CN110492060B - Preparation method of nano-micro grade lithium manganese phosphate/carbon composite anode material - Google Patents
Preparation method of nano-micro grade lithium manganese phosphate/carbon composite anode material Download PDFInfo
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- CN110492060B CN110492060B CN201810460766.6A CN201810460766A CN110492060B CN 110492060 B CN110492060 B CN 110492060B CN 201810460766 A CN201810460766 A CN 201810460766A CN 110492060 B CN110492060 B CN 110492060B
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- ILXAVRFGLBYNEJ-UHFFFAOYSA-K lithium;manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[O-]P([O-])([O-])=O ILXAVRFGLBYNEJ-UHFFFAOYSA-K 0.000 title claims abstract description 60
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 40
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 40
- 239000002131 composite material Substances 0.000 title claims abstract description 36
- 238000002360 preparation method Methods 0.000 title claims abstract description 19
- 239000010405 anode material Substances 0.000 title description 12
- VKYKSIONXSXAKP-UHFFFAOYSA-N hexamethylenetetramine Chemical compound C1N(C2)CN3CN1CN2C3 VKYKSIONXSXAKP-UHFFFAOYSA-N 0.000 claims abstract description 117
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims abstract description 70
- 239000000463 material Substances 0.000 claims abstract description 69
- 239000004312 hexamethylene tetramine Substances 0.000 claims abstract description 58
- 235000010299 hexamethylene tetramine Nutrition 0.000 claims abstract description 58
- 239000011572 manganese Substances 0.000 claims abstract description 27
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 21
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 20
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 19
- 238000001035 drying Methods 0.000 claims abstract description 18
- 238000010438 heat treatment Methods 0.000 claims abstract description 18
- 239000011164 primary particle Substances 0.000 claims abstract description 17
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 15
- 239000011163 secondary particle Substances 0.000 claims abstract description 15
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 14
- 239000011574 phosphorus Substances 0.000 claims abstract description 14
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims abstract description 13
- 239000002994 raw material Substances 0.000 claims abstract description 11
- 239000012298 atmosphere Substances 0.000 claims abstract description 6
- 230000001681 protective effect Effects 0.000 claims abstract description 5
- 239000000243 solution Substances 0.000 claims description 99
- 238000003756 stirring Methods 0.000 claims description 29
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 claims description 26
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 24
- 239000013078 crystal Substances 0.000 claims description 24
- 238000006243 chemical reaction Methods 0.000 claims description 23
- 238000000034 method Methods 0.000 claims description 23
- 239000010406 cathode material Substances 0.000 claims description 22
- 239000002245 particle Substances 0.000 claims description 22
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 claims description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 17
- 229910021380 Manganese Chloride Inorganic materials 0.000 claims description 15
- GLFNIEUTAYBVOC-UHFFFAOYSA-L Manganese chloride Chemical compound Cl[Mn]Cl GLFNIEUTAYBVOC-UHFFFAOYSA-L 0.000 claims description 15
- 235000002867 manganese chloride Nutrition 0.000 claims description 15
- 239000011565 manganese chloride Substances 0.000 claims description 15
- 229940099607 manganese chloride Drugs 0.000 claims description 15
- SQQMAOCOWKFBNP-UHFFFAOYSA-L manganese(II) sulfate Chemical compound [Mn+2].[O-]S([O-])(=O)=O SQQMAOCOWKFBNP-UHFFFAOYSA-L 0.000 claims description 14
- 229940099596 manganese sulfate Drugs 0.000 claims description 13
- 235000007079 manganese sulphate Nutrition 0.000 claims description 13
- 239000011702 manganese sulphate Substances 0.000 claims description 13
- 238000005303 weighing Methods 0.000 claims description 13
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 12
- 238000005406 washing Methods 0.000 claims description 12
- SNKMVYBWZDHJHE-UHFFFAOYSA-M lithium;dihydrogen phosphate Chemical compound [Li+].OP(O)([O-])=O SNKMVYBWZDHJHE-UHFFFAOYSA-M 0.000 claims description 10
- 239000000376 reactant Substances 0.000 claims description 10
- 239000003575 carbonaceous material Substances 0.000 claims description 8
- 150000002696 manganese Chemical class 0.000 claims description 7
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 6
- 229910003481 amorphous carbon Inorganic materials 0.000 claims description 6
- XIXADJRWDQXREU-UHFFFAOYSA-M lithium acetate Chemical compound [Li+].CC([O-])=O XIXADJRWDQXREU-UHFFFAOYSA-M 0.000 claims description 6
- MIVBAHRSNUNMPP-UHFFFAOYSA-N manganese(2+);dinitrate Chemical compound [Mn+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MIVBAHRSNUNMPP-UHFFFAOYSA-N 0.000 claims description 6
- 239000011259 mixed solution Substances 0.000 claims description 6
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 6
- 239000012266 salt solution Substances 0.000 claims description 6
- 229910003002 lithium salt Inorganic materials 0.000 claims description 5
- 159000000002 lithium salts Chemical class 0.000 claims description 5
- 239000002202 Polyethylene glycol Substances 0.000 claims description 4
- 229920002472 Starch Polymers 0.000 claims description 4
- 239000001913 cellulose Substances 0.000 claims description 4
- 229920002678 cellulose Polymers 0.000 claims description 4
- 239000007788 liquid Substances 0.000 claims description 4
- 229920001223 polyethylene glycol Polymers 0.000 claims description 4
- 229920000642 polymer Polymers 0.000 claims description 4
- 238000000926 separation method Methods 0.000 claims description 4
- 239000008107 starch Substances 0.000 claims description 4
- 235000019698 starch Nutrition 0.000 claims description 4
- 239000003054 catalyst Substances 0.000 claims description 2
- 229940071125 manganese acetate Drugs 0.000 claims description 2
- UOGMEBQRZBEZQT-UHFFFAOYSA-L manganese(2+);diacetate Chemical compound [Mn+2].CC([O-])=O.CC([O-])=O UOGMEBQRZBEZQT-UHFFFAOYSA-L 0.000 claims description 2
- 238000000197 pyrolysis Methods 0.000 claims description 2
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 17
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 16
- 238000001354 calcination Methods 0.000 abstract description 11
- 238000002156 mixing Methods 0.000 abstract description 9
- 238000009792 diffusion process Methods 0.000 abstract description 8
- 230000009286 beneficial effect Effects 0.000 abstract description 6
- 238000009827 uniform distribution Methods 0.000 abstract description 2
- 229960004011 methenamine Drugs 0.000 description 36
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 13
- 239000008367 deionised water Substances 0.000 description 13
- 229910021641 deionized water Inorganic materials 0.000 description 13
- 239000000839 emulsion Substances 0.000 description 10
