CN114171729A - Preparation method of graphene-based lithium iron phosphate positive electrode material - Google Patents
Preparation method of graphene-based lithium iron phosphate positive electrode material Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 117
- 229910021389 graphene Inorganic materials 0.000 title claims abstract description 105
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 74
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 17
- 238000002360 preparation method Methods 0.000 title claims abstract description 15
- 229910000398 iron phosphate Inorganic materials 0.000 claims abstract description 48
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims abstract description 33
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 30
- 239000002131 composite material Substances 0.000 claims abstract description 25
- 238000001035 drying Methods 0.000 claims abstract description 22
- 239000002243 precursor Substances 0.000 claims abstract description 20
- 239000010406 cathode material Substances 0.000 claims abstract description 17
- 239000000203 mixture Substances 0.000 claims abstract description 16
- 238000001816 cooling Methods 0.000 claims abstract description 14
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims abstract description 13
- 229910052808 lithium carbonate Inorganic materials 0.000 claims abstract description 13
- 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 abstract description 12
- 239000008103 glucose Substances 0.000 claims abstract description 12
- 238000000034 method Methods 0.000 claims abstract description 12
- 239000012298 atmosphere Substances 0.000 claims abstract description 10
- 238000010438 heat treatment Methods 0.000 claims abstract description 10
- 229910052742 iron Inorganic materials 0.000 claims abstract description 9
- 230000008569 process Effects 0.000 claims abstract description 7
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims abstract description 6
- 238000006243 chemical reaction Methods 0.000 claims abstract description 5
- 239000007795 chemical reaction product Substances 0.000 claims abstract description 5
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 claims abstract description 5
- 238000005245 sintering Methods 0.000 claims abstract description 4
- 239000004254 Ammonium phosphate Substances 0.000 claims abstract description 3
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims abstract description 3
- LFVGISIMTYGQHF-UHFFFAOYSA-N ammonium dihydrogen phosphate Chemical compound [NH4+].OP(O)([O-])=O LFVGISIMTYGQHF-UHFFFAOYSA-N 0.000 claims abstract description 3
- 229910000387 ammonium dihydrogen phosphate Inorganic materials 0.000 claims abstract description 3
- 229910000148 ammonium phosphate Inorganic materials 0.000 claims abstract description 3
- 235000019289 ammonium phosphates Nutrition 0.000 claims abstract description 3
- 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 abstract description 3
- 238000000975 co-precipitation Methods 0.000 claims abstract description 3
- 235000019837 monoammonium phosphate Nutrition 0.000 claims abstract description 3
- 235000011007 phosphoric acid Nutrition 0.000 claims abstract description 3
- 238000000227 grinding Methods 0.000 claims description 22
- 238000001354 calcination Methods 0.000 claims description 14
- 238000002156 mixing Methods 0.000 claims description 13
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 claims description 12
- 229960005070 ascorbic acid Drugs 0.000 claims description 6
- 235000010323 ascorbic acid Nutrition 0.000 claims description 6
- 239000011668 ascorbic acid Substances 0.000 claims description 6
- 238000001914 filtration Methods 0.000 claims description 6
- 238000005406 washing Methods 0.000 claims description 6
- 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 claims description 4
- 239000003638 chemical reducing agent Substances 0.000 claims description 2
- 238000001704 evaporation Methods 0.000 claims description 2
- 230000008020 evaporation Effects 0.000 claims description 2
- 229940062993 ferrous oxalate Drugs 0.000 claims description 2
- 235000003891 ferrous sulphate Nutrition 0.000 claims description 2
- 239000011790 ferrous sulphate Substances 0.000 claims description 2
- 239000012535 impurity Substances 0.000 claims description 2
- 238000005342 ion exchange Methods 0.000 claims description 2
- OWZIYWAUNZMLRT-UHFFFAOYSA-L iron(2+);oxalate Chemical compound [Fe+2].[O-]C(=O)C([O-])=O OWZIYWAUNZMLRT-UHFFFAOYSA-L 0.000 claims description 2
- 229910000359 iron(II) sulfate Inorganic materials 0.000 claims description 2
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 claims 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 9
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 9
- 239000010405 anode material Substances 0.000 abstract description 7
- 230000007547 defect Effects 0.000 abstract description 3
- 238000004519 manufacturing process Methods 0.000 abstract description 3
- 239000000463 material Substances 0.000 description 15
- 229910052799 carbon Inorganic materials 0.000 description 12
