CN117878310A - Modified lithium iron phosphate positive electrode material and preparation method thereof - Google Patents
Modified lithium iron phosphate positive electrode material and preparation method thereof Download PDFInfo
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- CN117878310A CN117878310A CN202311630666.0A CN202311630666A CN117878310A CN 117878310 A CN117878310 A CN 117878310A CN 202311630666 A CN202311630666 A CN 202311630666A CN 117878310 A CN117878310 A CN 117878310A
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- iron phosphate
- positive electrode
- electrode material
- magnesium
- lithium iron
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical class [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 52
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 46
- 238000002360 preparation method Methods 0.000 title claims abstract description 14
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical group [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims abstract description 39
- 229910052749 magnesium Inorganic materials 0.000 claims abstract description 38
- 239000011777 magnesium Substances 0.000 claims abstract description 38
- 150000002736 metal compounds Chemical class 0.000 claims abstract description 37
- 238000000034 method Methods 0.000 claims abstract description 26
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 21
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 claims abstract description 20
- 239000000126 substance Substances 0.000 claims abstract description 4
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims description 30
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 26
- 229910000398 iron phosphate Inorganic materials 0.000 claims description 26
- 239000002994 raw material Substances 0.000 claims description 18
- 238000005245 sintering Methods 0.000 claims description 18
- 239000002243 precursor Substances 0.000 claims description 17
- 229910052799 carbon Inorganic materials 0.000 claims description 15
- 239000000463 material Substances 0.000 claims description 15
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 13
- 229910052744 lithium Inorganic materials 0.000 claims description 13
- ALTWGIIQPLQAAM-UHFFFAOYSA-N metavanadate Chemical compound [O-][V](=O)=O ALTWGIIQPLQAAM-UHFFFAOYSA-N 0.000 claims description 13
- GNTDGMZSJNCJKK-UHFFFAOYSA-N divanadium pentaoxide Chemical compound O=[V](=O)O[V](=O)=O GNTDGMZSJNCJKK-UHFFFAOYSA-N 0.000 claims description 12
- 239000011268 mixed slurry Substances 0.000 claims description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 11
- ZLNQQNXFFQJAID-UHFFFAOYSA-L magnesium carbonate Chemical compound [Mg+2].[O-]C([O-])=O ZLNQQNXFFQJAID-UHFFFAOYSA-L 0.000 claims description 11
- 239000001095 magnesium carbonate Substances 0.000 claims description 11
- 229910000021 magnesium carbonate Inorganic materials 0.000 claims description 11
- 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 10
- 239000008103 glucose Substances 0.000 claims description 10
- 239000006258 conductive agent Substances 0.000 claims description 9
- 239000007921 spray Substances 0.000 claims description 9
- 239000002202 Polyethylene glycol Substances 0.000 claims description 8
- 239000002041 carbon nanotube Substances 0.000 claims description 8
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 8
- 229920001223 polyethylene glycol Polymers 0.000 claims description 8
- 239000010405 anode material Substances 0.000 claims description 7
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 5
- 238000000498 ball milling Methods 0.000 claims description 5
- WQZGKKKJIJFFOK-VFUOTHLCSA-N beta-D-glucose Chemical compound OC[C@H]1O[C@@H](O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-VFUOTHLCSA-N 0.000 claims description 5
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 5
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- DPTATFGPDCLUTF-UHFFFAOYSA-N phosphanylidyneiron Chemical compound [Fe]#P DPTATFGPDCLUTF-UHFFFAOYSA-N 0.000 claims description 5
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 5
- 238000007873 sieving Methods 0.000 claims description 5
- 238000007599 discharging Methods 0.000 claims description 4
- 238000005469 granulation Methods 0.000 claims description 4
- 230000003179 granulation Effects 0.000 claims description 4
- 238000010438 heat treatment Methods 0.000 claims description 4
- 238000002156 mixing Methods 0.000 claims description 4
- 239000012299 nitrogen atmosphere Substances 0.000 claims description 4
- LSGOVYNHVSXFFJ-UHFFFAOYSA-N vanadate(3-) Chemical compound [O-][V]([O-])([O-])=O LSGOVYNHVSXFFJ-UHFFFAOYSA-N 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical compound [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 claims description 3
- 235000005979 Citrus limon Nutrition 0.000 claims description 3
- 244000248349 Citrus limon Species 0.000 claims description 3
- 229920002472 Starch Polymers 0.000 claims description 3
- 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 3
- 229930006000 Sucrose Natural products 0.000 claims description 3
- UNTBPXHCXVWYOI-UHFFFAOYSA-O azanium;oxido(dioxo)vanadium Chemical compound [NH4+].[O-][V](=O)=O UNTBPXHCXVWYOI-UHFFFAOYSA-O 0.000 claims description 3
- 239000010406 cathode material Substances 0.000 claims description 3
- 229910021389 graphene Inorganic materials 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 239000000395 magnesium oxide Substances 0.000 claims description 3
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims description 3
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims description 3
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 3
- 239000005011 phenolic resin Substances 0.000 claims description 3
- 229920001568 phenolic resin Polymers 0.000 claims description 3
- 235000019422 polyvinyl alcohol Nutrition 0.000 claims description 3
- 229920000036 polyvinylpyrrolidone Polymers 0.000 claims description 3
- 239000001267 polyvinylpyrrolidone Substances 0.000 claims description 3
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 claims description 3
- 235000019698 starch Nutrition 0.000 claims description 3
