CN113555557B - Lithium iron phosphate positive electrode material, preparation method and application thereof - Google Patents
Lithium iron phosphate positive electrode material, preparation method and application thereof Download PDFInfo
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- 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 95
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 60
- 238000002360 preparation method Methods 0.000 title claims abstract description 15
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 54
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 39
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 20
- 239000002344 surface layer Substances 0.000 claims abstract description 20
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 19
- 239000010405 anode material Substances 0.000 claims abstract description 13
- 239000000243 solution Substances 0.000 claims description 173
- 238000006243 chemical reaction Methods 0.000 claims description 83
- 239000002243 precursor Substances 0.000 claims description 81
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 74
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 64
- 239000013078 crystal Substances 0.000 claims description 58
- 239000007864 aqueous solution Substances 0.000 claims description 54
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 41
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 32
- 229910010707 LiFePO 4 Inorganic materials 0.000 claims description 28
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims description 27
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 27
- 239000008139 complexing agent Substances 0.000 claims description 27
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 26
- 239000002253 acid Substances 0.000 claims description 25
- 239000012046 mixed solvent Substances 0.000 claims description 25
- 229910018119 Li 3 PO 4 Inorganic materials 0.000 claims description 24
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 claims description 21
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 19
- 238000000034 method Methods 0.000 claims description 19
- 229940085991 phosphate ion Drugs 0.000 claims description 17
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 claims description 15
- 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 14
- 150000001875 compounds Chemical class 0.000 claims description 14
- 239000002245 particle Substances 0.000 claims description 13
- 238000002156 mixing Methods 0.000 claims description 11
- 235000015165 citric acid Nutrition 0.000 claims description 9
- 239000003960 organic solvent Substances 0.000 claims description 9
- 235000006408 oxalic acid Nutrition 0.000 claims description 9
- 239000011668 ascorbic acid Substances 0.000 claims description 7
- 235000010323 ascorbic acid Nutrition 0.000 claims description 7
- 229960005070 ascorbic acid Drugs 0.000 claims description 7
- 239000002041 carbon nanotube Substances 0.000 claims description 7
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 7
- 229910021389 graphene Inorganic materials 0.000 claims description 7
- 239000012295 chemical reaction liquid Substances 0.000 claims description 6
- 239000010410 layer Substances 0.000 claims description 6
- 229910019142 PO4 Inorganic materials 0.000 claims description 5
- 229910003481 amorphous carbon Inorganic materials 0.000 claims description 4
- 239000011230 binding agent Substances 0.000 claims description 4
- 239000006258 conductive agent Substances 0.000 claims description 4
- 239000010452 phosphate Substances 0.000 claims description 4
- 239000002904 solvent Substances 0.000 claims description 4
- 125000003158 alcohol group Chemical group 0.000 claims description 2
- 238000003756 stirring Methods 0.000 description 34
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 27
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 19
- 239000008367 deionised water Substances 0.000 description 18
- 229910021641 deionized water Inorganic materials 0.000 description 18
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 16
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 15
- 239000002002 slurry Substances 0.000 description 14
- 229910010710 LiFePO Inorganic materials 0.000 description 13
- 230000001105 regulatory effect Effects 0.000 description 13
- 239000010406 cathode material Substances 0.000 description 12
- 230000001276 controlling effect Effects 0.000 description 12
- 230000008569 process Effects 0.000 description 12
- 239000000463 material Substances 0.000 description 10
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 description 9
- 239000012535 impurity Substances 0.000 description 9
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 8
- 229910052744 lithium Inorganic materials 0.000 description 8
- 229910052757 nitrogen Inorganic materials 0.000 description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 7
- 230000009286 beneficial effect Effects 0.000 description 7
- 238000001816 cooling Methods 0.000 description 7
- 238000001035 drying Methods 0.000 description 7
- 239000001301 oxygen Substances 0.000 description 7
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- 230000000052 comparative effect Effects 0.000 description 5
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- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 4
- 238000012512 characterization method Methods 0.000 description 4
- 230000007774 longterm Effects 0.000 description 4
- 235000021317 phosphate Nutrition 0.000 description 4
- 229940113115 polyethylene glycol 200 Drugs 0.000 description 4
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- 229920001940 conductive polymer Polymers 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000010304 firing Methods 0.000 description 3
- 230000014759 maintenance of location Effects 0.000 description 3
- 230000005012 migration Effects 0.000 description 3
- 238000013508 migration Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical class [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 2
- 239000002202 Polyethylene glycol Substances 0.000 description 2
- 230000001476 alcoholic effect Effects 0.000 description 2
- JYYOBHFYCIDXHH-UHFFFAOYSA-N carbonic acid;hydrate Chemical compound O.OC(O)=O JYYOBHFYCIDXHH-UHFFFAOYSA-N 0.000 description 2
- 239000013522 chelant Substances 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000001938 differential scanning calorimetry curve Methods 0.000 description 2
- 239000012895 dilution Substances 0.000 description 2
- 238000010790 dilution Methods 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
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- 229920000767 polyaniline Polymers 0.000 description 2
- 229920001223 polyethylene glycol Polymers 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 239000011164 primary particle Substances 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- NCZYUKGXRHBAHE-UHFFFAOYSA-K [Li+].P(=O)([O-])([O-])[O-].[Fe+2].[Li+] Chemical compound [Li+].P(=O)([O-])([O-])[O-].[Fe+2].[Li+] NCZYUKGXRHBAHE-UHFFFAOYSA-K 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 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
- 238000000498 ball milling Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000005587 bubbling Effects 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000009831 deintercalation Methods 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 1
- 229940068918 polyethylene glycol 400 Drugs 0.000 description 1
- 229920005862 polyol Polymers 0.000 description 1
- 150000003077 polyols Chemical class 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
-
- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
-
- 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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The application provides a lithium iron phosphate positive electrode material, a preparation method and application thereof. The lithium iron phosphate anode material comprises spherical lithium iron phosphate and carbon compounded on the surface of the spherical lithium iron phosphate, wherein the spherical lithium iron phosphate is provided with an inner core and a surface layer positioned on the periphery of the inner core, the carbon is coated on the surface layer, and the porosity of the inner core is larger than that of the surface layer. The lithium iron phosphate anode material provided by the application has good dynamic performance (rate capability) and discharge gram capacity after being applied to a lithium ion battery, has excellent electrochemical performance, and is outstanding in capacity, service life and safety.
Description
Technical Field
The application relates to the technical field of lithium ion batteries, in particular to a lithium iron phosphate positive electrode material, a preparation method and application thereof.
Background
Lithium iron phosphate (LiFePO) 4 ) The high safety performance and the considerable electrochemical performance of the lithium ion battery are one of the most successful commercial anode materials in the field of lithium ion batteries at present. However, the disadvantages of low energy density, poor kinetic performance, lithium ion diffusion capability and the like limit the commercialization development and progress of lithium iron phosphate. The positive electrode material is an important component in the lithium ion battery, and has the performances of capacity, service life, cost, safety and the like of the lithium ion battery. Therefore, the development of the lithium iron phosphate positive electrode material with high reversible discharge capacity, excellent cycle performance and high thermal stability has important practical significance.
