CN114572956B - Nanoscale olivine type sodium iron phosphate and preparation method and application thereof - Google Patents
Nanoscale olivine type sodium iron phosphate and preparation method and application thereof Download PDFInfo
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- 239000010450 olivine Substances 0.000 title claims abstract description 12
- 229910052609 olivine Inorganic materials 0.000 title claims abstract description 12
- AWRQDLAZGAQUNZ-UHFFFAOYSA-K sodium;iron(2+);phosphate Chemical compound [Na+].[Fe+2].[O-]P([O-])([O-])=O AWRQDLAZGAQUNZ-UHFFFAOYSA-K 0.000 title claims abstract description 11
- 238000002360 preparation method Methods 0.000 title claims abstract description 8
- 239000005955 Ferric phosphate Substances 0.000 claims abstract description 30
- 229940032958 ferric phosphate Drugs 0.000 claims abstract description 30
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims abstract description 30
- 229910000399 iron(III) phosphate Inorganic materials 0.000 claims abstract description 30
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 claims abstract description 28
- 239000011734 sodium Substances 0.000 claims abstract description 27
- 229910001415 sodium ion Inorganic materials 0.000 claims abstract description 26
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 claims abstract description 25
- 239000007774 positive electrode material Substances 0.000 claims abstract description 25
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims abstract description 24
- 238000003756 stirring Methods 0.000 claims abstract description 19
- 239000000463 material Substances 0.000 claims abstract description 16
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims abstract description 14
- 229910052708 sodium Inorganic materials 0.000 claims abstract description 14
- 229910052786 argon Inorganic materials 0.000 claims abstract description 12
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 11
- 239000003960 organic solvent Substances 0.000 claims abstract description 11
- 238000005303 weighing Methods 0.000 claims abstract description 11
- 238000000227 grinding Methods 0.000 claims abstract description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 10
- 239000007800 oxidant agent Substances 0.000 claims abstract description 8
- 230000001590 oxidative effect Effects 0.000 claims abstract description 8
- 238000001035 drying Methods 0.000 claims abstract description 5
- 238000010521 absorption reaction Methods 0.000 claims abstract description 4
- 238000009837 dry grinding Methods 0.000 claims abstract description 3
- FVAUCKIRQBBSSJ-UHFFFAOYSA-M sodium iodide Chemical group [Na+].[I-] FVAUCKIRQBBSSJ-UHFFFAOYSA-M 0.000 claims description 27
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 claims description 12
- 235000009518 sodium iodide Nutrition 0.000 claims description 9
- 239000002105 nanoparticle Substances 0.000 claims description 7
- 239000001301 oxygen Substances 0.000 claims description 7
- 229910052760 oxygen Inorganic materials 0.000 claims description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 6
- 238000001291 vacuum drying Methods 0.000 claims description 6
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 4
- 229910002651 NO3 Inorganic materials 0.000 claims description 4
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 4
- 239000002253 acid Substances 0.000 claims description 4
- 238000000034 method Methods 0.000 abstract description 20
- 230000008569 process Effects 0.000 abstract description 11
- 230000008859 change Effects 0.000 abstract description 6
- 230000007246 mechanism Effects 0.000 abstract description 3
- 238000009826 distribution Methods 0.000 abstract description 2
- 229910000162 sodium phosphate Inorganic materials 0.000 abstract description 2
- 239000001488 sodium phosphate Substances 0.000 abstract description 2
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 abstract description 2
- 238000011056 performance test Methods 0.000 description 11
- 238000006243 chemical reaction Methods 0.000 description 8
- 238000000498 ball milling Methods 0.000 description 7
- 238000012360 testing method Methods 0.000 description 6
- 150000001875 compounds Chemical class 0.000 description 5
- 229920000447 polyanionic polymer Polymers 0.000 description 5
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 4
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 4
- 239000002033 PVDF binder Substances 0.000 description 4
- 238000004146 energy storage Methods 0.000 description 4
- 238000005342 ion exchange Methods 0.000 description 4
- 229910052744 lithium Inorganic materials 0.000 description 4
- 229910001416 lithium ion Inorganic materials 0.000 description 4
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 4
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 239000013543 active substance Substances 0.000 description 3
- 239000010406 cathode material Substances 0.000 description 3
- 230000007613 environmental effect Effects 0.000 description 3
- -1 nitro tetrafluoroborate Chemical compound 0.000 description 3
- 239000012071 phase Substances 0.000 description 3
- 238000011160 research Methods 0.000 description 3