- 239000005955 Ferric phosphate Substances 0.000 description 8
- 229940032958 ferric phosphate Drugs 0.000 description 8
- 229910000399 iron(III) phosphate Inorganic materials 0.000 description 8
- 239000002002 slurry Substances 0.000 description 8
- 238000003756 stirring Methods 0.000 description 7
- 229910052493 LiFePO4 Inorganic materials 0.000 description 6
- 238000000498 ball milling Methods 0.000 description 6
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 4
- 239000013078 crystal Substances 0.000 description 4
- 238000001291 vacuum drying Methods 0.000 description 4
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 3
- 239000013543 active substance Substances 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 239000007772 electrode material Substances 0.000 description 3
- SURQXAFEQWPFPV-UHFFFAOYSA-L iron(2+) sulfate heptahydrate Chemical compound O.O.O.O.O.O.O.[Fe+2].[O-]S([O-])(=O)=O SURQXAFEQWPFPV-UHFFFAOYSA-L 0.000 description 3
- 230000014759 maintenance of location Effects 0.000 description 3
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 2
- 239000002033 PVDF binder Substances 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 235000011114 ammonium hydroxide Nutrition 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
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- 239000003792 electrolyte Substances 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
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- 150000002500 ions Chemical class 0.000 description 2
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- 238000012360 testing method Methods 0.000 description 2
- 238000005303 weighing Methods 0.000 description 2
- 229910032387 LiCoO2 Inorganic materials 0.000 description 1
- 229910010710 LiFePO Inorganic materials 0.000 description 1
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- 229910001290 LiPF6 Inorganic materials 0.000 description 1
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 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
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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
- 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
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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
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—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
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- 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 discloses a preparation method of a graphene-based lithium iron phosphate positive electrode material, and belongs to the technical field of manufacturing of power lithium ion batteries. In the preparation process of the iron phosphate, the graphene oxide is used as a graphene source, the graphene oxide and an iron source solution for preparing the iron phosphate are uniformly mixed, then the mixture is subjected to coprecipitation reaction with phosphoric acid, ammonium phosphate or ammonium dihydrogen phosphate, and a reaction product is washed, filtered, dried, calcined and ground to prepare the graphene oxide-iron phosphate composite material; the iron source is used as an iron source for producing the lithium iron phosphate anode material, and is uniformly ground and dispersed with lithium carbonate and glucose in a ball millUniformly drying to prepare a precursor of the lithium iron phosphate at the temperature of 250 ℃ and 500 ℃ and H2/Ar/N2And (3) presintering for 3-6 hours in a reducing atmosphere, heating to 600-800 ℃, continuously sintering for 6-12 hours, and cooling along with the furnace to obtain the graphene-based lithium iron phosphate cathode material. The invention can improve the dispersibility and uniformity of the graphene in the anode material and overcome the defect that the graphene is not easy to disperse in water in the process of preparing the anode material.
Description
Technical Field
The invention relates to a preparation method of a graphene-based lithium iron phosphate positive electrode material, which is used in the technical field of manufacturing of power lithium ion batteries.
Background
With lithium ion batteries inThe expansion in practical application, the performance of the anode material directly determines the development of the lithium ion battery. Olivine structured LiFePO4The anode material has wide raw material source, low price and environmental friendliness, and has higher specific capacity and voltage platform which gradually become the main corners of the anode material of the lithium ion battery. Compared with other anode materials, LiFePO4Has relatively high safety and is more suitable for being used as a power source of a large-scale power battery. But LiFePO4As the application of the large-scale power ion battery material, the following problems still exist to be solved:
1)LiFePO4electron conductivity (10)-9S/cm) is much lower than LiCoO2(10-3S/cm) and LiMnO2(10- 5S/cm), which severely affects the diffusion of lithium ions.
