CN114447307B - 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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- CN114447307B CN114447307B CN202210124254.9A CN202210124254A CN114447307B CN 114447307 B CN114447307 B CN 114447307B CN 202210124254 A CN202210124254 A CN 202210124254A CN 114447307 B CN114447307 B CN 114447307B
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- lithium ferrite
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- 239000002131 composite material Substances 0.000 title claims abstract description 49
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 45
- 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 71
- 238000000034 method Methods 0.000 claims abstract description 28
- 229920006243 acrylic copolymer Polymers 0.000 claims abstract description 25
- 239000002904 solvent Substances 0.000 claims abstract description 24
- 229920000642 polymer Polymers 0.000 claims abstract description 22
- 239000000843 powder Substances 0.000 claims abstract description 21
- 229920005680 ethylene-methyl methacrylate copolymer Polymers 0.000 claims description 20
- 229920001577 copolymer Polymers 0.000 claims description 17
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-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
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 11
- 229910052744 lithium Inorganic materials 0.000 claims description 11
- 238000002156 mixing Methods 0.000 claims description 11
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 10
- 239000010405 anode material Substances 0.000 claims description 9
- 238000003756 stirring Methods 0.000 claims description 9
- 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
- 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 description 3
- 235000014413 iron hydroxide Nutrition 0.000 claims description 3
- MVFCKEFYUDZOCX-UHFFFAOYSA-N iron(2+);dinitrate Chemical compound [Fe+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MVFCKEFYUDZOCX-UHFFFAOYSA-N 0.000 claims description 3
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical compound [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 claims description 3
- 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
- IDBFBDSKYCUNPW-UHFFFAOYSA-N lithium nitride Chemical compound [Li]N([Li])[Li] IDBFBDSKYCUNPW-UHFFFAOYSA-N 0.000 claims 1
- 239000000758 substrate Substances 0.000 claims 1
- 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 24
- 230000000052 comparative effect Effects 0.000 description 17
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 11
- 229910001416 lithium ion Inorganic materials 0.000 description 11
- 239000011248 coating agent Substances 0.000 description 10
- 238000000576 coating method Methods 0.000 description 10
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- 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
- 229910052799 carbon Inorganic materials 0.000 description 5
- 239000012300 argon atmosphere Substances 0.000 description 4
- NDLPOXTZKUMGOV-UHFFFAOYSA-N oxo(oxoferriooxy)iron hydrate Chemical compound O.O=[Fe]O[Fe]=O NDLPOXTZKUMGOV-UHFFFAOYSA-N 0.000 description 4
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 3
- 239000010406 cathode material Substances 0.000 description 3
- 238000007600 charging Methods 0.000 description 3
- 239000011247 coating layer Substances 0.000 description 3
- -1 for example Chemical compound 0.000 description 3
- 238000004519 manufacturing process Methods 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
- 150000001335 aliphatic alkanes Chemical class 0.000 description 2
- 229910003481 amorphous carbon Inorganic materials 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 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
- 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
- 239000011241 protective layer 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
- 241001391944 Commicarpus scandens Species 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
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 238000013019 agitation Methods 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
- 229910052786 argon Inorganic materials 0.000 description 1
- 239000011230 binding agent Substances 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
- 238000010280 constant potential charging Methods 0.000 description 1
- 238000010277 constant-current charging Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 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
- 239000000463 material Substances 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
- 239000003960 organic solvent Substances 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000001105 regulatory effect Effects 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
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
- H01M4/58—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
Abstract
The invention provides a composite positive electrode 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-acrylic copolymer. According to the invention, the olefin-acrylic 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-acrylic copolymer can be uniformly dispersed in the N-methylpyrrolidone solvent when the composite positive electrode material is in the preparation process of the slurry of the positive electrode plate, and meanwhile, the lithium ferrite removal process is not influenced, and the method can effectively improve the practical application performance of the lithium ferrite.
Description
Technical Field
The invention belongs to the technical field of electrode materials, and particularly relates to a composite positive electrode material, a preparation method thereof and an electrochemical energy storage device.
Background
At present, lithium ferrite is widely used in various fields in life, and is a common positive electrode material, which has a specific capacity of up to 650mAh/g, and in order to further improve the energy density and the cycle life of the lithium ion battery, researchers supplement active lithium lost in the lithium ion battery due to Solid Electrolyte (SEI) film formation by adding a lithium ferrite supplement additive into the lithium ion battery, so that the lithium ferrite has a wide application prospect, but some problems still need to be solved in the application process at present.
