion liquid, and uniformly mixing the dispersion liquid with the porous graphite obtained in the step (1) to obtain a mixed solution, wherein the mass ratio of the total mass of the silicon powder and the glucose in the dispersion liquid to the porous graphite is 0.05:1;
(3) Carrying out spray granulation on the mixed solution obtained in the step (2) to obtain core particles, wherein the air inlet temperature of spray granulation is 180 ℃, and the air outlet temperature is 140 ℃; the silicon powder and the glucose in the mixed solution form a silicon-carbon composite material and are filled into the pore canal structure of the porous graphite, and the filling amount of the silicon-carbon composite material is 2wt% of the total mass of the core particles; meanwhile, redundant glucose forms a coated carbon layer with the thickness of 1nm on the outer surface of the porous graphite;
(4) Uniformly mixing zirconia, polyvinylidene fluoride and deionized water according to the mass ratio of 1:0.4:1.1 to obtain coating slurry, putting the coating slurry and the core particles obtained in the step (3) into a planetary ball mill, and mixing and ball milling for 12 hours at the rotating speed of 700rpm in a nitrogen atmosphere to obtain an intermediate product;
(5) Heating the intermediate product obtained in the step (4) to 800 ℃ in a nitrogen atmosphere, and preserving heat for 2 hours in the temperature environment; subsequently, the temperature was continuously increased to 1100℃at a heating rate of 3℃per minute, and at that temperature for 3 hours; and finally, cooling to room temperature along with the furnace, so that a coating layer with the thickness of 10nm is formed on the surface of the core particle, and the lithium battery composite anode material with the porous structure is obtained.
The embodiment also provides a lithium battery composite anode material with a porous structure, which is prepared by the preparation method, and comprises core particles and a coating layer coated on the surfaces of the core particles, wherein the core particles comprise porous graphite and a carbon coating layer formed on the outer surfaces of the porous graphite, and silicon-carbon composite materials are filled and dispersed in pore channels of the porous graphite.
Wherein the average particle diameter of the porous graphite is 5.18 mu m, the average pore diameter of the porous graphite is 5.2nm, the filling amount of the silicon-carbon composite material is 2wt% of the total mass of the core particle, the thickness of the coated carbon layer is 1nm, and the thickness of the coated layer is 10nm.
Example 2
The embodiment provides a preparation method of a lithium battery composite anode material with a porous structure, as shown in fig. 1, the preparation method specifically comprises the following steps:
(1) Mixing natural crystalline flake graphite, concentrated sulfuric acid and potassium permanganate to a viscous state at a mass ratio of 2:20:1 at a temperature of 2 ℃; subsequently, the mixed solution is dried in an environment with the temperature of 95 ℃; finally, calcining for 14 hours at the temperature of 450 ℃ to obtain porous graphite with the average particle diameter of 5.3 mu m, wherein the average pore diameter of the porous graphite is 8.4nm;
(2) Adding silicon powder, polyethylene and carboxymethyl cellulose into polyacrylamide according to a mass ratio of 0.72:1.6:1, uniformly mixing to obtain a dispersion liquid, and uniformly mixing the dispersion liquid and the porous graphite obtained in the step (1) to obtain a mixed solution, wherein the mass ratio of the total mass of the silicon powder and the polyethylene in the dispersion liquid to the porous graphite is 0.06:1;
(3) Carrying out spray granulation on the mixed solution obtained in the step (2) to obtain core particles, wherein the air inlet temperature of spray granulation is 185 ℃, and the air outlet temperature is 142 ℃; the silicon powder and the polyethylene in the mixed solution form a silicon-carbon composite material and are filled into the pore canal structure of the porous graphite, and the filling amount of the silicon-carbon composite material is 3wt% of the total mass of the core particles; meanwhile, redundant polyethylene forms a 2nm thick coated carbon layer on the outer surface of the porous graphite;
(4) Uniformly mixing cobalt oxide, styrene-butadiene rubber and N-methylpyrrolidone according to a mass ratio of 1:0.42:1.12 to obtain coating slurry, putting the coating slurry and the core particles obtained in the step (3) into a planetary ball mill, and mixing and ball milling for 11.5 hours at a rotating speed of 720rpm in a nitrogen atmosphere to obtain an intermediate product;
(5) Heating the intermediate product obtained in the step (4) to 850 ℃ in a nitrogen atmosphere, and preserving heat for 1.8h in the temperature environment; subsequently, the temperature was continued to rise to 1120℃at a heating rate of 3.5℃per minute and at that temperature for 2.8h; and finally, cooling to room temperature along with the furnace, so that a 20nm thick coating layer is formed on the surface of the core particle, and the lithium battery composite anode material with the porous structure is obtained.
