CN116409772A - Secondary growth preparation method of nano lithium iron phosphate - Google Patents
Secondary growth preparation method of nano lithium iron phosphate Download PDFInfo
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- CN116409772A CN116409772A CN202310407851.7A CN202310407851A CN116409772A CN 116409772 A CN116409772 A CN 116409772A CN 202310407851 A CN202310407851 A CN 202310407851A CN 116409772 A CN116409772 A CN 116409772A
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- iron phosphate
- lithium iron
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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 89
- 238000002360 preparation method Methods 0.000 title claims abstract description 35
- 230000034655 secondary growth Effects 0.000 title claims abstract description 24
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 40
- 239000013078 crystal Substances 0.000 claims abstract description 38
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 32
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 31
- 239000011574 phosphorus Substances 0.000 claims abstract description 31
- 238000001027 hydrothermal synthesis Methods 0.000 claims abstract description 19
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 16
- 229910052742 iron Inorganic materials 0.000 claims abstract description 16
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 16
- 239000002243 precursor Substances 0.000 claims abstract description 14
- 239000000126 substance Substances 0.000 claims abstract description 14
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 9
- 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 42
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims description 36
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 24
- 229960005070 ascorbic acid Drugs 0.000 claims description 21
- 235000010323 ascorbic acid Nutrition 0.000 claims description 21
- 239000011668 ascorbic acid Substances 0.000 claims description 21
- SURQXAFEQWPFPV-UHFFFAOYSA-L iron(2+) sulfate heptahydrate Chemical compound O.O.O.O.O.O.O.[Fe+2].[O-]S([O-])(=O)=O SURQXAFEQWPFPV-UHFFFAOYSA-L 0.000 claims description 21
- 238000006243 chemical reaction Methods 0.000 claims description 13
- 238000001816 cooling Methods 0.000 claims description 13
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 12
- PQVSTLUFSYVLTO-UHFFFAOYSA-N ethyl n-ethoxycarbonylcarbamate Chemical compound CCOC(=O)NC(=O)OCC PQVSTLUFSYVLTO-UHFFFAOYSA-N 0.000 claims description 12
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 claims description 12
- GLXDVVHUTZTUQK-UHFFFAOYSA-M lithium hydroxide monohydrate Substances [Li+].O.[OH-] GLXDVVHUTZTUQK-UHFFFAOYSA-M 0.000 claims description 12
- 229940040692 lithium hydroxide monohydrate Drugs 0.000 claims description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 12
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 11
- 229910001416 lithium ion Inorganic materials 0.000 claims description 11
- 238000005406 washing Methods 0.000 claims description 11
- 229910003002 lithium salt Inorganic materials 0.000 claims description 5
- 159000000002 lithium salts Chemical class 0.000 claims description 5
- 239000002245 particle Substances 0.000 claims description 5
- 239000007774 positive electrode material Substances 0.000 claims description 5
- 238000001035 drying Methods 0.000 claims description 4
- 239000012046 mixed solvent Substances 0.000 claims description 3
- 239000002904 solvent Substances 0.000 claims description 3
- 239000002105 nanoparticle Substances 0.000 claims description 2
- 238000004321 preservation Methods 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 18
- 238000000034 method Methods 0.000 abstract description 10
- 238000004519 manufacturing process Methods 0.000 abstract description 7
- 230000009286 beneficial effect Effects 0.000 abstract description 3
- 239000000411 inducer Substances 0.000 abstract 1
- 239000007864 aqueous solution Substances 0.000 description 28
- 239000000243 solution Substances 0.000 description 28
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 27
- 230000000052 comparative effect Effects 0.000 description 14
- 239000000203 mixture Substances 0.000 description 11
- 235000003891 ferrous sulphate Nutrition 0.000 description 9
- 239000011790 ferrous sulphate Substances 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 9
- 229910000359 iron(II) sulfate Inorganic materials 0.000 description 9
- 238000005303 weighing Methods 0.000 description 9
- 238000002156 mixing Methods 0.000 description 5
- 238000001000 micrograph Methods 0.000 description 4
- 239000000843 powder Substances 0.000 description 4
- 239000002033 PVDF binder Substances 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 230000033228 biological regulation Effects 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 239000002028 Biomass Substances 0.000 description 2
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 2
- 230000006978 adaptation Effects 0.000 description 2
- 239000010405 anode material Substances 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 238000000227 grinding Methods 0.000 description 2
- 230000012010 growth Effects 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- -1 lithium hexafluorophosphate Chemical compound 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 229910021392 nanocarbon Inorganic materials 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 102000004310 Ion Channels Human genes 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect 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