Disclosure of Invention
The application mainly aims to provide a lithium iron phosphate positive electrode material, a preparation method and application thereof, so as to solve the defects of lithium iron phosphate in the aspects of capacity, service life, safety and the like in the prior art.
In order to achieve the above object, according to one aspect of the present application, there is provided a lithium iron phosphate cathode material including spherical lithium iron phosphate and carbon composited on the surface of the spherical lithium iron phosphate, the spherical lithium iron phosphate having an inner core and a surface layer located at the periphery of the inner core, the carbon coated on the surface layer, the inner core having a porosity greater than that of the surface layer.
Further, the particle size of the spherical lithium iron phosphate is 4-6 mu m; the particle size of the inner core is 1-3 mu m.
Further, the porosity of the inner core is 60-90%; the porosity of the surface layer is 0-20%.
Further, the carbon is selected from one or more of graphene, carbon nanotubes, conductive carbon black and amorphous carbon; the carbon content is 1.5-2.5% of the weight of the lithium iron phosphate anode material.
According to another aspect of the present application, there is also provided a method for preparing a lithium iron phosphate positive electrode material, comprising the steps of: preparing a mixed solvent of water and an organic solvent, adding a binary solution, a complexing agent solution and an acid solution into the mixed solvent, and performing a first-stage reaction under the condition of a pH value of 1.8-2.4 to form an intermediate reaction solution; adjusting the pH value of the intermediate reaction liquid to 2.6-3.2, and performing a second stage reaction to form Fe 3 (PO 4 ) 2 A precursor; wherein the binary solution is a solution of soluble ferrous salt and a phosphate ion-containing soluble compound; fe is added to 3 (PO 4 ) 2 Dispersing the precursor into Li 3 PO 4 Crystal nucleus growth is carried out in the crystal solution to obtain LiFePO 4 A precursor; liFePO is prepared 4 And mixing the precursor with a carbon source, and roasting in an inert atmosphere to obtain the lithium iron phosphate anode material.
Further, the organic solvent in the mixed solvent is an alcohol solvent, and the volume ratio of water to the organic solvent in the mixed solvent is (1-3).
Further, the soluble ferrous salt is selected from FeCl 2 、FeC 2 O 4 、(CH 3 COO) 2 Fe、FeSO 4 One or more of the following; the phosphate ion-containing soluble compound is selected from phosphoric acid and/or soluble phosphate, and the soluble phosphate is selected from NH 4 H 2 PO 4 ，Na 2 HPO 4 ，(NH 4 ) 2 HPO 4 One or more of the following; the binary solution is aqueous solution of soluble ferrous salt and phosphate ion-containing soluble compound, whereinFe in soluble ferrous salt 2+ With PO in phosphate ion-containing soluble compounds 4 3+ The molar ratio of (2.85-3.15) is 2, and the total molar concentration of the soluble ferrous salt and the phosphate ion is 1-3 mol/L; in the complexing agent solution, the complexing agent is one or more selected from citric acid, oxalic acid and ascorbic acid.
Further, the crystal nucleus growth step includes: adding phosphoric acid solution into lithium hydroxide solution to react to form Li 3 PO 4 A crystal solution; fe is added to 3 (PO 4 ) 2 Dispersing the precursor into Li 3 PO 4 Crystal nucleus growth is carried out in the crystal solution to obtain LiFePO 4 A precursor; the phosphoric acid solution is phosphoric acid aqueous solution, and the molar concentration of the phosphoric acid aqueous solution is 1.0-2.5 mol/L; the lithium hydroxide solution is lithium hydroxide aqueous solution, and the molar concentration of the lithium hydroxide aqueous solution is 1.0-2.5 mol/L; li in lithium hydroxide solution + With PO in phosphoric acid solution 4 3- The molar ratio of (2.85-3.15) is 1.
According to still another aspect of the present application, there is also provided a positive electrode material, which is the above lithium iron phosphate positive electrode material, or is the lithium iron phosphate positive electrode material prepared by the above preparation method.
According to still another aspect of the present application, there is provided a lithium ion battery, including a positive electrode, the positive electrode including a positive electrode current collector and a positive electrode active layer located on a surface of the positive electrode current collector, the positive electrode active layer including a positive electrode material, a conductive agent and a binder, wherein the positive electrode material is the above lithium iron phosphate positive electrode material, or is the lithium iron phosphate positive electrode material prepared by the above preparation method.
The lithium iron phosphate anode material provided by the application comprises spherical lithium iron phosphate and carbon compounded on the surface of the spherical lithium iron phosphate, wherein the spherical lithium iron phosphate is provided with an inner core and a surface layer positioned on the periphery of the inner core, and the porosity of the inner core is larger than that of the surface layer. The porosity of the spherical lithium iron phosphate inner core is larger than that of the surface layer, and the spherical lithium iron phosphate inner core is equivalent to a hollow structure with a loose internal structure and a compact shell structure. The structure can obviously improve the specific surface area of the material, and further effectively improve the lithium storage efficiency of the positive electrode. Meanwhile, carbon compounded on the surface can also cooperate with spherical lithium iron phosphate with a hollow structure to improve the conductivity of the material, so that the lithium ion diffusion capacity is improved, and the two reasons of the conductivity improve the lithium iron phosphate positive electrode material to have good dynamic performance (rate performance) and discharge gram capacity and excellent electrochemical performance after being applied to a lithium ion battery. Meanwhile, the lithium iron phosphate anode material has good thermal stability. The above aspects make the material show outstanding capacity, service life and safety after being applied to a battery.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:
FIG. 1 shows the XRD structure corresponding to the lithium iron phosphate positive electrode material prepared in example 1;
fig. 2 shows a first charge-discharge curve of a button cell corresponding to the lithium iron phosphate cathode material prepared in example 1;
FIG. 3 shows a plot of the rate performance of the soft pack cell corresponding to the lithium iron phosphate positive electrode material prepared in example 1;
fig. 4 shows a corresponding button cell GITT curve of the lithium iron phosphate cathode material prepared in example 1;
fig. 5 shows a 45 ℃ cycle capacity retention curve of the soft pack battery cell corresponding to the lithium iron phosphate cathode material prepared in example 1;
FIG. 6 shows a DSC thermogram corresponding to the lithium iron phosphate positive electrode material prepared in example 1;
fig. 7 shows a first charge-discharge curve of a button cell corresponding to the lithium iron phosphate cathode material prepared in comparative example 1.
Detailed Description
It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other. The application will be described in detail below with reference to the drawings in connection with embodiments.
As described in the background section, lithium iron phosphate in the prior art has drawbacks in terms of capacity, lifetime, safety, and the like. In order to solve the problem, the application provides a lithium iron phosphate positive electrode material, which is characterized by comprising spherical lithium iron phosphate and carbon compounded on the surface of the spherical lithium iron phosphate, wherein the spherical lithium iron phosphate is provided with an inner core and a surface layer positioned at the periphery of the inner core, the surface layer is coated with the carbon, and the porosity of the inner core is larger than that of the surface layer.
