CN118651838A - Modification method of lithium iron manganese phosphate - Google Patents
Modification method of lithium iron manganese phosphate Download PDFInfo
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- CN118651838A CN118651838A CN202411151794.1A CN202411151794A CN118651838A CN 118651838 A CN118651838 A CN 118651838A CN 202411151794 A CN202411151794 A CN 202411151794A CN 118651838 A CN118651838 A CN 118651838A
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- manganese phosphate
- lithium
- iron manganese
- phosphate
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- DVATZODUVBMYHN-UHFFFAOYSA-K lithium;iron(2+);manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[Fe+2].[O-]P([O-])([O-])=O DVATZODUVBMYHN-UHFFFAOYSA-K 0.000 title claims abstract description 108
- 238000002715 modification method Methods 0.000 title claims abstract description 12
- -1 fluorine metal compound Chemical class 0.000 claims abstract description 41
- 238000000034 method Methods 0.000 claims abstract description 37
- 239000002243 precursor Substances 0.000 claims abstract description 29
- LIQLLTGUOSHGKY-UHFFFAOYSA-N [B].[F] Chemical compound [B].[F] LIQLLTGUOSHGKY-UHFFFAOYSA-N 0.000 claims abstract description 26
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 20
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 20
- 238000010438 heat treatment Methods 0.000 claims abstract description 19
- 239000011737 fluorine Substances 0.000 claims abstract description 18
- 229910052731 fluorine Inorganic materials 0.000 claims abstract description 18
- 229910003481 amorphous carbon Inorganic materials 0.000 claims abstract description 13
- 239000000203 mixture Substances 0.000 claims abstract description 11
- 229910021645 metal ion Inorganic materials 0.000 claims abstract description 6
- 238000002156 mixing Methods 0.000 claims abstract description 4
- 239000010450 olivine Substances 0.000 claims abstract description 4
- 229910052609 olivine Inorganic materials 0.000 claims abstract description 4
- 229910015900 BF3 Inorganic materials 0.000 claims abstract description 3
- WTEOIRVLGSZEPR-UHFFFAOYSA-N boron trifluoride Chemical group FB(F)F WTEOIRVLGSZEPR-UHFFFAOYSA-N 0.000 claims abstract description 3
- 239000000126 substance Substances 0.000 claims abstract description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 12
- 238000000498 ball milling Methods 0.000 claims description 11
- 238000004729 solvothermal method Methods 0.000 claims description 10
- 238000010532 solid phase synthesis reaction Methods 0.000 claims description 9
- 239000012300 argon atmosphere Substances 0.000 claims description 8
- 239000002612 dispersion medium Substances 0.000 claims description 6
- 238000001035 drying Methods 0.000 claims description 6
- 239000008103 glucose Substances 0.000 claims description 6
- 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 5
- 238000003980 solgel method Methods 0.000 claims description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 4
- 229910052786 argon Inorganic materials 0.000 claims description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 3
- WRIDQFICGBMAFQ-UHFFFAOYSA-N (E)-8-Octadecenoic acid Natural products CCCCCCCCCC=CCCCCCCC(O)=O WRIDQFICGBMAFQ-UHFFFAOYSA-N 0.000 claims description 2
- LQJBNNIYVWPHFW-UHFFFAOYSA-N 20:1omega9c fatty acid Natural products CCCCCCCCCCC=CCCCCCCCC(O)=O LQJBNNIYVWPHFW-UHFFFAOYSA-N 0.000 claims description 2
- QSBYPNXLFMSGKH-UHFFFAOYSA-N 9-Heptadecensaeure Natural products CCCCCCCC=CCCCCCCCC(O)=O QSBYPNXLFMSGKH-UHFFFAOYSA-N 0.000 claims description 2
- 239000005642 Oleic acid Substances 0.000 claims description 2
- ZQPPMHVWECSIRJ-UHFFFAOYSA-N Oleic acid Natural products CCCCCCCCC=CCCCCCCCC(O)=O ZQPPMHVWECSIRJ-UHFFFAOYSA-N 0.000 claims description 2
- 239000002202 Polyethylene glycol Substances 0.000 claims description 2
- 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 2
- 229930006000 Sucrose Natural products 0.000 claims description 2
- QXJSBBXBKPUZAA-UHFFFAOYSA-N isooleic acid Natural products CCCCCCCC=CCCCCCCCCC(O)=O QXJSBBXBKPUZAA-UHFFFAOYSA-N 0.000 claims description 2
- 239000012299 nitrogen atmosphere Substances 0.000 claims description 2
- ZQPPMHVWECSIRJ-KTKRTIGZSA-N oleic acid Chemical compound CCCCCCCC\C=C/CCCCCCCC(O)=O ZQPPMHVWECSIRJ-KTKRTIGZSA-N 0.000 claims description 2
- 229920001223 polyethylene glycol Polymers 0.000 claims description 2
- 239000005720 sucrose Substances 0.000 claims description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 9
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 9
