CN114447307A - Composite positive electrode material, preparation method thereof and electrochemical energy storage device - Google Patents
Composite positive electrode material, preparation method thereof and electrochemical energy storage device Download PDFInfo
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- CN114447307A CN114447307A CN202210124254.9A CN202210124254A CN114447307A CN 114447307 A CN114447307 A CN 114447307A CN 202210124254 A CN202210124254 A CN 202210124254A CN 114447307 A CN114447307 A CN 114447307A
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- lithium
- positive electrode
- olefin
- electrode material
- acrylate copolymer
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- 239000002131 composite material Substances 0.000 title claims abstract description 50
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 22
- 238000012983 electrochemical energy storage Methods 0.000 title claims abstract description 7
- 238000002360 preparation method Methods 0.000 title abstract description 20
- JXGGISJJMPYXGJ-UHFFFAOYSA-N lithium;oxido(oxo)iron Chemical compound [Li+].[O-][Fe]=O JXGGISJJMPYXGJ-UHFFFAOYSA-N 0.000 claims abstract description 59
- 229920001577 copolymer Polymers 0.000 claims abstract description 43
- 239000002904 solvent Substances 0.000 claims abstract description 24
- 238000000034 method Methods 0.000 claims abstract description 23
- 229920000642 polymer Polymers 0.000 claims abstract description 22
- 239000000843 powder Substances 0.000 claims abstract description 20
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 14
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 14
- 239000010406 cathode material Substances 0.000 claims description 25
- 229920005680 ethylene-methyl methacrylate copolymer Polymers 0.000 claims description 20
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 14
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 14
- 238000001354 calcination Methods 0.000 claims description 13
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 12
- 238000002156 mixing Methods 0.000 claims description 11
- 238000003756 stirring Methods 0.000 claims description 10
- 238000001816 cooling Methods 0.000 claims description 7
- 229910052742 iron Inorganic materials 0.000 claims description 7
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 7
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 7
- 239000003792 electrolyte Substances 0.000 claims description 4
- FUJCRWPEOMXPAD-UHFFFAOYSA-N lithium oxide Chemical compound [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 claims description 3
- 229910001947 lithium oxide Inorganic materials 0.000 claims description 3
- 235000014413 iron hydroxide Nutrition 0.000 claims description 2
- VEPSWGHMGZQCIN-UHFFFAOYSA-H ferric oxalate Chemical compound [Fe+3].[Fe+3].[O-]C(=O)C([O-])=O.[O-]C(=O)C([O-])=O.[O-]C(=O)C([O-])=O VEPSWGHMGZQCIN-UHFFFAOYSA-H 0.000 claims 1
- MVFCKEFYUDZOCX-UHFFFAOYSA-N iron(2+);dinitrate Chemical compound [Fe+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MVFCKEFYUDZOCX-UHFFFAOYSA-N 0.000 claims 1
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical compound [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 claims 1
- IDBFBDSKYCUNPW-UHFFFAOYSA-N lithium nitride Chemical compound [Li]N([Li])[Li] IDBFBDSKYCUNPW-UHFFFAOYSA-N 0.000 claims 1
- 239000010405 anode material Substances 0.000 abstract description 11
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 abstract description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 4
- 229920001600 hydrophobic polymer Polymers 0.000 abstract description 3
- 239000002002 slurry Substances 0.000 abstract description 3
- 239000010410 layer Substances 0.000 description 23
- 230000000052 comparative effect Effects 0.000 description 15
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 10
- 239000011248 coating agent Substances 0.000 description 10
- 238000000576 coating method Methods 0.000 description 10
- 229910001416 lithium ion Inorganic materials 0.000 description 10
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 description 8
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 description 6
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 5
- 229910052799 carbon Inorganic materials 0.000 description 5
- 239000012300 argon atmosphere Substances 0.000 description 4
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 3
- QSNQXZYQEIKDPU-UHFFFAOYSA-N [Li].[Fe] Chemical compound [Li].[Fe] QSNQXZYQEIKDPU-UHFFFAOYSA-N 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 3
- 239000011247 coating layer Substances 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 2
- 229910002651 NO3 Inorganic materials 0.000 description 2
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 2
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 2
- 150000001335 aliphatic alkanes Chemical class 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 2
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical compound [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 description 2