The porosity of the spherical lithium iron phosphate inner core is larger than that of the surface layer, and the spherical lithium iron phosphate inner core is equivalent to a hollow structure with a loose internal structure and a compact shell structure. The lithium battery lithium storage device has the advantages that the specific surface area of the material can be remarkably improved, the lithium storage efficiency of the positive electrode is further effectively improved, more electrolyte can be effectively stored, the long-term cycle performance in the charge and discharge process is improved, more storage accommodating spaces can be provided under the condition that the lithium ion battery is overcharged, and the structural stability and the safety performance are improved. And the existence of special hollow structure, li + The migration path distance and the diffusion migration resistance of the lithium ion battery are reduced, and the increase of the surface contact active sites ensures the smooth deintercalation of Li+ and improves the migration capability of ions. Accordingly, the first charge and discharge efficiency, coulombic efficiency, rate capability and long-term cycle performance of the battery are improved. Meanwhile, carbon compounded on the surface can also cooperate with spherical lithium iron phosphate with a hollow structure to improve the conductivity of the material and the diffusion capacity of lithium ions. The reason promotes that the lithium iron phosphate positive electrode material has good dynamic performance (rate capability) and discharge gram capacity after being applied to a lithium ion battery, and has excellent electrochemical performance. Meanwhile, the lithium iron phosphate anode material has good thermal stability. The above aspects make the material show outstanding capacity, service life and safety after being applied to a battery.
In order to further improve various properties of the positive electrode material and more fully exert advantages brought by the hollow structure, in a preferred embodiment, the particle size of the spherical lithium iron phosphate is 4-6 μm; preferably, the particle size of the inner core is 1 to 3. Mu.m. More preferably, the porosity of the inner core is 60 to 90%; the porosity of the surface layer is 0-20%.
The above carbon compounded on the surface of the spherical lithium iron phosphate may have good conductivity, and the above carbon includes, for example, but not limited to, one or more of graphene, carbon nanotubes, conductive carbon black, amorphous carbon; preferably, the carbon content is 1.5 to 2.5% by weight of the lithium iron phosphate cathode material. The composite amount of carbon is controlled within the range, so that the conductivity of the positive electrode material can be further improved, and meanwhile, the positive electrode material is also beneficial to ensuring that the positive electrode material has higher energy density.
According to another aspect of the present application, there is also provided a method for preparing a lithium iron phosphate positive electrode material, comprising the steps of: preparing a mixed solvent of water and an organic solvent, adding a binary solution, a complexing agent solution and an acid solution into the mixed solvent, and performing a first-stage reaction under the condition of a pH value of 1.8-2.4 to form an intermediate reaction solution; adjusting the pH value of the intermediate reaction liquid to 2.6-3.2, and performing a second stage reaction to form Fe 3 (PO 4 ) 2 A precursor; wherein the binary solution is a solution of soluble ferrous salt and a phosphate ion-containing soluble compound; fe is added to 3 (PO 4 ) 2 Dispersing the precursor into Li 3 PO 4 Crystal nucleus growth is carried out in the crystal solution to obtain LiFePO 4 A precursor; liFePO is prepared 4 And mixing the precursor with a carbon source, and roasting in an inert atmosphere to obtain the lithium iron phosphate anode material.
In the preparation method, a binary solution formed by soluble ferrous salt and phosphate ion-containing soluble compound is firstly utilized to react in a mixed solvent to prepare Fe 3 (PO 4 ) 2 A precursor. On one hand, the process takes the mixed solvent as the reaction liquid, which can provide a milder environment for the production of the precursor and is beneficial to the growth nucleation and the oriented growth of the grain seeds; the amorphous precursor is separated out in the solution to generate tiny particles, the initially formed crystal particles are increased, the tiny particles take the micro-clusters as crystal nuclei to reduce the surface tension effect and free energy, and the particles are gradually aggregated and accumulated and grown on the periphery to finally form a spherical structure. On the other hand, by carrying out the reactions of the two stages in succession in the respective specific pH environments, fe is caused to 3 (PO 4 ) 2 Internal of precursorThe primary particle structure of the core and the shell is different, specifically, the shell is compact in agglomeration, the sintering temperature is high, the structure formed inside is loose, and the formed pores are more. Subsequent further growth of LiFePO on a primary particle basis 4 This structure can still be maintained after the precursor, and thus a special hollow structure with internal porosity greater than external porosity can be formed during final firing. In addition, in the reaction process of two stages, the pH value can be adjusted to a target range by utilizing an acid solution, and the addition of a complexing agent solution is more beneficial to Fe 3 (PO 4 ) 2 The growth of the precursor can further improve the morphology of the final lithium iron phosphate, so that the lithium iron phosphate has a complete spherical structure, and has better promotion effect on various performances of the positive electrode material.
In the formation of Fe 3 (PO 4 ) 2 After the precursor, it is added to Li 3 PO 4 Crystal nucleus growth is carried out in the crystal solution to obtain LiFePO 4 A precursor. In the roasting stage, liFePO 4 The precursor is mixed with a carbon source, so that the carbon material can be compounded on the surface of the spherical lithium iron phosphate, and the conductivity of the positive electrode material is improved.
By adopting the preparation method, spherical lithium iron phosphate with a hollow structure can be formed, and the surface of the spherical lithium iron phosphate is compounded with a carbon material, so that the positive electrode material has better first charge and discharge efficiency, coulombic efficiency, rate capability, long-term cycle performance and the like of a battery, and is outstanding in capacity, service life, safety and the like.
To further increase Fe 3 (PO 4 ) 2 Stability of precursor reaction and growth, in a preferred embodiment, the organic solvent in the mixed solvent is an alcoholic solvent, preferably an alcoholic solvent polyol, more preferably one or more selected from ethylene glycol, liquid polyethylene glycol (such as polyethylene glycol 200, polyethylene glycol 400, etc.), glycerol; preferably, the volume ratio of water to organic solvent in the mixed solvent is (1-3): (1-3), such as 1:1, 1:2, 1:3, 1:1, 2:1, 3:1, etc. The adoption of the mixed solvent is favorable for further improving Fe 3 (PO 4 ) 2 Precursor(s)Reaction and growth stability of the precursor, more complete crystal structure of the precursor, and subsequent LiFePO treatment 4 After the precursor grows and is roasted, the obtained lithium iron phosphate hollow spherical structure is more complete, and the improvement of the comprehensive performance of the positive electrode material is facilitated.