The embodiment also provides a lithium battery composite anode material with a porous structure, which is prepared by the preparation method, and comprises core particles and a coating layer coated on the surfaces of the core particles, wherein the core particles comprise porous graphite and a carbon coating layer formed on the outer surfaces of the porous graphite, and silicon-carbon composite materials are filled and dispersed in pore channels of the porous graphite.
Wherein the average grain diameter of the porous graphite is 5.3 mu m, the average pore diameter of the porous graphite is 8.4nm, the filling amount of the silicon-carbon composite material is 3wt% of the total mass of the core particle, the thickness of the coated carbon layer is 2nm, and the thickness of the coated layer is 20nm.
Example 3
The embodiment provides a preparation method of a lithium battery composite anode material with a porous structure, as shown in fig. 1, the preparation method specifically comprises the following steps:
(1) Mixing natural crystalline flake graphite, concentrated sulfuric acid and hydrogen peroxide in a mass ratio of 3:10:1 at a temperature of 5 ℃ to a viscous state; subsequently, the mixed solution is dried in an environment with the temperature of 95 ℃; finally, calcining for 13 hours at 480 ℃ to obtain porous graphite with an average particle size of 5.57 mu m, wherein the average pore diameter of the porous graphite is 10.3nm;
(2) Adding silicon powder, polyethylene glycol and carboxymethyl cellulose into polyacrylamide according to a mass ratio of 0.75:2:1, uniformly mixing to obtain a dispersion liquid, and uniformly mixing the dispersion liquid and the porous graphite obtained in the step (1) to obtain a mixed solution, wherein the mass ratio of the total mass of the silicon powder and the polyethylene glycol in the dispersion liquid to the porous graphite is 0.07:1;
(3) Carrying out spray granulation on the mixed solution obtained in the step (2) to obtain core particles, wherein the air inlet temperature of spray granulation is 190 ℃, and the air outlet temperature is 145 ℃; silicon powder and polyethylene glycol in the mixed solution form a silicon-carbon composite material and are filled into a pore channel structure of the porous graphite, and the filling amount of the silicon-carbon composite material is 3wt% of the total mass of the core particles; meanwhile, redundant polyethylene glycol forms a 3 nm-thick coated carbon layer on the outer surface of the porous graphite;
(4) Uniformly mixing ferric oxide, polyacrylic acid and tetrahydrofuran according to the mass ratio of 1:0.45:1.15 to obtain coating slurry, putting the coating slurry and the core particles obtained in the step (3) into a planetary ball mill, and mixing and ball milling for 11 hours at the rotating speed of 750rpm in a nitrogen atmosphere to obtain an intermediate product;
(5) Heating the intermediate product obtained in the step (4) to 900 ℃ in a nitrogen atmosphere, and preserving heat for 1.5h in the temperature environment; subsequently, the temperature was continuously increased to 1150 ℃ at a heating rate of 4 ℃/min, and at that temperature for 2.5 hours; and finally, cooling to room temperature along with the furnace, so that a coating layer with the thickness of 30nm is formed on the surface of the core particle, and the lithium battery composite anode material with the porous structure is obtained.
The embodiment also provides a lithium battery composite anode material with a porous structure, which is prepared by the preparation method, and comprises core particles and a coating layer coated on the surfaces of the core particles, wherein the core particles comprise porous graphite and a carbon coating layer formed on the outer surfaces of the porous graphite, and silicon-carbon composite materials are filled and dispersed in pore channels of the porous graphite.