- -1 lithium hexafluorophosphate Chemical group 0.000 description 2
- CASZBAVUIZZLOB-UHFFFAOYSA-N lithium iron(2+) oxygen(2-) Chemical compound [O-2].[Fe+2].[Li+] CASZBAVUIZZLOB-UHFFFAOYSA-N 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 239000011268 mixed slurry Substances 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 239000013589 supplement Substances 0.000 description 2
- BHZCMUVGYXEBMY-UHFFFAOYSA-N trilithium;azanide Chemical compound [Li+].[Li+].[Li+].[NH2-] BHZCMUVGYXEBMY-UHFFFAOYSA-N 0.000 description 2
- SCYULBFZEHDVBN-UHFFFAOYSA-N 1,1-Dichloroethane Chemical compound CC(Cl)Cl SCYULBFZEHDVBN-UHFFFAOYSA-N 0.000 description 1
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 description 1
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- QPHXCDBDXANFAU-UHFFFAOYSA-N [Li].[Li].[Fe] Chemical compound [Li].[Li].[Fe] QPHXCDBDXANFAU-UHFFFAOYSA-N 0.000 description 1
- 238000007792 addition Methods 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 239000003570 air Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 229910003481 amorphous carbon Inorganic materials 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 150000001720 carbohydrates Chemical class 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 239000006258 conductive agent Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 238000001027 hydrothermal synthesis Methods 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 229910003002 lithium salt Inorganic materials 0.000 description 1
- 159000000002 lithium salts Chemical class 0.000 description 1
- 239000012046 mixed solvent Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 239000005416 organic matter Substances 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 239000007784 solid electrolyte Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
-
- 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
- H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
- H01M4/602—Polymers
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Composite Materials (AREA)
- Crystallography & Structural Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a composite anode material, a preparation method thereof and an electrochemical energy storage device. The composite positive electrode material comprises lithium ferrite and a polymer layer coated on the surface of the lithium ferrite; the polymer layer is an olefin-acrylate copolymer. According to the invention, the olefin-acrylate copolymer is coated on the surface of the lithium ferrite to form a hydrophobic polymer layer, so that the structure of the lithium ferrite powder is prevented from being damaged by water molecules, and the olefin-acrylate copolymer can be uniformly dispersed in an N-methyl pyrrolidone solvent and cannot influence the lithium removal process of the lithium ferrite when the composite anode material is in the slurry preparation process of the anode plate.
Description
Technical Field
The invention belongs to the technical field of electrode materials, and particularly relates to a composite cathode material, a preparation method thereof and an electrochemical energy storage device.
Background
At present, lithium iron is widely applied to various fields in life, lithium iron is used as a common positive electrode material and has a specific capacity of up to 650mAh/g, in order to further improve the energy density and the cycle life of the lithium ion battery, researchers add a lithium iron lithium supplement additive into the lithium ion battery to supplement active lithium lost due to the formation of a Solid Electrolyte Interface (SEI) film in the lithium ion battery, so that the lithium iron has a wide application prospect, but some problems still exist in the application process at present and need to be solved urgently.
In order to solve the problem that lithium ferrite powder is exposed in the air and is easy to generate side reaction with water, so that the charge capacity of the lithium ferrite is seriously lost, at present, an amorphous carbon protective layer is coated on the surface of the lithium ferrite, so that the lithium ferrite is prevented from being directly contacted with moisture in the environment, and the damage of the moisture to the lithium ferrite powder is reduced; and a layer of uniform carbon layer is formed on the surface of the lithium ferrite powder by utilizing alkane gases such as methane or ethane and the like through a chemical vapor deposition method, but the cost of pure alkane gases is higher, so that the coating and the application of the anode material on a large scale are not facilitated. In addition, in the hydrothermal method, after a lithium source, a carbon source, saccharides and other organic carbon sources are uniformly mixed, an organic matter is carbonized on the surface of lithium ferrite through calcination to perform in-situ carbon coating, however, the method easily causes the surface carbon layer to reduce ferric iron in the lithium ferrite, and thus capacity loss is caused to the lithium ferrite.
