CN110931787B - Preparation method and application of in-situ grown lithium iron phosphate whisker - Google Patents
Preparation method and application of in-situ grown lithium iron phosphate whisker Download PDFInfo
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- CN110931787B CN110931787B CN201911328226.3A CN201911328226A CN110931787B CN 110931787 B CN110931787 B CN 110931787B CN 201911328226 A CN201911328226 A CN 201911328226A CN 110931787 B CN110931787 B CN 110931787B
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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 87
- 238000011065 in-situ storage Methods 0.000 title claims abstract description 19
- 238000002360 preparation method Methods 0.000 title claims abstract description 16
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims abstract description 38
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims abstract description 38
- 238000004108 freeze drying Methods 0.000 claims abstract description 36
- 239000000463 material Substances 0.000 claims abstract description 36
- 238000005245 sintering Methods 0.000 claims abstract description 35
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims abstract description 26
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 26
- 238000000034 method Methods 0.000 claims abstract description 26
- 239000005955 Ferric phosphate Substances 0.000 claims abstract description 23
- 229940032958 ferric phosphate Drugs 0.000 claims abstract description 23
- 229910000399 iron(III) phosphate Inorganic materials 0.000 claims abstract description 23
- 239000000243 solution Substances 0.000 claims abstract description 23
- 239000002245 particle Substances 0.000 claims abstract description 21
- 239000002243 precursor Substances 0.000 claims abstract description 17
- 229910000398 iron phosphate Inorganic materials 0.000 claims abstract description 15
- 238000009766 low-temperature sintering Methods 0.000 claims abstract description 15
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 14
- 239000013078 crystal Substances 0.000 claims abstract description 14
- 229910052786 argon Inorganic materials 0.000 claims abstract description 13
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 13
- 239000003085 diluting agent Substances 0.000 claims abstract description 12
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 10
- 229910003002 lithium salt Inorganic materials 0.000 claims abstract description 7
- 159000000002 lithium salts Chemical class 0.000 claims abstract description 7
- 238000002791 soaking Methods 0.000 claims abstract description 6
- 239000012266 salt solution Substances 0.000 claims abstract description 5
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 15
- 238000010438 heat treatment Methods 0.000 claims description 13
- 238000009792 diffusion process Methods 0.000 claims description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 9
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 claims description 8
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 7
- 229910001416 lithium ion Inorganic materials 0.000 claims description 7
- 229930006000 Sucrose Natural products 0.000 claims description 6
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 6
- CZMRCDWAGMRECN-UGDNZRGBSA-N Sucrose Chemical compound O[C@H]1[C@H](O)[C@@H](CO)O[C@@]1(CO)O[C@@H]1[C@H](O)[C@@H](O)[C@H](O)[C@@H](CO)O1 CZMRCDWAGMRECN-UGDNZRGBSA-N 0.000 claims description 5
- 238000005229 chemical vapour deposition Methods 0.000 claims description 5
- 238000007598 dipping method Methods 0.000 claims description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 4
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 claims description 3
- 239000008103 glucose Substances 0.000 claims description 3
- 239000005720 sucrose Substances 0.000 claims description 3
- 239000004743 Polypropylene Substances 0.000 claims description 2
- 229920002472 Starch Polymers 0.000 claims description 2
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 claims description 2
- WQZGKKKJIJFFOK-VFUOTHLCSA-N beta-D-glucose Chemical compound OC[C@H]1O[C@@H](O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-VFUOTHLCSA-N 0.000 claims description 2
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 claims description 2
- -1 polypropylene Polymers 0.000 claims description 2
- 229920001155 polypropylene Polymers 0.000 claims description 2
- 239000008107 starch Substances 0.000 claims description 2
- 235000019698 starch Nutrition 0.000 claims description 2
- 238000000859 sublimation Methods 0.000 claims description 2
- 230000008022 sublimation Effects 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 1
- 230000001502 supplementing effect Effects 0.000 claims 1
- 230000001351 cycling effect Effects 0.000 abstract description 3
- 238000001035 drying Methods 0.000 abstract description 2
- 230000008014 freezing Effects 0.000 abstract description 2
- 238000007710 freezing Methods 0.000 abstract description 2
- 238000005470 impregnation Methods 0.000 abstract 1
- 239000013589 supplement Substances 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 22
- 238000011056 performance test Methods 0.000 description 12
- 230000000694 effects Effects 0.000 description 6
- 238000007599 discharging Methods 0.000 description 5