In order to solve the problem that lithium ferrite powder is easy to generate side reaction with water when exposed in air, so that the serious loss of the charging capacity of the lithium ferrite is caused, a layer of amorphous carbon protective layer is coated on the surface of the lithium ferrite, so that direct contact between the lithium ferrite and moisture in the environment is avoided, the damage of the moisture to the lithium ferrite powder is reduced, and meanwhile, the conductivity of the lithium ferrite powder can be improved by coating a layer of amorphous carbon protective layer on the surface of the lithium ferrite, so that the lithium ion in the lithium ferrite is facilitated to be extracted, for example, the lithium ferrite and graphite are directly mixed and ground, and the graphite is coated on the surface of the lithium ferrite, but the method is easy to coat unevenly; and a uniform carbon layer is formed on the surface of the lithium ferrite powder by using methane or ethane and other alkane gases through a chemical vapor deposition method, but the cost of pure alkane gases is higher, which is not beneficial to the coating and application of large-scale anode materials. In addition, the hydrothermal method adopts the method that after a lithium source, a carbon source, saccharides and other organic carbon sources are uniformly mixed, the organic matters are carbonized on the surface of lithium ferrite through calcination to carry out in-situ carbon coating, however, the method easily causes a surface carbon layer to reduce ferric iron in the lithium ferrite, and capacity loss is caused to the lithium ferrite.
Therefore, in the field, it is desired to develop a positive electrode material, which not only can improve the stability of the lithium ferrite material in the air, but also has a simple preparation method, and the prepared lithium ion battery has good electrochemical performance.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a composite positive electrode material, a preparation method thereof and an electrochemical energy storage device. The composite positive electrode 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 positive electrode material.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a composite positive electrode material, the composite positive electrode material including lithium ferrite and a polymer layer coated on the surface of the lithium ferrite;
the polymer layer is an olefin-acrylic copolymer.
According to the invention, the olefin-acrylic 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-acrylic copolymer can be uniformly dispersed in the N-methylpyrrolidone solvent when the composite positive electrode material is in the preparation process of the slurry of the positive electrode plate, and meanwhile, the lithium ferrite removal process is not influenced, and the method can effectively improve the practical application performance of the lithium ferrite.
Preferably, the olefin-acrylic 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 not limited to the listed types, and the same types not listed in the range of the olefin-acrylic copolymer are applicable.
Preferably, the weight average molecular weight of the olefin-acrylic copolymer is 10000 to 100000, for example, 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.
In the invention, the weight average molecular weight of the olefin-acrylic copolymer is regulated so that the copolymer can be uniformly coated on the surface of lithium ferrite, and when the weight average molecular weight of the olefin-acrylic copolymer is too low, the lithium ferrite is coated unevenly, otherwise, the copolymer is difficult to uniformly disperse in a solvent, and lithium ferrite particles cannot be coated.
Preferably, the mass percentage of the polymer layer in the composite positive electrode material is 1-10%, for example, 1%,2%,3%,4%,5%,6%,7%,8%,9%,10%.
In the invention, the mass percentage of the polymer layer in the composite positive electrode material is adjusted to ensure that the composite positive electrode material has higher specific charge capacity and promotes lithium ion transmission, and if the mass percentage of the polymer layer in the composite positive electrode material is too low, the coating layer is too thin and is easy to break, otherwise, the coating layer is too thick, so that lithium ion transmission is difficult.
In a second aspect, the present invention provides a method for preparing the composite positive electrode material according to the first aspect, the method comprising the steps of:
mixing a lithium source with an iron source, calcining to obtain lithium ferrite powder, secondarily mixing the lithium ferrite powder with an olefin-acrylic copolymer solution, and removing a solvent to obtain the composite anode 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, for example, lithium carbonate and lithium hydroxide, lithium oxide or lithium nitride, but not limited to the listed types, and those not listed in the range of the lithium source are equally applicable.
Preferably, the iron source includes any one or a combination of at least two of iron oxide, iron hydroxide, iron nitrate or iron oxalate, and may be, for example, iron oxide and iron hydroxide, iron nitrate or iron oxalate, but not limited to the listed types, and those not listed in the range of iron sources are equally applicable.
Preferably, the mass ratio of the lithium source to the iron source is (5-10): 1, which may be, for example, 5:1,6:1,7:1,8:1,9:1, 10:1.
Preferably, the calcination temperature is 700-900 ℃, for example, 700 ℃,720 ℃,750 ℃,770 ℃,800 ℃,820 ℃,850 ℃,870 ℃,900 ℃.
Preferably, the calcination time is 8 to 12 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours.
In the present invention, the calcination is performed in air, nitrogen or argon.
Preferably, the mass concentration of the olefin-acrylic copolymer solution is 1 to 10%, for example, 1%,2%,3%,4%,5%,6%,7%,8%,9%,10%.
