CN114203991A - Positive electrode material additive, positive electrode and lithium ion battery - Google Patents
Positive electrode material additive, positive electrode and lithium ion battery Download PDFInfo
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- CN114203991A CN114203991A CN202111465549.4A CN202111465549A CN114203991A CN 114203991 A CN114203991 A CN 114203991A CN 202111465549 A CN202111465549 A CN 202111465549A CN 114203991 A CN114203991 A CN 114203991A
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- positive electrode
- lithium iron
- lithium
- phosphate
- iron phosphate
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- 239000007774 positive electrode material Substances 0.000 title claims abstract description 86
- 239000000654 additive Substances 0.000 title claims abstract description 64
- 230000000996 additive effect Effects 0.000 title claims abstract description 63
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 25
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 25
- 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 claims abstract description 77
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 claims abstract description 66
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 36
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 21
- 239000011258 core-shell material Substances 0.000 claims abstract description 14
- 239000000463 material Substances 0.000 claims description 44
- 239000011248 coating agent Substances 0.000 claims description 30
- 238000000576 coating method Methods 0.000 claims description 30
- 239000000243 solution Substances 0.000 claims description 21
- 238000002360 preparation method Methods 0.000 claims description 18
- 238000000034 method Methods 0.000 claims description 17
- 238000001027 hydrothermal synthesis Methods 0.000 claims description 16
- 239000000843 powder Substances 0.000 claims description 12
- 239000000725 suspension Substances 0.000 claims description 11
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 claims description 10
- 238000003756 stirring Methods 0.000 claims description 10
- 239000010405 anode material Substances 0.000 claims description 9
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 8
- 239000002041 carbon nanotube Substances 0.000 claims description 8
- 238000001816 cooling Methods 0.000 claims description 8
- 239000011261 inert gas Substances 0.000 claims description 8
- 239000011230 binding agent Substances 0.000 claims description 7
- 239000006258 conductive agent Substances 0.000 claims description 7
- 239000012266 salt solution Substances 0.000 claims description 7
- 229910003481 amorphous carbon Inorganic materials 0.000 claims description 6
- 239000011267 electrode slurry Substances 0.000 claims description 6
- 229910021389 graphene Inorganic materials 0.000 claims description 5
- 229910014985 LiMnxFe1-xPO4 Inorganic materials 0.000 claims description 3
- 229910014982 LiMnxFe1−xPO4 Inorganic materials 0.000 claims description 3
- 239000003792 electrolyte Substances 0.000 claims description 3
- 238000010304 firing Methods 0.000 claims 1
- ILXAVRFGLBYNEJ-UHFFFAOYSA-K lithium;manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[O-]P([O-])([O-])=O ILXAVRFGLBYNEJ-UHFFFAOYSA-K 0.000 abstract description 9
- 239000002253 acid Substances 0.000 abstract description 6
- 239000010941 cobalt Substances 0.000 abstract description 6
- 229910017052 cobalt Inorganic materials 0.000 abstract description 6
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 abstract description 6
- 239000010410 layer Substances 0.000 description 28
- 238000001291 vacuum drying Methods 0.000 description 13
- 238000002474 experimental method Methods 0.000 description 8
- 239000002245 particle Substances 0.000 description 8
- 239000002131 composite material Substances 0.000 description 7
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 6
- 239000010406 cathode material Substances 0.000 description 6
- 229910052744 lithium Inorganic materials 0.000 description 6
- 239000011572 manganese Substances 0.000 description 6
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 5
- 239000002033 PVDF binder Substances 0.000 description 5
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 5
- 238000001354 calcination Methods 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 238000002156 mixing Methods 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 230000035484 reaction time Effects 0.000 description 4
- 229910019142 PO4 Inorganic materials 0.000 description 3
- 238000007599 discharging Methods 0.000 description 3
- 238000004090 dissolution Methods 0.000 description 3
- 235000003891 ferrous sulphate Nutrition 0.000 description 3
- 239000011790 ferrous sulphate Substances 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 229910000359 iron(II) sulfate Inorganic materials 0.000 description 3
- 230000001681 protective effect Effects 0.000 description 3
- 238000000967 suction filtration Methods 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 229910032387 LiCoO2 Inorganic materials 0.000 description 2
- 229910052493 LiFePO4 Inorganic materials 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- HFCVPDYCRZVZDF-UHFFFAOYSA-N [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O Chemical compound [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O HFCVPDYCRZVZDF-UHFFFAOYSA-N 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 229910021383 artificial graphite Inorganic materials 0.000 description 2
- 239000006229 carbon black Substances 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- 239000011247 coating layer Substances 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 239000012065 filter cake Substances 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 239000007773 negative electrode material Substances 0.000 description 2
- 230000000149 penetrating effect Effects 0.000 description 2
- 238000011056 performance test Methods 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- NLHHRLWOUZZQLW-UHFFFAOYSA-N Acrylonitrile Chemical compound C=CC#N NLHHRLWOUZZQLW-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910015645 LiMn Inorganic materials 0.000 description 1
- 229910000668 LiMnPO4 Inorganic materials 0.000 description 1
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005538 encapsulation Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
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- 230000008020 evaporation Effects 0.000 description 1
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- 230000003179 granulation Effects 0.000 description 1
- 238000005469 granulation Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 229910052603 melanterite Inorganic materials 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 239000011268 mixed slurry Substances 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 239000010413 mother solution Substances 0.000 description 1
- 239000002105 nanoparticle Substances 0.000 description 1
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- 239000002904 solvent Substances 0.000 description 1
- 238000001694 spray drying Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 229910001868 water Inorganic materials 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Composite Materials (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The application discloses a positive electrode material additive, a positive electrode and a lithium ion battery. In the application, the positive electrode material additive has a core-shell structure, and the core-shell structure comprises an inner core, a first shell layer coated on the surface of the inner core, and a second shell layer coated on the surface of the first shell layer; the core comprises lithium manganese iron phosphate; the first shell layer comprises lithium iron phosphate; the second shell layer comprises carbon. In the lithium ion battery added with the positive electrode material additive of the first aspect of the invention, after the lithium iron phosphate and the lithium manganese phosphate are mixed in a cobalt acid physical mode, the system contains the lithium iron phosphate and the lithium manganese phosphate with high-stability P-O bonds, and the lithium iron phosphate and the lithium manganese phosphate are difficult to decompose, so that the safety and the stability are improved, and the chain reaction under thermal runaway can be inhibited to a certain extent, thereby improving the safety performance of a battery cell.