- 230000014759 maintenance of location Effects 0.000 description 5
- 229960004793 sucrose Drugs 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 125000004122 cyclic group Chemical group 0.000 description 4
- 239000003792 electrolyte Substances 0.000 description 4
- 230000006911 nucleation Effects 0.000 description 4
- 238000010899 nucleation Methods 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 239000002002 slurry Substances 0.000 description 4
- 239000010405 anode material Substances 0.000 description 3
- 238000002425 crystallisation Methods 0.000 description 3
- 230000008025 crystallization Effects 0.000 description 3
- 238000001878 scanning electron micrograph Methods 0.000 description 3
- QSNQXZYQEIKDPU-UHFFFAOYSA-N [Li].[Fe] Chemical compound [Li].[Fe] QSNQXZYQEIKDPU-UHFFFAOYSA-N 0.000 description 2
- 239000011230 binding agent Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000003153 chemical reaction reagent Substances 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000004146 energy storage Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 230000008595 infiltration Effects 0.000 description 2
- 238000001764 infiltration Methods 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 238000001338 self-assembly Methods 0.000 description 2
- 238000009827 uniform distribution Methods 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910001290 LiPF6 Inorganic materials 0.000 description 1
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- 239000006230 acetylene black Substances 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
- 239000006258 conductive agent Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 125000002791 glucosyl group Chemical group C1([C@H](O)[C@@H](O)[C@H](O)[C@H](O1)CO)* 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 231100000956 nontoxicity Toxicity 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000011232 storage material Substances 0.000 description 1
- 125000000185 sucrose group Chemical group 0.000 description 1
- 239000002562 thickening agent Substances 0.000 description 1
- 238000009736 wetting Methods 0.000 description 1
Images
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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
-
- 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
- C01B25/37—Phosphates of heavy metals
- C01B25/375—Phosphates of heavy metals of iron
-
- 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
-
- 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
-
- 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
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Crystallography & Structural Chemistry (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a preparation method and application of in-situ grown lithium iron phosphate whiskers; the method comprises the following steps: 1) adding a dilute hydrochloric acid solution into the ferric phosphate, and completely dissolving the ferric phosphate to prepare a hydrochloric acid diluent of the ferric phosphate; 2) then soaking the lithium iron phosphate into hydrochloric acid diluent of the iron phosphate, and then freezing and drying; 3) placing the freeze-dried lithium iron phosphate into nitrogen and/or argon for low-temperature sintering; 4) immersing lithium iron phosphate sintered at a low temperature into a prepared soluble lithium salt solution for impregnation, and then freeze-drying to obtain a precursor; 5) the precursor is subjected to carbon source supplement and high-temperature sintering under the condition of nitrogen and/or argon, and needle-shaped lithium iron phosphate whiskers which are densely and uniformly distributed can grow on the existing lithium iron phosphate particles. The length range of the whisker is 0.1-10um, and the diameter range is 10-100 nm. The invention solves the problem that the lithium iron phosphate crystal whisker is difficult to grow in situ under the condition of not damaging the original structure of the lithium iron phosphate material, and obviously improves the cycling stability of the material.
Description
Technical Field
The invention belongs to the technical field of energy storage materials, and particularly relates to a preparation method and application of in-situ grown lithium iron phosphate whiskers.
Background
With the continuous development of human society, environmental problems are increasingly prominent, and with the rise of new energy strategies in China, lithium ion batteries are widely applied as clean energy due to the advantages of small size, high energy density, safety, environmental protection and the like since the early development of the last 90 th century.
The lithium iron phosphate serving as the lithium ion battery anode material has the advantages of wide raw material source, low price, good material thermal stability, high voltage platform, long cycle life, no toxicity, no harm, high safety and the like, is separated from a plurality of anode materials, and becomes the first choice of the power and energy storage lithium ion battery anode material at present.
However, the cycling stability of the polymer needs to be improved, and how to improve the cycling stability of the polymer is a technical problem to be solved urgently.