In the invention, the olefin-acrylic copolymer solution is prepared by dispersing olefin-acrylic copolymer into an organic solution, wherein 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 present invention, by adjusting the mass concentration of the olefin-acrylic copolymer solution, the coating layer is too thin if the mass concentration of the olefin-acrylic copolymer solution is too low, and otherwise, the dispersion is not uniform.
Preferably, the secondary mixing is performed under agitation.
Preferably, the stirring time is 30-90 min, for example, 30min,35min,40min,45min,50min,55min,60min,65min,70min,75min,80min,85min,90min.
Preferably, the pressure of the removal 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, -500kpa.
Preferably, the temperature of the solvent removal is 80-200deg.C, such as 80deg.C, 85deg.C, 90deg.C, 95deg.C, 100deg.C, 105deg.C, 110deg.C, 115deg.C, 120deg.C, 125deg.C, 130deg.C, 135deg.C, 140deg.C, 150deg.C, 130deg.C, 160deg.C, 165, 170deg.C, 175, 180deg.C, 185, 190, 195, 200deg.C.
Preferably, the solvent removal 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, the positive electrode being 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 coating an olefin-acrylic ester copolymer on the surface of lithium ferrite to form a hydrophobic polymer layer, which not only prevents water molecules from damaging the structure of lithium ferrite powder, but also can uniformly disperse the olefin-acrylic ester copolymer in N-methyl pyrrolidone solvent when the composite positive electrode material is in the preparation process of slurry of a positive electrode plate, and can not influence the lithium ferrite delithiation process, thereby effectively improving the practical application performance of lithium ferrite.
Drawings
FIG. 1 is an SEM characterization of the composite positive electrode material provided in example 1, with a scale of 1 μm;
fig. 2 is a charging graph of the composite positive electrode material provided in example 1.
Detailed Description
The technical scheme of the invention is further described below by combining the attached drawings and the specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.
Example 1
The embodiment provides a composite positive electrode material, which comprises lithium ferrite and a polymer layer of ethylene-methyl 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 5%.
The preparation method comprises the following steps:
mixing lithium carbonate and ferric oxide in a mass ratio of 7:1, calcining for 10 hours at 800 ℃ in an argon atmosphere to obtain lithium ferrite powder, dispersing 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 pressure and 140 ℃, and cooling to obtain the composite anode material.
Fig. 1 is an SEM characterization diagram of the composite cathode material provided in example 1, and it can be seen that the composite cathode material is irregular block particles.
Example 2
The embodiment provides a composite positive electrode 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 positive electrode material is 3%.
The preparation method comprises the following steps:
mixing lithium hydroxide and ferric nitrate in a 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 a weight average molecular weight of 30000 in an N, N-dimethylformamide solvent to form a propylene-methyl methacrylate copolymer solution with a mass concentration of 3%, stirring the lithium ferrite powder and the propylene-methyl methacrylate copolymer for 45 minutes, removing the solvent at-150 kpa pressure and 110 ℃, and cooling to obtain the composite anode material.
Example 3
The embodiment provides a composite positive electrode material, which comprises lithium ferrite and a polymer layer of 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 ferric oxide in a mass ratio of 8:1, calcining for 9 hours at 850 ℃ in nitrogen atmosphere to obtain lithium ferrite powder, dispersing a propylene-ethyl methacrylate copolymer with a weight average molecular weight of 70000 in an ethyl acetate solvent to form a propylene-ethyl methacrylate copolymer solution with a mass concentration of 7%, stirring the lithium ferrite powder and the propylene-ethyl methacrylate copolymer solution for 75 minutes, removing the solvent at-380 kpa pressure and 170 ℃, and cooling to obtain the composite anode material.
Example 4
The embodiment provides a composite positive electrode material, which comprises lithium ferrite and a polymer layer of ethylene-methyl 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 1%.
The preparation method comprises the following steps:
mixing lithium carbonate and ferric 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-50 kpa pressure and 80 ℃, and cooling to obtain the composite anode material.
Example 5
The embodiment provides a composite positive electrode material, which comprises lithium ferrite and a polymer layer of ethylene-methyl 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 10%.
The preparation method comprises the following steps:
mixing lithium carbonate and ferric 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 pressure and 200 ℃, and cooling to obtain the composite anode material.
Comparative example 1
This comparative example differs from example 1 in that the weight average molecular weight of the ethylene-methyl methacrylate copolymer during the production process was 5000, and the other was the same as in example 1.
Comparative example 2
This comparative example differs from example 1 in that the weight average molecular weight of the ethylene-methyl methacrylate copolymer during the production process was 150000, and the other was the same as in example 1.