- 229910000668 LiMnPO4 Inorganic materials 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 9
- 239000002904 solvent Substances 0.000 description 9
- 238000001816 cooling Methods 0.000 description 8
- 239000002002 slurry Substances 0.000 description 8
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 6
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 6
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 description 6
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 6
- 239000012300 argon atmosphere Substances 0.000 description 6
- 230000005540 biological transmission Effects 0.000 description 6
- 239000004202 carbamide Substances 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 235000019441 ethanol Nutrition 0.000 description 6
- 239000002086 nanomaterial Substances 0.000 description 6
- 239000007774 positive electrode material Substances 0.000 description 6
- 230000008569 process Effects 0.000 description 6
- 238000001878 scanning electron micrograph Methods 0.000 description 6
- 230000001276 controlling effect Effects 0.000 description 5
- 239000002135 nanosheet Substances 0.000 description 5
- 239000000047 product Substances 0.000 description 5
- 238000011160 research Methods 0.000 description 5
- 238000002441 X-ray diffraction Methods 0.000 description 4
- 150000002500 ions Chemical class 0.000 description 4
- 239000002114 nanocomposite Substances 0.000 description 4
- 239000002159 nanocrystal Substances 0.000 description 4
- 238000004729 solvothermal method Methods 0.000 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 description 3
- 238000003917 TEM image Methods 0.000 description 3
- 239000008103 glucose Substances 0.000 description 3
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 3
- 238000001338 self-assembly Methods 0.000 description 3
- 239000012798 spherical particle Substances 0.000 description 3
- 230000002194 synthesizing effect Effects 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 238000001027 hydrothermal synthesis Methods 0.000 description 2
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 2
- 229910001386 lithium phosphate Inorganic materials 0.000 description 2
- CNFDGXZLMLFIJV-UHFFFAOYSA-L manganese(II) chloride tetrahydrate Chemical compound O.O.O.O.[Cl-].[Cl-].[Mn+2] CNFDGXZLMLFIJV-UHFFFAOYSA-L 0.000 description 2
- 238000013508 migration Methods 0.000 description 2
- 230000005012 migration Effects 0.000 description 2
- 239000002105 nanoparticle Substances 0.000 description 2
- 238000010899 nucleation Methods 0.000 description 2
- 230000006911 nucleation Effects 0.000 description 2
- 239000010450 olivine Substances 0.000 description 2
- 229910052609 olivine Inorganic materials 0.000 description 2
- 150000003017 phosphorus Chemical class 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 229910052493 LiFePO4 Inorganic materials 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 239000011149 active material Substances 0.000 description 1
- 239000013543 active substance Substances 0.000 description 1
- 230000004931 aggregating effect Effects 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 238000005119 centrifugation Methods 0.000 description 1
- 239000012295 chemical reaction liquid Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000009831 deintercalation Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000003487 electrochemical reaction Methods 0.000 description 1
- 238000004945 emulsification Methods 0.000 description 1
- 230000001804 emulsifying effect Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000000413 hydrolysate Substances 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 238000009830 intercalation Methods 0.000 description 1
- 230000002687 intercalation Effects 0.000 description 1
- 230000037427 ion transport Effects 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 229910000357 manganese(II) sulfate Inorganic materials 0.000 description 1
- WSFSSNUMVMOOMR-NJFSPNSNSA-N methanone Chemical compound O=[14CH2] WSFSSNUMVMOOMR-NJFSPNSNSA-N 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 239000011859 microparticle Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000036314 physical performance Effects 0.000 description 1
- 239000002296 pyrolytic carbon Substances 0.000 description 1
- 230000027756 respiratory electron transport chain Effects 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 150000005846 sugar alcohols Polymers 0.000 description 1
- 150000004685 tetrahydrates Chemical class 0.000 description 1
- 238000007669 thermal treatment Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical compound [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 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
-
- 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
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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
- H01M4/362—Composites
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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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- 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
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- 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
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Abstract
The invention belongs to the technical field of batteries, and particularly discloses a preparation method of a lithium manganese phosphate/carbon composite material with a nano-micro hierarchical structure, which is obtained by carrying out heat treatment on a raw material solution containing a manganese source, a lithium source, a phosphorus source, hexamethylenetetramine and ethylene glycol at 70-80 ℃ in advance and then carrying out solvothermal treatment at 160-200 ℃. Mixing the prepared lithium manganese phosphate material with a nano-micro hierarchical structure with a high molecular carbon source, drying and calcining at 500-650 ℃ in a protective atmosphere to obtain the lithium manganese phosphate material. The primary particles of the material prepared by the invention are nano-scale, have preferential growth and uniform distribution, and are beneficial to the diffusion of lithium ions in the material. The size of the secondary particles is in the micron level, which is beneficial to the stable structure, and the prepared material has higher charge and discharge capacity, excellent cycle stability and good rate capability.
Description
Technical Field
The invention belongs to the technical field of preparation of lithium ion battery anode materials, and relates to a lithium ion battery composite anode material LiMnPO with a hierarchical structure4A method for synthesizing the/C.
Background
The development of a novel power type lithium ion battery with high safety, high energy density and long service life has become a research hotspot. LiMnPO4Has an olivine structure, the theoretical capacity is 170mAh/g equivalent to that of lithium iron phosphate, but the voltage platform is 4.1V (for Li/Li +), which is 0.7V higher than that of lithium iron phosphate (3.4V), thereby improving the energy density, so that LiMnPO4The positive electrode material has attracted the research interest of a great number of researchers.