Disclosure of Invention
In view of the above, the present invention aims to provide a preparation method and use of in-situ grown lithium iron phosphate whiskers, so as to overcome the defects of the prior art, the present invention can achieve the effects of uniform distribution of particles immersed in lithium iron phosphate particles and formation of whisker growth environment through freeze drying combined with a low-temperature sintering process, and after high-temperature nitrogen and/or argon heat treatment, the particles grow directionally and epitaxially through self-assembly crystallization, and finally whiskers densely and uniformly distributed on the surfaces of the lithium iron phosphate particles are generated, so that the infiltration effect with an electrolyte is increased, and thus, the material circulation stability is improved.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a preparation method of in-situ grown lithium iron phosphate whiskers comprises the following steps,
(1) adding a dilute hydrochloric acid solution into the ferric phosphate, and completely dissolving the ferric phosphate to prepare a hydrochloric acid diluent of the ferric phosphate;
(2) soaking lithium iron phosphate into the hydrochloric acid diluent of the iron phosphate obtained in the step (1) for a period of time, and then freeze-drying;
(3) placing the freeze-dried lithium iron phosphate obtained in the step (2) into nitrogen and/or argon for low-temperature sintering;
(4) immersing the lithium iron phosphate sintered at low temperature in the step (3) into a soluble lithium salt solution for a period of time, and then freeze-drying to obtain a precursor;
(5) and (4) sintering the precursor obtained in the step (4) at high temperature under the condition of nitrogen and/or argon, and growing the needle-shaped lithium iron phosphate whiskers which are densely and uniformly distributed on the existing lithium iron phosphate particles.
In the preparation method provided by the invention, after the primary dipping stage in the step (2) is finished, freeze drying is adopted, so that the nucleation and directional growth environment is improved for the subsequent whisker growth; and (4) promoting the growth of iron phosphate crystals on the surface by adding low-temperature sintering in the step (3), providing a nucleation and growth environment for the lithium iron phosphate whiskers in the step (5), and improving the cycle performance of the material.
The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
Preferably, in step (1), the concentration of the dilute hydrochloric acid solution is 0.001-0.005 mol/L, such as 0.001mol/L, 0.002mol/L, 0.0025mol/L, 0.003mol/L, 0.004mol/L, or 0.005mol/L, but is not limited to the enumerated values, and other values within the range are also applicable;
and in the completely dissolved solution, the concentration of the ferric phosphate is 0.1-0.2 mol/L. For example, 0.1mol/L, 0.12mol/L, 0.13mol/L, 0.15mol/L, 0.18mol/L, 0.2mol/L, etc., but not limited to the values listed, and other values not listed in the numerical range are also applicable.
Preferably, in the step (2), the molar ratio of the lithium iron phosphate to the iron phosphate is (1-2): (0.1-0.2), the immersion time is 1-2 h, such as 1h, 1.1h, 1.3h, 1.5h, 1.7h, 1.8h, 2h, etc., but not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, in the step (2) and the step (4), the freeze-drying comprises the steps of,
a. putting a material to be freeze-dried into a freeze-drying box which is cooled to minus 10 ℃ to minus 50 ℃ for 3 to 5 hours to freeze the material; b. opening the vacuum diffusion pump, and when the pressure is reduced to 1.3-13 Pa, the ice just begins to sublimate, and the sublimated water vapor is frozen into ice crystals in the condenser; to ensure sublimation of the ice, the heating system was turned on and the shelf was heated to 30-60 ℃.
The temperature of the freeze drying chamber is in the range of-10 ℃ to-50 ℃, for example, -10 ℃, -20 ℃, -30 ℃, -40 ℃, -50 ℃ and the like, but is not limited to the recited values, and other values not recited in the range of values are also applicable.
The freezing time is in the range of 3-5 hours, such as 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc., but is not limited to the recited values, and other values not recited in the range of values are also applicable.
The pressure of the vacuum diffusion pump is in the range of 1.3 to 13Pa, for example, 1.3Pa, 2.3Pa, 4.3Pa, 6.3Pa, 8.3Pa, 10.3Pa, 12Pa, 13Pa, etc., but the pressure is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.
