CN112607725A - Nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite positive electrode material and preparation method thereof - Google Patents
Nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite positive electrode material and preparation method thereof Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 71
- 239000002041 carbon nanotube Substances 0.000 title claims abstract description 69
- 229910021393 carbon nanotube Inorganic materials 0.000 title claims abstract description 69
- 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 59
- 229910052761 rare earth metal Inorganic materials 0.000 title claims abstract description 50
- 150000002910 rare earth metals Chemical class 0.000 title claims abstract description 28
- 239000002131 composite material Substances 0.000 title claims abstract description 15
- 238000002360 preparation method Methods 0.000 title claims abstract description 10
- 239000007774 positive electrode material Substances 0.000 title claims description 6
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims abstract description 39
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims abstract description 39
- 238000000498 ball milling Methods 0.000 claims abstract description 29
- 239000000463 material Substances 0.000 claims abstract description 26
- -1 rare earth metal ion Chemical class 0.000 claims abstract description 22
- NWZSZGALRFJKBT-KNIFDHDWSA-N (2s)-2,6-diaminohexanoic acid;(2s)-2-hydroxybutanedioic acid Chemical compound OC(=O)[C@@H](O)CC(O)=O.NCCCC[C@H](N)C(O)=O NWZSZGALRFJKBT-KNIFDHDWSA-N 0.000 claims abstract description 14
- IKDUDTNKRLTJSI-UHFFFAOYSA-N hydrazine monohydrate Substances O.NN IKDUDTNKRLTJSI-UHFFFAOYSA-N 0.000 claims abstract description 14
- 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 13
- 239000008103 glucose Substances 0.000 claims abstract description 13
- 229910000398 iron phosphate Inorganic materials 0.000 claims abstract description 13
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims abstract description 13
- 235000006408 oxalic acid Nutrition 0.000 claims abstract description 13
- 239000010406 cathode material Substances 0.000 claims abstract description 10
- 238000004108 freeze drying Methods 0.000 claims abstract description 9
- 238000010992 reflux Methods 0.000 claims abstract description 9
- 229910001404 rare earth metal oxide Inorganic materials 0.000 claims abstract description 7
- 239000006185 dispersion Substances 0.000 claims abstract description 5
- 239000007788 liquid Substances 0.000 claims abstract description 5
- WQZGKKKJIJFFOK-VFUOTHLCSA-N beta-D-glucose Chemical compound OC[C@H]1O[C@@H](O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-VFUOTHLCSA-N 0.000 claims abstract description 3
- 238000000967 suction filtration Methods 0.000 claims abstract description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 47
- 239000000203 mixture Substances 0.000 claims description 41
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 36
- 238000001816 cooling Methods 0.000 claims description 32
- 238000001035 drying Methods 0.000 claims description 32
- 239000008367 deionised water Substances 0.000 claims description 26
- 229910021641 deionized water Inorganic materials 0.000 claims description 26
- 238000010438 heat treatment Methods 0.000 claims description 16
- 238000001354 calcination Methods 0.000 claims description 15
- 239000007787 solid Substances 0.000 claims description 10
- 238000000034 method Methods 0.000 claims description 9
- 238000003756 stirring Methods 0.000 claims description 8
- 238000005406 washing Methods 0.000 claims description 8
- 238000001132 ultrasonic dispersion Methods 0.000 claims description 7
- YBMRDBCBODYGJE-UHFFFAOYSA-N germanium dioxide Chemical group O=[Ge]=O YBMRDBCBODYGJE-UHFFFAOYSA-N 0.000 claims description 4
- 238000011282 treatment Methods 0.000 claims description 4
- 238000005292 vacuum distillation Methods 0.000 claims description 3
- 238000006243 chemical reaction Methods 0.000 claims description 2
- CMIHHWBVHJVIGI-UHFFFAOYSA-N gadolinium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[Gd+3].[Gd+3] CMIHHWBVHJVIGI-UHFFFAOYSA-N 0.000 claims description 2
- FKTOIHSPIPYAPE-UHFFFAOYSA-N samarium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[Sm+3].[Sm+3] FKTOIHSPIPYAPE-UHFFFAOYSA-N 0.000 claims description 2
- 238000000926 separation method Methods 0.000 claims description 2
- ZIKATJAYWZUJPY-UHFFFAOYSA-N thulium (III) oxide Inorganic materials [O-2].[O-2].[O-2].[Tm+3].[Tm+3] ZIKATJAYWZUJPY-UHFFFAOYSA-N 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 3
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 8
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 8
- 239000012467 final product Substances 0.000 abstract description 2
- 238000002156 mixing Methods 0.000 abstract 1
- 239000002994 raw material Substances 0.000 abstract 1
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 16
- 238000001914 filtration Methods 0.000 description 12
- 229910052757 nitrogen Inorganic materials 0.000 description 8