However pure phase LiMnPO4Conductivity ratio LiFePO4Worse, the lithium ion diffusion is also a limited one-dimensional channel, so that the migration rate of lithium ions at room temperature is smaller. The invention discloses a Chinese patent with the patent publication number of CN105070912A and the name of 'a method for preparing spherical lithium ion battery anode material lithium manganese phosphate', which introduces the method of co-precipitating to assist in calcining and generating Li3PO4. Then synthesizing by a polyalcohol-assisted hydrothermal method to obtain LiMnPO 4. The scheme is complex to operate, the particle size of the obtained lithium manganese phosphate spherical particles is 0.3-2 mu m, the particles are large, and primary particles with nanoscale sizes are difficult to obtain. Researchers mainly synthesized nano-sized LiMnPO4The material can shorten the diffusion path of lithium ions and enhance the reversibility of lithium ion extraction. Dokko et al [ Kaoru Dokko, Takeshi Hachida, Masayoshi Watanabe. J Electrochem Soc, 2011158 (12): A1275-A1281]With Li3PO4With MnSO4·nH2O is taken as a raw material to synthesize nano LiMnPO at 190 ℃ by a hydrothermal method4Then, coating treatment is carried out by using glucose as a carbon source. 0.01C has a specific discharge capacity of 135mAhg-1However, the specific discharge capacity at a higher rate of 1C is only 83mAhg-1Only 5 cycles of performance are mentioned and do not perform well. Due to LiMnPO4Anisotropy of Li ion transport in the structure, Li + edge [010]The direction migration activation energy is the lowest, and the proper direction is obtained by controlling the growth direction of crystal planesThe crystal face orientation and the regular crystallization material are very important for ensuring the lithium ion and electron transmission channel. Nano LiMnPO with specific crystal orientation4Becomes the focus of the appearance adjustment.
Ping Nie et al report that LiMnPO composed of single crystal nanosheets is synthesized by solvothermal method4The flower-shaped hierarchical structure is low in electrochemical activity, and the capacity is lower than 60mAh/g at low rates of C/40 and C/20. [ Ping Nie, Laifa Shen, Fang Zhang, Lin Chen, Haifu Deng, Xiaoogang Zhang. CrystEngComm, 2012, 14, 4284-]
Therefore, the preparation of the micro-nano composite structure with the oriented growth of the specific crystal face is to obtain high-rate LiMnPO4A challenge for materials.
Disclosure of Invention
Aiming at the existing micro-nano structure LiMnPO4The invention provides a preparation method of a manganese phosphate lithium material with a nano-micro hierarchical structure, and aims to obtain a micro-nano structure LiMnPO of secondary porous particles assembled by primary nanocrystals by controlling particle growth4A material.
The second objective of the invention is to provide a preparation method of a lithium manganese phosphate/carbon composite cathode material in nano-micro grade, aiming at obtaining secondary porous particles assembled by primary nanocrystals coated by amorphous carbon by controlling the particle growth, and improving the electrochemical activity and rate cycle stability of the material.
A preparation method of a manganese lithium phosphate material with a nano-micro hierarchical structure comprises the steps of carrying out heat treatment (first stage heating) on a raw material solution containing a manganese source, a lithium source, a phosphorus source, Hexamethylenetetramine (HMT) and ethylene glycol at 70-80 ℃ in advance, and then carrying out solvothermal (second stage heating) at 160-200 ℃.
The method of the invention adopts a solvent system of hexamethylene tetramine and ethylene glycol innovatively, and can prepare the lithium manganese phosphate material with a nano-micro hierarchical structure by matching with a treatment method of a two-stage gradient temperature zone of the gradient temperature zone. Researches find that the prepared lithium manganese phosphate material is porous secondary particles self-assembled by nanoscale primary particles with crystal face orientation through treatment of a two-section gradient temperature zone under a solvent system; the primary particles have (010) dominant crystal plane orientation, and the secondary particles are micron-sized or submicron-sized particles. By the method, the lithium manganese phosphate material with excellent performance can be prepared.
It has been found that the use of HMT has surprising advantages. According to the invention, hexamethylenetetramine is matched with the ethylene glycol solution system and the innovative two-stage gradient temperature zone treatment, so that crystal nucleation can be controlled, crystal nucleus preferred orientation growth is facilitated, and in addition, the emulsification effect of the HMT hydrolysate can achieve the effect of uniform reaction, so that the lithium iron phosphate material with excellent structure, smaller crystal grains, narrow particle size distribution range, different appearances and excellent performance is synergistically prepared.
In the invention, HMT is slowly hydrolyzed to generate NH in the treatment process of the two-stage gradient temperature zone3The reaction can be uniformly carried out while the pH value can be adjusted by the formaldehyde, and the growth of crystal grains is controlled; secondly, the properly generated formaldehyde has an emulsifying effect, and is matched with the two-stage solvent heat, so that the particle refinement is facilitated. In addition, the invention selects the solvothermal reaction in an ethylene glycol solution system, which has higher viscosity, slower ion diffusion in the ethylene glycol solution and no crystal growth too fast. In addition, ethylene glycol has reducing and surface active effects, and can prevent Mn2+The crystal growth can be controlled by oxidation, the fine structure of the particles is kept, and the porous nano-micro grade lithium manganese phosphate material is more favorably formed.
According to the invention, hexamethylene tetramine is adopted to be matched with the ethylene glycol and the two-stage gradient temperature treatment, so that the nano-micro hierarchical structure can be prepared, and the shape of the manganese lithium phosphate with the nano-micro hierarchical structure can be regulated and controlled by regulating and controlling the using amount of the hexamethylene tetramine. That is, the present invention has innovatively found that the morphology of the primary particles can be controlled by controlling the amount of hexamethylenetetramine, and the morphology of the secondary particles (the morphology of lithium manganese phosphate) obtained by self-assembly of the primary particles having a specific morphology can be controlled.