- 238000001308 synthesis method Methods 0.000 abstract description 2
- 238000012986 modification Methods 0.000 description 34
- 230000004048 modification Effects 0.000 description 33
- 239000010410 layer Substances 0.000 description 30
- 239000000047 product Substances 0.000 description 15
- 230000000052 comparative effect Effects 0.000 description 13
- 239000000463 material Substances 0.000 description 12
- 238000002360 preparation method Methods 0.000 description 12
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 11
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 9
- 229910052796 boron Inorganic materials 0.000 description 9
- 239000013078 crystal Substances 0.000 description 8
- PQXKHYXIUOZZFA-UHFFFAOYSA-M lithium fluoride Chemical compound [Li+].[F-] PQXKHYXIUOZZFA-UHFFFAOYSA-M 0.000 description 8
- 230000008569 process Effects 0.000 description 8
- 238000002441 X-ray diffraction Methods 0.000 description 7
- 239000002245 particle Substances 0.000 description 6
- 239000011248 coating agent Substances 0.000 description 5
- 238000000576 coating method Methods 0.000 description 5
- 239000010405 anode material Substances 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- 229910052593 corundum Inorganic materials 0.000 description 4
- 239000010431 corundum Substances 0.000 description 4
- 239000012071 phase Substances 0.000 description 4
- PUZPDOWCWNUUKD-UHFFFAOYSA-M sodium fluoride Chemical compound [F-].[Na+] PUZPDOWCWNUUKD-UHFFFAOYSA-M 0.000 description 4
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 3
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000004090 dissolution Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000012467 final product Substances 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 229910052744 lithium Inorganic materials 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
- 229910052748 manganese Inorganic materials 0.000 description 3
- 239000011572 manganese Substances 0.000 description 3
- 239000007774 positive electrode material Substances 0.000 description 3
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000005253 cladding Methods 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 230000001351 cycling effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000000227 grinding Methods 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 2
- 239000010452 phosphate Substances 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 235000013024 sodium fluoride Nutrition 0.000 description 2
- 239000011775 sodium fluoride Substances 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- 230000005536 Jahn Teller effect Effects 0.000 description 1
- 241000124033 Salix Species 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- GZCGUPFRVQAUEE-SLPGGIOYSA-N aldehydo-D-glucose Chemical compound OC[C@@H](O)[C@@H](O)[C@H](O)[C@@H](O)C=O GZCGUPFRVQAUEE-SLPGGIOYSA-N 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 239000010406 cathode material Substances 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- ILXAVRFGLBYNEJ-UHFFFAOYSA-K lithium;manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[O-]P([O-])([O-])=O ILXAVRFGLBYNEJ-UHFFFAOYSA-K 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 239000012046 mixed solvent Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Landscapes
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a modification method of lithium iron manganese phosphate, which belongs to the technical field of lithium ion batteries and comprises the following specific steps: step 1: mixing a lithium iron manganese phosphate precursor or lithium iron manganese phosphate with a carbon source and a fluorine boron compound; step 2: carrying out high-temperature heat treatment on the mixture obtained in the step 1 to obtain modified lithium manganese iron phosphate; the outermost layer of the modified lithium manganese iron phosphate is a fluorine metal compound, the middle layer is amorphous carbon doped with fluorine boron, and the inner core is boron fluoride or/and metal ion doped lithium manganese iron phosphate; the chemical components of the lithium iron manganese phosphate precursor or the lithium iron manganese phosphate are，The space group is Pnma, which belongs to the olivine structure. The modified lithium iron manganese phosphate synthesized by the method has the advantages of higher capacity, energy density, good cycle stability and rate capability, and simple synthesis method.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a modification method of lithium iron manganese phosphate.