- 239000008107 starch Substances 0.000 claims description 3
- 239000005720 sucrose Substances 0.000 claims description 3
- 230000005389 magnetism Effects 0.000 claims description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 28
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 28
- 230000008569 process Effects 0.000 abstract description 21
- 150000002500 ions Chemical class 0.000 abstract description 10
- 230000009467 reduction Effects 0.000 abstract description 10
- 230000005540 biological transmission Effects 0.000 abstract description 9
- 230000014759 maintenance of location Effects 0.000 abstract description 9
- 239000013078 crystal Substances 0.000 abstract description 8
- 239000002131 composite material Substances 0.000 abstract description 6
- 230000006872 improvement Effects 0.000 abstract description 6
- 230000009286 beneficial effect Effects 0.000 abstract description 5
- DUBJMEWQSPHFGK-UHFFFAOYSA-N [Mg].[V] Chemical compound [Mg].[V] DUBJMEWQSPHFGK-UHFFFAOYSA-N 0.000 abstract description 4
- 230000007547 defect Effects 0.000 abstract description 4
- 239000006183 anode active material Substances 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 21
- 238000011056 performance test Methods 0.000 description 9
- 239000011164 primary particle Substances 0.000 description 9
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 8
- 239000011248 coating agent Substances 0.000 description 6
- 238000000576 coating method Methods 0.000 description 6
- 239000003792 electrolyte Substances 0.000 description 6
- 229910021645 metal ion Inorganic materials 0.000 description 5
- 239000002245 particle Substances 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 239000005955 Ferric phosphate Substances 0.000 description 4
- 229910019142 PO4 Inorganic materials 0.000 description 4
- 238000005056 compaction Methods 0.000 description 4
- 229940032958 ferric phosphate Drugs 0.000 description 4
- 229910000399 iron(III) phosphate Inorganic materials 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 238000012986 modification Methods 0.000 description 4
- 239000007773 negative electrode material Substances 0.000 description 4
- 239000012071 phase Substances 0.000 description 4
- 239000010452 phosphate Substances 0.000 description 4
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 4
- QSNQXZYQEIKDPU-UHFFFAOYSA-N [Li].[Fe] Chemical compound [Li].[Fe] QSNQXZYQEIKDPU-UHFFFAOYSA-N 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 238000009831 deintercalation Methods 0.000 description 3
- 230000002349 favourable effect Effects 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 238000010298 pulverizing process Methods 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 229910010710 LiFePO Inorganic materials 0.000 description 2
- 229910006715 Li—O Inorganic materials 0.000 description 2
- 229910021383 artificial graphite Inorganic materials 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000004146 energy storage Methods 0.000 description 2
- 238000001027 hydrothermal synthesis Methods 0.000 description 2
- 238000010902 jet-milling Methods 0.000 description 2
- 229910003002 lithium salt Inorganic materials 0.000 description 2
- 159000000002 lithium salts Chemical class 0.000 description 2
- 238000011068 loading method Methods 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000007709 nanocrystallization Methods 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 229910000510 noble metal Inorganic materials 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- 150000002910 rare earth metals Chemical class 0.000 description 2
- 230000002441 reversible effect Effects 0.000 description 2
- 238000007789 sealing Methods 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical group [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- IZELSCCZMDXDAG-UHFFFAOYSA-K P(=O)([O-])([O-])[O-].P(=O)(O)(O)O.[Fe+2].[Li+] Chemical compound P(=O)([O-])([O-])[O-].P(=O)(O)(O)O.[Fe+2].[Li+] IZELSCCZMDXDAG-UHFFFAOYSA-K 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical group [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- -1 and more preferably Chemical compound 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- 239000002019 doping agent Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical group 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000002715 modification method Methods 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000010532 solid phase synthesis reaction Methods 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000009827 uniform distribution Methods 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention discloses a modified lithium iron phosphate positive electrode material and a preparation method thereof, wherein the chemical formula of the positive electrode material is LiFe 1‑x‑y M x N y PO 4 And C, wherein M is magnesium element, N is vanadium element, and x is less than or equal to 0.01. According to the invention, through doping of the vanadium-magnesium composite metal compound, the unit cell parameters and the grain size of lithium iron phosphate can be adjusted, and the lithium ion transmission distance is shortened, so that the ion conductivity is improved; meanwhile, the reduction of the unit cell parameters a and c reduces the gaps between the crystal faces of the a and c phases, so that the ion conductivity is further improved; the reduction of the parameters a and c of the unit cell is also beneficial to reducing the stress of two phases in the charge and discharge process, improving the structural strength between grains and avoiding the phenomenon of grain-to-grain structureThe risk of damaging structures such as cracks is avoided, so that the defect of an anode active material is avoided, the capacity retention rate in the circulation process is improved, and the improvement of the circulation performance in particular in the multiplying power and low-temperature scenes is more obvious.
Description
Technical Field
The invention relates to the technical field of secondary batteries, in particular to a modified lithium iron phosphate positive electrode material and a preparation method thereof.