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 4
- 229910000420 cerium oxide Inorganic materials 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 3
- 230000002195 synergetic effect Effects 0.000 description 3
- 239000003990 capacitor Substances 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 125000000524 functional group Chemical group 0.000 description 2
- 238000002715 modification method Methods 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 239000002360 explosive Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 239000010450 olivine Substances 0.000 description 1
- 229910052609 olivine Inorganic materials 0.000 description 1
- 239000005416 organic matter Substances 0.000 description 1
- 230000027756 respiratory electron transport chain Effects 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/15—Nano-sized carbon materials
- C01B32/158—Carbon nanotubes
- C01B32/168—After-treatment
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/45—Phosphates containing plural metal, or metal and ammonium
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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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- 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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Abstract
The invention discloses a nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite cathode material and a preparation method thereof, which are applied to the field of lithium ion batteries. The preparation method of the material comprises the following steps: mixing hydrazine hydrate and carbon nano tubes, and then carrying out reflux, suction filtration and freeze drying to prepare nitrogen-doped carbon nano tubes; preparing rare earth metal ion doped lithium iron phosphate by using lithium hydroxide, iron phosphate, oxalic acid, glucose and rare earth metal oxide as raw materials; and finally, adding the nitrogen-doped carbon nanotube and the rare earth metal ion-doped lithium iron phosphate into the dispersion liquid for dispersing and ball-milling to obtain a final product. Compared with the traditional lithium iron phosphate, the nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite cathode material prepared by the invention has excellent rate charge and discharge performance.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite cathode material and a preparation method thereof.
Background
With the rapid development of new energy vehicles and UPS power supply energy storage industries, the demand of lithium batteries is greatly stimulated. Compared with the traditional battery, the lithium ion battery is charged more quickly, and longer battery service time can be realized through higher power density; compared with ternary material batteries, the battery has higher safety. The cost and performance of the lithium ion battery are mainly influenced by the anode material, so that the olivine type lithium iron phosphate with low cost, environmental protection, high specific energy and high cycle characteristic is very concerned, and simultaneously, the lithium ion battery has relatively high safety performance: the puncture is not explosive, and the explosion and the burning are not easy to happen during the overcharge. However, the lithium iron phosphate is influenced by its own structure, and its ion mobility is low, thereby influencing the cycle capacity and the rate charge and discharge performance of the battery.
At present, the modes for improving the conductivity of lithium iron phosphate and the diffusion rate of Li + in the lithium iron phosphate are mainly modification, and the modification method comprises the steps of doping conductive carbon or coating carbon on the surface of lithium iron phosphate particles, coating metal, doping metal ions, controlling the particle size and the like. However, the existing modification method still has limitations on the performance improvement of the final product, and how to further improve the performance of the lithium iron phosphate material is a technical problem to be solved urgently.
Disclosure of Invention
The invention aims to provide a nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite positive electrode material and a preparation method thereof, wherein nitrogen doping is carried out on a carbon nanotube, so that the hydrophilicity of the carbon nanotube can be improved, and nitrogen-doped atoms can change the local charge density of the carbon nanotube, improve the electron transferability of the carbon nanotube and reduce the resistance coefficient; meanwhile, the specific capacity of the carbon nanotube electrochemical capacitor can be obviously improved by nitrogen-containing functional groups introduced by nitrogen doping; by simultaneously introducing the nitrogen-doped carbon nanotube and the rare earth metal ions into the lithium iron phosphate material, a product with more excellent performance is prepared by utilizing the synergistic effect generated by the nitrogen-doped carbon nanotube and the rare earth metal ions.