2) In LiFePO4During the preparation and synthesis process, Fe is easy to generate2+The mass of the active substance is reduced, resulting in higher irreversible capacity and poor cycle performance of the material.
3) The industrial production mainly adopts a solid phase method, and the method has the defects that the prepared material has larger grain diameter and nonuniform appearance, and is not beneficial to the infiltration of electrolyte and the diffusion of lithium ions.
In response to the above problems, researchers have made a lot of efforts and made good progress, mainly including:
(1) surface modification
Refers to LiFePO4The surface of the crystal is coated with good electronic conductors (carbon, metal oxide, conductive polymer and the like) to promote the transmission of electrons or ions on the surface of the crystal, thereby improving the electrochemical performance of the material.
(2) Bulk phase doping
Doping is mainly to reduce the band gap width of the material and enhance the electronic conductivity of the bulk phase, and to induce lattice distortion and improve the diffusion rate of lithium ions in the crystal lattice.
3) Topography optimization
The main aims are to increase the reactive sites, shorten the lithium ion transfer distance, increase the tap density of the material and the like, and the method comprises the following steps: reducing the grain size, regulating and controlling crystal face, constructing a porous structure and the like.
The above-mentioned improvements improve the performance of the material to some extent, and recently, graphene, as an advanced carbon material, is considered as an ideal component of a composite electrode material due to its superior electronic conductivity, large specific surface area, and special two-dimensional structure. The previous research work shows that the LiFePO with special appearance and microstructure is designed by using the graphene as a composition unit4The graphene composite electrode material can effectively improve various electrochemical properties of the material. However, these studies are limited to using graphene as a raw material, and the graphene is added when a precursor is prepared from a lithium iron phosphate positive electrode material, so that the problems of complicated preparation process, high energy consumption, difficulty in dispersion in the precursor, and the like inherent in the production of graphene products cannot be solved.
Disclosure of Invention
The invention provides a preparation method of a graphene-based lithium iron phosphate positive electrode material, which comprises the following steps:
(1) using graphene oxide as a graphene source, uniformly mixing the graphene oxide with an iron source solution for preparing iron phosphate in the preparation process of the iron phosphate, carrying out coprecipitation reaction on the mixture and phosphoric acid, ammonium phosphate or ammonium dihydrogen phosphate, washing, filtering and drying a reaction product, wherein the drying method can be vacuum or flash evaporation drying, and then calcining and grinding the reaction product to prepare the graphene oxide-iron phosphate composite material, wherein the addition amount of the graphene oxide is 1-15% of the iron phosphate;
wherein the iron source solution for preparing the iron phosphate in the step (1) is ferric nitrate, ferrous sulfate, ferrous oxalate and the like.
(2) Taking the graphene oxide-iron phosphate composite material in the step (1) as an iron source for producing the lithium iron phosphate positive electrode material, grinding and dispersing the graphene oxide-iron phosphate composite material, lithium carbonate and glucose in a ball mill uniformly, drying to prepare a precursor of the lithium iron phosphate, and performing H ion exchange at the temperature of 250 ℃ and 500 DEG C2/Ar/N2And (3) presintering for 3-6 hours in a reducing atmosphere, heating to 600-800 ℃, continuously sintering for 6-12 hours, and cooling along with the furnace to obtain the graphene-based lithium iron phosphate cathode material.
Wherein the molar ratio of the graphene oxide-iron phosphate composite material to the Fe to Li of the lithium carbonate in the step (2) is 1:0.98-1.05, and the addition amount of the glucose is 3-20% of the mass of the prepared lithium iron phosphate.
In the step (1), graphene oxide can also be used as a graphene source, and in the preparation process of the iron phosphate, the graphene oxide and the iron phosphate after impurity removal are uniformly mixed, filtered and dried, wherein the drying method can be vacuum or flash drying, and then the graphene oxide-iron phosphate composite material is prepared after calcining and grinding, wherein the adding amount of the graphene oxide is 1-15% of that of the iron phosphate.