Background
The phosphate positive electrode material such as lithium iron phosphate has the advantages of rich raw materials, low cost, high mass specific capacity and the like, and is the first positive electrode material of the energy storage type and power type lithium ion battery at present, but the phosphate positive electrode material has lower diffusion coefficient and electronic conductivity of lithium ions, so that the performance of the phosphate positive electrode material in the fields of low-temperature energy storage and high power is influenced, and the service life of the phosphate positive electrode material is prolonged. In the existing preparation process of the phosphate lithium iron phosphate, capacity exertion, multiplying power, low temperature, circulation and other performances of the lithium iron phosphate in the application process are mostly improved through modification methods such as nanocrystallization, metal doping, carbon coating and the like.
The morphology of the lithium iron phosphate is adjusted by the processes such as a hydrothermal method, the transmission distance of lithium ions can be reduced to a certain extent by realizing nanocrystallization, and the diffusion efficiency of lithium ions is improved, but the hydrothermal method has higher cost, complex process, and lower compacted density of nanocrystallized particles, generally 2.0-2.3g/cm 3 And is unfavorable for marketization.
Carbon coating is one of the conventional means of improving the performance of lithium iron phosphate, but reduces the energy density of lithium iron phosphate batteries to some extent. And along with the improvement of the coating dosage, the reduced carbon can further inhibit the growth of primary particles of lithium iron phosphate in the sintering process, so that the compaction density is further reduced, the energy density of the lithium iron battery is reduced, and the market popularization is also not facilitated.
The ion doping means are Li site doping, fe site doping and O site doping, so that the crystal lattice of the material can generate defects and crystal lattice distortion, and the electronic conductivity and the ion conductivity of the material are improved. The doped ions of Li site doping and O site doping are few in species, and the performance improvement is not obvious; the Fe site doping is a main current lithium iron phosphate doping modification means due to the fact that the variety of metal ions is multiple, and the modification effect is remarkable.
Common Fe-site doped metal elements are Ti, cu, V, mo, mg, al, mn, and in recent years, rare earth metals such as Y, la, ce and the like are doped. When LiFePO 4 After the Fe position of the crystal is replaced by equivalent or aliovalent metal ions, the unit cell parameters are changed, thereby increasing LiFePO 4 Is a lattice defect of (2). Meanwhile, fe site doping can generate ion vacancies, reduce bond energy of Li-O bonds and improve Li + Thereby improving LiFePO 4 Electrochemical properties of the material.
At present, the ion doped short plates are doped with a small amount of single metal ions, and the simple metal oxide structure dopants cannot achieve better performance improvement; increasing the doping amount increases the cost and increases the risk of the formation of non-pure phases of lithium iron phosphate, which affects the crystal stability; the use of rare earth or noble metal doping elements is often unfavorable for the marketization of products due to the high cost.
In view of the above-mentioned drawbacks of the current preparation of lithium iron phosphate cathode materials, it is necessary to provide a solution to the above-mentioned problems.
Disclosure of Invention
The invention aims at: the modified lithium iron phosphate positive electrode material can adjust the unit cell parameters and the grain size of lithium iron phosphate through doping of a composite metal compound, improves the transmission efficiency of lithium ions and improves the structure of the unit cell, thereby improving the multiplying power, low temperature and cycle performance.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a modified lithium iron phosphate positive electrode material has a chemical formula of LiFe 1-x-y M x N y PO 4 And C, wherein M is magnesium element, N is vanadium element, and x is less than or equal to 0.01.
Preferably, the positive electrode material unit cell parameters satisfy: 1.0280nm is less than or equal to a and less than or equal to 1.0310nm;0.6003nm is less than or equal to b is less than or equal to 0.6010nm;0.4610 nm.ltoreq.c.ltoreq. 0.4680nm.
Preferably, the molar ratio of the two elements of magnesium and vanadium is (5-8): 2-5.
Preferably, the element C accounts for 1.1-1.9% of the total mass of the positive electrode material, and more preferably, 1.2-1.5% of the total mass.
The invention also provides a preparation method of the modified lithium iron phosphate anode material, which comprises the following steps:
(1) Mixing an iron phosphate raw material, a lithium source, a carbon source, a metal compound and a conductive agent in water, pouring into a ball mill for ball milling to obtain mixed slurry;
(2) Carrying out spray granulation on the mixed slurry under the conditions that the inlet temperature is 240-280 ℃, the outlet temperature is 100-110 ℃ and the spray pressure is 3-5MPa to obtain a precursor;
(3) Heating the precursor for 5-6 hours to 700-750 ℃ in a nitrogen environment, preserving heat for 9-10 hours at the temperature, naturally cooling to less than 50 ℃ and discharging to obtain a sintered material;
(4) Sieving the sintering material in a constant temperature and humidity room, removing magnetism and crushing to obtain the anode material.
Preferably, in step (1), the iron phosphate raw material has an iron-phosphorus molar ratio of 0.97 to 0.982, more preferably 0.973 to 0.98; the specific surface area of the iron phosphate raw material is 10-15 m 2 Preferably from 12 to 13m 2 /g。
Preferably, in the step (1), the lithium source is battery grade lithium carbonate, and the molar ratio of lithium in the lithium source to iron in the iron phosphate raw material is 1:1.015-1.050.