Background
Lithium ion batteries are a clean, efficient, renewable secondary battery, and positive electrode materials are an important component thereof. Lithium iron phosphate is one of the most important lithium ion cathode materials, and has the advantages of excellent cycle stability, high safety and low cost. However, further development is limited by the low energy density that it provides, which is caused by the low plateau voltage. Lithium iron manganese phosphate (LMFP) has a higher redox potential and is considered to be a very promising positive electrode material for lithium ion batteries, but it is poor in conductivity and cycle performance.
Bulk doping is an important modification of LMFP. The Fingered City German Co., ltd. Discloses a lithium ion battery anode material and a preparation method thereof (CN 109192935A). The university of double denier discloses a phosphorus-site boron doped lithium manganese phosphate/carbon composite material and a preparation method thereof (CN 102931404A). The German science and technology company of Buddha discloses a phosphorus-position boron-doped nano disk-shaped lithium iron manganese phosphate anode material, a preparation method and application thereof (CN 116666624A). Jiangsu Bei Terui nanometer technology Co., ltd. Discloses a fluorine doped lithium iron manganese phosphate anode material and a preparation method thereof (CN 114373912A). The method has the common characteristics that fluorine or boron elements are doped in a phosphate olivine system, so that the conductivity and the lithium ion transmission rate are improved.
Surface coating can make the material exhibit better electrochemical properties. The carbon coating has low cost and simple method, not only can improve the conductivity of the material, but also can prevent the oxidation of transition metal in the sintering process. The carbon coating doping helps to further improve conductivity and improve cycling stability. The Zhejiang south all power supply power company, inc. discloses a carbon-doped coating modified lithium iron phosphate positive electrode material and a preparation method and application thereof (CN 118164457A). The Guangxi willow industrial machinery Co., ltd discloses a coated lithium iron manganese phosphate material, a preparation method and application thereof (CN 118136813A). The common feature of the above methods is that doping the carbon layer with fluorine or other elements can further increase the conductivity of the carbon layer and can suppress the formation of the CEI film during cycling.
The two methods of cladding doping are more advanced modification methods in parallel. The German and German company of Buddha discloses a lithium iron phosphate anode material, a preparation method thereof and a lithium ion battery (CN 117720113A). A lithium ion battery applied to a portable mobile power supply and a preparation method thereof (CN 117174831A) are disclosed by Hangzhou Buttrey new energy science and technology Co. The common feature of the above methods is that fluorine or fluorine boron is doped simultaneously in the carbon layer and phosphate lattice by sol-gel or solid phase methods.
The above-mentioned various modification methods together prove that fluorine/boron doped carbon or bulk phase can effectively improve the electrochemical performance of the material. However, each of these methods suffers from at least one of the following problems:
(1) The process is complex, and is not beneficial to industrialized application;
(2) The doping source is expensive;
(3) The battery performance after modification still cannot be expected.
Disclosure of Invention
The invention aims to provide a modification method of lithium iron manganese phosphate, and the modified lithium iron manganese phosphate synthesized by the method has the advantages of higher capacity, energy density, good cycle stability and rate capability, and simple synthesis method.
In order to solve the technical problems, the invention adopts the following technical scheme:
a modification method of lithium iron manganese phosphate comprises the following specific steps:
step 1: mixing a lithium iron manganese phosphate precursor or lithium iron manganese phosphate with a carbon source and a fluorine boron compound;
step 2: carrying out high-temperature heat treatment on the mixture obtained in the step 1 to obtain modified lithium manganese iron phosphate; the outermost layer of the modified lithium manganese iron phosphate is a fluorine metal compound, the middle layer is amorphous carbon doped with fluorine boron, and the inner core is boron fluoride or/and metal ion doped lithium manganese iron phosphate;
wherein, the chemical composition of the precursor of the lithium iron manganese phosphate or the lithium iron manganese phosphate ，The space group is Pnma, which belongs to the olivine structure.
Wherein the lithium iron manganese phosphate precursor is from at least one of a solvothermal method or a sol-gel method.