The shelf heating temperature is in the range of 30 ℃ to 60 ℃, for example 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃ and the like, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, in step (3), the sintering temperature is 150-350 ℃, preferably 200-300 ℃, for example, 150 ℃, 200 ℃, 250 ℃, 300 ℃ or 350 ℃, but not limited to the recited values, and other unrecited values within the range of values are also applicable.
In the invention, if the sintering temperature is lower than 150 ℃, the iron phosphate crystal can not grow; if the pre-sintering temperature is higher than 350 ℃, secondary recrystallization of iron phosphate crystals can be caused, and an environment for subsequent whisker growth cannot be provided. The sintering temperature range of 200-300 ℃ is adopted, so that the crystallization of the iron phosphate and the normal growth of the follow-up whiskers can be better realized.
The sintering time is 2-3 h. For example, 2h, 2.2h, 2.4h, 2.8h, 3h, etc., but are not limited to the recited values, and other values not recited within the numerical range are also applicable.
Preferably, in the step (4), the soluble lithium salt is any one or a combination of two of lithium hydroxide or lithium nitrate; the concentration of lithium ions in the soluble lithium salt solution is 0.1 to 0.2mol/L, such as 0.1mol/L, 0.12mol/L, 0.13mol/L, 0.15mol/L, 0.18mol/L, 0.2mol/L, etc., but not limited to the recited values, and other values not recited in the numerical range are also applicable; the dipping time is 1-2 h; for example, 1h, 1.1h, 1.3h, 1.5h, 1.7h, 1.8h, 2h, etc., but are not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, in the step (5), the sintering temperature is 600-800 ℃, and preferably 650-750 ℃; the sintering time is 5-8 h.
The sintering temperature is, for example, 600 ℃, 650 ℃, 700 ℃, 750 ℃, or 800 ℃, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.
The sintering time is, for example, 5 hours, 6 hours, 6.5 hours, 7 hours, or 8 hours, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, before the high-temperature sintering in step (5), a carbon source is supplemented, wherein the carbon source comprises any one or a combination of at least two of sucrose, glucose, starch, citric acid, polypropylene, acetylene or methane; the mass of the carbon source is 0.1-0.5 wt% of the mass of the precursor; for example, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%, etc., but is not limited to the recited values, and other values not recited within the numerical range are also applicable.
Preferably, the sintering in step (5) is rotary kiln dry sintering and/or chemical vapor deposition sintering, preferably chemical vapor deposition sintering.
The length of the lithium iron phosphate whisker prepared by the preparation method of the invention is in the range of 0.1-10um, for example, 0.1 μm, 0.5 μm, 2 μm, 4 μm, 6 μm, 8 μm or 10 μm, etc., but the invention is not limited to the values listed, and other values not listed in the range of the values are also applicable.
The diameter of the lithium iron phosphate whisker is in the range of 10 to 100nm, for example, 10nm, 20nm, 40nm, 50nm, 60nm, 80nm or 100nm, but the lithium iron phosphate whisker is not limited to the recited values, and other values not recited in the numerical range are also applicable.
The invention also provides the whisker-containing lithium iron phosphate particles prepared by the preparation method.
The invention also provides application of the whisker-containing lithium iron phosphate prepared by the preparation method in a lithium ion battery.
Compared with the prior art, the preparation method of the in-situ growth lithium iron phosphate whisker has the following advantages:
(1) according to the invention, the particles immersed in the lithium iron phosphate particles can achieve the effects of uniform distribution and forming a whisker growth environment through the combination of freeze drying and a low-temperature sintering process, and after the particles are subjected to heat treatment in a high-temperature protective atmosphere, the particles are subjected to self-assembly crystallization and directional epitaxial growth to finally generate whiskers densely and uniformly distributed on the surfaces of the lithium iron phosphate particles, so that the infiltration effect with an electrolyte is increased, and the circulation stability of the material is improved.
(2) The lithium iron phosphate material provided by the invention is a granular material with whiskers, has good electrochemical performance and excellent cycle performance, and after freeze drying and low-temperature sintering, the 1C initial discharge specific capacity is more than or equal to 146.2mAh/g, the 2000 th cycle discharge specific capacity is more than or equal to 137.3mAh/g, and the 2000 cycle capacity retention rate is more than or equal to 93.3%.