Wherein the average particle diameter of the porous graphite is 5.57 mu m, the average pore diameter of the porous graphite is 10.3nm, the filling amount of the silicon-carbon composite material is 3wt% of the total mass of the core particle, the thickness of the coated carbon layer is 3nm, and the thickness of the coated layer is 30nm.
Example 4
The embodiment provides a preparation method of a lithium battery composite anode material with a porous structure, as shown in fig. 1, the preparation method specifically comprises the following steps:
(1) Mixing natural crystalline flake graphite, concentrated hydrochloric acid and hydrogen peroxide to a viscous state at a mass ratio of 4:40:1 at a temperature of 8 ℃; subsequently, the mixed solution is dried in the environment of 98 ℃; finally, calcining for 12 hours at the temperature of 500 ℃ to obtain porous graphite with the average particle diameter of 5.83 mu m, wherein the average pore diameter of the porous graphite is 12.4nm;
(2) Adding silicon powder, polyvinyl alcohol and hydroxypropyl methylcellulose into polyacrylamide according to a mass ratio of 0.78:2.3:1, uniformly mixing to obtain a dispersion liquid, and uniformly mixing the dispersion liquid with the porous graphite obtained in the step (1) to obtain a mixed solution, wherein the mass ratio of the total mass of the silicon powder and the polyvinyl alcohol in the dispersion liquid to the porous graphite is 0.08:1;
(3) Carrying out spray granulation on the mixed solution obtained in the step (2) to obtain core particles, wherein the air inlet temperature of spray granulation is 195 ℃ and the air outlet temperature is 148 ℃; the silicon powder and the polyvinyl alcohol in the mixed solution form a silicon-carbon composite material and are filled into the pore canal structure of the porous graphite, and the filling amount of the silicon-carbon composite material is 4wt% of the total mass of the core particles; meanwhile, redundant polyvinyl alcohol forms a 4nm thick coated carbon layer on the outer surface of the porous graphite;
(4) Uniformly mixing ferroferric oxide, polyacrylonitrile and methanol according to the mass ratio of 1:0.48:1.18 to obtain coating slurry, putting the coating slurry and the core particles obtained in the step (3) into a planetary ball mill, and mixing and ball milling for 10.5 hours at the rotating speed of 780rpm in a nitrogen atmosphere to obtain an intermediate product;
(5) Heating the intermediate product obtained in the step (4) to 950 ℃ in a nitrogen atmosphere, and preserving heat for 1.2h in the temperature environment; subsequently, the temperature was continuously increased to 1180℃at a heating rate of 4.5℃per minute, and at that temperature for 2.2 hours; and finally, cooling to room temperature along with the furnace, so that a coating layer with the thickness of 40nm is formed on the surface of the core particle, and the lithium battery composite anode material with the porous structure is obtained.
The embodiment also provides a lithium battery composite anode material with a porous structure, which is prepared by the preparation method, and comprises core particles and a coating layer coated on the surfaces of the core particles, wherein the core particles comprise porous graphite and a carbon coating layer formed on the outer surfaces of the porous graphite, and silicon-carbon composite materials are filled and dispersed in pore channels of the porous graphite.
Wherein the average particle diameter of the porous graphite is 5.83 mu m, the average pore diameter of the porous graphite is 12.4nm, the filling amount of the silicon-carbon composite material is 4wt% of the total mass of the core particle, the thickness of the coated carbon layer is 4nm, and the thickness of the coated layer is 40nm.