Wherein the lithium iron manganese phosphate is derived from at least one of solvothermal method, sol-gel method or solid phase method.
Further, the carbon source comprises one or more of glucose, polyethylene glycol, sucrose and oleic acid.
Wherein the carbon source is added in the form of a lithium iron manganese phosphate precursor or lithium iron manganese phosphate。
Wherein the fluoroboric acid compound comprises at least one of lithium fluoroborate, sodium fluoroborate, magnesium fluoroborate, potassium fluoroborate, calcium fluoroborate, manganese fluoroborate, iron fluoroborate, cobalt fluoroborate, nickel fluoroborate, copper fluoroborate, zinc fluoroborate, stannous fluoroborate and ammonium fluoroborate.
In step 1, at least one dispersion medium of water and ethanol is added, ball-milled for 30 min and then dried.
Wherein the high temperature heat treatment condition is that under the argon or nitrogen atmosphere, the temperature rise is thatHeating to 200-800 deg.C, maintaining the temperature for 2-12 h deg.CCooled to room temperature.
The invention also discloses lithium iron manganese phosphate which is prepared by adopting the modification method of the lithium iron manganese phosphate.
The positive pole piece is prepared from the lithium iron manganese phosphate.
Compared with the prior art, the invention has the following beneficial effects:
compared with the original synthesis scheme, the precursor-based process of the invention only adds the fluorine boron compound additionally, and has no other redundant steps. The bulk phase doping of lithium manganese iron phosphate, the doping of the carbon coating layer and the coating of the fluorine metal compound are realized simultaneously through simple modification steps.
Meanwhile, the combined action of multiple modification effects enables the modified lithium manganese iron phosphate to have very excellent electrochemical performance, and voltage attenuation and manganese dissolution in the circulation process are relieved. The modification method has flexibility, doping and/or cladding of different types of ions can be realized through adding different fluorine boron compounds, and the types of fluorine boron compounds and the proportion of various fluorine boron compounds can be specifically changed to pertinently improve the cycle performance, the multiplying power performance and the like of the material so as to realize different modification schemes aiming at different application scenes.
According to the invention, a lithium iron manganese phosphate precursor or lithium iron manganese phosphate is mixed with a carbon source and a fluorine boron compound and then subjected to high-temperature heat treatment to obtain the modified lithium iron manganese phosphate. The outermost layer of the modified lithium manganese iron phosphate is a fluorine metal compound, the middle layer is fluorine boron doped amorphous carbon, and the inner core is fluorine boron or/and metal ion doped lithium manganese iron phosphate. The fluorine metal compound can regulate and control CEI film and prevent HF generated by electrolyte decomposition from damaging lithium manganese iron phosphate, fluorine boron doped amorphous carbon can play a role in conducting electricity and promoting ion transmission, fluorine boron or/and metal ion doping can improve the structural stability of lithium manganese iron phosphate, inhibit Jahn-Teller effect and manganese/iron dissolution, and improve the electronic and ion conductivity of the material. In addition, the fluorine boron compound can also improve the utilization rate of the coated carbon source and the residual carbon content of the coated carbon layer. The modified lithium iron manganese phosphate has higher voltage stability and capacity stability, and shows higher energy retention rate and rate capability.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some examples of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic structural diagram of a material synthesized by the method.
FIG. 2 is a block diagram of the process of example 1SEM pictures of precursor.
FIG. 3 is a modification prepared in example 1SEM pictures of (a).
FIG. 4 is a sample of the preparation in example 1Precursor and modificationIs a XRD pattern of (C).
FIG. 5 is a modification of example 1Is a rate charge-discharge curve.
FIG. 6 is a modification made in example 2SEM pictures of (a).
FIG. 7 is a modification prepared in example 2Is a XRD pattern of (C).
FIG. 8 is a modification of example 2Is a rate charge-discharge curve.
FIG. 9 is a modification prepared in example 3SEM pictures of (a).
FIG. 10 is a modification made in example 3Is a XRD pattern of (C).
FIG. 11 is a modification of example 3Is a rate charge-discharge curve.
FIG. 12 is a modification made in example 4SEM pictures of (a).
FIG. 13 is a modification made in example 4Is a XRD pattern of (C).