In a preferred embodiment, the soluble ferrous salts include, but are not limited to FeCl 2 、FeC 2 O 4 、(CH 3 COO) 2 Fe、FeSO 4 One or more of the following; preferably, the phosphate ion-containing soluble compound is selected from phosphoric acid and/or soluble phosphates, more preferably the soluble phosphate is selected from NH 4 H 2 PO 4 ，Na 2 HPO 4 ，(NH 4 ) 2 HPO 4 One or more of the following. The soluble ferrous salts and the phosphate ion-containing soluble compounds can react and grow more stably in the mixed solvent. Preferably, the binary solution is an aqueous solution of a soluble ferrous salt and a phosphate ion-containing soluble compound, wherein Fe in the soluble ferrous salt 2+ With PO in phosphate ion-containing soluble compounds 4 3+ The molar ratio of (2.85-3.15) is 2, and the total molar concentration of the soluble ferrous salt and the phosphate ion is 1-3 mol/L.
The addition of the complexing agent solution is beneficial to Fe 3 (PO 4 ) 2 Precursor crystal growth, in order to further enhance this effect, in a preferred embodiment,
the complexing agent is one or more selected from citric acid, oxalic acid and ascorbic acid in the complexing agent solution; preferably, the complexing agent solution is an aqueous solution of the complexing agent, and the molar concentration of the complexing agent solution is 3-5 mol/L; in addition, the pH value of the reaction system can be timely adjusted through an acid solution, more preferably, the acid in the acid solution is selected from one or more of carbonic acid, phosphoric acid and acetic acid, and preferably, the acid solution is an aqueous solution of the acid, and the molar concentration of the acid solution is 0.1-0.5 mol/L. In order to make the reaction more stable, in a preferred embodiment, when the binary solution is added to the mixed solvent, the addition amount of the binary solution is 80-90% of the volume of the mixed solvent, the addition amount of the complexing agent solution is 10-20% of the volume of the mixed solvent, and the addition amount of the acid solution is adjusted according to the pH value of the first-stage reaction.
Preferably, the first-stage reaction is carried out at a stirring speed of 200-600 rpm for 5-8 h; preferably, after the first-stage reaction is finished, the pH value of the intermediate reaction solution is adjusted to the target pH value of the second-stage reaction by adding an acid solution or adding water for dilution; more preferably, the second stage reaction is carried out at a stirring speed of 150 to 500rpm for a reaction time of 8 to 12 hours. The reaction of two stages is carried out under the process conditions, which is favorable for further improving the reaction stability and forming Fe 3 (PO 4 ) 2 The loose interior of the precursor crystal is more compatible with the denser surface layer, and finally LiFePO is carried out 4 After the precursor grows and is roasted, the obtained spherical lithium iron phosphate with a hollow structure has more complete structure and more proper internal and external pore degree, and is beneficial to further improving the overall electrochemical performance of the positive electrode material.
In the actual operation process, the pH value of the system can be monitored at any time in the first-stage reaction and the second-stage reaction, and the pH value can be regulated and controlled by adding acid solution or dilution water during the reaction process, so that the pH value of the breath in the reaction process is ensured to be within a preset range. After the second-stage reaction is finished, the reacted slurry can be centrifuged, dried and decontaminated to obtain Fe 3 (PO 4 ) 2 A precursor. The specific impurity removal process is preferably as follows: chelate resin is added into the reaction liquid with the addition amount of 0.5-2 g/L, and deionized water and absolute ethyl alcohol are used for repeatedly cleaning for 3-4 times.
In the process of the growth of the crystal nucleus, li 3 PO 4 The crystal nucleus can be in Fe 3 (PO 4 ) 2 The surface of the precursor is nucleated and grows to finish the mixing of the two structural crystals to form LiFePO 4 A precursor. In a preferred embodiment, the above-mentioned crystal nucleus growing step includes: adding phosphoric acid solution into lithium hydroxide solution to react to form Li 3 PO 4 A crystal solution; fe is added to 3 (PO 4 ) 2 Dispersing the precursor into Li 3 PO 4 Crystal nucleus growth is carried out in the crystal solution to obtain LiFePO 4 A precursor. Adopts the above methodMode of adding lithium source and Li 3 PO 4 Crystal growth mode, liFePO formed 4 The precursor has a more complete crystal structure, which is beneficial to further improving the crystal structure of the final spherical lithium iron phosphate and promotes the positive electrode material to have better electrochemical performance.
Above Fe 3 (PO 4 ) 2 Precursor and LiFePO 4 In the precursor reaction growth process, inert gas such as nitrogen is preferably introduced into the reaction system to remove oxygen in the solution and prevent Fe 2+ The reaction is more stable by oxidation.
Preferably, the phosphoric acid solution is phosphoric acid aqueous solution with the molar concentration of 1.0-2.5 mol/L; the lithium hydroxide solution is lithium hydroxide aqueous solution, and the molar concentration of the lithium hydroxide aqueous solution is 1.0-2.5 mol/L; li in lithium hydroxide solution + With PO in phosphoric acid solution 4 3- The molar ratio of (2.85-3.15) is 1; preferably, the adding speed of the phosphoric acid solution is 10-30L/h, the reaction time of the phosphoric acid solution and the lithium hydroxide solution is 2-3 h, and the reaction is carried out under the condition of stirring speed of 150-250 rpm; preferably Fe 3 (PO 4 ) 2 The addition amount of the precursor is Li 3 PO 4 5-10% of the weight of the crystal solution; preferably, the crystal nucleus growth process is carried out under the condition of stirring speed of 100-150 rpm, and the growth time is 3-5 h. The adoption of the process conditions is beneficial to further improving LiFePO 4 Stability of precursor nucleus growth process.
The above carbon source may be any carbon source capable of forming a carbon material composited to the surface of spherical lithium iron phosphate in an inert atmosphere in a firing stage, and in a preferred embodiment, the carbon source is selected from one or more of graphene, carbon nanotubes, conductive carbon black, and conductive polymers; preferably, the conductive polymer is polyaniline. Conductive polymers such as polyaniline can be pyrolyzed during the firing process to form amorphous carbon. Preferably, the carbon source is added in an amount of LiFePO 4 5-7% of the total weight of the precursor and the carbon raw material source. With the addition, the carbon content in the baked positive electrode material is more suitable, and the conductivity of the material can be further improved. Preferably, the calcination temperature is 600 to the range of the calcinationThe roasting time is 5-7 h at 700 ℃. Roasting under the conditions, the hollow structure of the spherical lithium iron phosphate structure is more complete, and the composite of the carbon material is more stable.
Before actual roasting, the reaction slurry formed in the crystal nucleus growing step can be centrifuged, dried and decontaminated to obtain LiFePO 4 And mixing the precursor with a carbon source and roasting. The above inert atmosphere includes, but is not limited to, nitrogen, argon, and the like. The above impurity removal process is preferably as follows: chelate resin is added into the reaction liquid with the addition amount of 0.5-2 g/L, and deionized water and absolute ethyl alcohol are used for repeatedly cleaning for 3-4 times.
According to another aspect of the present application, there is also provided a positive electrode material, which is the above lithium iron phosphate positive electrode material, or is the lithium iron phosphate positive electrode material prepared by the above preparation method.