Description
Technical Field
The embodiment of the invention relates to the field of lithium ion batteries, in particular to a positive electrode material additive, a positive electrode and a lithium ion battery.
Background
As a novel renewable green energy source, the lithium ion battery has been widely applied to small electronic devices (mobile phones, notebook computers, and the like) by virtue of its advantages of high specific energy, high voltage, long cycle life, greenness, no pollution, and the like, and gradually becomes one of the most main candidate power sources of electric vehicles; in addition, the lithium ion battery is widely applied in the field of national defense and military, and covers equipment of various arms such as land, sea, air, sky and the like. With the progress of science and technology, people put forward higher requirements on lithium ion batteries, and the finding of high-performance lithium ion batteries has very important practical significance.
The performance of the anode and cathode materials of the lithium ion battery has very important influence on the finished battery, and the anode material becomes a key factor for limiting the further improvement of the performance of the lithium ion battery, so that the search for the high-performance anode material of the lithium ion battery is very important. The existing anode material is easy to generate thermal runaway chain reaction, and is difficult to pass safety experiments such as needling overcharge and the like, so that the safety performance of a battery cell cannot be guaranteed. To solve this problem, attempts have been made in the prior art to blend a small amount of LFMP (LiFe)1-yMnyPO4(0.5≤y<1.0) positive electrode material) to achieve a certain suppression of the chain reaction under thermal runaway of the positive electrode material. For example:
therefore, there is a need in the art to find a safe Mn inhibitor that can inhibit Mn in the cyclic process2+And Fe3+And (4) the dissolved cathode material.
Disclosure of Invention
The invention aims to provide a positive electrode material additive, so that the safety performance and the electrochemical performance of a lithium ion battery prepared by using the positive electrode material additive are improved.
Another object of the present invention is to provide a positive electrode.
Another object of the present invention is to provide a lithium ion battery.
The invention also aims to provide a preparation method of the positive electrode material additive.
In order to solve the technical problems, the invention provides, in a first aspect, an additive for a positive electrode material, wherein the additive for a positive electrode material has a core-shell structure, and the core-shell structure comprises an inner core, a first shell layer coated on the surface of the inner core, and a second shell layer coated on the surface of the first shell layer;
the core comprises lithium manganese iron phosphate;
the first shell layer comprises lithium iron phosphate;
the second shell layer comprises carbon.
In some preferred schemes, the core-shell structure consists of an inner core, a first shell layer coated on the surface of the inner core, and a second shell layer coated on the surface of the first shell layer;
the core is lithium manganese iron phosphate;
the first shell layer is made of lithium iron phosphate;
the second shell layer is carbon.
In some preferred schemes, the lithium iron manganese phosphate is LiMnxFe1-xPO4Wherein x ranges from 0.2 to 0.8(SOC 7/3), preferably from 0.5 to 0.7(SOC 7/3), for example 0.7(SOC 7/3).
In some preferred schemes, the mass of the lithium iron manganese phosphate accounts for 70 to 99% of the total mass of the positive electrode material additive; more preferably 80 to 90%.
In some preferred schemes, the mass of the lithium iron phosphate accounts for 1 to 15% of the total mass of the positive electrode material additive.
In some preferred embodiments, the carbon accounts for 2 to 10% by mass of the total mass of the positive electrode material additive.
In some preferred embodiments, the lithium iron manganese phosphate has a D50 of 2 to 50 μm; preferably 2 to 20 μm.
In some preferable schemes, the specific surface area of the lithium iron manganese phosphate is more than or equal to 10.0m2/g。
In some preferred embodiments, the preparation of the positive electrode material additive includes the steps of:
and coating carbon source powder on the lithium iron manganese phosphate material with the surface coated with the lithium iron phosphate through a coating reaction to obtain the anode material additive.
In some preferred embodiments, the coating reaction comprises the steps of: and (4) roasting and cooling.