Preferably, in the step (1), the carbon source is one or more of glucose, sucrose, starch, lemon tree, polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, and phenolic resin, more preferably one or more of glucose, polyvinyl alcohol, and polyethylene glycol, and still more preferably glucose accounts for 60% or more of the carbon source by mass.
Preferably, in the step (1), the metal compound is one or more of magnesium vanadate, magnesium metavanadate, magnesium pyrovanadate, ammonium metavanadate, vanadium pentoxide, magnesium carbonate and magnesium oxide, and more preferably, magnesium metavanadate or a mixture of magnesium metavanadate and the other components.
Preferably, in the step (1), the metal compound is 0.8 to 2.2% by mass of the iron phosphate, and more preferably 1.1 to 1.7% by mass of the iron phosphate.
Preferably, in the step (1), the conductive agent is one or more of carbon nanotubes, graphene, carbon nanotubes and conductive carbon black, and the conductive agent accounts for 0.1-0.75% of the mass of the ferric phosphate.
Preferably, in the step (1), the particle size of the mixed slurry is 0.4 to 0.44 μm.
Preferably, in step (1), the mixed slurry has a solids content of 30 to 40%.
Preferably, in step (2), the particle size D50 of the precursor is 5-8 μm.
Preferably, in the step (3), the precursor is sintered under the condition of nitrogen atmosphere, the oxygen content is less than 20ppm, the pressure in a hearth of a sintering furnace is more than 20Pa, the loading thickness of the precursor in a sagger is 3-6cm, and the total sintering time is 14-16 hours.
Preferably, in the step (4), the temperature of the constant temperature and humidity room is 18-22 ℃ and the relative humidity is 3-5%.
Preferably, in step (4), the sieving is a 400 mesh screen and the pulverizing is jet milling.
The invention has the beneficial effects that: according to the invention, the modified lithium iron phosphate anode material is prepared by adopting a solid phase method, and the metal compound is doped along the fixed crystal face direction by matching with the doping metal compound and the sintering process, so that the growth of the lithium iron phosphate primary particles is effectively controlled, and the lithium iron phosphate primary particles with uniform morphology are obtained. By doping vanadium and magnesium metal oxides, the unit cell parameters a and c of the lithium iron phosphate are smaller, so that the unit cell volume is reduced, the lithium ion transmission distance is shortened, and the ion conductivity is improved; meanwhile, the reduction of the unit cell parameters a and c reduces the gaps between the crystal faces of the a and c phases, so that the ion conductivity is further improved; during the lithium ion deintercalation process, due to LiFePO 4 /FePO 4 The reduction of the cell parameters a and c is favorable for reducing the stress of two phases in the charge and discharge process, improves the structural strength between grains, and avoids the risk of damaging the structures such as cracks, thereby avoiding the loss of the positive electrode active material, improving the capacity retention rate in the circulation process, and particularly improving the circulation performance in the multiplying power and low temperature scenes.
Drawings
Fig. 1 is a test result of the rate performance test of the lithium ion battery prepared from the positive electrode material of example 1 of the present invention.
Fig. 2 is a test result of low temperature performance test of the lithium ion battery prepared from the positive electrode material of example 1 of the present invention.
Fig. 3 is a test result of cycle performance test of the lithium ion battery prepared from the positive electrode material of example 1 of the present invention.
Detailed Description
In order to make the technical solution and advantages of the present invention more apparent, the technical solution of the present invention will be clearly and completely described in conjunction with specific embodiments, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In a first aspect, the present invention provides a modified lithium iron phosphate positive electrode material having the chemical formula LiFe 1-x-y M x N y PO 4 And C, wherein M is magnesium element, N is vanadium element, and x is less than or equal to 0.01. Too much doping amount reduces the gram capacity exertion of lithium iron phosphate. The magnesium-vanadium composite metal compound can effectively control the unit cell parameters of the growth of lithium iron phosphate grains in the sintering process, so that the unit cell volume of the lithium iron phosphate is reduced, the transmission distance of lithium ions is shortened, the transmission rate of the lithium ions is improved, and the multiplying power and the low-temperature performance are improved. The reduction of the unit cell volume is beneficial to reducing LiFePO in the lithium ion deintercalation process 4 /FePO 4 Reduces the risk of loss of living matter due to structural failure, thereby improving cycle performance. The metal compound avoids the use of rare metals and noble metals, the dosage is controlled, and simultaneously, the magnesium-vanadium composite metal compound which is more beneficial to doping is selected, the doping dosage is adjusted, the performance after doping is better improved, and meanwhile, the production cost is prevented from being improved.
In one embodiment according to the invention, the unit cell of the positive electrode materialThe parameters are as follows: 1.0280nm is less than or equal to a and less than or equal to 1.0310nm;0.6003nm is less than or equal to b is less than or equal to 0.6010nm;0.4610 nm.ltoreq.c.ltoreq. 0.4680nm. By adjusting the magnesium-vanadium composite metal compound, the cell parameters a and c of the generated lithium iron phosphate are greatly reduced, while the cell parameter b is not greatly changed. Under certain conditions, the reduction of the unit cell parameter a and the unit cell parameter c is greatly improved along with the increase of the magnesium metavanadate dosage. The cell parameter a and the cell parameter c have larger reduction amplitude, which is beneficial to the reduction of the cell volume, shortens the transmission distance of lithium ions and improves the conductivity of the lithium ions, thereby improving the multiplying power and the low-temperature performance; during the lithium ion deintercalation process, due to LiFePO 4 /FePO 4 The reduction of the cell parameters a and c is favorable for reducing the stress of two phases in the charge and discharge process, improves the structural strength between grains, and avoids the risk of damaging the structures such as cracks, thereby avoiding the loss of the positive electrode active material, improving the capacity retention rate in the circulation process, and particularly improving the circulation performance in the multiplying power and low temperature scenes.