According to another aspect of the present application, there is provided a lithium ion battery, including a positive electrode, the positive electrode including a positive electrode current collector and a positive electrode active layer located on a surface of the positive electrode current collector, the positive electrode active layer including a positive electrode material, a conductive agent and a binder, wherein the positive electrode material is the above lithium iron phosphate positive electrode material, or is the lithium iron phosphate positive electrode material prepared by the above preparation method.
The lithium iron phosphate positive electrode material can effectively improve the first charge and discharge efficiency, coulombic efficiency, multiplying power performance, long-term cycle performance and the like of a lithium ion battery, and has outstanding performances in the aspects of capacity, service life, safety and the like.
The application is described in further detail below in connection with specific examples which are not to be construed as limiting the scope of the application as claimed.
Example 1
1. Configuration of FeCl 2 And (NH) 4 ) 2 HPO 4 The total concentration of solute is 2mol/L, fe 2+ With PO (PO) 4 3+ The molar ratio of (2) is 3:2; the citric acid aqueous solution is used as a complexing agent solution, and the molar concentration of the citric acid aqueous solution is 3mol/L; the carbonic acid water solution is taken as an acid solution, and the molar concentration of the carbonic acid water solution is 0.2mol/L;
2. preparing a mixed solvent of glycol and deionized water as a solventThe volume ratio of deionized water to glycol is 3:1, and the binary aqueous solution, the citric acid aqueous solution and the carbonic acid aqueous solution are added into the reaction solution to perform the reaction of the stage 1 and the stage 2, and high-purity N is continuously blown in the reaction process 2 To remove oxygen from the solution. The adding amount of the binary solution is 85% of the volume of the reaction solution, the adding amount of the complexing agent solution is 15% of the volume of the reaction solution, and the adding amount of the acid solution is adjusted according to the following pH value:
stage 1: adjusting the adding amount of the carbonic acid solution, regulating and controlling the pH value of the reaction system to be 1.8-2.0, reacting for 5 hours, and controlling the stirring rotating speed to be 500rpm;
stage 2: adding the carbonic acid solution, regulating the pH value of the reaction system to 2.8-3.0, controlling the stirring rotation speed to 350rpm, and stopping stirring after continuing to react for 8 hours;
3. centrifuging and drying the reacted slurry, repeatedly cleaning with deionized water and ethanol for 3-4 times to remove impurities to obtain Fe 3 (PO 4 ) 2 A precursor.
4. LiOH and H 3 PO 4 Respectively preparing 1.5mol/L aqueous solution; will H 3 PO 4 The solution was slowly added to the LiOH solution at a rate of 10L/h, where the molar amount n (Li + ):n(PO 4 3- ) Stirring for 2-3 h to obtain Li at a ratio of 3:1 3 PO 4 And (5) a crystal. The Fe is mixed with 3 (PO 4 ) 2 The precursor is uniformly dispersed into Li 3 PO 4 In a crystal solution, wherein Fe 3 (PO 4 ) 2 The addition amount of the precursor is Li 3 PO 4 5% of the weight of the crystal solution is continuously stirred for 3h, the stirring rotation speed is controlled to be 150rpm, the adding speed is controlled to be 10L/h to ensure the growth of crystal nuclei, the reacted slurry is centrifuged, dried and decontaminated to obtain LiFePO 4 A precursor.
5. LiFePO is prepared 4 Mixing the precursor and graphene, wherein the addition amount of the graphene is 7% of the total mass of the precursor and the graphene, roasting for 6 hours at 600 ℃ under the protection of inert atmosphere nitrogen, and naturally cooling to room temperature to obtain the hollow LiFePO 4 The carbon content of the positive electrode material/C (XRD structure spectrum, see figure 1) was 1.5%.
Example 2
1. Configuration of FeSO 4 And NH 4 H 2 PO 4 The total concentration of solute is 1.5mol/L, fe 2+ With PO (PO) 4 3+ The molar ratio of (2) is 3.15:2; the oxalic acid aqueous solution is used as complexing agent solution, and the molar concentration of the oxalic acid aqueous solution is 5mol/L; acetic acid aqueous solution as acid solution with a molar concentration of 0.2mol/L;
2. preparing a mixed solvent of polyethylene glycol 200 and deionized water as a reaction solution, wherein the volume ratio of the deionized water to the polyethylene glycol is 2:1, and simultaneously adding the binary aqueous solution, the oxalic acid aqueous solution and the acetic acid aqueous solution into the reaction solution to perform the reaction of the stage 1 and the stage 2, and continuously blowing high-purity N in the reaction process 2 To remove oxygen from the solution. The adding amount of the binary solution is 85% of the volume of the reaction solution, the adding amount of the complexing agent solution is 15% of the volume of the reaction solution, and the adding amount of the acid solution is adjusted according to the following pH value:
stage 1: adjusting the adding amount of the acetic acid solution, regulating and controlling the pH value of a reaction system to be between 1.9 and 2.2, reacting for 6 hours, and controlling the stirring rotating speed to be 400rpm;
stage 2: increasing the addition amount of the acetic acid solution, regulating the pH value of the reaction system to be 2.6-2.8, controlling the stirring rotation speed to be 300rpm, and stopping stirring after the reaction is continued for 10 hours;
3. centrifuging and drying the reacted slurry, repeatedly cleaning with deionized water and ethanol for 3-4 times to remove impurities to obtain Fe 3 (PO 4 ) 2 A precursor.
4. LiOH and H 3 PO 4 Respectively preparing 1.5mol/L aqueous solution; will H 3 PO 4 The solution was slowly added to the LiOH solution at a rate of 20L/h, where the molar amount n (Li + ):n(PO 4 3- ) Stirring for 2h to obtain Li at a ratio of 3:1 3 PO 4 And (5) a crystal. The Fe is mixed with 3 (PO 4 ) 2 The precursor is uniformly dispersed into Li 3 PO 4 In a crystal solution, wherein Fe 3 (PO 4 ) 2 The addition amount of the precursor is Li 3 PO 4 7% of the weight of the crystal solution, stirring for 3hThe rotating speed is controlled at 100rpm, the adding speed is controlled at 10L/h to ensure the growth of crystal nuclei, the reacted slurry is centrifuged, dried and decontaminated to obtain LiFePO 4 A precursor.
5. LiFePO is prepared 4 Mixing the precursor with carbon nano tube, adding carbon nano tube with an addition amount of 7% of the total mass of the precursor and the carbon nano tube, roasting for 6 hours at 650 ℃ under the protection of inert atmosphere nitrogen, and naturally cooling to room temperature to obtain the hollow structure LiFePO 4 and/C positive electrode material, which contains 2% of carbon.