The temperature of the calcination is not less than 400 ℃ and not more than 1000 ℃, preferably not less than 500 ℃ and not more than 800 ℃, more preferably not less than 600 ℃ and not more than 750 ℃, for example: 600-750 ℃.
The time of the calcination is not less than 1 hour and not more than 10 hours, more preferably not less than 2 hours and not more than 8 hours, for example, 4 to 6 hours.
The cooling cools the material at least to a temperature not higher than t, wherein 200 ℃ C. or higher t.gtoreq.room temperature (room temperature 23 to 26 ℃, e.g., 25 ℃) C, more preferably 150 ℃ C. or higher t.gtoreq.room temperature, e.g., 25 to 150 ℃.
In some preferred embodiments, the carbon source powder is selected from at least one of amorphous carbon, carbon nanotubes, and graphene.
In some preferred embodiments, the coating reaction is carried out in the presence of an inert gas.
In some preferred embodiments, the temperature of the coating reaction is not lower than 400 ℃ and not higher than 1000 ℃, preferably not lower than 500 ℃ and not higher than 800 ℃, more preferably not lower than 600 ℃ and not higher than 750 ℃, for example: 600-750 ℃.
In some preferred embodiments, the coating reaction time is not less than 1 hour and not more than 10 hours, more preferably not less than 2 hours and not more than 8 hours, for example, 4 to 6 hours.
In some preferred schemes, the preparation of the lithium iron manganese phosphate material with the surface coated with lithium iron phosphate comprises the following steps:
and carrying out hydrothermal reaction on a reaction solution containing lithium manganese iron phosphate and lithium iron phosphate to obtain the lithium manganese iron phosphate material with the surface coated with the lithium iron phosphate.
In some preferred embodiments, the reaction temperature is 150 ℃ and 180 ℃, more preferably 160 ℃.
In some preferred embodiments, the reaction pressure is 0.48 to 1.0MPa, and more preferably 0.6 MPa.
In some preferred embodiments, in the reaction solution, the mass ratio of the lithium iron manganese phosphate to the lithium iron phosphate is 1: 9-4: 6, more preferably 2: 8.
in some preferred embodiments, the reaction solution further comprises a ferrous salt solution; such as ferrous sulfate solution.
In some preferred embodiments, the hydrothermal reaction time is not less than 3 hours and not more than 60 hours, more preferably, not less than 5 hours and not more than 50 hours, and more preferably, not less than 10 hours and not more than 36 hours.
In some preferred schemes, the preparation of the lithium iron manganese phosphate material with the surface coated with lithium iron phosphate comprises the following steps:
in the presence of inert gas, adding a ferrous salt solution into a suspension mixed with lithium iron manganese phosphate and a lithium iron phosphate solution dropwise, stirring, and then placing the suspension in a high-pressure reaction kettle at the temperature of 150-180 ℃ and the pressure of 0.48-1.0 Mpa for hydrothermal reaction to obtain the lithium iron manganese phosphate material with the surface coated with lithium iron phosphate.
In some preferred embodiments, the hydrothermal reaction further comprises a post-treatment step:
and carrying out suction filtration, washing and vacuum drying on the hydrothermal reaction product.
In some preferred schemes, the temperature of the vacuum drying is not lower than 70 ℃ and not higher than 160 ℃; more preferably, the temperature of the vacuum drying is not lower than 80 ℃ and not higher than 120 ℃.
In some preferred embodiments, the vacuum drying time is not less than 1 hour and not more than 60 hours; more preferably, the time of the vacuum drying is not less than 2 hours and not more than 50 hours; more preferably, the time of the vacuum drying is not less than 3 hours and not more than 36 hours.
The invention provides a positive electrode, which is formed by coating positive electrode slurry on the surface of a current collector, wherein the positive electrode slurry comprises a positive electrode active material, a conductive agent and a binder;
wherein the positive electrode active material comprises a positive electrode active material and the positive electrode material additive.
In some preferred embodiments, the mass ratio of the positive electrode active material to the positive electrode material additive is (90.0 to 99.9): (0.1 to 10.0), and more preferably: (95.0 to 99.0): (1.0 to 5.0), for example: 99:1.
In some preferred embodiments, the positive electrode active material is selected from at least one of lithium cobaltate, lithium manganate, and lithium nickel cobalt manganate; lithium cobaltate is preferred.
In some preferred embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder is l: m: n, and l + m + n is 100, where l is 95 to 99, m is 0.5 to 3, and n is 1 to 5, for example: 96:1.5:2.5.
In some preferred embodiments, D50 of the positive electrode active material is 5 to 10 um; more preferably 6 to 8 μm, for example 8 μm.
In some preferred embodiments, the specific surface area of the positive electrode active material is 2.0m or more2A/g, more preferably 2.0 to 6.0m2(ii)/g; for example 4.2m2/g。
In some preferred embodiments, the conductive agent is carbon nanotubes, carbon black, graphite, or graphene.
In some preferred schemes, the specific surface area of the carbon nano tube is 200-300m2/g。
In some preferred embodiments, the binder is PVDF, SBR, or PAA.
In some preferred embodiments, the PVDF has a specific surface area of 40 to 70m2(ii)/g; more preferably 60-65 μm.