In the process of preparing the lithium iron phosphate precursor in the step (2), reducing agents such as ascorbic acid and the like can be added at the same time to promote the conversion of graphene oxide to graphene and improve the electrochemical performance of graphene-based lithium iron phosphate. The addition amount of the ascorbic acid is 5-10% of the mass of the prepared lithium iron phosphate.
The invention has the advantages that:
the graphene-based lithium iron phosphate cathode material prepared by the method taking the graphene oxide as the graphene source can improve the dispersibility and uniformity of the graphene in the cathode material, and overcomes the defect that the graphene is not easy to disperse in water in the process of preparing the cathode material, so that the use of an organic solvent is omitted, the technical process of reducing the graphene oxide into the graphene is combined with the sintering process of the iron phosphate and the lithium iron phosphate, and the energy consumption is effectively reduced.
The 0.2C charging and discharging specific capacity and the capacity retention rate of 1000 times of circulation under the multiplying power of 10C of the lithium battery assembled by using the graphene-based lithium iron phosphate cathode material are superior to those of the carbon-coated lithium iron phosphate cathode material widely used at present.
Drawings
Fig. 1 XRD patterns of the graphene oxide-iron phosphate composite prepared according to example 1 and iron phosphate.
Figure 2 SEM images of oxidized graphene-iron phosphate and iron phosphate prepared according to example 1,
wherein (a) graphene oxide-iron phosphate, and (b) iron phosphate.
Fig. 3 XRD patterns of the graphene-based lithium iron phosphate prepared according to example 1 and the carbon-coated lithium iron phosphate prepared according to the comparative example.
Fig. 4 is an SEM image of the graphene-based lithium iron phosphate and the carbon-coated lithium iron phosphate prepared according to example 1,
wherein (a) carbon-coated lithium iron phosphate, and (b) graphene-based lithium iron phosphate.
Fig. 5 is TEM images of graphene-based lithium iron phosphate prepared according to example 1 and carbon-coated lithium iron phosphate prepared according to a comparative example, in which (a) graphene-based lithium iron phosphate and (b) carbon-coated lithium iron phosphate.
Fig. 6 is a button cell assembly technology roadmap.
Fig. 7 is a first charge-discharge diagram of the lithium iron phosphate material prepared under different conditions at 0.2C (C is the nominal capacity of the battery).
Fig. 8 shows the rate capability of lithium iron phosphate materials prepared under different conditions.
Fig. 9 shows cycle performance of the lithium iron phosphate material 10C prepared under different conditions.
Example 1
Weighing ferrous sulfate heptahydrate, dissolving to prepare a solution, adding graphene oxide slurry, uniformly stirring, wherein the addition of graphene oxide is 5% of the mass of the prepared ferric phosphate, adding an ammonium hydrogen phosphate solution under stirring according to the molar ratio of Fe to P of 1:1.1, adjusting the pH value to 2.0-2.5 by using ammonia water, adding a surfactant OP-10 (nonionic surfactant alkylphenol polyoxyethylene ether), adding hydrogen peroxide under stirring, reacting and precipitating at 70-80 ℃ to separate out ferric phosphate, washing and filtering the generated ferric phosphate, performing vacuum drying at 100 ℃, calcining the dried sample at 500 ℃ for 4hr, cooling and grinding to obtain the graphene oxide-ferric phosphate composite material.
Mixing the composite material with lithium carbonate according to the molar ratio of Fe to Li of 1:1.01, adding glucose accounting for 10% of the mass of the lithium iron phosphate, dispersing in water at a high speed, ball-milling for 4hr, taking out the mixture, drying in vacuum at 100 ℃, grinding to prepare a precursor, and finally putting the precursor into N2Presintering for 4hr at 300 ℃ in a reducing atmosphere, heating to 700 ℃, calcining for 10hr, cooling to room temperature along with a furnace, and grinding to obtain the graphene-based lithium iron phosphate cathode material.
XRD in fig. 1 and scanning electron microscope in fig. 2 show that graphene oxide has been successfully composited with iron phosphate, and is coated on the surface of iron phosphate in a thin film manner.