Drawings
Fig. 1 is an SEM image of whisker-containing lithium iron phosphate obtained in example 1 of the present invention.
FIG. 2 is an SEM magnified view of whiskers obtained in example 1 of the present invention.
FIG. 3 is an SEM image of a sample of comparative example 1 of the present invention.
Detailed Description
In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.
Unless defined otherwise, technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods are conventional methods unless otherwise specified.
The following are typical, but non-limiting, examples of the invention.
Example 1
In this example, lithium iron phosphate whiskers were prepared as follows:
(1) adding a dilute hydrochloric acid solution into the ferric phosphate, and completely dissolving the ferric phosphate to prepare a hydrochloric acid diluent of the ferric phosphate;
wherein the volume of the dilute hydrochloric acid solution is 1L, the concentration of the dilute hydrochloric acid is 0.002mol/L, and the concentration of the ferric phosphate in the completely dissolved solution is 0.1 mol/L;
(2) soaking 1mol of lithium iron phosphate into the hydrochloric acid diluent of the iron phosphate obtained in the step (1) for 1 hour, and then freeze-drying, wherein the freeze-drying comprises the following two steps:
a. the material to be freeze-dried is placed in a freeze-drying box for 3 hours at the temperature of minus 30 ℃.
b. The vacuum diffusion pump was turned on and the pressure dropped to 5Pa, and the heating system was turned on to heat the shelf to 50 ℃.
(3) And (3) sintering the freeze-dried lithium iron phosphate obtained in the step (2) at a low temperature of 200 ℃ for 2 hours under the condition of nitrogen and/or argon.
(4) Immersing the lithium iron phosphate sintered at the low temperature in the step (3) into a prepared lithium hydroxide solution with the concentration of 0.1mol/L for 1 hour, and then freeze-drying to obtain a precursor;
the freeze drying comprises the following two steps:
a. the material to be freeze-dried is placed in a freeze-drying box for 3 hours at the temperature of minus 30 ℃.
b. The vacuum diffusion pump was turned on and the pressure dropped to 5Pa, and the heating system was turned on to heat the shelf to 50 ℃.
(5) And (3) sintering the precursor obtained in the step (4) and cane sugar by a chemical vapor deposition method under the condition of nitrogen and/or argon at the temperature of 700 ℃, wherein the sintering time is 6h, and thus the lithium iron phosphate whisker is obtained.
Wherein the mass of the carbon source is 0.2 wt% of the mass of the precursor;
the average length of the lithium iron phosphate whisker is 4.2um, and the average diameter of the whisker is 45 nm.
Fig. 1 is an SEM image of the product obtained in the present example, and it can be seen from this image that whisker growth on the surface of lithium iron phosphate particles was good.
The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.
Example 2
In this example, the raw materials and operations were the same as in example 1 except that the low-temperature sintering temperature in step (3) was 250 ℃.
The average length of the lithium iron phosphate whisker is 4.5um, and the average diameter of the whisker is 55 nm.
The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.
Example 3
This example was carried out in the same manner as in example 1 except that lithium hydroxide was replaced with lithium nitrate in step (4).
The average length of the lithium iron crystal whisker is 5um, and the average diameter of the crystal whisker is 80 nm.
The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.
Example 4
This example was carried out in the same manner as in example 1 except that sucrose was replaced with glucose in step (5).
The average length of the lithium iron phosphate whisker is 4.4um, and the average diameter of the whisker is 48 nm.
The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.
Example 5
In this example, lithium iron phosphate whiskers were prepared as follows:
(1) adding a dilute hydrochloric acid solution into the ferric phosphate, and completely dissolving the ferric phosphate to prepare a hydrochloric acid diluent of the ferric phosphate;
wherein the volume of the dilute hydrochloric acid solution is 1L, the concentration of the dilute hydrochloric acid is 0.003mol/L, and the concentration of the ferric phosphate in the completely dissolved solution is 0.1 mol/L;
(2) soaking 1.5mol of lithium iron phosphate into the hydrochloric acid diluent of the iron phosphate obtained in the step (1) for 2h, and then freeze-drying, wherein the freeze-drying comprises the following two steps:
a. the material to be freeze-dried is placed in a freeze-drying box for 2 hours at the temperature of-20 ℃.
b. Turning on vacuum diffusion pump, reducing pressure to 8Pa, turning on heating system, heating shelf to 30 deg.C
(3) And (3) sintering the freeze-dried lithium iron phosphate obtained in the step (2) at a low temperature of 180 ℃ for 3 hours under the condition of nitrogen and/or argon.