Example 5
The embodiment provides a preparation method of a lithium battery composite anode material with a porous structure, as shown in fig. 1, the preparation method specifically comprises the following steps:
(1) Mixing natural crystalline flake graphite, concentrated hydrochloric acid and hydrogen peroxide to a viscous state at a mass ratio of 5:30:1 at a temperature of 10 ℃; subsequently, the mixed solution is dried in an environment with the temperature of 100 ℃; finally, calcining for 10 hours at the temperature of 520 ℃ to obtain porous graphite with the average particle diameter of 5.94 mu m, wherein the average pore diameter of the porous graphite is 14.8nm;
(2) Adding silicon powder, epoxy resin and hydroxypropyl methylcellulose into polyacrylamide according to a mass ratio of 0.8:2.2:1, uniformly mixing to obtain a dispersion liquid, and uniformly mixing the dispersion liquid with the porous graphite obtained in the step (1) to obtain a mixed solution, wherein the mass ratio of the total mass of the silicon powder and the epoxy resin in the dispersion liquid to the porous graphite is 0.1:1;
(3) Carrying out spray granulation on the mixed solution obtained in the step (2) to obtain core particles, wherein the air inlet temperature of spray granulation is 200 ℃, and the air outlet temperature is 150 ℃; the silicon powder and the epoxy resin in the mixed solution form a silicon-carbon composite material and are filled into the pore canal structure of the porous graphite, and the filling amount of the silicon-carbon composite material is 5wt% of the total mass of the core particles; meanwhile, redundant epoxy resin forms a 5nm thick coated carbon layer on the outer surface of the porous graphite;
(4) Uniformly mixing titanium dioxide, polyacrylate and ethanol according to the mass ratio of 1:0.5:1.2 to obtain coating slurry, putting the coating slurry and the core particles obtained in the step (3) into a planetary ball mill, and mixing and ball milling for 10 hours at the rotating speed of 800rpm in a nitrogen atmosphere to obtain an intermediate product;
(5) Heating the intermediate product obtained in the step (4) to 1000 ℃ in nitrogen atmosphere, and preserving heat for 1h in the temperature environment; subsequently, the temperature is continuously increased to 1200 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 2 hours; and finally, cooling to room temperature along with the furnace, so that a 50nm thick coating layer is formed on the surface of the core particle, and the lithium battery composite anode material with the porous structure is obtained.
The embodiment also provides a lithium battery composite anode material with a porous structure, which is prepared by the preparation method, and comprises core particles and a coating layer coated on the surfaces of the core particles, wherein the core particles comprise porous graphite and a carbon coating layer formed on the outer surfaces of the porous graphite, and silicon-carbon composite materials are filled and dispersed in pore channels of the porous graphite.
Wherein the average particle diameter of the porous graphite is 5.94 mu m, the average pore diameter of the porous graphite is 14.8nm, the filling amount of the silicon-carbon composite material is 5wt% of the total mass of the core particle, the thickness of the coated carbon layer is 5nm, and the thickness of the coated layer is 50nm.
Example 6
The present embodiment provides a method for preparing a porous lithium battery composite anode material, which is different from embodiment 1 in that in step (1), the mass ratio of natural crystalline flake graphite, concentrated sulfuric acid and potassium permanganate is adjusted to be 1:8:1, and other operation steps and process parameters are identical to those of embodiment 1.
Example 7
The present embodiment provides a method for preparing a porous lithium battery composite anode material, which is different from embodiment 1 in that in step (1), the mass ratio of natural crystalline flake graphite, concentrated sulfuric acid and potassium permanganate is adjusted to be 1:45:1, and other operation steps and process parameters are identical to those of embodiment 1.
Scanning electron microscope analysis is carried out on the porous graphite prepared in the embodiment 1, the embodiment 6 and the embodiment 7 to obtain electron micrographs shown in the fig. 2 (embodiment 1), the fig. 3 (embodiment 6) and the fig. 4 (embodiment 7), and it can be seen that the interlayer distance of the porous graphite in the fig. 2 is moderate, which is beneficial to embedding the silicon-carbon composite material. However, the interlayer distance of the porous graphite in fig. 3 is small, because the amount of concentrated sulfuric acid in example 6 is too small, which results in incomplete intercalation process of the natural crystalline flake graphite, insufficient delamination of part of the crystalline flake edges of the natural crystalline flake graphite, and no penetration of concentrated sulfuric acid between the flakes. The reason why the interlayer distance of the porous graphite in fig. 4 is too large is that the amount of concentrated sulfuric acid used in example 7 is too large, resulting in excessive intercalation reaction, breaking the lamellar structure of the natural crystalline flake graphite, and resulting in escape of the concentrated sulfuric acid permeated into the interlayer.