After the graphene oxide-iron phosphate material is further reacted with lithium carbonate to prepare the graphene-based lithium iron phosphate positive electrode material, the XRD diagram in fig. 3 shows that the graphene oxide-iron phosphate material has a structure similar to that of carbon-coated lithium iron phosphate, but the electron microscope in fig. 4 and 5 reflects the combination of graphene and lithium iron phosphate in the graphene-based lithium iron phosphate positive electrode material, and compared with carbon-coated lithium iron phosphate, the graphene oxide-iron phosphate material is more uniform and compact, and is beneficial to better showing of electrochemical properties.
Example 2
Weighing ferrous sulfate heptahydrate, dissolving to prepare a solution, adding graphene oxide slurry, uniformly stirring, wherein the addition of graphene oxide is 10% of the mass of the prepared ferric phosphate, adding an ammonium hydrogen phosphate solution according to the molar ratio of Fe to P of 1:1.1 under stirring, adjusting the pH value to be 2.0-2.5 by using ammonia water, adding a surfactant OP-10, adding hydrogen peroxide under stirring, reacting and precipitating at 70-80 ℃ to separate out ferric phosphate, washing and filtering the generated ferric phosphate, performing vacuum drying at 100 ℃, calcining the dried sample at 500 ℃ for 4hr, cooling and grinding to obtain the graphene oxide-ferric phosphate composite material.
Mixing the composite material with lithium carbonate according to the molar ratio of Fe to Li of 1:1.01, adding glucose accounting for 7% of the mass of the lithium iron phosphate, dispersing in water at a high speed, ball-milling for 4hr, taking out the mixture, drying in vacuum at 100 ℃, grinding to prepare a precursor, and finally putting the precursor into N2Presintering for 4hr at 300 ℃ in a reducing atmosphere, heating to 700 ℃, calcining for 10hr, cooling to room temperature along with a furnace, and grinding to obtain the graphene-based lithium iron phosphate cathode material.
Example 3
And (2) mixing the iron phosphate slurry before washing with graphene oxide slurry, wherein the addition of the graphene oxide is 2% of the mass of the iron phosphate, washing and filtering the mixture, drying the dried mixture in vacuum at 100 ℃, calcining the dried sample at 500 ℃ for 4 hours, cooling and grinding the calcined sample to obtain the graphene oxide-iron phosphate composite material.
Mixing the composite material with lithium carbonate according to the molar ratio of Fe to LiMixing at a ratio of 1:1.03, adding glucose accounting for 10% of the mass of lithium iron phosphate, dispersing in water at a high speed, ball-milling for 4hr, taking out the mixture, vacuum drying at 100 ℃, grinding to obtain a precursor, and finally putting the precursor into N2Presintering for 4hr at 300 ℃ in a reducing atmosphere, heating to 700 ℃, calcining for 10hr, cooling to room temperature along with a furnace, and grinding to obtain the graphene-based lithium iron phosphate cathode material.
Example 4
And (3) mixing the washed iron phosphate slurry with graphene oxide slurry, wherein the addition amount of the graphene oxide is 12% of the mass of the iron phosphate, filtering the mixture, drying the dried mixture in vacuum at 100 ℃, calcining the dried sample at 500 ℃ for 4 hours, cooling and grinding the calcined sample to obtain the graphene oxide-iron phosphate composite material.
Mixing the composite material with lithium carbonate according to the molar ratio of Fe to Li of 1:1.01, adding glucose accounting for 6% of the mass of the lithium iron phosphate, dispersing in water at a high speed, ball-milling for 4hr, taking out the mixture, drying in vacuum at 100 ℃, grinding to prepare a precursor, and finally putting the precursor into N2Presintering for 4hr at 300 ℃ in a reducing atmosphere, heating to 700 ℃, calcining for 10hr, cooling to room temperature along with a furnace, and grinding to obtain the graphene-based lithium iron phosphate cathode material.
Example 5
Mixing the graphene oxide-iron phosphate composite material prepared in example 1 and lithium carbonate according to a molar ratio of Fe to Li of 1:1.02 mixing, adding glucose accounting for 10 percent of the mass of the lithium iron phosphate and ascorbic acid accounting for 5 percent of the mass of the lithium iron phosphate, dispersing in water at a high speed, ball-milling for 4hr, taking out the mixture, drying in vacuum at 100 ℃, grinding to prepare a precursor, and finally putting the precursor into N2Presintering for 4hr at 300 ℃ in a reducing atmosphere, heating to 700 ℃, calcining for 10hr, cooling to room temperature along with a furnace, and grinding to obtain the graphene-based lithium iron phosphate cathode material.