In a third aspect, the invention provides a lithium ion battery, which comprises the positive electrode, the negative electrode, the electrolyte and the diaphragm provided by the second aspect of the invention.
In a fourth aspect of the present invention, there is provided a method for preparing the positive electrode material additive according to the first aspect of the present invention, the method comprising the steps of:
preparing a lithium manganese iron phosphate material with the surface coated with lithium iron phosphate; and
and coating the carbon source powder on the lithium iron manganese phosphate material with the surface coated with the lithium iron phosphate through a coating reaction. In some preferred embodiments, the step of preparing the lithium iron manganese phosphate material with a surface coated with lithium iron phosphate includes:
and carrying out hydrothermal reaction on a reaction solution containing lithium manganese iron phosphate and lithium iron phosphate to obtain the lithium manganese iron phosphate material with the surface coated with the lithium iron phosphate.
In some preferred embodiments, the step of preparing the lithium iron manganese phosphate material with a surface coated with lithium iron phosphate includes: in the presence of inert gas, adding a ferrous salt solution into a suspension mixed with lithium iron manganese phosphate and a lithium iron phosphate solution dropwise, stirring, and then placing the suspension in a high-pressure reaction kettle at the temperature of 150-180 ℃ and the pressure of 0.48-1.0 Mpa for hydrothermal reaction to obtain the lithium iron manganese phosphate material with the surface coated with lithium iron phosphate.
Compared with the prior art, the invention has at least the following advantages:
(1) the positive electrode material additive provided by the first aspect of the invention is added into a positive electrode material, and lithium iron manganese phosphate coated nano particles are fixed on the surfaces of cobalt acid physical material particles by a mechanical fusion method to form a compact porous coating layer, so that the problem that the cobalt acid physical material and the lithium manganese phosphate material are easy to segregate due to different densities when mixed slurry of the cobalt acid physical material and the lithium manganese phosphate material is required to be obtained in a slurry mixing stage in the mixed use process of the cobalt acid physical material and the lithium manganese phosphate material in the prior art is solved, the consistency of the positive electrode material can be improved, and the material is easier to disperse;
(2) the positive electrode material additive provided by the first aspect of the invention has little influence on the capacity density of the battery;
(3) the lithium ion battery added with the positive electrode material additive has better rate capability, good conductivity and small impedance;
(4) the addition of the positive electrode material additive according to the first aspect of the invention can suppress Mn during cycling2+And Fe3 +Dissolving out even no middle Mn2+The dissolution is beneficial to the stability of the voltage of the battery;
(5) in the lithium ion battery added with the positive electrode material additive of the first aspect of the invention, after the lithium iron phosphate and the lithium manganese phosphate are mixed in a cobalt acid physical mode, the system contains the lithium iron phosphate and the lithium manganese phosphate with high-stability P-O bonds, and the lithium iron phosphate and the lithium manganese phosphate are difficult to decompose, so that the safety and the stability are improved, and the chain reaction under thermal runaway can be inhibited to a certain extent, thereby improving the safety performance of a battery cell;
(6) the LiFePO4 and the lithium iron manganese phosphate particles can form a good solid solution according to any proportion, so the LiMnPO4 can be coated on the surfaces of the lithium iron manganese phosphate particles, and the lithium iron manganese phosphate particles coated with the LiFePO4 are easier to coat carbon than pure lithium iron manganese phosphate particles, so the preparation cost is lower, the formed coating layer is more uniform and compact, and the cycle performance of the battery is better.
It is to be understood that within the scope of the present invention, the above-described features of the present invention and those specifically described below (e.g., in the examples) may be combined with each other to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.
Drawings
One or more embodiments are illustrated by the corresponding figures in the drawings, which are not meant to be limiting.
FIG. 1 is a graph showing the results of a pin-punch temperature increase test of a battery according to the present invention in comparative example 1;
FIG. 2 is a graph showing the results of a pin-punch temperature increase test of a battery in example 4 according to the present invention.
Detailed Description
The inventor finds that the existing cathode material has poor safety performance and Mn in the circulation process2+And Fe3+Dissolution and deterioration of the cycle performance of the battery. Therefore, through exhaustive experiments, the inventors have developed a positive electrode material additive having a shell-core structure, which is mixed with a positive electrode active material to greatly reduce Mn during battery cycling2+And Fe3+The dissolution improves the cycle performance and the safety performance of the battery, and moreover, the conductivity of the lithium ion battery prepared by the anode containing the anode material additive is also greatly improved.
Further, the inventors have also found the mass of each shell layer of the above-described positive electrode material additive of a shell-core structure; the particle size and the specific surface area of the particles forming each shell layer; the method for preparing the shell-core structure has great influence on the performance of the finished battery, and the inventor speculates that the kinetic properties of the obtained positive electrode are different due to the difference of the coating rate and the coating effect of the shell-core structure caused by the process, so that the cycle and the conductivity of the battery are influenced.