- 238000001878 scanning electron micrograph Methods 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 239000006183 anode active material Substances 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 239000011230 binding agent Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000003487 electrochemical reaction Methods 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000006245 Carbon black Super-P Substances 0.000 description 1
- 229910013063 LiBF 4 Inorganic materials 0.000 description 1
- MKYBYDHXWVHEJW-UHFFFAOYSA-N N-[1-oxo-1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propan-2-yl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(C(C)NC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 MKYBYDHXWVHEJW-UHFFFAOYSA-N 0.000 description 1
- KEAYESYHFKHZAL-UHFFFAOYSA-N Sodium Chemical group [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 description 1
- 239000011149 active material Substances 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000006258 conductive agent Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 238000001027 hydrothermal synthesis Methods 0.000 description 1
- DCYOBGZUOMKFPA-UHFFFAOYSA-N iron(2+);iron(3+);octadecacyanide Chemical compound [Fe+2].[Fe+2].[Fe+2].[Fe+3].[Fe+3].[Fe+3].[Fe+3].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-] DCYOBGZUOMKFPA-UHFFFAOYSA-N 0.000 description 1
- 229910003002 lithium salt Inorganic materials 0.000 description 1
- 159000000002 lithium salts Chemical class 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 238000007709 nanocrystallization Methods 0.000 description 1
- 239000005373 porous glass Substances 0.000 description 1
- 229960003351 prussian blue Drugs 0.000 description 1
- 239000013225 prussian blue Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000012798 spherical particle Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- 229910000314 transition metal oxide Inorganic materials 0.000 description 1
Classifications
-
- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/40—Electric properties
-
- 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
-
- 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
- Y02E70/00—Other energy conversion or management systems reducing GHG emissions
- Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin
Abstract
The invention belongs to the technical field of sodium ion battery materials, and particularly relates to nanoscale olivine type ferric sodium phosphate, a preparation method and application thereof. Weighing lithium iron phosphate, and placing the lithium iron phosphate into a planetary ball mill for dry grinding to obtain nano-scale lithium iron phosphate; in an argon glove box, weighing nanoscale lithium iron phosphate, placing the nanoscale lithium iron phosphate in an organic solvent, adding an oxidant, stirring, centrifuging and drying in vacuum to generate ferric phosphate; grinding ferric phosphate in an argon glove box to prevent water absorption and avoid caking, weighing ferric phosphate, placing the ferric phosphate in an organic solvent, adding a reducing agent, stirring, centrifuging and drying in vacuum to obtain sodium ferric phosphate, namely nanoscale olivine-type sodium ferric phosphate. The nano-scale sodium iron phosphate changes the phase change mechanism in the charge and discharge process, visually shows the smearing of a charging platform, and improves the circulation stability. In addition, the elements of the positive electrode material are rich in content and wide in distribution in the crust, and the positive electrode material is low in cost and environment-friendly.
Description
Technical Field
The invention belongs to the technical field of sodium ion battery materials, and particularly relates to nanoscale olivine type ferric sodium phosphate, a preparation method and application thereof.
Background
Energy crisis and environmental pollution are common problems facing countries in the world today. Improving the resource ratio of renewable energy sources such as solar energy, wind energy, tidal energy, geothermal energy and the like is considered as an optimal solution for solving the energy and environmental problems. However, these energy sources are affected by weather and regions, and only intermittent energy is formed, which makes it difficult to directly use them. Therefore, there is an urgent need for a low-cost, environmentally friendly energy storage technology that integrates such intermittent energy into a continuous, stable and controllable grid.
Among various energy storage devices, secondary batteries represented by lithium ion batteries have been applied to various portable devices and electric vehicles due to their efficient energy conversion storage devices, portability, environmental friendliness, high energy density and power density. However, due to the wide range of applications of lithium ion batteries, there is a growing demand for lithium ore resources, leading to a growing price of lithium and related lithium salts, and therefore lithium ion batteries are not ideal choices for low cost energy storage technologies. Sodium ion batteries are widely distributed due to sufficient sodium ore resources, and meanwhile, due to the fact that sodium and lithium are similar in physicochemical properties, compounds of the sodium ion batteries have great similarity in research methods and applications, and the sodium ion batteries are considered to be the best choice of a large-scale energy storage system.