Therefore, in the field, it is desirable to develop a cathode material, which not only can improve the stability of the lithium ferrite material in air, but also has a simple preparation method, and the prepared lithium ion battery has good electrochemical properties.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a composite cathode material, a preparation method thereof and an electrochemical energy storage device. The composite cathode material provided by the invention effectively solves the problems that lithium ferrite is unstable in air and is easy to absorb moisture, and improves the electrochemical performance of the composite cathode material.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a composite positive electrode material, which comprises lithium ferrite and a polymer layer coated on the surface of the lithium ferrite;
the polymer layer is an olefin-acrylate copolymer.
According to the invention, the olefin-acrylate copolymer is coated on the surface of the lithium ferrite to form a hydrophobic polymer layer, so that the structure of the lithium ferrite powder is prevented from being damaged by water molecules, and the olefin-acrylate copolymer can be uniformly dispersed in an N-methyl pyrrolidone solvent and cannot influence the lithium removal process of the lithium ferrite when the composite anode material is in the slurry preparation process of the anode plate.
Preferably, the olefin-acrylate copolymer includes any one or a combination of at least two of ethylene-methyl methacrylate copolymer, propylene-methyl methacrylate copolymer, ethylene-ethyl methacrylate, propylene-ethyl methacrylate, ethylene-propyl methacrylate, or propylene-butyl methacrylate, for example, ethylene-methyl methacrylate copolymer and propylene-methyl methacrylate copolymer, ethylene-ethyl methacrylate, or propylene-ethyl methacrylate, but is not limited to the enumerated species, and the species not enumerated in the range of the olefin-acrylate copolymer are also applicable.
Preferably, the weight average molecular weight of the olefin-acrylate copolymer is 10000 to 100000, and may be 10000, 12000, 15000, 17000, 20000, 22000, 25000, 27000, 30000, 32000, 35000, 37000, 40000, 42000, 45000, 47000, 50000, 52000, 55000, 57000, 60000, 62000, 65000, 67000, 70000, 72000, 75000, 77000, 80000, 82000, 85000, 87000, 90000, 92000, 95000, 97000, 100000, for example.
In the invention, the weight average molecular weight of the olefin-acrylate copolymer is adjusted to enable the copolymer to be uniformly coated on the surface of lithium ferrite, and if the weight average molecular weight of the olefin-acrylate copolymer is too low, the coating of the lithium ferrite is not uniform, otherwise, the copolymer is difficult to uniformly disperse in a solvent, and the lithium ferrite particles cannot be coated.
Preferably, the mass percentage content of the polymer layer in the composite cathode material is 1-10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.
In the invention, the composite anode material has higher specific charge capacity and promotes lithium ion transmission by adjusting the mass percentage of the polymer layer in the composite anode material, and if the mass percentage of the polymer layer in the composite anode material is too low, the coating layer is too thin and is easy to crack, otherwise, the coating layer is too thick, so that the lithium ion transmission is difficult.
In a second aspect, the present invention provides a method for preparing the composite positive electrode material of the first aspect, the method comprising the steps of:
and mixing a lithium source and an iron source, calcining to obtain lithium ferrite powder, mixing the lithium ferrite powder with the olefin-acrylate copolymer solution for the second time, and removing the solvent to obtain the composite cathode material.
Preferably, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium oxide or lithium nitride, such as lithium carbonate and lithium hydroxide, lithium oxide or lithium nitride, but not limited to the listed species, and species not listed in the lithium source range are equally applicable.
Preferably, the iron source comprises any one or a combination of at least two of iron oxide, hydroxide, nitrate or oxalate, such as iron oxide and hydroxide, nitrate or oxalate, but not limited to the species listed, and the species not listed in the iron source range are equally applicable.
Preferably, the mass ratio of the lithium source to the iron source is (5-10):1, and for example, may be 5:1, 6:1, 7:1, 8:1, 9:1, 10: 1.
Preferably, the calcining temperature is 700-900 ℃, for example, 700 ℃, 720 ℃, 750 ℃, 770 ℃, 800 ℃, 820 ℃, 850 ℃, 870 ℃ and 900 ℃.
Preferably, the calcination time is 8-12 h, for example, 8h, 9h, 10h, 11h, 12 h.
In the present invention, the calcination is carried out in air, nitrogen or argon.
Preferably, the olefin-acrylate copolymer solution has a mass concentration of 1 to 10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.
In the invention, the olefin-acrylate copolymer solution is prepared by dispersing the olefin-acrylate copolymer into an organic solution, and the organic solvent is selected from any one of N, N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, dichloromethane, dichloroethane, ethyl acetate or ethylene glycol dimethyl ether.