- SRSXLGNVWSONIS-UHFFFAOYSA-N benzenesulfonic acid Chemical compound OS(=O)(=O)C1=CC=CC=C1 SRSXLGNVWSONIS-UHFFFAOYSA-N 0.000 description 1
- 229940092714 benzenesulfonic acid Drugs 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 238000003763 carbonization Methods 0.000 description 1
- 239000010406 cathode material Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000002349 favourable effect Effects 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
- 230000006872 improvement Effects 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 230000037427 ion transport Effects 0.000 description 1
- 239000012982 microporous membrane Substances 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 238000007709 nanocrystallization Methods 0.000 description 1
- 239000002086 nanomaterial Substances 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 150000003017 phosphorus Chemical class 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000006479 redox reaction Methods 0.000 description 1
- 230000008844 regulatory mechanism Effects 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/45—Phosphates containing plural metal, or metal and ammonium
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- 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
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Abstract
The invention discloses a secondary growth preparation method of nano lithium iron phosphate, which comprises the following steps: carrying out hydrothermal reaction on nano lithium iron phosphate serving as a seed crystal, a two-dimensional phosphorus simple substance and a reducing agent in a lithium iron phosphate precursor solution; the lithium iron phosphate precursor solution includes an iron source, a lithium source, and a phosphorus source. According to the invention, the primary nano lithium iron phosphate is used as a seed crystal, and the two-dimensional phosphorus simple substance and the lithium iron phosphate precursor solution are introduced to perform secondary growth in the hydrothermal process, so that the preparation of the high-performance nano lithium iron phosphate material is realized. Compared with the prior art, the method is efficient and environment-friendly, does not need to use an additional organic inducer, and greatly reduces pollution in the preparation process. Meanwhile, the method has simple steps and strong controllability, and is more beneficial to industrialized production of high-performance nano lithium iron phosphate.
Description
Technical Field
The invention relates to the technical field of lithium ion battery anode materials, in particular to a secondary growth preparation method of nano lithium iron phosphate.
Background
The lithium iron phosphate is a lithium ion battery anode material, has higher safety, stability, cycle life and energy density, and is widely applied to the fields of portable electronic equipment, electric vehicles, energy storage systems and the like. Compared with the traditional lithium cobaltate, lithium nickelate and ternary materials, the material has higher safety and environmental protection, and is more suitable for large-scale application. But its rate capability is poor due to its low lithium ion mobility and electron conductivity. Currently, nanocrystallization, doping and coating of lithium iron phosphate are important methods for improving the rate capability of lithium iron phosphate.
Chinese patent CN115367724a discloses a method for producing lithium iron phosphate material by using biomass agent, firstly grinding lithium source, iron source and phosphorus source to obtain aqueous solution, adding mixture of biomass agent and benzenesulfonic acid as additive, mixing the materials prepared in the previous two steps according to proportion, making hydrothermal reaction, and finally eluting material to obtain lithium iron phosphate powder. Similarly, chinese patent CN102013490a discloses a high-rate performance lithium iron phosphate positive electrode material and a preparation method thereof, wherein ball-milled graphite is mixed with ferric salt, phosphate and lithium salt, absolute ethyl alcohol is used as a medium for secondary ball milling, slurry is spray-dried to obtain a powder material, and the powder material is placed in a rotary furnace for atmosphere sintering to obtain the high-rate performance lithium iron phosphate positive electrode material. In addition, chinese patent CN114171740a discloses a preparation method of nano lithium iron phosphate cathode material, firstly hollow nano carbon spheres are prepared, then the hollow nano carbon spheres are mixed with lithium salt, ferric salt and phosphorus salt to prepare a reaction solution, the reaction solution is subjected to hydrothermal reaction under inert gas to obtain a lithium iron phosphate precursor, and finally roasting is performed. The method has relatively complicated process, lacks controllability of the lithium iron phosphate nano structure, particularly lithium ion transmission dominant channels, and can introduce some impurities which cannot be removed, thus bringing uncontrollable potential risks to the application of the method. There is therefore an urgent need to develop new lithium iron phosphate production methods to achieve regulation of lithium iron phosphate structure and properties.