As with lithium ion batteries, sodium ion battery cathode materials have been a difficulty and hotspot in sodium ion battery research. The positive electrode material of the sodium ion battery is mainly divided into layered transition metal oxide Na x TMO 2 (TM is an excessive metal element), polyanion compounds, prussian blue-based compounds, and the like. The polyanion compound has better cycle performance and multiplying power performance due to the characteristics of higher ionic conductivity and stable structure, and is widely focused by researchers.
LiFePO 4 With excellent thermal safety, high reversibility and high operating voltage (3.45 vs Li + Li), exhibit high competitiveness, and have been beginning to be applied to commercial automobiles. In sodium ion batteries, naFePO 4 Due to its same LiFePO 4 Similar olivine-type structures have better electrochemical properties. However, naFePO 4 Is a nano-ferrophosphorus structure. Therefore, the nano-ferrophosphorus structure is very easy to prepare by solid phase, hydrothermal method and the like. In the nano-ferrophosphorus structure, na + And no diffusion channel, the nano-ferrophosphorus structure shows electrochemical inertia from the structural point of view. Therefore, it was studied how to synthesize olivine-type NaFePO with electrochemical properties 4 Is a difficult point to be solved urgently.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a nano-sized olivine-type polyanion positive electrode material Na x FePO 4 And a preparation method and a sodium ion battery thereof, so as to solve or partially solve the problems in the prior art.
In a first aspect, the present invention provides a method for preparing a nano-sized olivine-type positive electrode material, comprising the steps of:
(1) Weighing lithium iron phosphate, and placing the lithium iron phosphate into a planetary ball mill for dry grinding to obtain nano-scale lithium iron phosphate;
(2) In an argon glove box with the water oxygen value lower than 0.01ppm, weighing nanoscale lithium iron phosphate, placing the nanoscale lithium iron phosphate in an organic solvent, adding an oxidant according to a certain stoichiometric ratio, stirring, centrifuging and vacuum drying to generate ferric phosphate;
(3) Grinding ferric phosphate in an argon glove box with the water oxygen value lower than 0.01ppm, preventing water absorption and avoiding caking, weighing ferric phosphate, placing the ferric phosphate in an organic solvent, adding a reducing agent according to a certain stoichiometric ratio, stirring, centrifuging and drying in vacuum to obtain the sodium ferric phosphate, namely the nanoscale olivine-type sodium ferric phosphate.
Preferably, in the step (1), the lithium iron phosphate is weighed according to the mass ratio of the balls of 10:1, and is pre-ground for 60min at the speed of 300rpm/min and then ball-milled for 60min at the speed of 300-900 rpm/min.
Preferably, in step (2) and step (3), the organic solvent is at least one of acetonitrile and ethanol.
Preferably, in the step (2), the oxidant is nitro tetrafluoroborate, and the molar ratio of the nitro tetrafluoroborate to the lithium iron phosphate is 1.5:1.
preferably, in the step (2), the stirring time is 24 hours, and the stirring temperature is normal temperature.
Preferably, in the step (3), the reducing agent is sodium iodide, and the molar ratio of sodium iodide to ferric phosphate is 2:1.
Preferably, in the step (3), the stirring time is 48-56 h, and the stirring temperature is 30-60 ℃.
In a second aspect, the present invention provides a nano-sized olivine Na x FePO 4 The purpose is to reduce the limit of the inversion defect on the specific capacity of sodium iron phosphate, promote the formation of a sodium ion diffusion channel by using an organic solvent, and improve the specific capacity of the positive electrode material to a certain extent.
Further, by changing the size, the structural change of the material in the electrochemical circulation process is stabilized, and the material is inhibitedPreparation of olivine type Na x FePO 4 The phase change process of the positive electrode material in the charging process can further improve the cycle performance of the positive electrode material.