Preferably, the molar amount of hexamethylenetetramine is 0.5 to 2.5 times that of lithium manganese phosphate. It is also believed that the molar ratio of hexamethylenetetramine to the manganese source (as Mn) is 0.5-2.5: 1.
According to the invention, the pH of the solvothermal reaction liquid can be controlled to be 6-10 through the addition of the HMT; the optimal range is 7-9, which is beneficial to preparing the lithium manganese phosphate material with excellent performance.
In the invention, the manganese source can provide Mn2+Preferably Mn2+Water-soluble salts of (a).
Preferably, the manganese source is at least one of manganese chloride, manganese acetate, manganese nitrate and manganese sulfate.
In the invention, the lithium source is a material capable of providing Li +, and the preferred lithium source is at least one of lithium nitrate, lithium chloride and lithium acetate.
In the present invention, the lithium source is PO4 3-The material of (3) is preferably at least one of lithium dihydrogen phosphate and phosphoric acid.
Preferably, the concentration of the reactant in the raw material solution is 0.1 to 3 mol/l. That is, the concentration of the reactant including the manganese source, the lithium source, the phosphorus source, and hexamethylenetetramine in the raw material solution is preferably 0.1 to 3 mol/l. Researches find that under the optimal concentration, the obtained lithium manganese phosphate material has better structure and appearance, and the performance of the product is further improved.
Preferably, the molar ratio of Li to Mn to P is 2.5-3.5 to 1-1.1. In this preferred range, lithium manganese phosphate materials are more advantageously obtained.
The invention innovatively carries out heat treatment and solvothermal treatment under the glycol solution system.
Preferably, the raw material solution may further contain water. For example, if the phosphorus source is PO4 3-And allowing the phosphorus source to be dissolved by water, and mixing the aqueous solution of the phosphorus source with the ethylene glycol solution of the lithium source, the manganese source and the hexamethylene tetramine to obtain the raw material solution.
The invention innovatively adopts heat treatment and solvent heat under the temperature in the two-stage temperature zone, and through the heat treatment and solvent heat of different temperature zones, the hydrolysis degree of HMT can be well controlled, the pH value of a system and the content of formaldehyde are controlled, so that nanoscale uniformly-distributed primary particles are prepared by regulation, and the manganese lithium phosphate secondary particles with excellent performance are obtained through self-assembly of the primary particles.
In the present invention, the thermal treatment and the solvothermal treatment are preferably performed in a closed vessel.
Preferably, the heat treatment time is 1-2 h.
Preferably, the solvothermal time is 10-15 h.
And after the solvent heat treatment is finished, cooling, carrying out solid-liquid separation, washing the separated solid with deionized water for 2 times, washing with at least one solvent of n-butyl alcohol, absolute ethyl alcohol and acetone for 2-3 times, and drying to obtain the lithium manganese phosphate material.
The solid-liquid separation mode of the invention can adopt the conventional method, such as centrifugation.
A more preferred preparation method of the present invention comprises the steps of:
respectively dissolving a manganese source, a lithium source and hexamethylenetetramine in ethylene glycol, stirring until the manganese source, the lithium source and the hexamethylenetetramine are fully dissolved to obtain a manganese salt solution A with the concentration of 0.1-1 mol/L, a lithium salt solution B with the concentration of 0.1-3mol/L and a hexamethylenetetramine solution C with the concentration of 0.2-2 mol/L, and respectively stirring for 30-60 min;
weighing a phosphorus source, dissolving the phosphorus source in ethylene glycol or water to form a solution with the concentration of 0.2-1 mol/L, dripping the solution into the solution A in the step (1) while stirring, then dripping the solution B in the step 1) into the solution A to obtain a mixed solution D, and stirring for 20-60 min;
step (3) dripping the solution C in the step (1) into the solution D in the step (2) to form a solution E, wherein the molar ratio of Li to Mn to P to HMT in the solution is 2.5-3.5: 1-1.1: 1-2.5, and fully stirring for 30-60 min;
and (4) transferring the solution E to a high-pressure reaction kettle, sequentially carrying out the heat treatment and the solvothermal treatment, and then carrying out solid-liquid separation, washing and drying to obtain the catalyst.
According to the preferable preparation method, the raw materials are respectively dissolved to respectively obtain the solution within the concentration range, and then the raw materials are fully dissolved and mixed through the proportioning relation, so that the preparation of the lithium manganese phosphate material with the nano structure, which is uniform in appearance and excellent in performance, is facilitated. Research also finds that the supersaturation degree is difficult to form due to too low solution concentration, the crystal nucleation is difficult, the yield is too low, the supersaturation degree is too fast due to too high solution concentration, the crystal growth is difficult to control, the particles are easy to grow up, the material morphology is difficult to control, and the particles are not uniform.
The nano-micro hierarchical structure LiMnPO with different shapes prepared by the preparation method4The material is characterized in that primary particles are of a nano-scale with crystal face oriented growth, the size is 10-60 nm, and secondary particles are of a micron-scale sphere-like shape with the size of 0.2-20 mu m. The lithium manganese phosphate anode material with small particle size, uniform distribution and stable circulation is synthesized by a solvothermal method. The method has simple process and easily controlled conditions.
The invention provides a preparation method of a nano-micro grade lithium manganese phosphate/carbon composite anode material, which is used for preparing the lithium manganese phosphate/carbon material with the nano-micro grade structure;
the lithium manganese phosphate material with the nano-micro hierarchical structure is mixed with a carbon source, dried and calcined in a protective atmosphere at 500-650 ℃ to obtain the lithium manganese phosphate material.
The manganese phosphate lithium material with the nano-micro hierarchical structure is prepared by the innovative method, and then is uniformly mixed with a carbon source by the carbon coating method, and then is calcined to obtain the composite cathode material with the carbon material coated on the surface of the primary particles or in porous gaps.
Preferably, the carbon source is at least one high polymer selected from cellulose, starch, polyethylene glycol and polyvinyl alcohol.
Preferably, the amount of the carbon source is 10wt% to 30wt% of the lithium manganese phosphate.
In the calcining process, the protective atmosphere is one of argon, nitrogen, argon-hydrogen mixed gas and nitrogen-hydrogen mixed gas.