Disclosure of Invention
Aiming at the technical problems, the invention provides a secondary growth preparation method of nano lithium iron phosphate, which takes primary nano lithium iron phosphate as a seed crystal, introduces a two-dimensional phosphorus simple substance and a lithium iron phosphate precursor, utilizes the two-dimensional phosphorus simple substance to induce the seed crystal to perform secondary growth in the hydrothermal process, realizes the regulation of dominant crystal planes, synthesizes a pure-phase lithium iron phosphate positive electrode material with high rate performance through a simple process, and solves the problem of impurities in the preparation process of the lithium iron phosphate in the prior art.
In order to achieve the above purpose, the present invention provides the following technical solutions:
in one aspect, the invention provides a secondary growth preparation method of nano lithium iron phosphate, comprising the following steps:
carrying out hydrothermal reaction on nano lithium iron phosphate serving as a seed crystal, a two-dimensional phosphorus simple substance and a reducing agent in a lithium iron phosphate precursor solution; the lithium iron phosphate precursor solution includes an iron source, a lithium source, and a phosphorus source.
As a preferred embodiment, the reaction temperature of the hydrothermal reaction is 150 ℃ to 220 ℃; the heat preservation time of the hydrothermal reaction is 150-220 min.
As a preferred embodiment, the reducing agent is ascorbic acid.
As a preferred embodiment, the iron source is a water-soluble ferrous salt, preferably ferrous sulfate heptahydrate;
preferably, the lithium source is a water-soluble lithium salt, preferably lithium hydroxide monohydrate;
preferably, the phosphorus source is a water-soluble phosphorus source, preferably phosphoric acid;
preferably, the solvent of the lithium iron phosphate precursor solution is a mixed solvent of water and ethylene glycol.
As a preferred embodiment, the two-dimensional elemental phosphorus is two-dimensional black phosphorus;
preferably, the transverse dimension of the two-dimensional phosphorus simple substance is 0.5-100 mu m, and the thickness is 1-30 nm.
As a preferred embodiment, the mass ratio of the two-dimensional phosphorus simple substance to the nano lithium iron phosphate serving as the seed crystal is 1:0.4 to 5;
preferably, in the lithium iron phosphate precursor solution, the molar ratio of iron in the iron source, lithium in the lithium source, and phosphorus in the phosphorus source is 1: 3-4: 1 to 2;
preferably, the mass ratio of the reducing agent to the iron source is 1-2: 2780;
preferably, the mass ratio of the nano lithium iron phosphate serving as the seed crystal to the iron source is 1-10: 125.
in some specific embodiments, the secondary growth preparation method further comprises post-treatment of washing and drying after cooling, wherein the cooling can adopt a natural cooling mode.
In the technical scheme of the invention, the mass ratio of the theoretical mass of the nano lithium iron phosphate obtained by adopting the secondary growth preparation method to the nano lithium iron phosphate serving as the seed crystal is 5-200: 1.
as a preferred embodiment, the nano lithium iron phosphate as a seed crystal is prepared by a hydrothermal method;
preferably, the particle size of the nano lithium iron phosphate used as the seed crystal is 30 nm-200 nm.
In some specific embodiments, the hydrothermal method for preparing nano lithium iron phosphate as seed crystal includes the following steps:
the solution comprising the reducing agent, the iron source, the lithium source and the phosphorus source is subjected to a hydrothermal reaction. Wherein the reducing agent is ascorbic acid; the iron source is water-soluble ferrous salt; preferably ferrous sulfate heptahydrate; the lithium source is a water-soluble lithium salt, preferably lithium hydroxide monohydrate; the phosphorus source is a water-soluble phosphorus source, preferably phosphoric acid; the solvent of the lithium iron phosphate precursor solution is a mixed solvent of water and ethylene glycol. The hydrothermal reaction condition is that the temperature is kept between 150 ℃ and 220 ℃ and the temperature is kept for 150min to 220min.