Example 3
1. Configuration of FeC 2 O 4 And Na (Na) 2 HPO 4 The total concentration of solute is 2mol/L, fe 2+ With PO (PO) 4 3+ The molar ratio of (2) is 3:2; the citric acid aqueous solution is used as complexing agent solution, and the molar concentration of the citric acid aqueous solution is 4mol/L; phosphoric acid aqueous solution is taken as acid solution, and the molar concentration is 0.2mol/L;
2. preparing a mixed solvent of glycerol and deionized water as a reaction solution, wherein the volume ratio of the deionized water to the glycerol is 2:1, and simultaneously adding the binary aqueous solution, the citric acid aqueous solution and the phosphoric acid aqueous solution into the reaction solution to perform the reaction of the stage 1 and the stage 2, and continuously blowing high-purity N in the reaction process 2 To remove oxygen from the solution. The adding amount of the binary solution is 90% of the volume of the reaction solution, the adding amount of the complexing agent solution is 10% of the volume of the reaction solution, and the adding amount of the acid solution is adjusted according to the following pH value:
stage 1: the adding amount of the phosphoric acid solution is finely adjusted, the pH value of the reaction system is regulated and controlled to be between 2.0 and 2.4, the reaction time is 5 hours, and the stirring rotating speed is controlled to be 450rpm;
stage 2: adding the phosphoric acid solution, regulating the pH of the reaction system to 3.0-3.2, controlling the stirring rotation speed to 300rpm, continuing the reaction for 10 hours, and stopping stirring;
3. centrifuging and drying the reacted slurry, repeatedly cleaning with deionized water and ethanol for 3-4 times to remove impurities to obtain Fe 3 (PO 4 ) 2 A precursor.
4. LiOH and H 3 PO 4 Respectively preparing 1.5mol/L aqueous solution; will H 3 PO 4 The solution was slowly added to the LiOH solution at a rate of 15L/h, where the molar amount n (Li + ):n(PO 4 3- ) Stirring for 2h to obtain Li at a ratio of 3:1 3 PO 4 And (5) a crystal. The Fe is mixed with 3 (PO 4 ) 2 The precursor is uniformly dispersed into Li 3 PO 4 In a crystal solution, wherein Fe 3 (PO 4 ) 2 The addition amount of the precursor is Li 3 PO 4 8% of the weight of the crystal solution is continuously stirred for 3h, the stirring rotation speed is controlled at 120rpm, the adding speed is controlled at 15L/h to ensure the growth of crystal nuclei, the reacted slurry is centrifuged, dried and decontaminated to obtain LiFePO 4 A precursor.
5. LiFePO is prepared 4 Mixing the precursor with conductive carbon black, wherein the addition amount of the conductive carbon black is 7% of the total mass of the precursor and the conductive carbon black, roasting for 6 hours at 600 ℃ under the protection of inert atmosphere nitrogen, and naturally cooling to room temperature to obtain the hollow structure LiFePO 4 and/C positive electrode material, which contains 2.2% of carbon.
Example 4
1. Configuration of FeSO 4 And NH 4 H 2 PO 4 The total concentration of solute is 2mol/L, fe 2+ With PO (PO) 4 3+ The molar ratio of (2) is 2.85:2; the oxalic acid aqueous solution is used as complexing agent solution, and the molar concentration of the oxalic acid aqueous solution is 5mol/L; phosphoric acid aqueous solution is taken as acid solution, and the molar concentration is 0.4mol/L;
2. preparing a mixed solvent of ethylene glycol and deionized water as a reaction solution, wherein the volume ratio of the deionized water to the ethylene glycol is 2:1, and simultaneously adding the binary aqueous solution, the oxalic acid aqueous solution and the phosphoric acid aqueous solution into the reaction solution to perform the reaction of the stage 1 and the stage 2, and continuously blowing high-purity N in the reaction process 2 To remove oxygen from the solution. The adding amount of the binary solution is 85% of the volume of the reaction solution, the adding amount of the complexing agent solution is 15% of the volume of the reaction solution, and the adding amount of the acid solution is adjusted according to the following pH value:
stage 1: the adding amount of the phosphoric acid solution is finely adjusted, the pH value of the reaction system is regulated and controlled to be between 2.0 and 2.2, the reaction time is 6 hours, and the stirring rotating speed is controlled to be 550rpm;
stage 2: adding the phosphoric acid solution, regulating the pH of the reaction system to 3.0-3.2, controlling the stirring rotation speed to 400rpm, and stopping stirring after the reaction is continued for 9 hours;
3. centrifuging and drying the reacted slurry, repeatedly cleaning with deionized water and ethanol for 3-4 times to remove impurities to obtain Fe 3 (PO 4 ) 2 A precursor.
4. LiOH and H 3 PO 4 Respectively preparing 1.5mol/L aqueous solution; will H 3 PO 4 The solution was slowly added to the LiOH solution at a rate of 20L/h, where the molar amount n (Li + ):n(PO 4 3- ) Stirring for 2-3 h to obtain Li at a ratio of 3:1 3 PO 4 And (5) a crystal. The Fe is mixed with 3 (PO 4 ) 2 The precursor is uniformly dispersed into Li 3 PO 4 In a crystal solution, wherein Fe 3 (PO 4 ) 2 The addition amount of the precursor is Li 3 PO 4 5% of the weight of the crystal solution is continuously stirred for 3h, the stirring rotation speed is controlled at 120rpm, the adding speed is controlled at 20L/h to ensure the growth of crystal nuclei, the reacted slurry is centrifuged, dried and decontaminated to obtain LiFePO 4 A precursor.
5. LiFePO is prepared 4 Mixing the precursor with conductive carbon black, wherein the addition amount of the conductive carbon black is 7% of the total mass of the precursor and the conductive carbon black, roasting for 6 hours at 600 ℃ under the protection of inert atmosphere nitrogen, and naturally cooling to room temperature to obtain the hollow structure LiFePO 4 and/C positive electrode material, which contains 1.8% of carbon.
Example 5
1. Configuration (CH) 3 COO) 2 Fe and NH 4 H 2 PO 4 The total concentration of solute is 2mol/L, fe 2+ With PO (PO) 4 3+ The molar ratio of (2) is 2.85:2; the molar concentration of the ascorbic acid aqueous solution serving as a complexing agent solution is 4mol/L; acetic acid aqueous solution as acid solution with a molar concentration of 0.2mol/L;
2. preparing a mixed solvent of polyethylene glycol 200 and deionized water as a reaction solution, wherein the volume ratio of the deionized water to the polyethylene glycol 200 is 2:1, and simultaneously adding the binary aqueous solution, the ascorbic acid aqueous solution and the acetic acid aqueous solution into the reaction solution for carrying outThe reaction of the stage 1 and the stage 2 is carried out by continuously bubbling high-purity N in the reaction process 2 To remove oxygen from the solution. The adding amount of the binary solution is 90% of the volume of the reaction solution, the adding amount of the complexing agent solution is 10% of the volume of the reaction solution, and the adding amount of the acid solution is adjusted according to the following pH value:
stage 1: adjusting the adding amount of the acetic acid solution, regulating and controlling the pH value of a reaction system to be 1.9-2.2, reacting for 5 hours, and controlling the stirring rotating speed to be 500rpm;
stage 2: increasing the addition amount of the acetic acid solution, regulating the pH value of the reaction system to be 2.9-3.2, controlling the stirring rotation speed to be 300rpm, and stopping stirring after the reaction is continued for 9 hours;
3. centrifuging, drying and removing impurities from the reacted slurry to obtain Fe 3 (PO 4 ) 2 A precursor.