Comparative example 3
This comparative example is different from example 1 in that the mass concentration of the ethylene-methyl methacrylate copolymer solution during the production process is 15%, and the other is the same as example 1.
Comparative example 4
The comparative example is different from example 1 in that the mass percentage of the polymer layer of the ethylene-methyl methacrylate copolymer in the composite positive electrode material during the preparation is 15%, and the other components are the same as example 1.
Comparative example 5
The comparative example is different from example 1 in that the mass percentage of the polymer layer of the ethylene-methyl methacrylate copolymer in the composite positive electrode material during the preparation is 0.5%, and the other is the same as example 1.
Application examples 1 to 5 and comparative application examples 1 to 5
The lithium ion batteries were prepared from the composite cathode materials provided in examples 1 to 5 and comparative examples 1 to 5, and the preparation method was as follows:
preparation of a positive plate: adding a composite anode material, carbon black as a conductive agent and polyvinylidene fluoride as a binder into a solvent according to the mass ratio of 8:1:1, fully stirring to obtain mixed slurry, uniformly coating the mixed slurry onto an aluminum foil, and drying, rolling and cutting to obtain a required anode sheet;
preparation of electrolyte: the lithium salt is adopted as 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 1mol/L;
preparation of a lithium ion battery: and assembling the prepared positive plate, the prepared diaphragm, the prepared counter electrode lithium plate and the prepared 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 the electrochemical performance test as follows:
constant-current and constant-voltage charging is carried out to 4.3V at 45 ℃ with the current density of 0.05C, a charging and discharging curve is observed to determine a lithium removal platform of lithium ferrite, and the specific capacity of the lithium ferrite charged for the first time is 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 improve the specific charge capacity of the lithium ferrite positive electrode material and reduce the damage of moisture to the structure of the lithium ferrite positive electrode material by coating the olefin-acrylic copolymer. Comparative application example 1 and comparative application example 2 show that the coating uniformity of the polymerized layer is affected by the high molecular weight of the olefin-acrylic copolymer, the olefin-acrylic copolymer is unevenly dispersed due to the higher molecular weight, and the coating is uneven due to the lower molecular weight. Comparative application example 4 and comparative application example 5 show that too much olefin-acrylic acid ester copolymer is coated on the surface of the lithium ferrite positive electrode material, the capacity exertion of the lithium ferrite positive electrode material can be influenced, too much olefin-acrylic acid ester copolymer coating can cause difficulty in lithium ion transmission, and too little olefin-acrylic acid ester coating can cause insufficient protection of the lithium ferrite positive electrode material.
The applicant states that the process of the invention is illustrated by the above examples, but the invention is not limited to, i.e. does not mean that the invention must be carried out in dependence on the above process steps. It should be apparent to those skilled in the art that any modification of the present invention, equivalent substitution of selected raw materials, addition of auxiliary components, selection of specific modes, etc. fall within the scope of the present invention and the scope of disclosure.
Claims (14)
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-acrylic copolymer;
the olefin-acrylic copolymer comprises 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;
the weight average molecular weight of the olefin-acrylic copolymer is 10000 ～ 100000；
The mass percentage of the polymer layer in the composite positive electrode material is 1 ～ 10％。
2. A method of preparing the composite positive electrode material of claim 1, comprising the steps of:
mixing a lithium source with an iron source, calcining to obtain lithium ferrite powder, secondarily mixing the lithium ferrite powder with an olefin-acrylic copolymer solution, and removing a solvent to obtain the composite anode material.
3. The method of claim 2, wherein the lithium source comprises any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium oxide, or lithium nitride.
4. The method of claim 2, wherein the iron source comprises any one or a combination of at least two of iron oxide, iron hydroxide, iron nitrate, or iron oxalate.
5. The method according to claim 2, wherein the mass ratio of the lithium source and the iron source is (5 ～ 10):1。
6. The method of claim 2, wherein the calcination temperature is 700 degrees f ～ 900℃。
7. The method of claim 2, wherein the step of determining the position of the substrate comprises,the calcination time was 8 ～ 12h。
8. The method according to claim 2, wherein the mass concentration of the olefin-acrylic copolymer solution is 1 ～ 10％。
9. The method of claim 2, wherein the secondary mixing is performed with stirring.
10. The method of claim 9, wherein the stirring is for a period of 30 ～ 90min。
11. The method according to claim 2, wherein the pressure for removing the solvent is-500 kpa ～ -50kpa。
12. The method according to claim 2, wherein the temperature of the removal solvent is 80 ～ 200℃。
13. The method of claim 2, wherein the removing the solvent further comprises a cooling process.
14. 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 claim 1.
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