In a third aspect, the present invention provides a nano-sized olivine-type polyanionic cathode material Na x FePO 4 With the application of the olivine type polyanion positive electrode material Na x FePO 4 The positive electrode material as a battery can be applied to a sodium ion battery, and comprises the following steps:
taking a nano olivine type polyanion compound as an anode active material, carrying out mixed grinding on the anode active material, conductive carbon black (Super P) and a binder (PVDF) according to the mass ratio of 8:1:1-6:3:1, preferably 7:2:1, carrying out mixed grinding for 25min, coating an active substance on an aluminum foil, and carrying out vacuum drying, rolling and slicing to prepare an anode plate; the metal sodium is used as a negative electrode; using GF/D battery diaphragm glass fiber filter paper as a diaphragm; matching sodium hexafluorophosphate electrolyte, assembling into a sodium ion battery in a glove box filled with argon, standing for 10h, and performing corresponding electrochemical performance test; the performance test voltage window is 1.5-4V; the performance test current density is selected from 0.1C and 1C.
The invention provides a method for successfully synthesizing nanoscale sodium iron phosphate by mechanical ball milling and ion exchange. The nano-scale sodium iron phosphate changes the phase change mechanism in the charge and discharge process, visually shows the smearing of a charging platform, and improves the circulation stability. In addition, the elements of the positive electrode material are rich in content and wide in distribution in the crust, have low cost, belong to environment-friendly elements and have good environment-friendly value. Compared with the prior art, the method has the following beneficial effects:
(1) The positive electrode material prepared by the method successfully synthesizes an olivine structure through an ion exchange method, avoids the generation of a nano-phosphosiderite structure, reduces the concentration of inversion defects to a certain extent by utilizing solvent synthesis, and ensures that more sodium ions participate in the charge and discharge process, thereby being beneficial to further improving the actual capacity.
(2) The invention stabilizes the structural change of the material in the electrochemical circulation process by nanocrystallization, and changes olivesStone type Na x FePO 4 The phase change process of the positive electrode material in the charging process leads the positive electrode material to tend to carry out ion exchange in a solid solution mode, thereby improving the cycle performance of the positive electrode material and obtaining higher cycle stability.
(3) The invention provides a preparation method of a nano-sized olivine type positive electrode material by a mechanical ball milling and ion exchange method, and the positive electrode material has the characteristics of higher cycle performance, good stability, low cost and environmental friendliness, and does not receive the restriction of lithium resources.
Drawings
FIG. 1 shows the positive electrode material NaFePO prepared in example 1 4 X-ray diffraction pattern (XRD) of (a).
Fig. 2 is a Scanning Electron Micrograph (SEM) of the positive electrode material prepared in example 1.
Fig. 3 is a typical charge-discharge curve of the first 3 turns of the battery prepared in example 1.
Fig. 4 is a graph showing the cycle performance of the battery prepared in example 1 for the first 50 cycles.
Fig. 5 is an electrochemical comparison (first circle) of example 3 and example 2.
Detailed Description
In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail with reference to specific embodiments. The following description is merely illustrative of the invention and is not intended to be limiting in any way, as reagents and materials are commercially available in the art.
Example 1
(one) preparing a cathode material NaFePO 4 。
(1) And (3) weighing lithium iron phosphate according to a ball-to-material ratio of 10:1, placing the lithium iron phosphate into a ball milling tank, performing dry ball milling in a planetary ball mill, wherein the rotating speed of the ball mill is 300rpm/min, the total ball milling time is 2h, grinding the sample for 3min after ball milling is finished, and placing the sample into an argon glove box with a water-oxygen value lower than 0.01ppm.
(2) In an argon glove box with the water oxygen value lower than 0.01ppm, putting nano lithium iron phosphate into acetonitrile, adding oxidant tetrafluoroboric acid nitrate in the ratio of 1.5:1, continuously stirring at normal temperature for 24 hours until the reaction is complete, centrifuging for 4 to 5 times to separate ferric phosphate, and vacuum drying at 60 ℃ to obtain the ferric phosphate.