4. LiOH and H 3 PO 4 Respectively preparing 1.8mol/L aqueous solution; will H 3 PO 4 The solution was slowly added to the LiOH solution at a rate of 25L/h, where the molar amount n (Li + ):n(PO 4 3- ) Stirring for 2-3 h to obtain Li at a ratio of 3:1 3 PO 4 And (5) a crystal. The Fe is mixed with 3 (PO 4 ) 2 The precursor is uniformly dispersed into Li 3 PO 4 In a crystal solution, wherein Fe 3 (PO 4 ) 2 The addition amount of the precursor is Li 3 PO 4 8% of the weight of the crystal solution is continuously stirred for 3h, the stirring rotation speed is controlled to be 150rpm, the adding speed is controlled to be 25L/h so as to ensure the growth of crystal nuclei, the reacted slurry is centrifuged, dried and decontaminated to obtain LiFePO 4 A precursor.
5. LiFePO is prepared 4 Mixing the precursor with conductive carbon black, wherein the addition amount of the conductive carbon black is 7% of the total mass of the precursor and the conductive carbon black, roasting for 6 hours at 600 ℃ under the protection of inert atmosphere nitrogen, and naturally cooling to room temperature to obtain the hollow structure LiFePO 4 and/C positive electrode material, which contains 2% of carbon.
Example 6
1. Configuration of FeC 2 O 4 And NH 4 H 2 PO 4 The total concentration of solute is 2mol/L, fe 2+ With PO (PO) 4 3+ The molar ratio of (2) is 2.85:2; the molar concentration of the ascorbic acid aqueous solution serving as a complexing agent solution is 5mol/L; phosphoric acid aqueous solution is taken as acid solution, and the molar concentration is 0.2mol/L;
2. preparing a mixed solvent of ethylene glycol and deionized water as a reaction solution, wherein the volume ratio of the deionized water to the ethylene glycol is 2:1, and simultaneously adding the binary aqueous solution, the ascorbic acid aqueous solution and the phosphoric acid aqueous solution into the reaction solution to perform the reaction of the stage 1 and the stage 2, and continuously blowing high-purity N in the reaction process 2 To remove oxygen from the solution. The adding amount of the binary solution is 90% of the volume of the reaction solution, the adding amount of the complexing agent solution is 10% of the volume of the reaction solution, and the adding amount of the acid solution is adjusted according to the following pH value:
stage 1: the adding amount of the phosphoric acid solution is finely adjusted, the pH value of the reaction system is regulated and controlled to be 1.8-2.0, the reaction time is 6h, and the stirring rotating speed is controlled to be 500rpm;
stage 2: adding the phosphoric acid solution, regulating the pH of the reaction system to 2.8-3.0, controlling the stirring rotation speed to 250rpm, and stopping stirring after continuing to react for 9 hours;
3. centrifuging, drying and removing impurities from the reacted slurry to obtain Fe 3 (PO 4 ) 2 A precursor.
4. LiOH and H 3 PO 4 Respectively preparing 2mol/L aqueous solutions; will H 3 PO 4 The solution was slowly added to the LiOH solution at a rate of 18L/h, where the molar amount n (Li + ):n(PO 4 3- ) Stirring for 2-3 h to obtain Li at a ratio of 3:1 3 PO 4 And (5) a crystal. The Fe is mixed with 3 (PO 4 ) 2 The precursor is uniformly dispersed into Li 3 PO 4 In a crystal solution, wherein Fe 3 (PO 4 ) 2 The addition amount of the precursor is Li 3 PO 4 6% of the weight of the crystal solution is continuously stirred for 3h, the stirring rotation speed is controlled at 100rpm, the adding speed is controlled at 18L/h to ensure the growth of crystal nuclei, the reacted slurry is centrifuged, dried and decontaminated to obtain LiFePO 4 A precursor.
5. LiFePO is prepared 4 Precursor and conductive carbon black are mixedAnd the addition amount of the conductive carbon black is 5% of the total mass of the conductive carbon black and the conductive carbon black, roasting for 6 hours at 600 ℃ under the protection of inert atmosphere nitrogen, and naturally cooling to room temperature to obtain the hollow structure LiFePO 4 and/C positive electrode material, which contains 2% of carbon.
Comparative example 1
1. Starting material LiOH, (NH) 4 )H 2 PO 4 ，FeC 2 O 4 Pouring the mixture into a ball mill tank according to the mol ratio of 1:1:1, and adding a certain amount of absolute ethyl alcohol for uniform dispersion; ball milling is carried out for 8 hours at the speed of 300r/min, so as to obtain suspension with good dispersibility; drying the reacted slurry in a vacuum oven, and removing impurities to obtain LiFePO 4 A precursor.
2. LiFePO is prepared 4 Uniformly mixing the precursor and a small amount of conductive carbon black, wherein the mass fraction of the addition amount of the conductive carbon is 7%, roasting for 6 hours at 600 ℃ under the protection of inert atmosphere, setting the heating rate to 3 ℃/min, and naturally cooling to room temperature to obtain LiFePO 4 and/C positive electrode material, which contains 2% of carbon.
Characterization of the properties:
material testing: using N 2 Absorption and desorption specific surface appearance characterization LiFePO 4 BET value of the positive electrode material; characterization of LiFePO using a densitometer 4 And (C) characterizing the particle size distribution by a laser particle size analyzer and the particle size of the inner high-porosity part, and characterizing the thermal stability and the safety performance of the material by a differential scanning calorimeter.
Cell performance test: liFePO prepared in each example and comparative example was prepared using metallic lithium as the negative electrode 4 The material/C is a 2032 button half cell assembled by the positive electrode, a conductive agent (conductive carbon black SP) and a binder (PVDF 5130) according to a formula of 90:5:5. 1.0mol/L LiPF 6 The mixed solution of/ec+emc+dmc (volume ratio EC: EMC: dmc=1:1) is an electrolyte. Aluminum foil as current collector, celgard 2400 as separator, and metallic lithium sheet as counter electrode. The charge-discharge gram capacity and the first charge-discharge efficiency (%) of the lithium iron phosphate cathode material were tested, while the diffusion coefficient (D) of lithium ions was tested using the GITT method Li + ). LiFePO prepared by taking commercial graphite as negative electrode 4 The material/C is a positive electrode assembled into a soft package battery core,testing the first charge and discharge efficiency, the multiplying power performance, the cycle performance and the safety performance of the soft-package battery core; the long circulation voltage range is 2.5-3.65V, the current density is 1℃/1℃, and the temperature is constant at 25+/-1 ℃.