In the invention, by adjusting the mass concentration of the olefin-acrylate copolymer solution, if the mass concentration of the olefin-acrylate copolymer solution is too low, the coating layer becomes too thin, otherwise, the dispersion becomes uneven.
Preferably, the second mixing is performed under stirring.
Preferably, the stirring time is 30-90 min, for example, 30min, 35min, 40min, 45min, 50min, 55min, 60min, 65min, 70min, 75min, 80min, 85min, 90 min.
Preferably, the pressure for removing the solvent is-500 kpa to-50 kpa, for example, -50kpa, -80kpa, -100kpa, -120kpa, -140kpa, -160kpa, -180kpa, -200kpa, -220kpa, -240kpa, -260kpa, -300kpa, -320kpa, -340kpa, -360kpa, -400kpa, -420kpa, -440kpa, -460kpa, -480kpa, -500 kpa.
Preferably, the temperature of the solvent removal is 80-200 ℃, for example, 80 ℃, 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃, 120 ℃, 125 ℃, 130 ℃, 135 ℃, 140 ℃, 145 ℃, 150 ℃, 155 ℃, 160 ℃, 165 ℃, 170 ℃, 175 ℃, 180 ℃, 185 ℃, 190 ℃, 195 ℃ and 200 ℃.
Preferably, the solvent removal process further comprises a cooling treatment.
In a third aspect, the present invention provides an electrochemical energy storage device comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is the composite positive electrode material of the first aspect.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a method for forming a hydrophobic polymer layer by coating olefin-acrylate copolymer on the surface of lithium ferrite, which not only prevents water molecules from damaging the structure of lithium ferrite powder, but also prevents the olefin-acrylate copolymer from being uniformly dispersed in an N-methyl pyrrolidone solvent when a composite anode material is in the slurry preparation process of an anode plate, and simultaneously does not influence the lithium removal process of the lithium ferrite, and the method can effectively improve the practical application performance of the lithium ferrite.
Drawings
Fig. 1 is an SEM characterization of the composite cathode material provided in example 1, with a scale of 1 μm;
fig. 2 is a charge graph of the composite positive electrode material provided in example 1.
Detailed Description
The technical solution of the present invention is further explained by combining the drawings and the detailed description. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a composite cathode material, which comprises lithium ferrite and a polymer layer of an ethylene-methyl methacrylate copolymer coated on the surface of the lithium ferrite, wherein the mass percentage of the polymer layer in the composite cathode material is 5%.
The preparation method comprises the following steps:
mixing lithium carbonate and iron oxide in a mass ratio of 7:1, calcining at 800 ℃ in an argon atmosphere for 10 hours to obtain lithium ferrite powder, dispersing an ethylene-methyl methacrylate copolymer with a weight-average molecular weight of 50000 in a dimethyl sulfoxide solvent to form an ethylene-methyl methacrylate copolymer solution with a mass concentration of 5%, stirring the lithium ferrite powder and the ethylene-methyl methacrylate copolymer solution for 60 minutes, removing the solvent at-250 kpa and 140 ℃, and cooling to finally obtain the composite cathode material.
Fig. 1 is an SEM characterization of the composite cathode material provided in example 1, and it can be seen that the composite cathode material is irregular bulk particles.
Example 2
The embodiment provides a composite cathode material, which comprises lithium ferrite and a polymer layer of propylene-methyl methacrylate copolymer coated on the surface of the lithium ferrite, wherein the mass percentage of the polymer layer in the composite cathode material is 3%.
The preparation method comprises the following steps:
mixing lithium hydroxide and ferric nitrate according to the mass ratio of 6:1, calcining for 11 hours at 750 ℃ in an argon atmosphere to obtain lithium ferrite powder, dispersing a propylene-methyl methacrylate copolymer with the weight-average molecular weight of 30000 in an N, N-dimethylformamide solvent to form a propylene-methyl methacrylate copolymer solution with the mass concentration of 3%, stirring the lithium ferrite powder and the propylene-methyl methacrylate copolymer for 45 minutes, removing the solvent at the pressure of-150 kpa and the temperature of 110 ℃, and cooling to finally obtain the composite cathode material.