In one embodiment according to the invention, the molar ratio of the two elements magnesium and vanadium is (5-8): (2-5), which may be 6:4, for example. The proportion of magnesium and vanadium can be adjusted by adding magnesium carbonate, the molar ratio of magnesium and vanadium can obtain lithium iron phosphate with better cycle performance at 6:4, and the reduction amplitude of the unit cell parameter a and the unit cell parameter c can be improved by improving the magnesium consumption to a certain extent, so that the unit cell volume is further reduced.
In an embodiment according to the present invention, the carbon element accounts for 1.1-1.9% of the total mass of the cathode material, and more preferably 1.2-1.5% of the total mass, for example, may be 1.2%,1.3%,1.4%,1.5%. Too much carbon coating can reduce the energy density of the lithium iron phosphate battery to some extent. Along with the improvement of the coating dosage, the reduced carbon can further inhibit the growth of primary particles of lithium iron phosphate in the sintering process, so that the compaction density is further reduced, the energy density of the lithium iron battery is reduced, and the market popularization is not facilitated.
In a second aspect according to the present invention, the present invention also provides a method for preparing a modified lithium iron phosphate positive electrode material, comprising the steps of:
(1) Mixing an iron phosphate raw material, a lithium source, a carbon source, a metal compound and a conductive agent in water, pouring into a ball mill for ball milling to obtain mixed slurry;
(2) Carrying out spray granulation on the mixed slurry under the conditions that the inlet temperature is 240-280 ℃, the outlet temperature is 100-110 ℃ and the spray pressure is 3-5MPa to obtain a precursor;
(3) Heating for 5-6 hours to 700-750 ℃ under the condition of precursor nitrogen atmosphere, preserving heat for 9-10 hours at the temperature, naturally cooling to less than 50 ℃ and discharging to obtain a sintered material;
(4) Sieving the sintering material in a constant temperature and humidity room, demagnetizing, and crushing to obtain the anode material.
In an embodiment according to the present invention, in the step (1), the iron-phosphorus molar ratio of the iron phosphate raw material is 0.97-0.982, more preferably 0.973-0.98, and may be, for example, 0.973, 0.974, 0.976, 0.977, 0.979, 0.98; the specific surface area of the iron phosphate raw material is 10-15 m 2 Preferably from 12 to 13m 2 /g, for example, may be 12m 2 /g、12.2m 2 /g、12.m 2 /g、12.5m 2 /g、12.6m 2 /g、12.7m 2 /g、12.9m 2 /g、13m 2 And/g. When LiFePO 4 After the Fe position of the crystal is replaced by equivalent or aliovalent metal ions, the unit cell parameters are changed, thereby increasing LiFePO 4 Is a lattice defect of (a). Meanwhile, fe site doping can generate ion vacancies, reduce bond energy of Li-O bonds and improve Li + Thereby improving LiFePO 4 Electrochemical properties of the material. When the raw materials are selected, the iron phosphate raw materials with high iron-phosphorus ratio are selected, at the moment, the iron phosphate raw materials have more Fe sites and can be doped with more equivalent or different valence metal ions, so that the change degree of unit cell parameters is improved, and LiFePO is further improved 4 Electrochemical properties of the material.
In one embodiment according to the present invention, in step (1), the lithium source is battery grade lithium carbonate, and the molar ratio of lithium in the lithium source to iron in the iron phosphate raw material is 1 (1.015-1.050). For example, it may be 1:1.020, 1:1.030, 1:1.040.
In an embodiment of the present invention, in the step (1), the carbon source is one or more of glucose, sucrose, starch, lemon tree, polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone P, and phenolic resin, more preferably one or a mixture of glucose, polyvinyl alcohol, and polyethylene glycol, and even more preferably glucose accounts for 60% or more of the mass of the carbon source combination.
In an embodiment of the present invention, in the step (1), the metal compound is one or more of magnesium vanadate, magnesium metavanadate, magnesium pyrovanadate, ammonium metavanadate, vanadium pentoxide, magnesium carbonate, and magnesium oxide, and more preferably is magnesium metavanadate or a mixture of magnesium metavanadate and other components. By adding metal compounds such as magnesium vanadate, magnesium metavanadate, magnesium pyrovanadate and the like, the unit cell parameters of the growth of lithium iron phosphate grains in the sintering process are effectively controlled, so that the unit cell volume of the lithium iron phosphate is reduced, the transmission distance of lithium ions is shortened, the transmission rate of the lithium ions is improved, and the multiplying power, low temperature and cycle performance are improved.