In order to achieve the purpose, the invention adopts the technical scheme that:
a preparation method of a nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite cathode material is characterized by comprising the following steps of: the method comprises the following steps:
(1) dispersing hydrazine hydrate and carbon nano tubes in deionized water to obtain a mixture, heating the mixture to carry out reflux reaction for 5-7h, carrying out suction filtration and separation to obtain a solid, and sequentially carrying out water washing and freeze drying on the solid to obtain nitrogen-doped carbon nano tubes; hydrazine hydrate is a high nitrogen-containing organic matter, and the intrinsic structure and the morphology of the hydrazine hydrate are not damaged while effective nitrogen doping is realized;
(2) preparing rare earth metal ion doped lithium iron phosphate, then simultaneously adding the rare earth metal ion doped lithium iron phosphate and the nitrogen-doped carbon nano tube into a dispersion liquid for ultrasonic dispersion, adding the material subjected to ultrasonic dispersion into a ball milling tank for ball milling treatment, drying and cooling the material obtained by ball milling treatment to room temperature to obtain the nitrogen-doped carbon nano tube/rare earth metal ion doped lithium iron phosphate composite cathode material.
As a preferable technical scheme, in the step (1), the mass ratio of hydrazine hydrate, carbon nano-tubes and deionized water is 0.5-2:500-2000: 200.
As a preferred technical scheme, in the step (2), the method for preparing the rare earth metal ion-doped lithium iron phosphate comprises the following steps: adding lithium hydroxide, iron phosphate, oxalic acid, glucose and deionized water into a three-neck flask, then adding rare earth metal oxide into the three-neck flask, heating the mixture to 80-90 ℃ in a water bath under the condition of rapid stirring, keeping the temperature for 3-5 hours, cooling the mixture to room temperature, then carrying out vacuum distillation to 70-80 ℃, taking out the mixture, drying the mixture, then adding ethanol into the mixture, carrying out ball milling for 2-3 hours, drying the mixture, and placing the mixture into N2Calcining at 400 deg.C for 3-5 hr under protection, cooling to room temperature, taking out, adding ethanol, ball milling for 4-6 hr, drying, and placing in N2Calcining the mixture for 8 to 10 hours in a tubular muffle furnace under protection at the temperature of 500-700 ℃, and cooling to obtain the rare earth metal ion doped lithium iron phosphate. More preferably, the mass ratio of the lithium hydroxide, the iron phosphate, the oxalic acid, the glucose and the deionized water is 1: 5-6: 9-10: 0.5-1: 15-2. The rare earth metal oxide is GeO2、Tm2O3、Sm2O3、Gd2O3At least one of (1). The addition amount of the rare earth metal oxide is 1-5% of the total mass of the lithium hydroxide, the iron phosphate, the oxalic acid and the glucose.
According to the preferable technical scheme, the mass ratio of the doped carbon nanotube to the rare earth metal ion doped lithium iron phosphate is 1: 30-40; the dispersion liquid is ethanol.
The invention also provides the nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite cathode material prepared by the preparation method.
The invention has the following beneficial effects:
(1) the carbon nano tube has ultrahigh mechanical property and huge specific surface area, and the invention adopts high nitrogen-containing organic hydrazine hydrate as a nitrogen source to carry out nitrogen doping on the carbon nano tube, thereby realizing effective nitrogen doping without damaging the intrinsic structure and appearance of the carbon nano tube; the carbon nano tube is doped with nitrogen, so that the hydrophilicity of the carbon nano tube can be improved, and nitrogen-doped atoms can change the local charge density of the carbon nano tube, improve the electron transfer property of the carbon nano tube and reduce the resistance coefficient; meanwhile, the specific capacity of the carbon nanotube electrochemical capacitor can be obviously improved by nitrogen-containing functional groups introduced by nitrogen doping; by simultaneously introducing the nitrogen-doped carbon nanotube and the rare earth metal ions into the lithium iron phosphate material, the rare earth metal ion-doped lithium iron phosphate is combined with the one-dimensional tubular structure of the carbon nanotube, and the transmission rate of lithium ions can be well enhanced by utilizing the synergistic effect generated by the nitrogen-doped carbon nanotube and the rare earth metal ions, so that the multiplying power charge-discharge performance of the battery is effectively improved, and a product with more excellent performance is prepared.
(2) By doping the rare earth metal ions to the lithium iron phosphate, the diffusion channel of the lithium ions can be effectively expanded.
(3) The components in the prepared composite cathode material can generate a synergistic effect, and the composite cathode material has more excellent electrical property compared with the traditional lithium iron phosphate material.
Drawings
FIG. 1 is a first charge-discharge curve (2.0-4.5V) of a battery prepared by doping nitrogen-doped carbon nanotubes/rare earth metal ion with lithium iron phosphate prepared in example 1;
FIGS. 2 to 6 are first charge-discharge curves (2.0 to 4.5V) of the batteries manufactured by the nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate prepared in examples 2 to 6, respectively;
FIG. 7 shows the first charge-discharge curve (2.0-4.5V) of a battery made of lithium iron phosphate without any modification.