Preferably, the calcination time is 2 to 6 hours.
The invention discloses a preferable preparation method of a nano-micro grade lithium manganese phosphate/carbon composite anode material, which comprises the following specific steps:
respectively dissolving manganese salt, lithium salt, phosphorus salt and hexamethylene tetramine in ethylene glycol, stirring until the manganese salt, the lithium salt, the phosphorus salt and the hexamethylene tetramine are fully dissolved to obtain a solution A of manganese salt with the concentration of 0.1-1 mol/L, a solution B of lithium salt with the concentration of 0.1-3mol/L and a solution C of hexamethylene tetramine with the concentration of 0.2-2 mol/L, and respectively stirring for 30-60 min; weighing a phosphorus source, dissolving the phosphorus source in ethylene glycol or deionized water to form a solution with the concentration of 0.2-1 mol/L, dripping the solution into a manganese salt solution, then dripping a lithium-containing solution into the manganese salt solution to obtain a mixed solution, wherein the molar ratio of Li to Mn to P in the solution is 2.5-3.5: 1-1.1, and stirring for 20-60 min;
dripping the solution containing HMT into the mixed solution of Li, Mn and P, keeping the molar ratio of Li to Mn to P to HMT to be 2.5-3.5: 1-1.1: 1.0-2.5, and stirring for 30-60 min to form emulsion; transferring the mixture to a high-pressure sealed reaction kettle, preserving heat for 1-2 h at 70-80 ℃, then continuing preserving heat for 10-15h at 160-200 ℃, washing the reactant slurry with deionized water for 2 times after cooling, and then washing with at least one solvent of n-butyl alcohol, absolute ethyl alcohol and acetone for 2-3 times; drying at 65-100 deg.C; mixing the dried material with 10-30 wt% of carbon source, drying, calcining at 500-650 ℃ for 2-6h in protective atmosphere to obtain completely crystallized LiMnPO4the/C composite cathode material.
The invention provides a nano-micro grade lithium manganese phosphate/carbon composite anode material prepared by the preparation method, which comprises a lithium manganese phosphate material with a nano-micro grade structure and a carbon material coated on the surface of the lithium manganese phosphate material;
the carbon material is amorphous carbon obtained by pyrolysis of a polymer carbon source, wherein the content of the carbon material is 2-5 wt% of the composite cathode material.
Advantageous effects
Designed to have dynamic stability characteristicsThe micro-nano composite structure comprehensively improves LiMnPO4The electrochemical performance is critical. For LiMnPO with good rate capability4For a material, the material needs to be capable of adapting to rapid lithium ion intercalation and deintercalation under a large current, and a stable structural morphology needs to be provided. The micro-nano composite structure is a structure system which takes a nano unit structure as a core and has the integral scale of micron or submicron, so that the micro-nano composite structure not only can provide higher stacking density and a short lithium ion diffusion path, but also can ensure the integral stability of the structure, not only can exert the kinetic advantages of lithium ion and electron conduction in the nano structure unit, but also embodies the advantages of stable structure and stable interface of the micro-nano structure in the lithium storage process.
The micro-nano hierarchical structure LiMnPO obtained by the invention4the/C composite material takes the rapid transmission (electron and ion) active particles with the nano structure as the core, and simultaneously has good stability. The porous secondary particles are assembled by primary nanocrystals with specific crystal plane orientations, and the surfaces of the nanocrystals are provided with pyrolytic carbon film conductive coating layers. The nanoscale primary particles shorten the distance between lithium ion diffusion and electron transfer, the secondary particles obtained by self-assembly have structural stability, and meanwhile, the electrolyte and active substances are in full effective contact, the electrochemical reaction is promoted, and LiMnPO under high magnification is promoted4The reversible capacity of the cathode material and the cycle performance thereof are improved. The invention provides a method for synthesizing a hierarchical-structure lithium manganese phosphate anode material, the method can regulate and control the morphology structure of the prepared material by changing the amount of hexamethylenetetramine, the process is simple, and the prepared material has the characteristics of high purity, perfect crystallization, excellent physical performance and good rate cycle performance.
Drawings
FIG. 1 is a morphology chart of a lithium manganese phosphate/carbon composite cathode material with a hierarchical structure prepared in example 1;
FIG. 2 is a morphology chart of a lithium manganese phosphate/carbon composite cathode material with a hierarchical structure prepared in example 2;
FIG. 3 is an X-ray diffraction (XRD) pattern of the lithium manganese phosphate nano-anode material of example 1 and 2;
FIG. 4 is a charge-discharge curve of the lithium manganese phosphate/carbon composite cathode material with a hierarchical structure of example 1 at different rates;
FIG. 5 is a charge-discharge curve of the lithium manganese phosphate/carbon composite positive electrode material with a hierarchical structure of example 2 at different rates;
FIG. 6 is a morphology chart of a lithium manganese phosphate/carbon composite cathode material with a hierarchical structure in example 3.
Fig. 7 is a charge-discharge curve at 1C rate of the lithium manganese phosphate/carbon composite positive electrode material of the hierarchical structure of example 3;
FIG. 8 is a morphology chart of a lithium manganese phosphate/carbon composite cathode material with a hierarchical structure in example 4.