FIG. 14 is a modification of example 4Is a rate charge-discharge curve.
FIG. 15 is a modification made in example 5SEM pictures of (a).
FIG. 16 is a modification made in example 5Is a XRD pattern of (C).
FIG. 17 is a modification of example 5Is a rate charge-discharge curve.
FIG. 18 is a graph of the preparation in comparative example 1SEM pictures of (a).
FIG. 19 is a graph of the results obtained in comparative example 1Is a XRD pattern of (C).
FIG. 20 is comparative example 1Is a rate charge-discharge curve.
FIG. 21 is a graph of the preparation in comparative example 2SEM pictures of (a).
FIG. 22 is a graph of the preparation in comparative example 2Is a XRD pattern of (C).
FIG. 23 is a graph of comparative example 2Is a rate charge-discharge curve.
Reference numerals:
101 outer layer, 102 inner layer, 103 intermediate layer.
Detailed Description
Hereinafter, only certain exemplary embodiments are briefly described. As will be recognized by those of skill in the pertinent art, the described embodiments may be modified in numerous different ways without departing from the spirit or scope of the embodiments of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive. Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
Example 1
In the method, a solvothermal method is adopted to synthesize a lithium iron manganese phosphate precursor, and then the precursor is modified. Will beTransferring the mixture into a reaction kettle filled with a water/glycol mixed solvent according to the mol ratio of 3:0.8:0.2:1, introducing argon protection gas, sealing the reaction kettle, heating to 180 ℃, preserving heat at the temperature of 2 h, washing and drying after the reaction is finished, and preparing the catalystA precursor.
Precursor is processedGlucose and of (2)Putting the lithium fluoborate into a ball milling tank, ball milling with 400 rpm of ethanol as a dispersion medium for 30min, and drying.
And (3) placing the mixture into a corundum boat, heating to 700 ℃ at a heating rate of 5 ℃/min under an argon atmosphere, preserving heat for 2h, and naturally cooling to room temperature. The obtained product has the outermost layer of lithium fluoride, the middle layer of amorphous carbon doped with fluorine and boron, and the inner core of lithium manganese iron phosphate doped with fluorine and boron.
According to fig. 2-5, the precursor is Pnma structure, the crystal structure of lithium iron manganese phosphate is not changed in the subsequent modification step, and the particle shape is not changed obviously after sintering. The modified lithium iron manganese phosphate has better rate capability and smaller polarization (higher discharge voltage).
Referring to fig. 1, an outer layer of the lithium iron manganese phosphate is a fluorine metal compound layer, an inner layer of the lithium iron manganese phosphate is a fluorine boron or/and metal ion doped lithium iron manganese phosphate layer, and an intermediate layer of the lithium iron manganese phosphate is a fluorine boron doped carbon layer, and the lithium iron manganese phosphate is used for preparing a positive electrode plate.
Example 2
In the method, a solvothermal method is adopted to synthesize a precursor of lithium iron manganese phosphate, the precursor is synthesized into lithium iron manganese phosphate, and then the lithium iron manganese phosphate is modified. In comparison with example 1, the only difference is thatAnd (3) after the precursor. Precursor is processedPlacing the glucose into a ball milling tank, ball milling with 400 rpm by using ethanol as a dispersion medium for 30min, and drying. And (3) placing the mixture into a corundum boat, heating to 700 ℃ at a heating rate of 5 ℃/min under an argon atmosphere, preserving heat for 2h, and naturally cooling to room temperature. The outermost layer of the obtained product is amorphous carbon, and the inner core is lithium manganese iron phosphate. The lithium iron manganese phosphate is used forPutting the lithium fluoborate into a ball milling tank, ball milling with 400 rpm of ethanol as a dispersion medium for 30 min, and drying. And (3) placing the mixture into a corundum boat, heating to 700 ℃ at a heating rate of 5 ℃/min under an argon atmosphere, preserving heat for 2 h, and naturally cooling to room temperature. The obtained product has the outermost layer of lithium fluoride, the middle layer of amorphous carbon doped with fluorine and boron, and the inner core of lithium manganese iron phosphate doped with fluorine and boron.