Example 8
The present embodiment provides a method for preparing a porous lithium battery composite anode material, which is different from embodiment 1 in that in step (2), the mass ratio of silicon powder, glucose and methylcellulose is adjusted to 0.5:1.8:1, and other operation steps and process parameters are identical to those of embodiment 1.
Example 9
The present embodiment provides a method for preparing a porous lithium battery composite anode material, which is different from embodiment 1 in that in step (2), the mass ratio of silicon powder, glucose and methylcellulose is adjusted to 1:1.8:1, and other operation steps and process parameters are identical to those of embodiment 1.
Example 10
The present embodiment provides a method for preparing a porous lithium battery composite anode material, which is different from embodiment 1 in that by adjusting the mass ratio of the coating slurry to the core particles in step (4), a coating layer with a thickness of 6nm is formed on the surface of the core particles, and other operation steps and process parameters are identical to those of embodiment 1.
Example 11
The present embodiment provides a method for preparing a porous lithium battery composite negative electrode material, which is different from embodiment 1 in that the mass ratio of the coating slurry to the core particles in step (4) is adjusted, so that a coating layer with a thickness of 60nm is formed on the surface of the core particles, and other operation steps and process parameters are identical to those of embodiment 1.
Example 12
The present embodiment provides a method for preparing a porous lithium battery composite anode material, which is different from embodiment 1 in that in step (5), the first sintering is omitted, the intermediate product is directly sintered for 3 hours at 1100 ℃, and other operation steps and process parameters are identical to those of embodiment 1.
The negative electrode material prepared in examples 1-12 is used for preparing a negative electrode plate, and the negative electrode plate, a diaphragm and a positive electrode plate are laminated and wound to form a battery core, and the battery core, a shell and electrolyte are assembled into a lithium battery, wherein the specific operation steps are as follows:
(1) The porous lithium battery composite anode material prepared in the examples 1-12, the conductive agent carbon black and the binder PVDF are added into N-methylpyrrolidone (NMP) according to the mass ratio of 95:2:3 and mixed uniformly to obtain anode active slurry; coating the negative electrode active slurry on the surface of a copper foil, drying for 8 hours at the temperature of 110 ℃ in a vacuum environment, and then sequentially trimming, cutting and slitting to obtain a negative electrode plate;
(2) Ternary material LiNi of nickel cobalt lithium manganate 9 Co 0.5 Mn 0.5 O 2 Adding the conductive agent SuperP, the adhesive PVDF and the carbon nano tube into NMP according to the mass ratio of 97:1:1.3:0.7, and uniformly mixing to obtain positive electrode active slurry Material preparation; coating the positive electrode active slurry on the surface of an aluminum foil, drying for 8 hours at the temperature of 110 ℃ in a vacuum environment, and then sequentially trimming, cutting and slitting to obtain a positive electrode plate;
(3) And (3) sequentially stacking the negative electrode plate obtained in the step (1), the PE diaphragm and the positive electrode plate obtained in the step (2), winding to obtain a battery cell, loading the battery cell into a shell, injecting electrolyte into the shell, wherein the electrolyte is a mixed solution (volume ratio of EC, DEC and EMC is 1:1) of Ethylene Carbonate (EC)/diethyl carbonate (DEC)/Ethyl Methyl Carbonate (EMC) containing 1mol/L LiPF6, and packaging to obtain the lithium battery.
The lithium battery prepared by the method is subjected to cyclic charge and discharge test in an environment at 25 ℃ in the following manner:
firstly, discharging to 5mV at a discharge rate of 0.5C, then discharging to 5mV at a discharge rate of 0.05C, discharging to 5mV at a discharge rate of 0.02C, then discharging to 5mV at a discharge rate of 0.01C, and finally charging to 1.5V at a charge rate of 0.1C, namely, one cycle of charge-discharge cycle, and recording the first cycle of charge specific capacity.