In an embodiment according to the present invention, in the step (1), the metal compound is 0.8 to 2.2% by mass of the iron phosphate, and more preferably 1.1 to 1.7% by mass of the iron phosphate, for example, 1.1%, 1.2%,1.3%,1.4%,1.5%, 1.6%, 1.7% by mass of the iron phosphate may be used. The proper doping amount of the metal compound can better improve the performance of the doped lithium iron phosphate and avoid the improvement of the production cost.
In an embodiment of the present invention, in the step (1), the conductive agent is one or more of carbon nanotubes, graphene, carbon nanotubes, and conductive carbon black, and the conductive agent accounts for 0.1-0.75% of the mass of the iron phosphate, and may be, for example, 0.15%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, and 0.7%.
In one embodiment according to the present invention, in step (1), the particle size of the mixed slurry is 0.4 to 0.44 μm. For example, it may be 0.41. Mu.m, 0.42. Mu.m, or 0.43. Mu.m.
In an embodiment according to the invention, the mixed slurry in step (1) has a solids content of 30-40%.
In one embodiment according to the invention, in step (2), the particle size D50 of the precursor is 5-8 μm. For example, it may be 5 μm, 6 μm or 7 μm.
In one embodiment according to the invention, in step (3), the precursor is sintered under the protection of nitrogen with the oxygen content less than 20ppm and the pressure in the hearth of the sintering furnace greater than 20Pa, wherein the thickness of the precursor in the sagger is 3-6cm, and the total sintering time is 14-16 hours.
In one embodiment according to the present invention, in step (3), the sintered material is a secondary sphere structure formed by uniformly distributed and topographically ordered primary particles. In the sintering process of the precursor, secondary sphere structures formed by primary particles with uniform distribution and regular morphology are generated, the compaction density is not reduced, the energy density is also higher, when the coating dosage is excessive, the growth of the primary particles of the lithium iron phosphate is suppressed by the reduced carbon, the compaction density is further reduced, and the energy density of the lithium iron battery is reduced.
In one embodiment according to the present invention, in the step (4), the temperature of the constant temperature and humidity room is 18 to 22 ℃ and the relative humidity is 3 to 5%.
In one embodiment according to the present invention, in step (4), the screen is passed through a 400 mesh screen, and the pulverization is jet pulverization.
In a third aspect of the present invention, the present invention further provides a positive electrode sheet, including a positive current collector and a positive electrode material coated on the positive current collector, wherein the positive electrode material is the modified lithium iron phosphate positive electrode material.
In a fourth aspect of the present invention, the present invention further provides a secondary battery, including a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, the positive electrode sheet being the positive electrode sheet described above; preferably, the lithium salt of the electrolyte used is 1M LiPF 6 The solvent is EC, DEC, DMC 3, DMC 4, DMC 3; the diaphragm is a PP film; the negative electrode active material used in the negative electrode active material layer is artificial graphite, and the negative electrode current collector is copper foil.
The preparation method of the lithium ion battery is well known to those skilled in the art, and generally, the preparation method of the battery comprises the steps of placing an electric core into a battery shell, adding electrolyte, and sealing to obtain the battery. Among these, the sealing method, the amount of electrolyte is well known to those skilled in the art.
The invention is further illustrated by the following examples.
Example 1
Preparation of a positive electrode material:
the embodiment provides a preparation method of a modified lithium iron phosphate positive electrode material, which comprises the following steps:
(1) Mixing an iron phosphate raw material, lithium carbonate, polyethylene glycol, glucose, a metal compound and a carbon nano tube in water, wherein the solid content is 30%, pouring the mixture into a ball mill for ball milling, and controlling the ball milling granularity to be 0.4-0.43 microns to obtain mixed slurry; wherein, the iron-phosphorus molar ratio of the iron phosphate raw material is 0.973; lithium carbonate is added in an amount of 1.02:1 molar ratio with the iron phosphate raw material Li/Fe; glucose: the mass ratio of polyethylene glycol is 3:1, polyethylene glycol and glucose account for 11% of the mass of the ferric phosphate; the metal compounds are magnesium metavanadate and magnesium carbonate, wherein the magnesium metavanadate accounts for 63% of the mass of the metal compounds, and at the moment, the molar ratio of magnesium to vanadium is about 6:4, and the metal compounds are 1.5% of the mass of the ferric phosphate; the mass of the carbon nano-tube is 1.5 percent of that of the ferric phosphate;
(2) Carrying out spray granulation on the mixed slurry under the conditions that the inlet temperature of a spray dryer is 260 ℃, the outlet temperature is 110 ℃ and the spray pressure is 4MPa to obtain a precursor;
(3) Placing the precursor into a sagger, placing the sagger into a sintering furnace, isolating the sintering furnace from the outside air under the condition of nitrogen atmosphere, heating the sagger to 730 ℃ for 9 hours, discharging the sagger when the natural cooling temperature is lower than 50 ℃, and controlling the total sintering time to 15 hours, wherein the loading thickness of the precursor in the sagger is 3cm, so as to obtain a sintering material with a secondary sphere structure;
(4) And finally, sieving, demagnetizing and jet milling the sintered material in a constant temperature and humidity room, wherein the temperature of the constant temperature and humidity room is 20 ℃, the relative humidity is 4%, and the mesh number of the sieved sintered material is 400, so as to obtain the modified lithium iron phosphate anode material.