Further, the inventors have found that the positive electrode material additive described above has a difference in compatibility with different positive electrode active materials, and even with the same positive electrode active material, the difference in particle size, specific surface area, and tap density affects the compatibility with the positive electrode material additive. Based on this, the inventors have conducted a large number of experiments and found that when the above-described positive electrode material additive and lithium cobaltate (positive electrode active material) are mixed, the performance is exerted to the best. Further, the inventors have found that when the mass ratio of the positive electrode material additive to the positive electrode active material is different, the cycle performance and the conductivity of the obtained lithium ion battery are greatly different. On this basis, the inventors have conducted a large number of experiments and found that the mass ratio of lithium cobaltate to the above positive electrode material additive is (90.0 to 99.9): (0.1 to 10.0), and more preferably: (95.0 to 99.0): (1.0 to 5.0) and most preferably 99:1, the conductivity and cycle performance of the resulting battery are optimized.
The invention provides a cathode material additive which has a core-shell structure, wherein the core-shell structure comprises an inner core, a first shell layer coated on the surface of the inner core and a second shell layer coated on the surface of the first shell layer;
the core comprises lithium manganese iron phosphate;
the first shell layer comprises lithium iron phosphate;
the second shell layer comprises carbon.
In some preferred schemes, the core-shell structure consists of an inner core, a first shell layer coated on the surface of the inner core, and a second shell layer coated on the surface of the first shell layer;
the core is lithium manganese iron phosphate;
the first shell layer is made of lithium iron phosphate;
the second shell layer is carbon.
In some preferred schemes, the lithium iron manganese phosphate is LiMnxFe1-xPO4Wherein x ranges from 0.2 to 0.8(SOC 7/3), preferably from 0.5 to 0.7(SOC 7/3), for example 0.7(SOC 7/3).
In some preferred schemes, the mass of the lithium iron manganese phosphate accounts for 70 to 99% of the total mass of the positive electrode material additive; more preferably 80 to 90%.
In some preferred schemes, the mass of the lithium iron phosphate accounts for 1 to 15% of the total mass of the positive electrode material additive.
In some preferred embodiments, the carbon accounts for 2 to 10% by mass of the total mass of the positive electrode material additive.
In some preferred embodiments, the lithium iron manganese phosphate has a D50 of 2 to 50 μm; preferably 2 to 20 μm.
In some preferable schemes, the specific surface area of the lithium iron manganese phosphate is more than or equal to 10.0m2/g。
In some preferred embodiments, the preparation of the positive electrode material additive includes the steps of:
and coating carbon source powder on the lithium iron manganese phosphate material with the surface coated with the lithium iron phosphate through a coating reaction to obtain the anode material additive.
In some preferred embodiments, the coating reaction comprises the steps of: and (4) roasting and cooling.
The temperature of the calcination is not less than 400 ℃ and not more than 1000 ℃, preferably not less than 500 ℃ and not more than 800 ℃, more preferably not less than 600 ℃ and not more than 750 ℃, for example: 600-750 ℃.
The time of the calcination is not less than 1 hour and not more than 10 hours, more preferably not less than 2 hours and not more than 8 hours, for example, 4 to 6 hours.
The cooling cools the material at least to a temperature not higher than t, wherein 200 ℃ C. or higher t.gtoreq.room temperature (room temperature 23 to 26 ℃, e.g., 25 ℃) C, more preferably 150 ℃ C. or higher t.gtoreq.room temperature, e.g., 25 to 150 ℃.
In some preferred embodiments, the carbon source powder is selected from at least one of amorphous carbon, carbon nanotubes, and graphene.
In some preferred embodiments, the coating reaction is carried out in the presence of an inert gas.
In some preferred embodiments, the temperature of the coating reaction is not lower than 400 ℃ and not higher than 1000 ℃, preferably not lower than 500 ℃ and not higher than 800 ℃, more preferably not lower than 600 ℃ and not higher than 750 ℃, for example: 600-750 ℃.
In some preferred embodiments, the coating reaction time is not less than 1 hour and not more than 10 hours, more preferably not less than 2 hours and not more than 8 hours, for example, 4 to 6 hours.
In some preferred schemes, the preparation of the lithium iron manganese phosphate material with the surface coated with lithium iron phosphate comprises the following steps:
and carrying out hydrothermal reaction on a reaction solution containing lithium manganese iron phosphate and lithium iron phosphate to obtain the lithium manganese iron phosphate material with the surface coated with the lithium iron phosphate.
In some preferred embodiments, the reaction temperature is 150 ℃ and 180 ℃, more preferably 160 ℃.
In some preferred embodiments, the reaction pressure is 0.48 to 1.0MPa, and more preferably 0.6 MPa.
In some preferred embodiments, in the reaction solution, the mass ratio of the lithium iron manganese phosphate to the lithium iron phosphate is 1: 9-4: 6, more preferably 2: 8.
in some preferred embodiments, the reaction solution further comprises a ferrous salt solution; such as ferrous sulfate solution.
In some preferred embodiments, the hydrothermal reaction time is not less than 3 hours and not more than 60 hours, more preferably, not less than 5 hours and not more than 50 hours, and more preferably, not less than 10 hours and not more than 36 hours.