FIG. 1 shows the XRD structure corresponding to the lithium iron phosphate positive electrode material prepared in example 1;
FIG. 2 shows the first charge and discharge curves (0.1C, 2.0-3.7V) of button cells corresponding to the lithium iron phosphate cathode material prepared in example 1;
FIG. 3 shows a plot of the rate performance of the soft pack cell corresponding to the lithium iron phosphate positive electrode material prepared in example 1;
FIG. 4 shows a button cell GITT curve corresponding to the lithium iron phosphate cathode material prepared in example 1, having an ordinate of a lithium ion diffusion coefficient value in (cm) 2 S); the abscissa is the lithium iron phosphate lithium removal depth, expressed as SOC%;
FIG. 5 shows the 45℃cycle capacity retention rate curves (1C/1C 2.5-3.65V) for the soft pack cells corresponding to the lithium iron phosphate positive electrode material prepared in example 1;
FIG. 6 shows a DSC thermogram corresponding to the lithium iron phosphate positive electrode material prepared in example 1;
FIG. 7 shows the first charge and discharge curves (0.1C, 2.0-3.7V) of button cells corresponding to the lithium iron phosphate cathode material prepared in comparative example 1;
characterization results are shown in table 1:
TABLE 1
Compared with the first charge-discharge curves in fig. 2 and 7, the charge-discharge gram capacity value of the corresponding lithium iron phosphate positive electrode material in fig. 2 is higher than that in fig. 7, and the first charge-discharge efficiency is higher. In addition, in fig. 2, the voltage difference between the charge and discharge voltage platforms is smaller, in fig. 7, the voltage difference between the charge and discharge voltage platforms is larger, obvious electrode polarization phenomenon exists, and the subsequent cycle performance is affected by the larger polarization. The above test shows that the lithium iron phosphate cathode material in example 1 has electrochemical properties superior to those of the cathode material in comparative example 1.
As can be seen from the data in table 1, the lithium iron phosphate prepared in examples 1 to 6 above has a remarkable hollow structure, and the porosity of the surface layer is much lower than that in the core. The surface of the composite carbon is used as a lithium battery anode material, so that the charge and discharge efficiency, capacity retention rate and cycle performance of the battery can be obviously improved, and the battery is correspondingly promoted to have longer service life by better cycle performance. Meanwhile, the lithium iron phosphate has better thermal stability, and the lithium iron phosphate is applied to the post-battery liquid, so that the safety of the battery is improved.
The above description is only of the preferred embodiments of the present application and is not intended to limit the present application, but various modifications and variations can be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims (8)
1. The preparation method of the lithium iron phosphate anode material is characterized by comprising the following steps of:
preparing a mixed solvent of water and an organic solvent, adding a binary solution, a complexing agent solution and an acid solution into the mixed solvent, and performing a first-stage reaction under the condition of a pH value of 1.8-2.4 to form an intermediate reaction solution; adjusting the pH value of the intermediate reaction liquid to 2.6-3.2, and performing a second stage reaction to form Fe 3 (PO 4 ) 2 A precursor; wherein the binary solution is a solution of soluble ferrous salt and a phosphate ion-containing soluble compound;
the Fe is 3 (PO 4 ) 2 Dispersing the precursor into Li 3 PO 4 Crystal nucleus growth is carried out in the crystal solution to obtain LiFePO 4 A precursor;
the LiFePO 4 Mixing the precursor with a carbon source, and roasting in an inert atmosphere to obtain the lithium iron phosphate anode material; wherein the lithium iron phosphate positive electrode material comprises spherical lithium iron phosphate and carbon compounded on the surface of the spherical lithium iron phosphate, and the spherical lithium iron phosphate is provided with an inner core and a surface positioned at the periphery of the inner coreAnd the carbon is coated on the surface layer, the porosity of the inner core is larger than that of the surface layer, the porosity of the inner core is 60-90%, and the porosity of the surface layer is below 20%.
2. The preparation method according to claim 1, wherein the particle size of the spherical lithium iron phosphate is 4-6 μm; the particle size of the inner core is 1-3 mu m.
3. The method of claim 1, wherein the carbon is selected from one or more of graphene, carbon nanotubes, conductive carbon black, amorphous carbon; the content of the carbon is 1.5-2.5% of the weight of the lithium iron phosphate anode material.
4. The method according to claim 1, wherein the organic solvent in the mixed solvent is an alcohol solvent, and the volume ratio of water to the organic solvent in the mixed solvent is (1-3).
5. The method of claim 1 or 2, wherein the soluble ferrous salt is selected from feci 2 、FeC 2 O 4 、(CH 3 COO) 2 Fe、FeSO 4 One or more of the following;
the phosphate ion-containing soluble compound is selected from phosphoric acid and/or soluble phosphate selected from NH 4 H 2 PO 4 ，Na 2 HPO 4 ，(NH 4 ) 2 HPO 4 One or more of the following;
the binary solution is an aqueous solution of the soluble ferrous salt and the phosphate ion-containing soluble compound, wherein Fe in the soluble ferrous salt 2+ With PO in the phosphate ion-containing soluble compound 4 3+ 2, wherein the total molar concentration of the soluble ferrous salt and the phosphate ion is 1 to 3mol/L;
in the complexing agent solution, the complexing agent is one or more selected from citric acid, oxalic acid and ascorbic acid.
6. The method according to claim 1 or 4, wherein the crystal nucleus growing step comprises:
adding phosphoric acid solution into lithium hydroxide solution to react to form the Li 3 PO 4 A crystal solution;
the Fe is 3 (PO 4 ) 2 Dispersing the precursor into the Li 3 PO 4 Crystal nucleus growth is carried out in the crystal solution to obtain the LiFePO 4 A precursor;
the phosphoric acid solution is phosphoric acid aqueous solution, and the molar concentration of the phosphoric acid aqueous solution is 1.0-2.5 mol/L; the lithium hydroxide solution is lithium hydroxide aqueous solution, and the molar concentration of the lithium hydroxide solution is 1.0-2.5 mol/L; li in the lithium hydroxide solution + And PO in the phosphoric acid solution 4 3- The molar ratio of (2.85-3.15) is 1.
7. A positive electrode material, characterized in that it is a lithium iron phosphate positive electrode material prepared by the preparation method according to any one of claims 1 to 6.
8. A lithium ion battery comprising a positive electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active layer positioned on the surface of the positive electrode current collector, and the positive electrode active layer comprises a positive electrode material, a conductive agent and a binder, and is characterized in that the positive electrode material is the lithium iron phosphate positive electrode material prepared by the preparation method according to any one of claims 1 to 6.
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| JP2009301813A (en) * | 2008-06-12 | 2009-12-24 | Tayca Corp | Method for manufacturing carbon-olivine type iron lithium phosphate complex, and cathode material for lithium ion battery |
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| US11456458B2 (en) * | 2016-12-08 | 2022-09-27 | Samsung Sdi Co., Ltd. | Nickel-based active material precursor for lithium secondary battery, preparing method thereof, nickel-based active material for lithium secondary battery formed thereof, and lithium secondary battery comprising positive electrode including the nickel-based active material |
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