Detailed Description
The present invention will be further described with reference to the following examples and the accompanying drawings. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the following examples, the starting materials and reagents used are commercially available.
Example 1:
(1) adding 25ml of hydrazine hydrate with solute mass fraction of 30% into 50ml of deionized water, adding 300mg of carbon nano tube, heating and refluxing for 6 hours at 60 ℃, washing and filtering with deionized water, and freeze-drying the solid obtained by filtering to obtain the nitrogen-doped carbon nano tube.
(2) Adding 5.0g of lithium hydroxide, 30.0g of iron phosphate, 50.0g of oxalic acid, 5.0g of glucose and 10.0g of deionized water into a three-neck flask together, then adding 4.5g of cerium oxide into the three-neck flask, heating the three-neck flask to 90 ℃ in a water bath under rapid stirring, keeping the temperature for 5 hours, cooling the three-neck flask to room temperature, distilling the three-neck flask to 80 ℃ in vacuum, taking out and drying the three-neck flask, then adding ethanol into the materials and carrying out ball milling on the materials for 3 hours, drying the materials, and placing the materials into N2Calcining at 400 deg.C for 5 hr in a protected tubular muffle furnace, cooling to room temperature, taking out, adding ethanol, ball milling for 6 hr, drying, and placing in N2Calcining the mixture for 10 hours at 700 ℃ in a protected tubular muffle furnace, and cooling to obtain the rare earth metal ion doped lithium iron phosphate.
(3)2g of nitrogen-doped carbon nano tube and 60g of rare earth metal ion-doped lithium iron phosphate are added with BIn a container of alcohol, ultrasonically dispersed for 3 hours, and then N2Ball milling for 10 hours under protection, finally drying the ball milled materials for 20 hours at 80 ℃, and cooling to room temperature to obtain the nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate.
Example 2:
(1) adding 50ml of hydrazine hydrate with solute mass fraction of 30% into 50ml of deionized water, adding 300mg of carbon nano tube, heating and refluxing for 6 hours at 60 ℃, washing and filtering with deionized water, and freeze-drying the solid obtained by filtering to obtain the nitrogen-doped carbon nano tube.
(2) 5.0g of lithium hydroxide, 25g of iron phosphate, 45g of oxalic acid, 3.0g of glucose, and 8g of deionized water were added together in a three-necked flask, and then 1.56g of Tm was added thereto2O3Heating in water bath to 90 deg.C under rapid stirring, maintaining for 5 hr, cooling to room temperature, vacuum distilling to 80 deg.C, taking out, drying, adding ethanol into the material, ball milling for 3 hr, drying, and placing the material in N2Calcining at 400 deg.C for 5 hr in a protected tubular muffle furnace, cooling to room temperature, taking out, adding ethanol, ball milling for 6 hr, drying, and placing in N2Calcining the mixture for 10 hours at 700 ℃ in a protected tubular muffle furnace, and cooling to obtain the rare earth metal ion doped lithium iron phosphate.
(3)2g of nitrogen-doped carbon nano tube and 60g of rare earth metal ion-doped lithium iron phosphate are added into a container filled with ethanol at the same time, ultrasonic dispersion is carried out for 3 hours, and then N is carried out2Ball milling for 10 hours under protection, finally drying the ball milled materials for 20 hours at 80 ℃, and cooling to room temperature to obtain the nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate.
Example 3:
(1) adding 50ml of hydrazine hydrate with solute mass fraction of 30% into 50ml of deionized water, adding 300mg of carbon nano tube, heating and refluxing for 6 hours at 60 ℃, washing and filtering with deionized water, and freeze-drying the solid obtained by filtering to obtain the nitrogen-doped carbon nano tube.
(2) 5.0g of lithium hydroxide, 30.0g of iron phosphate, 50.0g of oxalic acid, 5.0g of glucose and 10.0g of deionized water are added together to a three-port furnaceAdding 4.5g of cerium oxide into the mixture in a bottle, heating the mixture to 90 ℃ in a water bath under rapid stirring, keeping the temperature for 5 hours, cooling the mixture to room temperature, distilling the mixture to 80 ℃ in vacuum, taking out the mixture, drying the mixture, adding ethanol into the mixture, ball-milling the mixture for 3 hours, drying the mixture, and placing the mixture in N2Calcining at 400 deg.C for 5 hr in a protected tubular muffle furnace, cooling to room temperature, taking out, adding ethanol, ball milling for 6 hr, drying, and placing in N2Calcining the mixture for 10 hours at 700 ℃ in a protected tubular muffle furnace, and cooling to obtain the rare earth metal ion doped lithium iron phosphate.