Fig. 9 is a charge-discharge curve at 1C rate of the lithium manganese phosphate/carbon composite positive electrode material of the hierarchical structure of example 4;
FIG. 10 is a morphology chart of a lithium manganese phosphate/carbon composite positive electrode material prepared in comparative example 1;
FIG. 11 is a morphology chart of a lithium manganese phosphate/carbon composite positive electrode material prepared in comparative example 2;
detailed description of the preferred embodiments
Example 1
The method comprises the following steps of (1) weighing 0.054mol of lithium nitrate, 0.019mol of manganese sulfate, 0.02mol of phosphoric acid (85%) and 0.024mol of hexamethylenetetramine according to a fixed metering ratio of Li, Mn, P and HMT of 2.7: 0.95: 1: 1.2, respectively dissolving the lithium nitrate, the manganese sulfate and the hexamethylenetetramine in 20ml of ethylene glycol to respectively obtain a lithium nitrate solution, a manganese sulfate solution, a phosphoric acid solution and a hexamethylenetetramine solution, and heating and stirring at 35 ℃ for 20 min; dripping a phosphoric acid solution into a manganese sulfate solution while stirring, dripping a lithium nitrate solution into the manganese sulfate solution, finally dripping a hexamethylenetetramine solution into the manganese sulfate solution, and fully stirring to obtain a mixed emulsion; transferring the emulsion slurry to a high-pressure reaction kettle of 180ml, placing the high-pressure reaction kettle in an oven, preserving heat at 80 ℃ for 1h, preserving heat at 180 ℃ for 10h, cooling, taking out the high-pressure reaction kettle, centrifuging the slurry, washing reactants twice respectively by deionized water and absolute ethyl alcohol, and placing the washed materials in the oven for drying at 65 ℃; and taking 1g of the dried material, weighing 0.2g of cellulose, mixing the cellulose and an appropriate amount of alcohol, drying, and calcining for 4 hours at 600 ℃ in an argon atmosphere to obtain the composite cathode material. The attached drawing of the material prepared by the embodiment is shown in figure 1, the upper left drawing of figure 1 is an SEM image, and the upper right drawing is a next particle morphology image of a Transmission Electron Microscope (TEM); the lower part of the attached drawing is a primary particle large-magnification transmission electron microscope image. The XRD pattern is shown in a of figure 3, and the diffraction pattern can be seen to be basically consistent with the lithium manganese phosphate standard card. The charge and discharge curves at different rates are shown in fig. 4.
Fig. 1 shows that the product is a symmetrical bell-shaped nano-micro particle, the thickness of the thin sheet composing the secondary particle is nano level, the length is in micrometer size, and the product presents an open three-dimensional porous structure. The TEM picture can see that the surfaces of the nano sheets have a plurality of small apertures, so that the microscopic particles forming the product are formed by assembling and aggregating the nano sheets with the large apertures on the surfaces, and simultaneously, 2-4nm amorphous carbon layers are continuously distributed on the surfaces of the nano sheets to form a good conductive network, thereby fully playing the role of ion and electron transmission. The composite anode material is detected to contain 3.56 wt% of carbon, the first discharge capacity at 0.1C is 141.5mAh/g, and the discharge specific capacity at 1C is kept at 119.9 mAh/g.
Example 2
Weighing 0.06mol of lithium chloride, 0.02mol of manganese chloride, 0.02mol of phosphoric acid (85%) and 0.034mol of hexamethylenetetramine according to the metering ratio of Li, Mn, P and HMT being 3: 1: 1.7, and respectively dissolving the lithium chloride, the manganese chloride tetrahydrate and the hexamethylenetetramine in 20ml of ethylene glycol to respectively obtain a lithium nitrate solution, a manganese chloride solution, a phosphoric acid solution and a hexamethylenetetramine solution; heating and stirring at 40 deg.C for 30 min; dripping a phosphoric acid solution into a manganese chloride solution in stirring, dripping a lithium chloride solution into the manganese chloride solution, finally dripping a hexamethylenetetramine solution into the manganese chloride solution, and stirring for 50min to obtain a mixed emulsion; transferring the emulsion to a high-pressure reaction kettle of 180ml, placing the high-pressure reaction kettle in an oven, keeping the temperature at 75 ℃ for 2h, keeping the temperature at 160 ℃ for 12h, cooling, taking out the high-pressure reaction kettle, centrifuging slurry, washing reactants twice with deionized water and absolute ethyl alcohol respectively, and placing the washed materials in the oven for drying at 65 ℃; and (3) taking 1g of the dried material, weighing 0.3g of polyvinyl alcohol, mixing the polyvinyl alcohol and an appropriate amount of alcohol, drying, and calcining for 4 hours at 550 ℃ in an argon atmosphere to obtain the composite cathode material. The attached drawing of the material prepared by the embodiment is shown in FIG. 2, the upper left drawing of FIG. 2 is a 5000-fold SEM image, and the upper right drawing is a TEM image; the lower part of the drawing is a high-magnification TEM image. The XRD pattern is shown in b of FIG. 3. The charge and discharge curves at different rates are shown in fig. 5.
Fig. 2 shows spindle-shaped particles as a fine product, with dimensions on the order of 0.3 microns, which constitute a cluster of particles that are uniform primary nanoparticles. TEM can observe that the grown 2-4nm amorphous carbon has a continuous conductive carbon film on the surface of 20-50nm crystal grains to form a carbon nano conductive network, so as to be beneficial to charge transfer and lithium ion transmission in the electrode process. XRD detects that the material has a single olivine structure (see an example figure 3), the composite cathode material contains 2.09 wt% of carbon, the discharge capacity is 140.5mAh/g at 0.2C, and the discharge specific capacity is maintained at 109.5mAh/g at 2C.
Example 3
0.06mol of lithium nitrate, 0.019mol of manganese nitrate (50%), 0.02mol of lithium dihydrogen phosphate and 0.02mol of hexamethylenetetramine are weighed according to the metering ratio of Li, Mn, P and HMT being 3: 0.95: 1, the lithium nitrate, the manganese nitrate and the hexamethylenetetramine are respectively dissolved in 20ml of ethylene glycol, and the lithium dihydrogen phosphate is dissolved in 30ml of deionized water, so as to respectively obtain a lithium nitrate solution, a manganese nitrate solution, a lithium dihydrogen phosphate solution and a hexamethylenetetramine solution. Dropping a lithium dihydrogen phosphate solution into a manganese nitrate solution while stirring, then dropping a lithium chloride solution into the solution, finally dropping a hexamethylenetetramine solution, and stirring for 30min to obtain a mixed emulsion; transferring the emulsion to a high-pressure reaction kettle of 180ml, placing the high-pressure reaction kettle in an oven, preserving heat for 1h at 70 ℃, preserving heat for 10h at 200 ℃, taking out the high-pressure reaction kettle after cooling, centrifuging slurry, washing reactants twice by deionized water and acetone respectively, and placing the washed materials in the oven for drying at 70 ℃; and (3) taking 1g of the dried material, weighing 0.25g of polyethylene glycol, mixing the polyethylene glycol and an appropriate amount of alcohol, drying, and calcining for 8 hours at 500 ℃ in an argon atmosphere to obtain the composite cathode material. The attached drawings of the material prepared by the embodiment are shown in FIG. 6, wherein the upper left drawing of FIG. 6 is a 5000-time SEM image, and the upper right drawing is a 1000-time SEM image; the lower part of the drawing is a TEM image under high magnification. Fig. 6 shows that the size of the nano-short rod grains is the smallest in the direction b and is beneficial to the diffusion of lithium ions for the secondary spherical particles assembled by the primary rod-shaped particles, the composite material shows a flat voltage platform, and the specific discharge capacity at 1C is 121.5mAh/g as shown in fig. 7. TEM can observe that the amorphous carbon has a continuous conductive carbon film on the surface of the primary crystal grain to form a carbon nano conductive network, and the composite cathode material contains 3.1 wt% of carbon.