Example 3
The embodiment provides a composite positive electrode material, which comprises lithium ferrite and a polymer layer of a propylene-ethyl methacrylate copolymer coated on the surface of the lithium ferrite, wherein the mass percentage of the polymer layer in the composite positive electrode material is 7%.
The preparation method comprises the following steps:
mixing lithium carbonate and iron oxide in a mass ratio of 8:1, calcining at 850 ℃ for 9 hours in a nitrogen atmosphere to obtain lithium iron oxide powder, dispersing an propylene-ethyl methacrylate copolymer with the weight-average molecular weight of 70000 in an ethyl acetate solvent to form a propylene-ethyl methacrylate copolymer solution with the mass concentration of 7%, stirring the lithium iron oxide powder and the propylene-ethyl methacrylate copolymer solution for 75 minutes, removing the solvent at the pressure of-380 kpa and the temperature of 170 ℃, and cooling to finally obtain the composite cathode material.
Example 4
The embodiment provides a composite cathode material, which comprises lithium ferrite and a polymer layer of an ethylene-methyl methacrylate copolymer coated on the surface of the lithium ferrite, wherein the mass percentage of the polymer layer in the composite cathode material is 1%.
The preparation method comprises the following steps:
mixing lithium carbonate and iron oxide in a mass ratio of 5:1, calcining for 12 hours at 700 ℃ in an argon atmosphere to obtain lithium ferrite powder, dispersing an ethylene-methyl methacrylate copolymer with a weight average molecular weight of 10000 in a dimethyl sulfoxide solvent to form an ethylene-methyl methacrylate copolymer solution with a mass concentration of 1%, stirring the lithium ferrite powder and the ethylene-methyl methacrylate copolymer solution for 30 minutes, removing the solvent at a pressure of-50 kpa and a temperature of 80 ℃, and cooling to finally obtain the composite cathode material.
Example 5
The embodiment provides a composite cathode material, which comprises lithium ferrite and a polymer layer of an ethylene-methyl methacrylate copolymer coated on the surface of the lithium ferrite, wherein the mass percentage of the polymer layer in the composite cathode material is 10%.
The preparation method comprises the following steps:
mixing lithium carbonate and iron oxide in a mass ratio of 10:1, calcining for 8 hours at 900 ℃ in an argon atmosphere to obtain lithium ferrite powder, dispersing an ethylene-methyl methacrylate copolymer with a weight-average molecular weight of 100000 in a dimethyl sulfoxide solvent to form an ethylene-methyl methacrylate copolymer solution with a mass concentration of 10%, stirring the lithium ferrite powder and the ethylene-methyl methacrylate copolymer solution for 90 minutes, removing the solvent at-500 kpa and 200 ℃, and cooling to finally obtain the composite cathode material.
Comparative example 1
This comparative example is different from example 1 in that the weight average molecular weight of the ethylene-methyl methacrylate copolymer was 5000 during the preparation process, and the others were the same as example 1.
Comparative example 2
This comparative example is different from example 1 in that the weight average molecular weight of the ethylene-methyl methacrylate copolymer was 150000 during the preparation process, and the others were the same as example 1.
Comparative example 3
This comparative example is different from example 1 in that the ethylene-methyl methacrylate copolymer solution had a mass concentration of 15% during the preparation, and the rest was the same as example 1.
Comparative example 4
The comparative example is different from example 1 in that the polymer layer of the ethylene-methyl methacrylate copolymer in the composite positive electrode material was 15% by mass in the preparation process, and the rest was the same as example 1.
Comparative example 5
The comparative example is different from example 1 in that the polymer layer of the ethylene-methyl methacrylate copolymer in the composite positive electrode material was 0.5% by mass in the preparation process, and the rest was the same as example 1.
Application examples 1-5 and comparative application examples 1-5
The lithium ion batteries are prepared by the composite cathode materials provided in examples 1-5 and comparative examples 1-5, and the preparation method is as follows:
preparing a positive plate: adding the composite positive electrode material, the conductive agent carbon black and the adhesive polyvinylidene fluoride into a solvent according to the mass ratio of 8:1:1, fully stirring to obtain mixed slurry, uniformly coating the mixed slurry on an aluminum foil, and drying, rolling and cutting to obtain a required positive electrode sheet;
preparing an electrolyte: lithium salt is lithium hexafluorophosphate, and the solvent is a mixed solvent of EC and DEC with the mass ratio of 1:1, wherein the concentration of the lithium hexafluorophosphate is 1 mol/L;
preparing a lithium ion battery: and assembling the prepared positive plate, the diaphragm, the counter electrode lithium plate and the electrolyte into a button half cell, and then testing the electrochemical performance.