In yet another aspect, the present invention provides the lithium iron phosphate nanoparticle obtained by the above-described secondary growth preparation method.
In yet another aspect, the present invention provides an application of the above nano lithium iron phosphate in preparing a lithium ion battery, in particular, an application in preparing a positive electrode material of a lithium ion battery.
The technical scheme has the following advantages or beneficial effects: according to the method, nano lithium iron phosphate is used as a seed crystal by a hydrothermal method, and two-dimensional phosphorus simple substances are added as a regulating agent to obtain the lithium iron phosphate with different crystal face exposure rates through secondary in-situ growth, wherein the two-dimensional phosphorus simple substances can be used for constructing microenvironments through oxidation-reduction reaction, so that secondary growth regulation and control of the lithium iron phosphate are realized.
Compared with the prior art, the invention has the following advantages:
1. innovation on the regulation mechanism: the two-dimensional phosphorus simple substance is subjected to oxidation reaction in the hydrothermal process, the surface is negatively charged, the crystal seeds and positive ions are attracted, the local ion concentration of the surface of the black phosphorus is increased, and the growth of lithium iron phosphate on the crystal seeds is regulated and controlled, so that the aim of finally changing the crystal face exposure rate is achieved;
2. the more crystal faces of the lithium ion channel are exposed, the shorter the channel distance is, the better the performance is, the crystal seeds are influenced by two-dimensional phosphorus simple substances, the crystal seeds can reach the effects that the channel crystal faces (010) occupy more than one, and the channel distance is relatively shorter through secondary growth;
3. the secondary growth lithium iron phosphate material is synthesized by a low-temperature hydrothermal method, has low energy consumption, simple equipment and operation, does not introduce other organic compounds, is easy to elute, and is beneficial to industrialized production of high-performance nano lithium iron phosphate.
Drawings
FIG. 1 is a scanning electron microscope image of a nano lithium iron phosphate seed crystal prepared in production example 1 of the present invention.
Fig. 2 is a scanning electron microscope image of lithium iron phosphate prepared in comparative examples 1, 3 of the present invention.
FIG. 3 is an X-ray diffraction pattern of lithium iron phosphate prepared in comparative examples 1-2, example 1 of the present invention.
Fig. 4 is a scanning electron microscope image of lithium iron phosphate prepared in example 1 of the present invention.
Fig. 5 is a graph showing the rate performance of lithium iron phosphate prepared in comparative example 2 and example 1 according to the present invention.
Fig. 6 is a charge and discharge graph of lithium iron phosphate prepared in example 1 of the present invention in 15C charge and discharge conditions.
Detailed Description
The following examples are only some, but not all, of the examples of the invention. Accordingly, the detailed description of the embodiments of the invention provided below is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by a person skilled in the art without making any inventive effort, are intended to fall within the scope of the present invention.
In the present invention, all the equipment, raw materials and the like are commercially available or commonly used in the industry unless otherwise specified. The methods in the following examples are conventional in the art unless otherwise specified.
Production example 1
Firstly, preparing an ascorbic acid aqueous solution with the concentration of 0.1mg/mL, weighing 2.78g of ferrous sulfate heptahydrate, and dissolving the ferrous sulfate heptahydrate in 10mL of the ascorbic acid aqueous solution; 1.4g of lithium hydroxide monohydrate is weighed to prepare 10mL of aqueous solution; 3mL of the prepared ferrous sulfate solution, 3mL of lithium hydroxide solution and 80 mu L of phosphoric acid are taken and added into 12mL of ethylene glycol, and finally added into a high-pressure reaction kettle;
step two, heating to 180 ℃, and preserving heat for 60min;
and thirdly, naturally cooling, washing with pure water for a plurality of times, and then drying to obtain the nano lithium iron phosphate seed crystal.
As shown in FIG. 1, the nano lithium iron phosphate seed crystal obtained in this production example has a particle diameter of 30nm to 200nm.