Preparation of a positive plate:
and preparing the modified lithium iron phosphate positive electrode material as a positive electrode active material into a positive electrode plate, wherein the positive electrode current collector is aluminum foil.
Preparation of a lithium battery:
manufacturing a negative plate, a positive plate, a diaphragm and electrolyte into a lithium ion battery according to a conventional process; wherein the negative electrode active material used in the negative electrode active material layer is artificial graphite, and the lithium salt of the electrolyte is 1MLiPF 6 The solvent is EC, DEC, DMC 3, DMC 4, DMC 3; the separator is a PP film.
Example 2
Unlike example 1, the metal compound in this example was 0.75% by mass of the iron phosphate.
Other details are not repeated here in the same way as in embodiment 1.
Example 3
Unlike example 1, the metal compound in this example was magnesium metavanadate, which was not compounded with other metal compounds.
Other details are not repeated here in the same way as in embodiment 1.
Comparative example 1
Unlike example 1, no metal compound doping was used in this example.
Other details are not repeated here in the same way as in embodiment 1.
Comparative example 2
Unlike example 1, the metal compound used in this example was magnesium carbonate, and the metal compound was 0.9% by mass of iron phosphate.
Other details are not repeated here in the same way as in embodiment 1.
Comparative example 3
Unlike example 1, in this example, the metal compound was a combination of vanadium pentoxide and magnesium carbonate, and the molar ratio of vanadium pentoxide to magnesium carbonate was 6:4.
Other details are not repeated here in the same way as in embodiment 1.
Performance test:
the coin cells prepared from the positive electrode materials of examples and comparative examples were subjected to cell performance tests such as 25℃ 0.1C discharge gram capacity, 25℃ 5C discharge gram capacity, and-20℃ 0.5C capacity retention, and the test results are shown in table 1.
Square batteries prepared from the positive electrode materials of examples and comparative examples were subjected to a capacity retention test at 25 c of 0.5c 4000 cycles, and the test results are shown in table 1.
The cell parameters of the positive electrode materials of examples and comparative examples were measured, and the test results are shown in table 1.
The button cell prepared in example 1 was subjected to a rate performance test, and the test results are shown in fig. 1.
The button cell prepared in example 1 was subjected to a low temperature performance test, and the test results are shown in fig. 2.
The 42Ah square battery prepared in example 1 was subjected to cycle performance test, and the test results are shown in fig. 3.
TABLE 1
From the test results of example 1 and comparative example 1 in table 1, it can be seen that the unit cell parameters a and C of example 1 are smaller than those of comparative example 1 and the unit cell volume is also smaller than that of comparative example 1, while the 25℃ 5C discharge gram capacity, -20℃ 0.5C capacity retention and 25℃ 0.5C 4000 turn capacity retention of example 1 are both superior to those of comparative example 1, while the gram capacity remains unchanged. It is explained that the parameters a and c of the unit cell can be changed through the composite metal compound of vanadium and magnesium, the unit cell volume can be reduced, and the rate performance, the low-temperature performance and the cycle performance of the lithium ion battery can be improved under the condition of not reducing gram capacity.
As can be seen from the test results in table 1, the unit cell parameters a and c of example 1 are smaller than those of comparative example 2, and the unit cell volume is also smaller than that; the cell parameters a, b, c of comparative example 1 and comparative example 2 are not significantly different. The magnesium carbonate of comparative example 2 is decomposed in advance to generate carbon dioxide in the sintering process, provides a certain space position for the generation process of lithium iron phosphate, is favorable for reducing the size of primary particles of lithium iron phosphate, improves the regularity of the primary particles, and accordingly improves the multiplying power and low-temperature performance to a certain extent, but the unit cell volume is not obviously changed, and each performance of the prepared lithium ion battery is not obviously improved, and the unit cell parameters can be obviously reduced only by doping vanadium and magnesium together, so that each performance of the prepared lithium ion battery is greatly improved.
As can be seen from the test results in table 1, the unit cell parameters a and c of example 1 are smaller than those of comparative example 3, whereas the unit cell parameters of comparative example 3 are close to those of comparative example 1 without doping metal compound, and the cycle performance of comparative example 3 is poor in terms of lithium ion battery performance. Illustrating that example 1 uses a combination of magnesium metavanadate and magnesium carbonate with a significant change in unit cell parameters, a smaller unit cell volume and better normal temperature cycle performance than the single metal compound combination of vanadium pentoxide and magnesium carbonate used in comparative example 3.
As can be seen from the test results in table 1, the rate capability and low temperature capability of example 1 are superior to those of example 2, and the rate capability and low temperature capability of example 2 are superior to those of comparative example 1. The doping amount of vanadium in example 1 is greater than that in example 2, and the doping amount of vanadium in comparative example 1 is 0, which means that the rate performance and low temperature performance are improved with the increase of the doping amount of vanadium.
From the test results in table 1, it can be seen that the unit cell parameters a and c of example 1 are slightly smaller than those of example 2, and the rate, low temperature and cycle performance of example 2 are inferior to those of example 1 in terms of lithium ion battery performance. It is shown that the rate, low temperature and cycle performance of the lithium iron phosphate positive electrode material can be improved by increasing the doping amount of the metal compound combination to a certain extent.