(3)2g of nitrogen-doped carbon nano tube and 60g of rare earth metal ion-doped lithium iron phosphate are added into a container filled with ethanol at the same time, ultrasonic dispersion is carried out for 3 hours, and then N is carried out2Ball milling for 10 hours under protection, finally drying the ball milled materials for 20 hours at 80 ℃, and cooling to room temperature to obtain the nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate.
Example 4:
(1) adding 50ml of hydrazine hydrate with solute mass fraction of 30% into 50ml of deionized water, adding 300mg of carbon nano tube, heating and refluxing for 6 hours at 60 ℃, washing and filtering with deionized water, and freeze-drying the solid obtained by filtering to obtain the nitrogen-doped carbon nano tube.
(2) Adding 5.0g of lithium hydroxide, 30.0g of iron phosphate, 50.0g of oxalic acid, 5.0g of glucose and 10.0g of deionized water into a three-neck flask, then adding 2.0GeO2, 1.0gTm2O3, 1.0gSm2O3 and 0.5gGd2O3 into the three-neck flask, heating the three-neck flask to 90 ℃ in a water bath under the condition of rapid stirring, keeping the temperature for 5 hours, cooling the mixture to room temperature, carrying out vacuum distillation to 80 ℃, taking out the mixture, drying the mixture, adding ethanol into the mixture, carrying out ball milling for 3 hours, drying the mixture, and placing the mixture into N2Calcining at 400 deg.C for 5 hr in a protected tubular muffle furnace, cooling to room temperature, taking out, adding ethanol, ball milling for 6 hr, drying, and placing in N2Calcining the mixture for 10 hours at 700 ℃ in a protected tubular muffle furnace, and cooling to obtain the rare earth metal ion doped lithium iron phosphate.
(3)2g of nitrogen-doped carbon nanotube and 70g of rare earth metal ion-doped lithium iron phosphate are simultaneously addedAdding into a container filled with ethanol, ultrasonically dispersing for 3 hours, and then adding N2Ball milling for 10 hours under protection, finally drying the ball milled materials for 20 hours at 80 ℃, and cooling to room temperature to obtain the nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate.
Example 5:
(1) adding 50ml of hydrazine hydrate with solute mass fraction of 30% into 50ml of deionized water, adding 300mg of carbon nano tube, heating and refluxing for 6 hours at 60 ℃, washing and filtering with deionized water, and freeze-drying the solid obtained by filtering to obtain the nitrogen-doped carbon nano tube.
(2) 5.0g of lithium hydroxide, 25.0g of iron phosphate, 45.0g of oxalic acid, 5.0g of glucose and 10.0g of deionized water were added together in a three-necked flask, and then 2.4g of Gd was added thereto2O3Heating in water bath to 90 deg.C under rapid stirring, maintaining for 5 hr, cooling to room temperature, vacuum distilling to 80 deg.C, taking out, drying, adding ethanol into the material, ball milling for 3 hr, drying, and placing the material in N2Calcining at 400 deg.C for 5 hr in a protected tubular muffle furnace, cooling to room temperature, taking out, adding ethanol, ball milling for 6 hr, drying, and placing in N2Calcining the mixture for 10 hours at 700 ℃ in a protected tubular muffle furnace, and cooling to obtain the rare earth metal ion doped lithium iron phosphate.
(3)2g of nitrogen-doped carbon nano tube and 70g of rare earth metal ion-doped lithium iron phosphate are added into a container filled with ethanol at the same time, ultrasonic dispersion is carried out for 3 hours, and then N is carried out2Ball milling for 10 hours under protection, finally drying the ball milled materials for 20 hours at 80 ℃, and cooling to room temperature to obtain the nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate.
Example 6:
(1) adding 50ml of hydrazine hydrate with solute mass fraction of 30% into 50ml of deionized water, adding 300mg of carbon nano tube, heating and refluxing for 6 hours at 60 ℃, washing and filtering with deionized water, and freeze-drying the solid obtained by filtering to obtain the nitrogen-doped carbon nano tube.