Example 4
0.062mol of lithium acetate, 0.02mol of manganese sulfate, 0.022mol of lithium dihydrogen phosphate and 0.024mol of hexamethylenetetramine are weighed according to the weight ratio of Li to Mn to P to HMT of 3.1 to 1 to 1.1 to 1.2, the lithium acetate, the manganese sulfate and the hexamethylenetetramine are respectively dissolved in 20ml of ethylene glycol, and the lithium dihydrogen phosphate is dissolved in 20ml of deionized water to respectively obtain a lithium acetate solution, a manganese sulfate solution, a lithium dihydrogen phosphate solution and a hexamethylenetetramine solution. Dropping the added lithium dihydrogen phosphate solution into the stirred manganese sulfate solution, then dropping the lithium acetate solution into the manganese sulfate solution, finally dropping the solution into the hexamethylenetetramine solution, and stirring for 30min to obtain a mixed emulsion; transferring the emulsion to a high-pressure reaction kettle of 180ml, placing the high-pressure reaction kettle in an oven, preserving heat for 2h at 70 ℃, preserving heat for 11h at 200 ℃, taking out the high-pressure reaction kettle after cooling, centrifuging slurry, washing reactants twice by deionized water and absolute ethyl alcohol respectively, and placing the washed materials in the oven for drying at 65 ℃; and (3) taking 1g of the dried material, weighing 0.21g of starch, mixing the starch and a proper amount of alcohol, drying, and calcining for 2 hours at 650 ℃ in an argon atmosphere to obtain the composite cathode material. The accompanying drawings of the material produced in this example are shown in fig. 8, the left drawing of fig. 8 is an SEM image of secondary particles having a diameter of 20 μm, and the right drawing is an SEM image of primary particles having a flake shape. Fig. 8 shows that the three-dimensional open-structure spherical particles assembled by nanosheets grown with crystal plane orientation are beneficial to full and effective contact between the electrolyte and the active material. The composite cathode material contains 4.1 wt% of carbon, and shows good cycle performance, and as shown in FIG. 9, after 100 cycles at 1C rate, the capacity retention rate is greater than 98%.
Comparative example 1
This comparative example discusses the replacement of the HMT with urea as the mineralizer, as follows:
weighing 0.06mol of lithium chloride, 0.02mol of manganese chloride, 0.02mol of phosphoric acid (85%) and 0.03mol of urea according to the metering ratio of Li, Mn, P and urea of 3: 1: 1.5, respectively dissolving the lithium chloride, the manganese chloride tetrahydrate and the urea in 20ml of ethylene glycol, and heating and stirring for 30min at the temperature of 30 ℃; dripping a phosphoric acid solution into a manganese chloride solution in stirring, dripping a lithium chloride solution into the manganese chloride solution, finally dripping a urea solution into the lithium chloride solution, and stirring for 50min to obtain a mixed solution; transferring the emulsion to a high-pressure reaction kettle of 180ml, placing the high-pressure reaction kettle in an oven, preserving heat for 2h at the temperature of 80 ℃, preserving heat for 12h at the temperature of 180 ℃, cooling, taking out the high-pressure reaction kettle, centrifuging slurry, washing reactants twice by deionized water and absolute ethyl alcohol respectively, and placing the washed materials in the oven for drying at the temperature of 65 ℃; and (3) taking 1g of the dried material, weighing 0.3g of polyvinyl alcohol, mixing the polyvinyl alcohol and an appropriate amount of alcohol, drying, and calcining for 4 hours at 550 ℃ in an argon atmosphere to obtain the composite cathode material. The accompanying drawing of the material obtained in this comparative example is shown in fig. 10, where urea is used as mineralizer, the morphology formed is not controllable, and the particles are large and random. The prepared material has only 95mAh/g under the charge-discharge test at 0.1C rate.
Comparative example 2
In this comparative example, a solution system without ethylene glycol was used for the second temperature zone heat treatment, the specific operation was as follows:
weighing 0.06mol of lithium chloride, 0.02mol of manganese chloride, 0.02mol of phosphoric acid (85%) and 0.03mol of hexamethylenetetramine according to the metering ratio of Li, Mn, P and HMT of 3: 1: 1.5, respectively dissolving the lithium chloride, the tetrahydrate of manganese chloride and the hexamethylenetetramine in 20ml of deionized water, and stirring for dissolving; dripping a phosphoric acid solution into a manganese chloride solution in stirring, dripping a lithium chloride solution into the manganese chloride solution, finally dripping a hexamethylenetetramine solution into the manganese chloride solution, and stirring for 30min to obtain a mixed solution; transferring the solution to a high-pressure reaction kettle of 180ml, placing the high-pressure reaction kettle in an oven, preserving heat for 2h at the temperature of 80 ℃, preserving heat for 10h at the temperature of 180 ℃, cooling, taking out the high-pressure reaction kettle, centrifuging slurry, washing reactants twice by deionized water and absolute ethyl alcohol respectively, and placing the washed materials in the oven for drying at the temperature of 65 ℃; and taking 1g of the dried material, weighing 0.3g of glucose, mixing the glucose and an appropriate amount of alcohol, drying, and calcining for 4 hours at 600 ℃ in an argon atmosphere to obtain the composite cathode material. The attached figure of the material prepared by the comparative example is shown in figure 11, deionized water is used as a solvent, ion diffusion is faster, the grain diameter of the material synthesized by crystal growth is more than a few microns, the material is very compact, and a porous grading nano-micro structure cannot be formed. The prepared material has a charge-discharge test of only 104.3mAh/g at a rate of 0.1C.