Referring to fig. 6-8, the subsequent modification step did not change the crystal structure of the lithium iron manganese phosphate and the particle shape did not change significantly. The difference between the morphology features and the electrochemical performance of the product and the example 1 is smaller, and the fluorine boron compound is proved to have better modification effect on the finished product of the lithium iron manganese phosphate.
Example 3
In the embodiment, the solid phase method is adopted to synthesize the lithium iron manganese phosphate, and then the lithium iron manganese phosphate is modified. Will be at a stoichiometric ratio of 1:0.8:0.2AndGrinding glucose, addingAfter ball milling for 6 hours at 400rpm, the materials are dried, the dry powder is presintered for 2 hours at 350 ℃ and is subjected to heat treatment for 6 hours at 600 ℃ in an argon atmosphere, and the solid-phase method lithium iron manganese phosphate is obtained. The lithium iron manganese phosphate is used forPutting the lithium fluoborate into a ball milling tank, ball milling with 400 rpm of ethanol as a dispersion medium for 30min, and drying. And (3) placing the mixture into a corundum boat, heating to 700 ℃ at a heating rate of 5 ℃/min under an argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature. The obtained product has the outermost layer of lithium fluoride, the middle layer of amorphous carbon doped with fluorine and boron, and the inner core of lithium manganese iron phosphate doped with fluorine and boron.
Referring to fig. 9-11, the modified lithium iron manganese phosphate still belongs to the crystal structure of the lithium iron manganese phosphate, and the modified lithium iron manganese phosphate has better electrochemical performance. The fluorine boron compound has a good modification effect on lithium iron manganese phosphate synthesized by a solid phase method.
Example 4
In the method, a solvothermal method is adopted to synthesize a lithium iron manganese phosphate precursor, and then the precursor is modified. The only difference compared to example 1 is the substitution of lithium fluoroborate for sodium fluoroborate. The obtained product has the outermost layer of sodium fluoride, the middle layer of amorphous carbon doped with fluorine boron, and the inner core of lithium manganese iron phosphate doped with fluorine boron and sodium.
Referring to fig. 12-14, the crystal structure of the lithium iron manganese phosphate is not changed in the subsequent modification step, the particle shape is not obviously changed, and the modified lithium iron manganese phosphate has better electrochemical performance. It is proved that sodium fluoroborate can also play a modifying role compared with lithium fluoroborate.
Example 5
In the method, a solvothermal method is adopted to synthesize a lithium iron manganese phosphate precursor, and then the precursor is modified. The only difference compared to example 1 is the substitution of lithium fluoroborate with an equimolar amount of a mixture of lithium fluoroborate and sodium fluoroborate. The obtained product has the outermost layer of lithium fluoride and sodium fluoride, the middle layer of amorphous carbon doped with fluorine boron, and the inner core of lithium manganese iron phosphate doped with fluorine boron and sodium.
Referring to fig. 15-17, the crystal structure of the lithium iron manganese phosphate is not changed in the subsequent modification step, the particle shape is not obviously changed, and the modified lithium iron manganese phosphate has better electrochemical performance. It is proved that the mixture of multiple fluorine boron compounds can also play a role in modifying the lithium iron manganese phosphate.
Comparative example 1
In the method, a solvothermal method is adopted to synthesize a precursor of lithium iron manganese phosphate, and the precursor is synthesized into the lithium iron manganese phosphate. The only difference compared to example 1 is that no lithium fluoroborate is added. The outer layer of the obtained product is amorphous carbon, and the inner core is lithium manganese iron phosphate.
Referring to fig. 18-20, the synthesized product was a crystal structure of lithium manganese iron phosphate, and the particle shape was substantially the same as examples 1,2, 4, and 5. The electrochemical properties are inferior to those of examples 1,2, 4 and 5, indicating that modification of the fluoroboric compound can improve the electrochemical properties of lithium manganese iron phosphate based on solvothermal method.
Comparative example 2
In this example, solid phase method is used to synthesize lithium iron manganese phosphate. Will be at a stoichiometric ratio of 1:0.8:0.2AndGrinding glucose, addingAfter ball milling for 6 hours at 400rpm, the materials are dried, the dry powder is presintered for 2 hours at 350 ℃ and is subjected to heat treatment for 6 hours at 600 ℃ in an argon atmosphere, and the solid-phase method lithium iron manganese phosphate is obtained. The outer layer of the obtained product is amorphous carbon, and the inner core is lithium manganese iron phosphate.