Example 6
And mixing the graphene oxide-iron phosphate composite material prepared in the second example and lithium carbonate according to the molar ratio of Fe to Li of 1:0.98 percent of glucose accounting for 7 percent of the mass of the lithium iron phosphate and ascorbic acid accounting for 10 percent of the mass of the lithium iron phosphate are added, the mixture is dispersed in water at a high speed, ball milled for 4 hours, the mixture is taken out to be dried in vacuum at 100 ℃, and the mixture is prepared after grindingPrecursor, finally adding the precursor into N2Presintering for 4hr at 300 ℃ in a reducing atmosphere, heating to 700 ℃, calcining for 10hr, cooling to room temperature along with a furnace, and grinding to obtain the graphene-based lithium iron phosphate cathode material.
Comparative example
Mixing battery-grade anhydrous iron phosphate and lithium carbonate according to the molar ratio of Fe to Li of 1:1.02, adding glucose accounting for 12% of the mass of the lithium iron phosphate, dispersing in water at a high speed, ball-milling for 4hr, taking out the mixture, drying in vacuum at 100 ℃, grinding to prepare a precursor, and finally putting the precursor into N2Presintering for 5hr at 400 ℃ in a reducing atmosphere, heating to 780 ℃, calcining for 10hr, cooling to room temperature along with a furnace, and grinding to obtain the carbon-coated lithium iron phosphate cathode material.
Examples of the experiments
In order to evaluate the electrochemical performance of the prepared cathode material, the prepared graphene-based lithium iron phosphate material is used as a positive electrode active substance to be assembled into a button cell, and a novice cell test system (BTS-5V/1-100mA) is adopted to carry out constant current charge/discharge and rate capability and cycle performance tests.
The button cell assembly technology route is shown in figure 6.
The composite electrode material is prepared by mixing active substances, a conductive agent and a binding agent polyvinylidene fluoride (PVDF, which is dissolved in N-methyl-2-pyrrolidone NMP and is used as a 5 wt% solution in an experiment) in a mass ratio of 8:1:1, stirring at a high speed for 20 minutes by using a homogenizer to prepare slurry, coating the slurry on an aluminum foil serving as a current collector, and transferring the coated pole piece into a drying oven to dry for 4 hours at 80 ℃. The dried pole piece is cut, rolled, weighed, placed in a vacuum drying oven for drying at 100 ℃ for 12 hours, and then moved into an argon atmosphere protective glove box. The prepared electrode plate is used as a positive electrode, a metal lithium plate is used as a negative electrode, a polypropylene porous material Celgard2300 is used as a diaphragm, and 1.0 mol.L of electrolyte is adopted-1The solute of (A) is LiPF6The solvent is EC + DEC + DMC (the volume ratio of the EC + DEC + DMC is 1:1:1), and the model of the assembled button cell is CR 2032.
Constant-current charge and discharge tests are carried out on the battery at the temperature of 20 +/-2 ℃ within the voltage range of 2.5V-4.2V, and fig. 7 is a charge and discharge curve at the time of 0.2C, the reversible specific capacity of the graphene-based lithium iron phosphate exceeds 160mAh/g, and the battery has higher charge and discharge specific capacity than the carbon-coated lithium iron phosphate.
Fig. 8 shows that the large-rate charge-discharge performance of the graphene-based lithium iron phosphate is excellent, and the specific charge capacities of the graphene-based lithium iron phosphate at 1C,5C,10C and 20C reach 153mAh/g, 140mAh/g, 127mAh/g and 114 mAh/g.
Fig. 9 shows that after 1000 cycles under the condition of 10C, the specific capacity of the graphene-based lithium iron phosphate positive electrode material still has 118mAh/g, and the retention rate reaches 92% compared with the initial charging specific capacity of 128mAh/g, after 1000 cycles under the condition of 10C, the retention rate of the charging specific capacity of the carbon-coated lithium iron phosphate positive electrode material is 82%, and the graphene-based lithium iron phosphate positive electrode material has more excellent cycle performance.