From the test results in table 1, it can be seen that the unit cell parameters a and c of example 1 are slightly smaller than those of example 2, and the unit cell volume ratio is also small, and the rate, low temperature and cycle performance of example 2 are inferior to those of example 1 in terms of lithium ion battery performance. It shows that under the condition of co-doping vanadium and magnesium, the dosage of the metal compound is increased to a certain extent, and the unit cell volume is reduced.
From the test results in table 1, it can be seen that the unit cell parameters a and c of example 1 are slightly smaller than those of example 3, and the unit cell volume is also smaller, and the cycle performance of example 3 is inferior to that of example 1 in terms of lithium ion battery performance. The molar ratio of vanadium to magnesium in the metal compound of example 3 was 51:12, whereas the molar ratio of magnesium to vanadium in the metal compound of example 1 was close to 6:4, indicating that the unit cell volume was greatly reduced at a molar ratio of magnesium to vanadium of 6:4, with a corresponding increase in cycle performance as the unit cell volume was reduced.
As can be seen from the test results in fig. 1, the positive electrode material example 1 of the present invention has a reversible specific capacity of 159.48mAh/g at a current density of 0.1C when applied to a button cell; at a current density of 5C, the battery has a reversible specific capacity of 136.65mAh/g, and the curves of the battery are smooth charge and discharge curves.
As can be seen from the test results in fig. 2, when the positive electrode material example 1 of the present invention is applied to a button cell, it is discharged at a low temperature of-20 c, and the capacity retention rate of the battery is 77.55%.
As can be seen from the test results in fig. 3, when the positive electrode material example 1 of the present invention was applied to a square battery, the battery was cycled over 4000 cycles in a 0.5C high rate cycle performance test, and the retention rate of the battery capacity was still over 90%.
Variations and modifications of the above embodiments will occur to those skilled in the art to which the invention pertains from the foregoing disclosure and teachings. Therefore, the present invention is not limited to the above-described embodiments, but is intended to be capable of modification, substitution or variation in light thereof, which will be apparent to those skilled in the art in light of the present teachings. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not limit the present invention in any way.
Claims (10)
1. A modified lithium iron phosphate positive electrode material is characterized in that the chemical formula of the positive electrode material is LiFe 1-x- y M x N y PO 4 And C, wherein M is magnesium element, N is vanadium element, and x is less than or equal to 0.01.
2. The modified lithium iron phosphate positive electrode material according to claim 1 or 2, wherein the positive electrode material cell parameters satisfy: 1.0280nm is less than or equal to a and less than or equal to 1.0310nm;0.6003nm is less than or equal to b is less than or equal to 0.6010nm;0.4610 nm.ltoreq.c.ltoreq. 0.4680nm.
3. The modified lithium iron phosphate cathode material according to claim 1, wherein the molar ratio of the two elements of magnesium and vanadium is (5-8): 2-5.
4. The modified lithium iron phosphate positive electrode material according to claim 1, wherein the element C is 1.1 to 1.9% of the total mass of the positive electrode material.
5. The preparation method of the modified lithium iron phosphate anode material is characterized by comprising the following steps of:
(1) Mixing an iron phosphate raw material, a lithium source, a carbon source, a metal compound and a conductive agent in water, pouring into a ball mill for ball milling to obtain mixed slurry;
(2) Carrying out spray granulation on the mixed slurry under the conditions that the inlet temperature is 240-280 ℃, the outlet temperature is 100-110 ℃ and the spray pressure is 3-5MPa to obtain a precursor;
(3) Heating the precursor for 5-6 hours to 700-750 ℃ under the condition of nitrogen atmosphere, preserving heat for 9-10 hours at the temperature, and discharging the precursor when the temperature is naturally cooled to be less than 50 ℃ to obtain a sintered material;
(4) Sieving the sintering material in a constant temperature and humidity room, removing magnetism and crushing to obtain the anode material.
6. The method for producing a modified lithium iron phosphate positive electrode material according to claim 5, wherein in the step (1), the iron phosphate raw material has an iron-phosphorus molar ratio of 0.97 to 0.982 and a specific surface area of 10 to 15m 2 /g。
7. The method of producing a modified lithium iron phosphate positive electrode material according to claim 5, wherein in the step (1), the lithium source is battery grade lithium carbonate, and the molar ratio of lithium in the lithium source to iron in the iron phosphate raw material is 1:1.015 to 1.050.
8. The method of producing a modified lithium iron phosphate positive electrode material according to claim 5, wherein in the step (1), the carbon source is one or a combination of two or more of glucose, sucrose, starch, lemon tree, polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, and a phenolic resin.
9. The method for producing a modified lithium iron phosphate positive electrode material according to claim 5, wherein in the step (1), the metal compound is one or a mixture of two or more of magnesium vanadate, magnesium metavanadate, magnesium pyrovanadate, ammonium metavanadate, vanadium pentoxide, magnesium carbonate and magnesium oxide, and the metal compound accounts for 0.8 to 2.2% by mass of the iron phosphate.
10. The method of producing a modified lithium iron phosphate positive electrode material according to claim 5, wherein in the step (1), the conductive agent is one or more of carbon nanotubes, graphene, carbon nanotubes, and conductive carbon black, and the conductive agent accounts for 0.1 to 0.75% of the mass of the iron phosphate.
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