The charge-discharge cycle test was performed for 200 times, and the charge specific capacity of the 200 th cycle was recorded, to obtain a cycle chart shown in fig. 5. Calculating the cyclic capacity retention rate according to the first cycle cyclic charging specific capacity and the 200 th cycle cyclic charging specific capacity, wherein the calculation formula is as follows:
。
The cycle capacity retention rates of the lithium batteries prepared in examples 1 to 12 were calculated according to the above formulas, and the calculation results are shown in table 1.
TABLE 1
As can be seen from the data in table 1, the lithium battery prepared by using the lithium battery composite anode materials prepared in examples 1-5 as the anode active material has higher first charge and discharge efficiency and cycle capacity retention rate, which indicates that the composite anode material prepared by the preparation method provided by the invention has excellent charge and discharge cycle performance and rate capability.
From the test data provided in examples 1, 6 and 7, it can be seen that the amount of the intercalating agent used in example 6 is too small, which results in that the porous graphite cannot form an effective pore structure, and thus the silicon-carbon composite material cannot be effectively embedded into the porous graphite; however, the excessive amount of the intercalation agent in example 7 resulted in excessive interlayer spacing of the porous graphite, and the particle size of the porous graphite was far beyond that of the silicon-carbon composite material, so that the silicon-carbon composite material was very easy to fall off from the pores of the porous graphite, and the effective filling amount of the silicon-carbon composite material was affected.
As can be seen from the test data provided in examples 1, 8 and 9, the amount of silicon powder used in example 8 is too small, and the improvement of the first charge-discharge efficiency and the cycle capacity retention rate of the lithium battery is not obvious; in example 9, too high silicon powder is used, so that the silicon source attached to the surface of the carbon source is increased, the thickness of the silicon layer coated on the surface of the carbon source is increased, and the silicon layer is easy to fall off; in addition, the silicon source which is not attached to the surface of the carbon source exists in the reaction system in a dispersed or self-polymerized form, so that the volume expansion effect of the silicon source is aggravated by the fact that the silicon source cannot be released, and the structure of the silicon-carbon composite material is damaged.
As can be seen from the test data provided in examples 1, 10 and 11, the coating layer in example 10 is too thin to completely coat the whole surface of the core particle, and the surface of the porous graphite is still exposed with partial areas, so that the exposed surface of the porous graphite can undergo side reaction with the solvent in the electrolyte in the charge and discharge process, thereby reducing the first charge and discharge efficiency and the cycle capacity retention rate of the lithium battery; whereas the coating layer in example 11 is excessively thick, so that the irreversible capacity of the lithium battery increases, resulting in a decrease in the first charge-discharge efficiency and the cyclic capacity retention rate of the lithium battery.
From the test data provided in examples 1 and 12, it can be seen that in example 1, in-situ compounding of the silicon-carbon composite material and formation of the transition metal oxide coating layer were achieved by two sintering processes, and example 12 employed only one sintering process, resulting in insufficient reaction of the silicon source and the carbon source in the core particle to form the silicon-carbon composite material.
The applicant declares that the above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present invention disclosed by the present invention fall within the scope of the present invention and the disclosure.
Claims (10)
1. The preparation method of the lithium battery composite anode material with the porous structure is characterized by comprising the following steps of:
mixing a silicon source, a carbon source, methylcellulose and a dispersing agent to obtain a dispersion liquid, mixing the dispersion liquid with porous graphite to obtain a mixed solution, and then carrying out spray granulation to fill the silicon source and the carbon source into pore channels of the porous graphite, and simultaneously, coating the superfluous carbon source on the outer surface of the porous graphite to finally form core particles;
mixing transition metal oxide, a binder and a solvent to obtain coating slurry, and mixing and ball-milling the coating slurry and core particles to obtain an intermediate product;
and (III) sintering the intermediate product in a protective atmosphere to obtain the lithium battery composite anode material with the porous structure.