Claims (5)
1. A preparation method of a graphene-based lithium iron phosphate positive electrode material is characterized by comprising the following steps:
(1) using graphene oxide as a graphene source, uniformly mixing the graphene oxide with an iron source solution for preparing iron phosphate in the preparation process of the iron phosphate, carrying out coprecipitation reaction on the mixture and phosphoric acid, ammonium phosphate or ammonium dihydrogen phosphate, washing, filtering and drying a reaction product, wherein the drying method can be vacuum or flash evaporation drying, and then calcining and grinding the reaction product to prepare the graphene oxide-iron phosphate composite material, wherein the addition amount of the graphene oxide is 1-15% of the iron phosphate;
(2) taking the graphene oxide-iron phosphate composite material in the step (1) as an iron source for producing the lithium iron phosphate positive electrode material, grinding and dispersing the graphene oxide-iron phosphate composite material, lithium carbonate and glucose in a ball mill uniformly, drying to prepare a precursor of the lithium iron phosphate, and performing H ion exchange at the temperature of 250 ℃ and 500 DEG C2/Ar/N2And (3) presintering for 3-6 hours in a reducing atmosphere, heating to 600-800 ℃, continuously sintering for 6-12 hours, and cooling along with the furnace to obtain the graphene-based lithium iron phosphate cathode material.
2. The method for preparing a graphene-based lithium iron phosphate cathode material according to claim 1, wherein the iron source solution for preparing the iron phosphate in the step (1) is ferric nitrate, ferrous sulfate or ferrous oxalate.
3. The method for preparing the graphene-based lithium iron phosphate positive electrode material according to claim 1, wherein the molar ratio of Fe to Li of the graphene oxide-iron phosphate composite material to the lithium carbonate in the step (2) is 1:0.98-1.05, and the addition amount of glucose is 3-20% of the mass of the prepared lithium iron phosphate.
4. The preparation method of the graphene-based lithium iron phosphate positive electrode material according to claim 1, wherein in the step (1), graphene oxide can be used as a graphene source, and in the preparation process of iron phosphate, the graphene oxide and the iron phosphate after impurity removal are uniformly mixed, filtered, dried, and the drying method can be vacuum or flash drying, and then the mixture is calcined and ground to prepare the graphene oxide-iron phosphate composite material, wherein the amount of the added graphene oxide is 1-15% of the amount of the iron phosphate.
5. The preparation method of the graphene-based lithium iron phosphate positive electrode material according to claim 1, wherein in the process of preparing the lithium iron phosphate precursor in the step (2), a reducing agent such as ascorbic acid can be added at the same time to promote the conversion of graphene oxide to graphene and improve the electrochemical performance of the graphene-based lithium iron phosphate; the addition amount of the ascorbic acid is 5-10% of the mass of the prepared lithium iron phosphate.
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| CN116154152A (en) * | 2022-12-16 | 2023-05-23 | 贵州胜泽威化工有限公司 | Lithium iron phosphate battery positive electrode slurry and preparation method thereof |
| CN117558903A (en) * | 2024-01-11 | 2024-02-13 | 湖南科晶新能源科技有限公司 | Preparation method of graphene coated lithium iron phosphate |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116154152A (en) * | 2022-12-16 | 2023-05-23 | 贵州胜泽威化工有限公司 | Lithium iron phosphate battery positive electrode slurry and preparation method thereof |
| CN116154152B (en) * | 2022-12-16 | 2023-12-26 | 贵州胜泽威化工有限公司 | Lithium iron phosphate battery positive electrode slurry and preparation method thereof |
| CN117558903A (en) * | 2024-01-11 | 2024-02-13 | 湖南科晶新能源科技有限公司 | Preparation method of graphene coated lithium iron phosphate |
| CN117558903B (en) * | 2024-01-11 | 2024-04-02 | 湖南科晶新能源科技有限公司 | Preparation method of graphene coated lithium iron phosphate |
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