In some preferred schemes, the preparation of the lithium iron manganese phosphate material with the surface coated with lithium iron phosphate comprises the following steps:
in the presence of inert gas, adding a ferrous salt solution into a suspension mixed with lithium iron manganese phosphate and a lithium iron phosphate solution dropwise, stirring, and then placing the suspension in a high-pressure reaction kettle at the temperature of 150-180 ℃ and the pressure of 0.48-1.0 Mpa for hydrothermal reaction to obtain the lithium iron manganese phosphate material with the surface coated with lithium iron phosphate.
In some preferred embodiments, the hydrothermal reaction further comprises a post-treatment step:
and carrying out suction filtration, washing and vacuum drying on the hydrothermal reaction product.
In some preferred schemes, the temperature of the vacuum drying is not lower than 70 ℃ and not higher than 160 ℃; more preferably, the temperature of the vacuum drying is not lower than 80 ℃ and not higher than 120 ℃.
In some preferred embodiments, the vacuum drying time is not less than 1 hour and not more than 60 hours; more preferably, the time of the vacuum drying is not less than 2 hours and not more than 50 hours; more preferably, the time of the vacuum drying is not less than 3 hours and not more than 36 hours.
The invention provides a positive electrode in some embodiments, which is formed by coating positive electrode slurry on the surface of a current collector, wherein the positive electrode slurry comprises a positive electrode active material, a conductive agent and a binder;
wherein the positive electrode active material comprises a positive electrode active material and the positive electrode material additive.
In some preferred embodiments, the mass ratio of the positive electrode active material to the positive electrode material additive is (90.0 to 99.9): (0.1 to 10.0), and more preferably: (95.0 to 99.0): (1.0 to 5.0), for example: 99:1.
In some preferred embodiments, the positive electrode active material is selected from at least one of lithium cobaltate, lithium manganate, and lithium nickel cobalt manganate; lithium cobaltate is preferred.
In some preferred embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder is l: m: n, and l + m + n is 100, where l is 95 to 99, m is 0.5 to 3, and n is 1 to 5, for example: 96:1.5:2.5.
In some preferred embodiments, D50 of the positive electrode active material is 5 to 10 um; more preferably 6 to 8 μm.
In some preferred embodiments, the specific surface area of the positive electrode active material is 2.0m or more2/g。
In some preferred embodiments, the conductive agent is carbon nanotubes, carbon black, graphite, or graphene.
In some preferred schemes, the specific surface area of the carbon nano tube is 200-300m2/g。
In some preferred embodiments, the binder is PVDF, SBR, or PAA.
In some preferred embodiments, the PVDF has a specific surface area of 40 to 70m2(ii)/g; more preferably 60-65 μm.
In some embodiments of the present invention there is provided a lithium ion battery comprising a positive electrode, a negative electrode, an electrolyte and a separator as provided in the second aspect of the present invention.
In some embodiments of the present invention, there is provided a method for preparing the positive electrode material additive according to the first aspect of the present invention, the method comprising the steps of:
preparing a lithium manganese iron phosphate material with the surface coated with lithium iron phosphate; and
and coating the carbon source powder on the lithium iron manganese phosphate material with the surface coated with the lithium iron phosphate through a coating reaction. In some preferred embodiments, the step of preparing the lithium iron manganese phosphate material with a surface coated with lithium iron phosphate includes:
and carrying out hydrothermal reaction on a reaction solution containing lithium manganese iron phosphate and lithium iron phosphate to obtain the lithium manganese iron phosphate material with the surface coated with the lithium iron phosphate.
In some preferred embodiments, the step of preparing the lithium iron manganese phosphate material with a surface coated with lithium iron phosphate includes: in the presence of inert gas, adding a ferrous salt solution into a suspension mixed with lithium iron manganese phosphate and a lithium iron phosphate solution dropwise, stirring, and then placing the suspension in a high-pressure reaction kettle at the temperature of 150-180 ℃ and the pressure of 0.48-1.0 Mpa for hydrothermal reaction to obtain the lithium iron manganese phosphate material with the surface coated with lithium iron phosphate.
As used herein, unless otherwise indicated, "room temperature" refers to the temperature measured in a common laboratory using a celsius thermometer, preferably 23 to 26 ℃, e.g., 25 ℃ (298.15K kelvin).
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the present invention is further described below with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out under conventional conditions or conditions recommended by the manufacturers. Unless otherwise indicated, percentages and parts are percentages and parts by weight. The test materials and reagents used in the following examples are commercially available without specific reference.
Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs, and it is to be noted that the terms used herein are merely for describing particular embodiments and are not intended to limit example embodiments of the present application.
Example 1 preparation of three-layer core-shell cathode Material additive
(1) Lithium manganese iron phosphate (LiMn)xFe1-xPO4, where X is between 0.2 and 0.8) preparation of the material
Mixing a lithium hydroxide aqueous solution, a ferrous sulfate aqueous solution and phosphoric acid (according to the proportion), stirring, sealing, heating to 150-180 ℃ within 0.5-2.0 hours, reacting for 0.5-4 hours under the pressure of 0.48-1.0 Mpa, cooling to below 80 ℃, and filtering to obtain a wet filter cake and a mother solution; drying the wet filter cake in air in a spray drying or flash evaporation drying mode to obtain lithium iron manganese phosphate powder; discharging below 150 ℃ to obtain the lithium iron manganese phosphate material.