Referring to fig. 21-23, the synthesized product was a crystal structure of lithium manganese iron phosphate, and the particle shape was substantially the same as in example 3. The electrochemical properties were inferior to those of example 3, indicating that modification of the fluoroboric compound improved the electrochemical properties of the solid-phase method-based lithium iron manganese phosphate.
Table 1 is the electrochemical performance of the battery materials at 1C.
As can be seen from Table 1, all examples 1-5 have improved initial coulombic efficiency and cycle stability compared with comparative examples 1-2, and manganese dissolution and voltage decay are suppressed after 500 cycles, which indicates that the all-in-one modification scheme used in the present patent can greatly alleviate side reactions on the surface of the material and structural failure of the bulk phase of the material in the charge and discharge process. Meanwhile, the method has the characteristics of low cost and simple process, and is a lithium iron manganese phosphate industrialized modification strategy.
According to the SEM morphology of the final product of this example or comparative example in fig. 3, 6, 9, 12, 15, 18 and 21, it is demonstrated that the present modification method does not significantly change the product morphology.
XRD phase analysis of the final product of this example or comparative example, according to fig. 4, 7, 10, 13, 16, 19 and 22, shows that the modification process does not significantly change the crystal structure of the product, and the synthesized product is free of other impurities.
The electrochemical performance of the final product of this example or the comparative example is illustrated to be superior to that of the comparative example according to fig. 5, 8, 11, 14, 17, 20 and 23.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
The foregoing description of the preferred embodiment of the invention is not intended to be limiting, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (8)
1. The modification method of the lithium iron manganese phosphate is characterized by comprising the following specific steps of:
step 1: mixing a lithium iron manganese phosphate precursor or lithium iron manganese phosphate with a carbon source and a fluorine boron compound;
step 2: carrying out high-temperature heat treatment on the mixture obtained in the step 1 to obtain modified lithium manganese iron phosphate; the outermost layer of the modified lithium manganese iron phosphate is a fluorine metal compound, the middle layer is amorphous carbon doped with fluorine boron, and the inner core is boron fluoride or/and metal ion doped lithium manganese iron phosphate;
wherein the chemical components of the precursor of the lithium iron manganese phosphate or the lithium iron manganese phosphate are The space group is Pnma, which belongs to the olivine structure.
2. The method for modifying lithium iron manganese phosphate according to claim 1, wherein the method comprises the following steps: the lithium iron manganese phosphate precursor is derived from at least one of a solvothermal method or a sol-gel method.
3. The method for modifying lithium iron manganese phosphate according to claim 1, wherein the method comprises the following steps: the lithium iron manganese phosphate is derived from at least one of solvothermal method, sol-gel method or solid phase method.
4. The method for modifying lithium iron manganese phosphate according to claim 1, wherein the method comprises the following steps: the carbon source comprises one or more of glucose, polyethylene glycol, sucrose and oleic acid.
5. The method for modifying lithium iron manganese phosphate according to claim 4, wherein the method comprises the following steps: the carbon source is added in the form of a precursor of lithium iron manganese phosphate or lithium iron manganese phosphate。
6. The method for modifying lithium iron manganese phosphate according to claim 1, wherein the method comprises the following steps: the fluoroboric acid compound includes at least one of lithium fluoroborate, sodium fluoroborate, magnesium fluoroborate, potassium fluoroborate, calcium fluoroborate, manganese fluoroborate, iron fluoroborate, cobalt fluoroborate, nickel fluoroborate, copper fluoroborate, zinc fluoroborate, stannous fluoroborate and ammonium fluoroborate.
7. The method for modifying lithium iron manganese phosphate according to claim 1, wherein the method comprises the following steps: in the step 1, the mixing mode is that at least one dispersion medium of water and ethanol is added, ball milling is carried out for 30min, and then drying is carried out.
8. The method for modifying lithium iron manganese phosphate according to claim 1, wherein the method comprises the following steps: the high-temperature heat treatment condition is that the temperature rise temperature is under the argon or nitrogen atmosphereHeating to 200-800 deg.C, maintaining the temperature for 2-12 h deg.CCooled to room temperature.
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