(2) 5.0g of lithium hydroxide, 30.0g of iron phosphate, 50.0g of oxalic acid, 5.0g of glucose and 10.0g of deionized water were mixed togetherAdding into a three-neck flask, adding 4.5g cerium oxide, rapidly stirring, heating in water bath to 90 deg.C for 5 hr, cooling to room temperature, vacuum distilling to 80 deg.C, taking out, drying, adding ethanol, ball milling for 3 hr, drying, and placing in N2Calcining at 400 deg.C for 5 hr in a protected tubular muffle furnace, cooling to room temperature, taking out, adding ethanol, ball milling for 6 hr, drying, and placing in N2Calcining the mixture for 10 hours at 700 ℃ in a protected tubular muffle furnace, and cooling to obtain the rare earth metal ion doped lithium iron phosphate.
(3)2g of nitrogen-doped carbon nano tube and 70g of rare earth metal ion-doped lithium iron phosphate are added into a container filled with ethanol at the same time, ultrasonic dispersion is carried out for 3 hours, and then N is carried out2Ball milling for 10 hours under protection, finally drying the ball milled materials for 20 hours at 80 ℃, and cooling to room temperature to obtain the nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate.
The materials prepared in the above examples 1 to 6 and unmodified lithium iron phosphate were assembled into 2016 coin cells by the same method, and the discharge capacity and cycle performance were measured in the voltage range of 2.0 to 4.5V, and the results are shown in table 1 and fig. 1 to 7, respectively.
TABLE 1 test results
It can be seen from the figures that the composite positive electrode material for lithium ion batteries (examples 1 to 6) prepared according to the present invention has excellent electrical properties compared to the lithium iron phosphate positive electrode material.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (9)
1. A preparation method of a nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite cathode material is characterized by comprising the following steps of: the method comprises the following steps:
(1) dispersing hydrazine hydrate and carbon nano tubes in deionized water to obtain a mixture, heating the mixture to carry out reflux reaction for 5-7h, carrying out suction filtration and separation to obtain a solid, and sequentially carrying out water washing and freeze drying on the solid to obtain nitrogen-doped carbon nano tubes;
(2) preparing rare earth metal ion doped lithium iron phosphate, then simultaneously adding the rare earth metal ion doped lithium iron phosphate and the nitrogen-doped carbon nano tube into the dispersion liquid for ultrasonic dispersion, adding the ultrasonically dispersed materials into a ball milling tank, and adding the materials into a reactor under the condition of N2And carrying out ball milling treatment under protection, and drying and cooling the material obtained by the ball milling treatment to room temperature to obtain the nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite cathode material.
2. The method of claim 1, wherein: in the step (1), the mass ratio of hydrazine hydrate, carbon nano-tube and deionized water is 0.5-2:500-2000: 200.
3. The method of claim 1, wherein: in the step (2), the method for preparing the rare earth metal ion-doped lithium iron phosphate comprises the following steps: adding lithium hydroxide, iron phosphate, oxalic acid, glucose and deionized water into a three-neck flask, then adding rare earth metal oxide into the three-neck flask, heating the mixture to 80-90 ℃ in a water bath under the condition of rapid stirring, keeping the temperature for 3-5 hours, cooling the mixture to room temperature, then carrying out vacuum distillation to 70-80 ℃, taking out the mixture, drying the mixture, then adding ethanol into the mixture, carrying out ball milling for 2-3 hours, drying the mixture, and placing the mixture into N2Calcining at 400 deg.C for 3-5 hr under protection, cooling to room temperature, taking out, adding ethanol, ball milling for 4-6 hr, drying, and placing in N2In a protected tubular muffle furnace at 500-70 deg.CCalcining for 8-10 hours at 0 ℃, and cooling to obtain the rare earth metal ion doped lithium iron phosphate.
4. The production method according to claim 3, characterized in that: the mass ratio of the lithium hydroxide to the iron phosphate to the oxalic acid to the glucose to the deionized water is 1: 5-6: 9-10: 0.5-1: 1.5-2.
5. The production method according to claim 3, characterized in that: the rare earth metal oxide is GeO2、Tm2O3、Sm2O3、Gd2O3At least one of (1).
6. The production method according to claim 3, characterized in that: the addition amount of the rare earth metal oxide is 1-5% of the total mass of the lithium hydroxide, the iron phosphate, the oxalic acid and the glucose.
7. The method of claim 1, wherein: in the step (2), the mass ratio of the doped carbon nanotube to the rare earth metal ion doped lithium iron phosphate is 1: 30-40.
8. The method of claim 1, wherein: in the step (2), the dispersion liquid is ethanol.
9. The nitrogen-doped carbon nanotube/rare earth metal ion-doped lithium iron phosphate composite positive electrode material prepared by the preparation method according to any one of claims 1 to 8.
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