(4) Immersing the lithium iron phosphate sintered at the low temperature in the step (3) into a prepared lithium hydroxide solution with the concentration of 0.1mol/L for 2 hours, and then freeze-drying to obtain a precursor;
the freeze drying comprises the following two steps:
a. the material to be freeze-dried is placed in a freeze-drying box for 2 hours at the temperature of-20 ℃.
b. The vacuum diffusion pump was turned on, the pressure dropped to 8Pa, and the heating system was turned on to heat the shelf to 30 ℃.
(5) And (3) carrying out dry sintering on the precursor obtained in the step (4) and cane sugar in a rotary kiln at the temperature of 750 ℃ under the condition of nitrogen and/or argon for 8 hours to obtain the lithium iron phosphate whisker.
Wherein the mass of the carbon source is 0.5 wt% of the mass of the precursor;
the average length of the lithium iron phosphate whisker is 3.4um, and the average diameter of the whisker is 66 nm.
The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.
Example 6
In this example, lithium iron phosphate whiskers were prepared as follows:
(1) adding a dilute hydrochloric acid solution into the ferric phosphate, and completely dissolving the ferric phosphate to prepare a hydrochloric acid diluent of the ferric phosphate;
wherein the volume of the dilute hydrochloric acid solution is 1L, the concentration of the dilute hydrochloric acid is 0.005mol/L, and the concentration of the ferric phosphate in the completely dissolved solution is 0.2 mol/L;
(2) soaking 1.8mol of lithium iron phosphate into the hydrochloric acid diluent of the iron phosphate obtained in the step (1) for 2h, and then freeze-drying, wherein the freeze-drying comprises the following two steps:
a. the material to be freeze-dried is placed in a freeze-drying box for 2 hours at the temperature of-20 ℃.
b. Turning on vacuum diffusion pump, reducing pressure to 10Pa, turning on heating system, heating shelf to 40 deg.C
(3) And (3) sintering the freeze-dried lithium iron phosphate obtained in the step (2) at a low temperature of 350 ℃ for 2 hours under the condition of nitrogen and/or argon.
(4) Immersing the lithium iron phosphate sintered at low temperature in the step (3) into a prepared lithium nitrate solution with the concentration of 0.2mol/L for 2 hours, and then freeze-drying to obtain a precursor;
the freeze drying comprises the following two steps:
a. the material to be freeze-dried is placed in a freeze-drying box for 2 hours at the temperature of-20 ℃.
b. The vacuum diffusion pump was turned on and the pressure dropped to 10Pa, and the heating system was turned on to heat the shelf to 40 ℃.
(5) And (3) sintering the precursor obtained in the step (4) and cane sugar by a chemical vapor deposition method under the condition of nitrogen and/or argon at the temperature of 800 ℃, wherein the sintering time is 5h, and thus the lithium iron phosphate whisker is obtained.
Wherein the mass of the carbon source is 0.1 wt% of the mass of the precursor;
the average length of the lithium iron crystal whisker is 8um, and the average diameter of the crystal whisker is 85 nm.
The performance test results of the lithium iron phosphate material prepared in this example are shown in table 1.
Comparative example 1
The comparative example is a blank control group, and the material is untreated lithium iron phosphate particles.
The performance test results of the lithium iron phosphate material prepared in the comparative example are shown in table 1.
Comparative example 2
This comparative example was identical in raw materials and operation to example 1, except that the low-temperature sintering process was omitted in step (3).
This example did not allow whisker formation.
The performance test results of the lithium iron phosphate material prepared in the comparative example are shown in table 1.
Comparative example 3
This comparative example was the same as example 1 except that the temperature for the low-temperature sintering in step (3) was set to 100 ℃.
The present comparative example failed to form whiskers.
The performance test results of the lithium iron phosphate material prepared in the comparative example are shown in table 1.