Comparative example 1
Firstly, preparing an ascorbic acid aqueous solution with the concentration of 0.1mg/mL, weighing 2.78g of ferrous sulfate heptahydrate, and dissolving the ferrous sulfate heptahydrate in 10mL of the ascorbic acid aqueous solution; 1.4g of lithium hydroxide monohydrate is weighed to prepare 10mL of aqueous solution; 10mg of seed crystal prepared in preparation example 1, 3mL of ferrous sulfate solution prepared in the above way, 3mL of lithium hydroxide solution and 80 mu L of phosphoric acid are taken and added into 12mL of ethylene glycol, and finally added into a high-pressure reaction kettle;
step two, heating to 180 ℃, and preserving heat for 200min;
and thirdly, naturally cooling, and washing with pure water for a plurality of times to obtain the lithium iron phosphate.
As shown in fig. 2, the present comparative example can obtain pure-phase lithium iron phosphate material, and the particles become significantly larger after the secondary growth of the seed crystal. The X-ray diffraction pattern of the lithium iron phosphate material prepared in this comparative example is shown in fig. 3, and the XRD test result of the sample corresponds to that of the standard card.
Comparative example 2
Firstly, preparing an ascorbic acid aqueous solution with the concentration of 0.1mg/mL, weighing 2.78g of ferrous sulfate heptahydrate, and dissolving the ferrous sulfate heptahydrate in 10mL of the ascorbic acid aqueous solution; 1.4g of lithium hydroxide monohydrate is weighed to prepare 10mL of aqueous solution; mixing 3mL of the prepared ferrous sulfate solution, 3mL of lithium hydroxide solution and 80 mu L of phosphoric acid, adding the mixture into 12mL of ethylene glycol, and finally adding the mixture into a high-pressure reaction kettle;
step two, heating to 180 ℃, and preserving heat for 200min;
and thirdly, naturally cooling and washing with pure water for a plurality of times to obtain the primary-growth pure-phase lithium iron phosphate material.
XRD test patterns of pure-phase lithium iron phosphate materials obtained in this comparative example are shown in FIG. 3.
Comparative example 3
Firstly, preparing an ascorbic acid aqueous solution with the concentration of 0.1mg/mL, weighing 2.78g of ferrous sulfate heptahydrate, and dissolving the ferrous sulfate heptahydrate in 10mL of the ascorbic acid aqueous solution; 1.4g of lithium hydroxide monohydrate is weighed to prepare 10mL of aqueous solution; mixing 3mL of the prepared ferrous sulfate solution, 3mL of lithium hydroxide solution and 80 mu L of phosphoric acid, adding the mixture into 12mL of ethylene glycol containing 20mg of black phosphorus, and finally adding the mixture into a high-pressure reaction kettle;
step two, heating to 180 ℃, and preserving heat for 200min;
and thirdly, naturally cooling and washing with pure water for a plurality of times to obtain the primary-growth pure-phase lithium iron phosphate material.
As shown in fig. 2, this comparative example shows that the particle size distribution of the synthesized lithium iron phosphate is extremely uneven.
Example 1
Firstly, preparing an ascorbic acid aqueous solution with the concentration of 0.1mg/mL, weighing 2.78g of ferrous sulfate heptahydrate, and dissolving the ferrous sulfate heptahydrate in 10mL of the ascorbic acid aqueous solution; 1.4g of lithium hydroxide monohydrate is weighed to prepare 10mL of aqueous solution; 8mg of seed crystal prepared in preparation example 1, 3mL of ferrous sulfate solution prepared in preparation example 1, 3mL of lithium hydroxide solution and 80 mu L of phosphoric acid are mixed and added into 12mL of ethylene glycol containing 20mg of black phosphorus, and finally the mixture is added into a high-pressure reaction kettle;
step two, heating to 180 ℃, and preserving heat for 200min;
and thirdly, naturally cooling, and washing with pure water for a plurality of times to obtain the secondarily grown lithium iron phosphate.
The X-ray diffraction diagram of the pure-phase lithium iron phosphate material prepared in this example is shown in fig. 3, and the XRD test result of the sample corresponds to the standard card. As can be seen from fig. 3, in example 1, the exposure ratio of the (020) crystal plane to the (200) crystal plane of the XRD of the lithium iron phosphate material is larger than that of comparative examples 1 and 2, which means that the more the lithium ion transport dominant direction (010) is exposed, the more favorable lithium ion migration is, and the improvement of the rate performance is facilitated.