Test conditions
The lithium ion batteries provided in application examples 1 to 5 and comparative application examples 1 to 5 were subjected to electrochemical performance tests, the test methods were as follows:
charging to 4.3V at 45 ℃ with a constant current and a constant voltage of 0.05C, observing a charge-discharge curve to determine a lithium removal platform of the lithium ferrite, and obtaining the specific capacity of the lithium ferrite for the first charging of more than 600mAh/g as shown in figure 2.
The results of the test are shown in table 1:
TABLE 1
As can be seen from the data in table 1, the composite positive electrode materials provided in application examples 1 to 5 of the present invention can effectively increase the specific charge capacity of the lithium ferrite positive electrode material by coating the olefin-acrylate copolymer, and reduce the damage of moisture to the structure of the lithium ferrite positive electrode material. The comparison of application example 1 and application example 2 shows that the coating uniformity of the polymerized layer is affected by the molecular weight of the olefin-acrylate copolymer, the olefin-acrylate copolymer is unevenly dispersed due to higher molecular weight, and the coating is uneven when the molecular weight is lower. The comparative application example 4 and the comparative application example 5 show that the lithium ferrite anode material is coated with too much olefin-acrylate copolymer, which also affects the capacity exertion of the lithium ferrite anode material, the too thick coating of the olefin-acrylate copolymer leads to difficult lithium ion transmission, and the too little coating of the olefin-acrylate copolymer leads to insufficient protection of the lithium ferrite anode material.
The applicant states that the present invention is illustrated by the above examples of the process of the present invention, but the present invention is not limited to the above process steps, i.e. it is not meant that the present invention must rely on the above process steps to be carried out. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.
Claims (10)
1. The composite positive electrode material is characterized by comprising lithium ferrite and a polymer layer coated on the surface of the lithium ferrite;
the polymer layer is an olefin-acrylate copolymer.
2. The composite positive electrode material according to claim 1, wherein the olefin-acrylate copolymer comprises any one of or a combination of at least two of ethylene-methyl methacrylate copolymer, propylene-methyl methacrylate copolymer, ethylene-ethyl methacrylate, propylene-ethyl methacrylate, ethylene-propyl methacrylate, or propylene-butyl methacrylate;
preferably, the weight average molecular weight of the olefin-acrylate copolymer is 10000-100000.
3. The composite positive electrode material according to claim 1 or 2, wherein the polymer layer in the composite positive electrode material is 1 to 10% by mass.
4. A method of preparing the composite positive electrode material according to any one of claims 1 to 3, characterized in that the method comprises the steps of:
and mixing a lithium source and an iron source, calcining to obtain lithium ferrite powder, mixing the lithium ferrite powder with the olefin-acrylate copolymer solution for the second time, and removing the solvent to obtain the composite cathode material.
5. The method of claim 4, wherein the lithium source comprises any one of lithium carbonate, lithium hydroxide, lithium oxide, or lithium nitride, or a combination of at least two thereof;
preferably, the iron source comprises any one of iron oxide, iron hydroxide, iron nitrate or iron oxalate, or a combination of at least two thereof.
6. The method according to claim 4 or 5, wherein the mass ratio of the lithium source to the iron source is (5-10): 1.
7. The method according to any one of claims 4 to 6, wherein the temperature of the calcination is 700 to 900 ℃;
preferably, the calcining time is 8-12 h.
8. The method according to any one of claims 4 to 7, wherein the mass concentration of the olefin-acrylate copolymer solution is 1 to 10%;
preferably, the second mixing is carried out under stirring;
preferably, the stirring time is 30-90 min.
9. The method according to any one of claims 4 to 8, wherein the pressure of the solvent removal is between-500 kpa and-50 kpa;
preferably, the temperature of the solvent removal is 80-200 ℃;
preferably, the solvent removal process further comprises a cooling process.
10. An electrochemical energy storage device, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is the composite positive electrode material according to any one of claims 1 to 3.
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