Comparative example 4
This comparative example was identical in raw materials and operation to example 1, except that the temperature for the low-temperature sintering in step (3) was set to 400 ℃.
The comparative example did not give whiskers.
The performance test results of the lithium iron phosphate material prepared in the comparative example are shown in table 1.
The performance test method comprises the following steps:
the lithium iron phosphate materials prepared in the examples and the comparative examples were subjected to the following performance tests:
(1) testing the size of the whisker: measuring the diameter and the length of the sample whisker by using an electronic scanning microscope;
(2) electrochemical testing: the lithium iron phosphate material prepared by the invention is prepared into a positive pole piece, the negative pole is a graphite negative pole, the diaphragm is Celgard2400, and the electrolyte is 1mol/L LiPF6And a mixed solution of dimethyl carbonate and ethyl methyl carbonate (the volume ratio is 1:1:1) is assembled into the 18650 cylindrical single battery. The preparation process of the positive pole piece comprises the following steps: mixing a positive electrode material, a conductive agent acetylene black and a binder PVDF according to the mass percentage of 94:3:3, taking N-methyl pyrrolidone as a solvent, preparing slurry, coating the slurry on an aluminum foil, and drying in vacuum to obtain the positive electrode piece. The preparation process of the negative pole piece comprises the steps of carrying out negative pole batching on graphite, a thickening agent CMC, a binder SBR and conductive carbon powder according to the weight ratio of 95:1:2:2 in a water system to obtain uniform negative pole slurry, and uniformly coating the prepared negative pole slurry on a negative pole current collector Cu foil and cooling to obtain the negative pole piece. Under the condition of normal temperature, the prepared cylindrical battery is tested on a LAND battery test system of Wuhan Jinnuo electronics, Inc., the charging and discharging voltage interval is 2.0-3.65V, the first discharging specific capacity and the 2000 th cyclic discharging specific capacity of the battery are tested under the current density of 1C, the 2000 th cyclic capacity retention ratio is calculated, and the 2000 th cyclic capacity retention ratio is equal to the 2000 th cyclic discharging specific capacity/the first discharging specific capacity.
The test results are shown in the following table:
TABLE 1
As can be seen from table 1, the lithium iron phosphate materials prepared in embodiments 1 to 6 of the present invention have good electrochemical properties, because the preparation method of the above embodiments grows lithium iron phosphate whiskers in situ on lithium iron phosphate particles by combining freeze drying with low-temperature sintering, and because the whiskers have a large specific surface area, they have a good wetting effect with an electrolyte, and can significantly improve the electrochemical properties of the materials.
The low-temperature sintering temperature of the comparative example 3 is too low, and the iron phosphate crystals on the particle surfaces cannot grow after one-time freeze drying, so that the subsequent crystal whisker growth environment is avoided, the interface resistance of the material is increased, and the capacity and the cycle performance of the material are reduced.
The low-temperature sintering temperature of the comparative example 4 is too high, and the iron phosphate crystals on the surfaces of the particles are recrystallized for the second time after the primary freeze drying, so that the nucleation environment of the whiskers is damaged, and the capacity and the cycle performance of the material are reduced.
As can be seen from table 1, the first discharge specific capacity, the 2000 th cycle discharge specific capacity and the 2000 th cycle capacity retention ratio of comparative example 1 are lower than those of example 1 because no whisker is formed on the surface of the material in comparative example 1.
As can be seen from table 1, the retention rate of the first discharge specific capacity, the 2000 th cycle discharge specific capacity and the 2000 th cycle capacity of the comparative example 2 is lower than that of the example 1, and probably because the low-temperature sintering process is omitted in the comparative example 2, the iron phosphate crystals on the particle surface after the primary freeze drying cannot grow, and further the whisker lacks a nucleation growth environment.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (12)
1. A preparation method of in-situ grown lithium iron phosphate whiskers is characterized by comprising the following steps: comprises the following steps of (a) carrying out,
(1) adding a dilute hydrochloric acid solution into the ferric phosphate, and completely dissolving the ferric phosphate to prepare a hydrochloric acid diluent of the ferric phosphate;
(2) soaking lithium iron phosphate into the hydrochloric acid diluent of the iron phosphate obtained in the step (1) for a period of time, and then freeze-drying;
(3) placing the freeze-dried lithium iron phosphate obtained in the step (2) into nitrogen and/or argon for low-temperature sintering; the sintering temperature is 150-350 ℃;
(4) immersing the lithium iron phosphate sintered at low temperature in the step (3) into a soluble lithium salt solution for a period of time, and then freeze-drying to obtain a precursor;
(5) sintering the precursor obtained in the step (4) at high temperature under the condition of nitrogen and/or argon, wherein the sintering temperature is 600-800 ℃; the acicular lithium iron phosphate whiskers which are densely and uniformly distributed can be grown on the existing lithium iron phosphate particles.