(3) Grinding ferric phosphate in an argon glove box with the water oxygen value lower than 0.01ppm, preventing water absorption and avoiding agglomeration so as to facilitate subsequent reaction, placing the ground ferric phosphate in acetonitrile, adding a reducing agent sodium iodide in a ratio of 2:1, stirring at a temperature of 60 ℃, preferably 5 ℃/min, continuously stirring for 48 hours so as to facilitate reaction, centrifuging for 4 to 5 times to separate sodium ferric phosphate, and vacuum drying at 60 ℃ to obtain sodium ferric phosphate.
It should be noted that in the steps (2) and (3), the total weight concentration of the raw materials in the stirring process is not more than 2.5g/50ml; in the embodiment of the application, 50% of oxidant and reducing agent are required to be excessively added;
specifically, in step (2) of the present application, lithium iron phosphate is placed in an organic solvent, and then an oxidant, namely tetrafluoroboric acid nitrate, is added, and the chemical reaction involved in the reaction to generate ferric phosphate is as follows:
LiFePO 4 +NO 2 BF 4 →FePO 4 +NO 2 +LiBF 4
in the step (3), lithium iron phosphate is placed in an organic solvent, then a reducing agent sodium iodide is added, and the chemical reaction involved in the reaction to generate sodium iron phosphate is as follows:
FePO 4 +3/2NaI→NaFePO 4 +1/2NaI 3
and (II) assembling the sodium ion battery.
And (3) taking the positive electrode material prepared in the step (one) as a positive electrode active substance, taking conductive carbon black Super P as a conductive agent, taking polyvinylidene fluoride (PVDF) as a binder, adding the active material, the Super P and the PVDF into a mortar according to a mass ratio of preferably 7:2:1, and grinding for 25min. Coating aluminum foil as a current collector into thin slices, drying in a vacuum drying oven completely, and making into positive plates by a slicing machine; the negative electrode is sodium metal, and the electrolyte is NaPF 6 (EC: dec=1:1 vol%) solution, porous glass fiber membrane (GF/D) was used as separator, and assembly of the button cell was performed in an argon glove box with a water oxygen value lower than 0.01ppm.
And (III) testing the electrochemical performance of the sodium ion battery.
Electrochemical performance testing was performed on the assembled cells using a blue cell testing system. The voltage window is set at 1.5-4V, and the electrochemical performance test is carried out by selecting the constant speed rate of the current density of 0.1C, 0.5C and 1C according to the specific capacity obtained by theoretical calculation and the quality of the corresponding positive electrode plate active substance. The typical charge-discharge curve is shown in fig. 3.
Example 2
The size of lithium iron phosphate was changed, and NaFePO was prepared in the same manner as in example 1 except that the stirring temperature was adjusted to 50℃in step (3) of example 2 by ball-milling at 300rpm/min for 60min and 600rpm/min for 60min in step (1) of example 2 4 。
The rest of the assembled sodium-ion battery and the electrochemical performance test were performed as in example 1.
Example 3
The NaFePO was prepared in the same manner as in example 1 except that the step (1) of example 3 was omitted without changing the size of lithium iron phosphate 4 。
The rest of the assembled sodium-ion battery and the electrochemical performance test were performed as in example 1.
Example 4
Changing the sodium ratio in the substance, wherein the molar ratio of the ferric phosphate to the reducing agent sodium iodide is 1 according to the step (3): 1, the remainder prepared Na in the same manner as in example 1 x FePO 4 。
The rest of the assembled sodium-ion battery and the electrochemical performance test were performed as in example 1.
Example 5
Changing the sodium ratio in the substance, wherein the molar ratio of the ferric phosphate to the reducing agent sodium iodide is 1 according to the step (3): 1, the remainder of the procedure in example 2 was followed to prepare Na x FePO 4 。
The rest of the assembled sodium-ion battery and the electrochemical performance test were performed as in example 1.
Example 6
Changing the sodium ratio in the material according to step (3) of ferric phosphate toThe molar ratio of the reducing agent sodium iodide is 1:1, the remainder of the procedure in example 3 was followed to prepare Na x FePO 4 。
The rest of the assembled sodium-ion battery and the electrochemical performance test were performed as in example 1.
The positive electrode material of the sodium ion battery prepared in the above example was assembled into a battery, and then the following electrochemical performance test was performed.