(2) Lithium manganese iron phosphate composite material with surface coated with lithium iron phosphate
Step 1, weighing a mixture with a stoichiometric ratio of 7: 3 LiOH. H2O、H3PO4And FeSO4·7H2O, respectively dissolving in proper amount of 1mol of distilled water to prepare lithium iron phosphate solution；
Step 2, adding a certain amount of 0.8mol of lithium iron manganese phosphate material into the prepared lithium iron phosphate solution, simultaneously adding a proper amount of 0.05mol of dispersant, mixing, and fully stirring to uniformly disperse the lithium iron manganese phosphate powder;
step 3, slowly dripping the lithium iron phosphate solution prepared in the step 1 into the rapidly-stirred lithium iron manganese phosphate suspension;
and 4, introducing protective gas into the mixed liquid obtained in the step 3, introducing the protective gas for 10-60 minutes, and then slowly dripping the protective gas into the FeSO prepared in the step 1 in a rapid stirring state4·7H2Rapidly stirring the solution O for 10-60 minutes;
and 6, performing suction filtration and washing on the product obtained in the step 5, and then performing vacuum drying at the temperature of 80-120 ℃ for 12-36 hours to obtain the lithium manganese iron phosphate composite material with the surface coated with the lithium iron phosphate, wherein the mass ratio of the lithium manganese iron phosphate to the lithium iron phosphate in the obtained lithium manganese iron phosphate composite material with the surface coated with the lithium iron phosphate is (60-90): (5-20).
(3) Preparation of three-layer core-shell cathode material additive
The preparation method comprises the following steps of carrying out carbon coating on a lithium iron manganese phosphate composite material with a surface coated with lithium iron phosphate and carbon source composite powder (such as amorphous carbon), specifically, mixing the lithium iron manganese phosphate composite material with the surface coated with the lithium iron phosphate and the amorphous carbon (the mass ratio of the lithium iron manganese phosphate composite material with the surface coated with the lithium iron phosphate to the amorphous carbon is (85-99): (1-15)), roasting at 600-750 ℃ for 4-6 hours, cooling to below 150 ℃, discharging, and sieving through a granulation process screen mesh to obtain the three-layer core-shell anode material additive.
The methods of preparing the positive electrode material additives in example 2 and example 3 were substantially the same as example 1, except that the mass ratio of each layer of the three-layer core-shell positive electrode material additive was different, as shown in table 1.
TABLE 1
Example 4 preparation of Positive electrode sheet (D50 is 8um)
D50 is 8um, the tap density is 2.2g/cm3, and the specific surface area is 4.2m2The positive electrode active material was prepared by dissolving LiCoO2 in an N-methylpyrrolidone solvent in a ratio of 96% of the positive electrode active material (based on the mass of the positive electrode), 2.5% of PVDF (based on the mass of the positive electrode), and 1.5% of the carbon nanotubes (based on the mass of the positive electrode), stirring and dispersing the mixture in a stirrer under vacuum, and adding the positive electrode material additive prepared in example one, the positive electrode material additive, and LiCoO2The mass ratio of the components is 1:99, and the positive pole piece is prepared by uniformly coating the aluminum foil with the coating.
In other examples and comparative examples, the method of preparing the positive electrode sheet was substantially the same as in example 4 except that each component and the amount of each component in the positive electrode sheet were different, as shown in table 2.
TABLE 2
Preparation of lithium ion battery
(1) Preparation of negative pole piece
Artificial graphite as negative active material, wherein the artificial graphite has an alignment type I (002)/I (110) of 4.8, a D50 of 6.5um, and a specific surface area of 2.1m2(ii) in terms of/g. According to 94 percent of negative electrode active material (based on the mass of the negative electrode), 2.8 percent of acrylonitrile multipolymer (based on the mass of the negative electrode), and 3.2 percent of conductive carbon black (based on the mass of the negative electrode)The components are dissolved in deionized water, and the mixture is vacuumized, stirred and dispersed in a stirrer to prepare uniform bubble-free slurry which is uniformly coated on copper foil to prepare the negative pole piece.
(2) Encapsulation and formation
The positive electrode plate and the diaphragm prepared in example 4 and the negative electrode plate prepared in the above were laminated to prepare a cell, the cell was a tab from the same side, the tab and the current collector were welded together by an ultrasonic welding machine, and then packaged with an aluminum-plastic film.
And after the battery cell is baked, injecting the non-aqueous electrolyte into the battery cell, and preparing the 4Ah lithium ion battery after chemical composition and capacity grading.
According to the above method for preparing the battery, the positive electrode plates of the examples 5 to the comparative example 4 in the above table 2 are prepared into a lithium ion battery for battery performance test.
Test example
The cell needling temperature rise experiment and the battery performance experiment were performed according to the following methods, and the results are recorded in table 3 below.
[ temperature raising experiment method for needling of cell ]
(1) Charging the experimental battery to 4.2V with a 1C constant current and a constant voltage until the current is 0.02C;
(2) penetrating through a high-temperature steel needle (the conical angle of the needle tip is 45-60 degrees, the surface of the needle is smooth, the needle is free of rust, an oxide layer and oil stain) with the diameter of 5-8 mm at the speed of (25 +/-5) mm/s from the direction vertical to the pole plate of the battery cell, wherein the penetrating position is close to the geometric center of the punctured surface, and the steel needle stays in the battery cell;
(3) and observing for 1h, and recording the state and the temperature rise of the battery cell.