2. The method according to claim 1, wherein in the step (I), the mass ratio of the silicon source, the carbon source and the methylcellulose is (0.7-0.8): 1.6-2.3): 1;
the silicon source comprises silicon powder;
the carbon source comprises any one or a combination of at least two of sucrose, glucose, polyacrylic acid, polyacrylonitrile, polyethylene, polyvinyl chloride, polyethylene glycol, polyvinyl alcohol, polyaniline, epoxy resin, phenolic resin, furfural resin and acrylic resin;
The methyl cellulose comprises carboxymethyl cellulose or hydroxypropyl methyl cellulose;
the dispersant comprises polyacrylamide.
3. The method according to claim 1, wherein in the step (I), the mass ratio of the total mass of the silicon source and the carbon source to the porous graphite is (0.05-0.1): 1;
the air inlet temperature of the spray granulation is 180-200 ℃;
the air outlet temperature of the spray granulation is 140-150 ℃.
4. The method of claim 1, wherein in step (i), the porous graphite is prepared by:
mixing natural crystalline flake graphite, an intercalator and an oxidant to a viscous state at low temperature, drying the mixed solution, and calcining to obtain the porous graphite;
the mass ratio of the natural crystalline flake graphite to the intercalator to the oxidant is (1-5): (10-40): 1;
the intercalation agent comprises concentrated sulfuric acid or concentrated hydrochloric acid;
the oxidant comprises potassium permanganate or hydrogen peroxide;
the temperature of the mixing is 0-10 ℃;
the temperature of the drying is 90-100 ℃;
the calcining temperature is 430-520 ℃;
the calcination time is 10-15h.
5. The preparation method according to claim 1, wherein in the step (II), the mass ratio of the transition metal oxide, the binder and the solvent is 1 (0.4-0.5): 1.1-1.2;
The transition metal oxide comprises any one or a combination of at least two of zirconium oxide, nickel oxide, ferric oxide, ferroferric oxide, cobalt oxide or titanium dioxide;
the binder comprises any one or a combination of at least two of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile or polyacrylate;
the solvent comprises any one or a combination of at least two of deionized water, N-methyl pyrrolidone, tetrahydrofuran, methanol or ethanol.
6. The method of claim 1, wherein in step (ii), the ball milling process is performed in a protective atmosphere;
the rotation speed of the ball milling is 700-800rpm;
the ball milling time is 10-12h.
7. The method of claim 1, wherein in step (iii), the sintering process comprises:
heating the intermediate product to a first sintering temperature in a protective atmosphere, and preserving heat at the first sintering temperature for a period of time; then, continuously heating to a second sintering temperature, and preserving heat for a period of time at the second sintering temperature; finally, cooling to room temperature along with the furnace;
the first sintering temperature is 800-1000 ℃, and the heat preservation is carried out for 1-2h at the first sintering temperature;
The heating rate is 3-5 ℃/min;
the second sintering temperature is 1100-1200 ℃, and the heat preservation is carried out for 2-3h at the first sintering temperature.
8. A porous lithium battery composite anode material, characterized in that the porous lithium battery composite anode material is prepared by the preparation method of any one of claims 1 to 7;
the lithium battery composite anode material with the porous structure comprises core particles and a coating layer coated on the surfaces of the core particles, wherein the core particles comprise porous graphite and a carbon coating layer formed on the outer surface of the porous graphite, and silicon-carbon composite materials are filled and dispersed in pore channels of the porous graphite.
9. The lithium battery composite anode material according to claim 8, wherein the porous graphite has an average particle diameter of 5 to 6 μm;
the average diameter of pore channels of the porous graphite is 5-15nm;
the filling amount of the silicon-carbon composite material is 2-5wt% of the total mass of the core particles;
the thickness of the carbon coating layer is 1-5nm;
the thickness of the coating layer is 10-50nm.
10. A lithium battery is characterized by comprising a shell and an electric core positioned in the shell, wherein electrolyte is injected into the shell; the battery cell is formed by sequentially laminating and winding a positive pole piece, a diaphragm and a negative pole piece;
The negative electrode plate comprises a negative electrode current collector and a negative electrode active layer arranged on the surface of the negative electrode current collector, wherein the negative electrode active layer comprises the lithium battery composite negative electrode material with the porous structure as claimed in claim 8 or 9.
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