1. The charge and discharge performance at a current density of 0.1C (1c=154 mA/g) was tested at a voltage between 1.5 and 4.0V, and the results are shown in the following table.
| Project | Specific charge capacity (mAh/g) | Specific discharge capacity (mAh/g) | Coulombic efficiency (%) |
| Example 1 | 122 | 118.4 | 97.04 |
| Example 2 | 100.6 | 97.9 | 97.31 |
| Example 3 | 120 | 115.9 | 96.58 |
| Example 4 | 94.5 | 93.8 | 99.25 |
| Example 5 | 68.3 | 65.5 | 95.90 |
| Example 6 | 108.3 | 107.7 | 99.44 |
2. The charge-discharge cycle stability is tested, the test voltage is 1.5-4.0V, the current density is 0.1C, the capacity can still be kept 88% after 100 cycles, and the cycle performance diagram is shown in figure 4.
3. The electrochemical curves of the materials with different sizes are changed, the test voltage is between 1.5 and 4.0V, and the electrochemical performance test is carried out under the condition that the current rate is 0.1C, and the test result is shown in figure 5.
FIG. 1 is an X-ray diffraction chart of the positive electrode material prepared in the embodiment 1 of the invention, and the characteristic peaks of the olivine-type sodium iron phosphate are met from the chart, so that the sample has a Pnma space group structure. Fig. 2 is a scanning electron micrograph of the material, from which spherical particles can be seen, with diameters less than 200nm.
The electrochemical performance of the sodium ion battery prepared above was tested, and the results are shown in fig. 3. As can be seen from FIG. 3, the material has voltage platforms around 2.8V and 3.1V, representing NaFePO 4 An electrochemical platform;
fig. 5 is a charge curve of nanoscale versus original material, the primary difference of nanoscale materials relative to original materials is the application of a voltage plateau. Raw material inVoltage platforms at 2.8V and 3.1V indicate NaFePO during electrochemical reaction 4 →Na 2/3 FePO 4 ，Na 2/3 FePO 4 →Na 0 FePO 4 Whereas nanoscale materials have no distinct voltage plateau, the overall behavior is a sloping voltage curve, indicating that electrochemical reaction processes tend to proceed in a solid solution mechanism.
The specific capacity of the nano-scale olivine-type positive electrode material keeps 78% of the initial capacity, and compared with other related sodium ion battery researches, the nano-scale olivine-type positive electrode material has extremely excellent cycle performance.
Claims (2)
1. The preparation method of the nanoscale olivine type sodium iron phosphate is characterized by comprising the following specific steps:
(1) Weighing lithium iron phosphate, and placing the lithium iron phosphate into a planetary ball mill for dry grinding to obtain nano-scale lithium iron phosphate; weighing lithium iron phosphate according to the ball material mass ratio of 10:1, pre-grinding the lithium iron phosphate for 60min at the speed of 300rpm/min, and ball-grinding the lithium iron phosphate for 60min at the speed of 300-900 rpm/min;
(2) In an argon glove box, weighing nanoscale lithium iron phosphate, placing the nanoscale lithium iron phosphate in an organic solvent, adding an oxidant according to a certain stoichiometric ratio, stirring, centrifuging and drying in vacuum to generate ferric phosphate; the oxidant is tetrafluoroboric acid nitrate, and the molar ratio of tetrafluoroboric acid nitrate to lithium iron phosphate is 1.5:1, a step of; stirring time is 24h, and stirring temperature is normal temperature;
(3) Grinding ferric phosphate in an argon glove box to prevent water absorption and avoid caking, weighing ferric phosphate, placing the ferric phosphate in an organic solvent, adding a reducing agent according to a certain stoichiometric ratio, stirring, centrifuging and vacuum drying to obtain sodium ferric phosphate, namely nanoscale olivine sodium ferric phosphate; the reducer is sodium iodide, and the molar ratio of the sodium iodide to the ferric phosphate is 2:1; stirring time is 48-56 h, and stirring temperature is 30-60 ℃;
in the step (2) and the step (3), the organic solvent is at least one of acetonitrile and ethanol; the water oxygen values in the argon glove box were all below 0.01ppm.
2. The use of the nano-sized olivine-type sodium iron phosphate prepared by the preparation method according to claim 1, wherein the nano-sized olivine-type sodium iron phosphate is used as a positive electrode material of a sodium ion battery to prepare the sodium ion battery.
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