Fig. 4 is a scanning electron microscope image of the lithium iron phosphate material prepared in this example.
The lithium iron phosphate materials prepared in this example and comparative example 2 were first carbonized, and the carbonization process reference [ Ind. Eng. Chem. Res.2017,56,10648-10657 ]. Button half-cell specification is CR2032, half-cell slurry preparation: mixing carbonized lithium iron phosphate with superconductive carbon black (SP) in a weight ratio of 8:1, after thorough grinding, adding a solution of polyvinylidene fluoride in N-methylpyrrolidone (PVDF/NMP) to the ground powder, at which time the carbonized lithium iron phosphate: SP: PVDF has a mass ratio of 8:1:1, then coating on aluminum foil, drying for 6 hours at 120 ℃ under vacuum, and cutting into positive plates with the diameter of 12mm for standby. The positive electrode shell, the diaphragm, the elastic sheet, the gasket, the lithium sheet, the negative electrode shell and the weighed positive electrode sheet are prepared. In the experiment, a lithium sheet is used as a negative electrode, a diaphragm is a Celgard 2400 microporous membrane, 3 drops of lithium hexafluorophosphate electrolyte are respectively dropped to 4 drops of lithium hexafluorophosphate electrolyte from a liquid-transferring gun to two measuring parts of the diaphragm, a battery is installed in a glove box filled with argon, and the battery is packaged by an electric packaging machine after the battery is installed. After half batteries are prepared, the batteries are stood for 12 hours, and the rate performance is tested, wherein the charging and discharging interval is 2.0-3.75V, and 1 C=170 mA/g. Among them, the rate performance graphs of half batteries prepared in the same manner as in this example and comparative example 2 are shown in fig. 5. The charge and discharge curves of the half cell prepared in this example at 15C are shown in fig. 6. As can be seen from the figure, the half cell prepared in this example has good charge and discharge performance and rate performance, which are significantly superior to those of comparative example 2.
Example 2
Firstly, preparing an ascorbic acid aqueous solution with the concentration of 0.1mg/mL, weighing 2.78g of ferrous sulfate heptahydrate, and dissolving the ferrous sulfate heptahydrate in 10mL of the ascorbic acid aqueous solution; 1.4g of lithium hydroxide monohydrate is weighed to prepare 10mL of aqueous solution; 50mg of seed crystal prepared in preparation example 1, 3mL of ferrous sulfate solution prepared in preparation example 1, 3mL of lithium hydroxide solution and 100 mu L of phosphoric acid are mixed and added into 12mL of ethylene glycol containing 10mg of black phosphorus, and finally the mixture is added into a high-pressure reaction kettle;
heating to 150 ℃, and preserving heat for 180min;
and thirdly, naturally cooling, and washing with pure water for a plurality of times to obtain the secondarily grown lithium iron phosphate.
Example 3
Firstly, preparing an ascorbic acid aqueous solution with the concentration of 0.1mg/mL, weighing 2.6g of ferrous sulfate heptahydrate, and dissolving the ferrous sulfate heptahydrate in 10mL of the ascorbic acid aqueous solution; 1.3g of lithium hydroxide monohydrate is weighed to prepare 10mL of aqueous solution; mixing 20mg of seed crystal prepared in preparation example 1, 3mL of ferrous sulfate solution prepared in preparation example 1, 3mL of lithium hydroxide solution and 80 mu L of phosphoric acid, adding the mixture into 12mL of ethylene glycol containing 10mg of black phosphorus, and finally adding the mixture into a high-pressure reaction kettle;
step two, heating to 180 ℃, and preserving heat for 220min;
and thirdly, naturally cooling, and washing with pure water for a plurality of times to obtain the secondarily grown lithium iron phosphate.