According to the embodiment and the comparative proportion, HMT is used as a mineralizer and is matched with the atmosphere of the solution containing glycol to carry out the two-stage temperature zone heat treatment, so that the performance of the material can be controlled, and the lithium manganese phosphate material with excellent electrical performance is prepared.
Claims (9)
1. A preparation method of a manganese lithium phosphate material with a nano-micro hierarchical structure is characterized in that a raw material solution containing a manganese source, a lithium source, a phosphorus source, hexamethylenetetramine and ethylene glycol is subjected to heat treatment at 70-80 ℃ in advance, and then is subjected to solvothermal treatment at 160-200 ℃;
the manganese source is at least one of manganese chloride, manganese acetate, manganese nitrate and manganese sulfate;
the lithium source is at least one of lithium nitrate, lithium chloride and lithium acetate;
the phosphorus source is at least one of lithium dihydrogen phosphate and phosphoric acid;
the lithium manganese phosphate material is porous secondary particles self-assembled by nanoscale primary particles with crystal face orientation; the secondary particles are micron-sized or submicron-sized particles.
2. The method according to claim 1, wherein the molar amount of hexamethylenetetramine is 0.5 to 2.5 times the molar amount of lithium manganese phosphate.
3. The method according to claim 1, wherein the concentration of the reactant in the raw material solution is 0.1 to 3 mol/l.
4. The method according to claim 1, wherein the molar ratio of Li to Mn to P is 2.5 to 3.5:1:1 to 1.1.
5. The method according to claim 1, wherein the heat treatment time is 1 to 2 hours; the solvothermal time is 10-15 h.
6. The method according to any one of claims 1 to 5, comprising the steps of:
respectively dissolving a manganese source, a lithium source and hexamethylenetetramine in ethylene glycol, stirring until the manganese source, the lithium source and the hexamethylenetetramine are fully dissolved to obtain a manganese salt solution A with the concentration of 0.1-1 mol/L, a lithium salt solution B with the concentration of 0.1-3mol/L and a hexamethylenetetramine solution C with the concentration of 0.2-2 mol/L, and respectively stirring for 30-60 min;
weighing a phosphorus source, dissolving the phosphorus source in ethylene glycol or water to form a solution with the concentration of 0.2-1 mol/L, dripping the solution into the solution A obtained in the step (1) while stirring, then dripping the solution B obtained in the step 1) into the solution A to obtain a mixed solution D, and stirring for 20-60 min;
and (3) dripping the solution C in the step (1) into the solution D in the step (2) to form a solution E, wherein the molar ratio of Li to Mn to P in the solution is that: HMT = 2.5-3.5: 1: 1-1.1: 1-2.5, and fully stirring for 30-60 min;
and (4) transferring the solution E to a high-pressure reaction kettle, sequentially carrying out the heat treatment and the solvothermal treatment, and then carrying out solid-liquid separation, washing and drying to obtain the catalyst.
7. A preparation method of a lithium manganese phosphate/carbon composite cathode material with nano-micro scale structure is characterized in that the lithium manganese phosphate material with the nano-micro scale structure is prepared by the preparation method of any one of claims 1 to 6;
the lithium manganese phosphate material with the nano-micro hierarchical structure is mixed with a carbon source, dried and calcined at 500-650 ℃ in a protective atmosphere to obtain the lithium manganese phosphate material.
8. The method according to claim 7, wherein the carbon source is at least one polymer selected from the group consisting of cellulose, starch, polyethylene glycol, and polyvinyl alcohol; the carbon source consumption is 10-30 wt% of the manganese lithium phosphate.
9. The lithium manganese phosphate/carbon composite cathode material prepared by the preparation method of claim 7 or 8, which is characterized by comprising a lithium manganese phosphate material with a nano-micro structure and a carbon material coated on the surface of the lithium manganese phosphate material;
the lithium manganese phosphate material with the nano-micro hierarchical structure is porous secondary particles self-assembled by nano-scale primary particles with crystal face orientation; the secondary particles are micron-sized or submicron-sized particles;
the primary particles have the oriented growth characteristic of (010) crystal planes;
the size of the primary particles is 10-60 nm; the size of the secondary particles is 0.2-20 mu m;
the carbon material is amorphous carbon formed by pyrolysis of a polymer carbon source, wherein the content of the carbon material is 2-5 wt% of the composite cathode material.
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| CN101673819A (en) * | 2009-09-25 | 2010-03-17 | 清华大学 | Method for preparing manganese lithium phosphate/carbon composite material by manganese phosphate |
| CN101785995A (en) * | 2010-02-05 | 2010-07-28 | 华中科技大学 | Solvothermal preparation method for visible-light photocatalyst Bi2WO6 nano structure |
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| CN104241645A (en) * | 2014-04-29 | 2014-12-24 | 常州普格纳能源材料有限公司 | Synthesis method of lithium-manganese-phosphate anode material |
| CN105417574A (en) * | 2014-09-05 | 2016-03-23 | 天津工业大学 | Preparation method of three-dimensional layered porous zinc oxide microspheres assembled from nano-sheets |
| CN104716318A (en) * | 2015-04-03 | 2015-06-17 | 长沙理工大学 | Preparation method of spherical nickel-cobalt-manganese precursor |
| CN107785570A (en) * | 2016-08-24 | 2018-03-09 | 德阳威旭锂电科技有限责任公司 | A kind of preparation method for improving olivine structural electrode material hydro-thermal method yield |
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