2. The method for preparing in-situ grown lithium iron phosphate whiskers as recited in claim 1, wherein the method comprises the following steps: in the step (1), the concentration of the dilute hydrochloric acid solution is 0.001-0.005 mol/L; and in the completely dissolved solution, the concentration of the ferric phosphate is 0.1-0.2 mol/L.
3. The method for preparing in-situ grown lithium iron phosphate whiskers as recited in claim 1, wherein the method comprises the following steps: in the step (2), the molar ratio of the lithium iron phosphate to the iron phosphate is (1-2): (0.1-0.2), and the dipping time is 1-2 h.
4. The method for preparing in-situ grown lithium iron phosphate whiskers as recited in claim 1, wherein the method comprises the following steps: in the step (2) and the step (4), the freeze-drying comprises the steps of,
a. putting a material to be freeze-dried into a freeze-drying box which is cooled to minus 10 ℃ to minus 50 ℃ for 3 to 5 hours to freeze the material; b. opening the vacuum diffusion pump, and when the pressure is reduced to 1.3-13 Pa, the ice just begins to sublimate, and the sublimated water vapor is frozen into ice crystals in the condenser; to ensure sublimation of the ice, the heating system was turned on and the shelf was heated to 30-60 ℃.
5. The method for preparing in-situ grown lithium iron phosphate whiskers as recited in claim 1, wherein the method comprises the following steps: in the step (3), the sintering time is 2-3 h.
6. The method for preparing in-situ grown lithium iron phosphate whiskers as recited in claim 1, wherein the method comprises the following steps: in the step (3), the sintering temperature is 200-300 ℃.
7. The method for preparing in-situ grown lithium iron phosphate whiskers as recited in claim 1, wherein the method comprises the following steps: in the step (4), the soluble lithium salt is any one or a combination of two of lithium hydroxide or lithium nitrate; the concentration of lithium ions in the soluble lithium salt solution is 0.1-0.2 mol/L; the dipping time is 1-2 h.
8. The method for preparing in-situ grown lithium iron phosphate whiskers as recited in claim 1, wherein the method comprises the following steps: in the step (5), the sintering time is 5-8 h.
9. The method for preparing in-situ grown lithium iron phosphate whiskers as recited in claim 1, wherein the method comprises the following steps: in the step (5), the sintering temperature is 650-750 ℃.
10. The method for preparing in-situ grown lithium iron phosphate whiskers as recited in claim 1, wherein the method comprises the following steps: supplementing a carbon source before the high-temperature sintering in the step (5), wherein the carbon source comprises any one or a combination of at least two of sucrose, glucose, starch, citric acid, polypropylene, acetylene or methane; the mass of the carbon source is 0.1-0.5 wt% of the mass of the precursor;
and (5) sintering in the step (5) is rotary kiln dry sintering and/or chemical vapor deposition sintering.
11. The whisker-containing lithium iron phosphate particles obtained by the production method according to any one of claims 1 to 10.
12. The application of the whisker-containing lithium iron phosphate particles prepared by the preparation method according to any one of claims 1 to 10 in lithium ion batteries.
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| CN106586999A (en) * | 2015-10-18 | 2017-04-26 | 深圳市沃特玛电池有限公司 | Method for preparing lithium iron phosphate precursor by virtue of vacuum freeze drying |
| CN107978752A (en) * | 2017-11-30 | 2018-05-01 | 宁波容百锂电材料有限公司 | A kind of high security lithium ion positive electrode for battery material and preparation method thereof |
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