Example 4
Firstly, preparing an ascorbic acid aqueous solution with the concentration of 0.1mg/mL, weighing 2.78g of ferrous sulfate heptahydrate, and dissolving the ferrous sulfate heptahydrate in 10mL of the ascorbic acid aqueous solution; 1.3g of lithium hydroxide monohydrate is weighed to prepare 10mL of aqueous solution; 15mg of seed crystal prepared in preparation example 1, 3mL of ferrous sulfate solution prepared in preparation example 1, 3mL of lithium hydroxide solution and 100 mu L of phosphoric acid are mixed and added into 12mL of ethylene glycol containing 5mg of black phosphorus, and finally the mixture is added into a high-pressure reaction kettle;
step two, heating to 150 ℃, and preserving heat for 220min;
and thirdly, naturally cooling, and washing with pure water for a plurality of times to obtain the secondarily grown lithium iron phosphate.
Example 5
Firstly, preparing an ascorbic acid aqueous solution with the concentration of 0.1mg/mL, weighing 2.78g of ferrous sulfate heptahydrate, and dissolving the ferrous sulfate heptahydrate in 10mL of the ascorbic acid aqueous solution; 1.4g of lithium hydroxide monohydrate is weighed to prepare 10mL of aqueous solution; 70mg of seed crystal prepared in preparation example 1, 3mL of ferrous sulfate solution prepared in preparation example 1, 3mL of lithium hydroxide solution and 100 mu L of phosphoric acid are mixed and added into 12mL of ethylene glycol containing 30mg of black phosphorus, and finally the mixture is added into a high-pressure reaction kettle;
step two, heating to 220 ℃, and preserving heat for 220min;
and thirdly, naturally cooling, and washing with pure water for a plurality of times to obtain the secondarily grown lithium iron phosphate.
The foregoing is only a preferred embodiment of the invention, it being noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present invention, and such modifications and adaptations are intended to be comprehended within the scope of the invention.
Claims (10)
1. The secondary growth preparation method of the nano lithium iron phosphate is characterized by comprising the following steps of:
carrying out hydrothermal reaction on nano lithium iron phosphate serving as a seed crystal, a two-dimensional phosphorus simple substance and a reducing agent in a lithium iron phosphate precursor solution; the lithium iron phosphate precursor solution includes an iron source, a lithium source, and a phosphorus source.
2. The secondary growth preparation method according to claim 1, wherein the reaction temperature of the hydrothermal reaction is 150 ℃ to 220 ℃; the heat preservation time of the hydrothermal reaction is 150-220 min.
3. The secondary growth preparation method according to claim 1, wherein the reducing agent is ascorbic acid.
4. The secondary growth preparation method according to claim 1, characterized in that the iron source is a water-soluble ferrous salt, preferably ferrous sulphate heptahydrate;
preferably, the lithium source is a water-soluble lithium salt, preferably lithium hydroxide monohydrate;
preferably, the phosphorus source is a water-soluble phosphorus source, preferably phosphoric acid;
preferably, the solvent of the lithium iron phosphate precursor solution is a mixed solvent of water and ethylene glycol.
5. The secondary growth preparation method according to claim 1, wherein the two-dimensional elemental phosphorus is two-dimensional black phosphorus;
preferably, the transverse dimension of the two-dimensional phosphorus simple substance is 0.5-100 mu m, and the thickness is 1-30 nm.
6. The secondary growth preparation method according to claim 4, wherein the mass ratio of the two-dimensional phosphorus simple substance to the nano lithium iron phosphate serving as the seed crystal is 1:0.4 to 5;
preferably, in the lithium iron phosphate precursor solution, the molar ratio of iron in the iron source, lithium in the lithium source, and phosphorus in the phosphorus source is 1: 3-4: 1 to 2;
preferably, the mass ratio of the reducing agent to the iron source is 1-2: 2780;
preferably, the mass ratio of the nano lithium iron phosphate serving as the seed crystal to the iron source is 1-10: 125.
7. the secondary growth preparation method according to claim 1, further comprising post-treatment of washing and drying after cooling.
8. The secondary growth preparation method according to claim 1, wherein the nano lithium iron phosphate as seed crystal is prepared by a hydrothermal method;
preferably, the particle size of the nano lithium iron phosphate used as the seed crystal is 30 nm-200 nm.
9. The lithium iron phosphate nanoparticle obtained by the secondary growth preparation method of any one of claims 1 to 8.
10. The use of the nano lithium iron phosphate according to claim 9 for preparing a lithium ion battery, characterized in that the nano lithium iron phosphate is used for preparing a positive electrode material of the lithium ion battery.
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