The results of the cell puncture test of example 4 are shown in fig. 2, and the results of the cell puncture test of the comparative example are shown in fig. 1. As can be seen from a comparison between fig. 1 and fig. 2, the battery containing the positive electrode material additive according to the present invention is less likely to suffer thermal runaway.
[ Battery Performance test method ]
(1) Charging the battery cell 0.5C to 4.2V at constant current and constant voltage under the condition of 25 +/-3 ℃ and cutting off the current to 0.02C;
(2) standing for 30 min;
(3) under the condition of 25 +/-3 ℃, discharging at a constant current of 1C to 3.0V, and recording the capacity D1 at the moment;
(4) standing for 30 min;
(5) under the condition of 25 +/-3 ℃, charging the battery cell to 4.2V at constant current and constant voltage, and cutting off the current to 0.02C;
(6) standing at-40 deg.C + -3 for 20 h;
(7)5C was discharged to 3.0V, at which time the capacity D2 was recorded;
capacity retention ratio D ═ D2/D1 × 100%.
TABLE 3
It will be understood by those of ordinary skill in the art that the foregoing embodiments are specific examples for carrying out the invention, and that various changes in form and details may be made therein without departing from the spirit and scope of the invention in practice.
Claims (11)
1. The positive electrode material additive is characterized by having a core-shell structure, wherein the core-shell structure comprises an inner core, a first shell layer coated on the surface of the inner core and a second shell layer coated on the surface of the first shell layer;
the core comprises lithium manganese iron phosphate;
the first shell layer comprises lithium iron phosphate;
the second shell layer comprises carbon.
2. The positive electrode material additive according to claim 1, wherein the lithium iron manganese phosphate is LiMnxFe1- xPO4Wherein x ranges from 0.2 to 0.8.
3. The positive electrode material additive according to claim 1, wherein the mass of the lithium iron manganese phosphate accounts for 70 to 99% of the total mass of the positive electrode material additive;
and/or the mass of the lithium iron phosphate accounts for 1 to 15 percent of the total mass of the positive electrode material additive;
and/or the mass of the carbon accounts for 2 to 10 percent of the total mass of the positive electrode material additive;
and/or the lithium iron manganese phosphate has a D50 of 2 to 50 μm;
and/or the specific surface area of the lithium iron manganese phosphate is more than or equal to 10.0m2/g。
4. The positive electrode material additive according to claim 1, wherein the preparation of the positive electrode material additive comprises the steps of:
and coating carbon source powder on the lithium iron manganese phosphate material with the surface coated with the lithium iron phosphate through a coating reaction to obtain the anode material additive.
5. The positive electrode material additive according to claim 4, wherein the coating reaction comprises the steps of: roasting and cooling;
and/or, the coating reaction is carried out in the presence of an inert gas;
and/or the carbon source powder is selected from at least one of amorphous carbon, carbon nanotubes and graphene.
6. The positive electrode material additive according to claim 5, wherein the temperature of the firing is not less than 400 ℃ and not more than 1000 ℃;
and/or, the roasting time is not less than 1 hour and not more than 10 hours;
and/or, the cooling at least cools the material to a temperature not higher than t, wherein t is not lower than 200 ℃ and t is not lower than room temperature (room temperature is 23-26 ℃).
7. The additive for the positive electrode material according to claim 4, wherein the preparation of the lithium iron manganese phosphate material with the surface coated with lithium iron phosphate comprises the following steps:
and carrying out hydrothermal reaction on a reaction solution containing lithium manganese iron phosphate and lithium iron phosphate to obtain the lithium manganese iron phosphate material with the surface coated with the lithium iron phosphate.
8. The additive for the positive electrode material according to claim 4, wherein the preparation of the lithium iron manganese phosphate material with the surface coated with lithium iron phosphate comprises the following steps:
in the presence of inert gas, adding a ferrous salt solution into the suspension mixed with the lithium iron manganese phosphate and the lithium iron phosphate solution dropwise, stirring, and then placing the suspension in a high-pressure reaction kettle at the temperature of 150-180 ℃ and the pressure of 0.48-1.0 Mpa for hydrothermal reaction to obtain the lithium iron manganese phosphate material with the surface coated with the lithium iron phosphate.
9. The positive electrode is characterized in that the positive electrode is formed by coating positive electrode slurry on the surface of a current collector, wherein the positive electrode slurry comprises a positive electrode active material, a conductive agent and a binder;
wherein the positive electrode active material includes a positive electrode active material and the positive electrode material additive according to any one of claims 1 to 8.
10. A lithium ion battery comprising the positive electrode according to claim 9, a negative electrode, an electrolyte, and a separator.
11. A method for preparing the positive electrode material additive according to any one of claims 1 to 3, characterized by comprising the steps of:
preparing a lithium manganese iron phosphate material with the surface coated with lithium iron phosphate; and
and coating carbon source powder on the lithium iron manganese phosphate material with the surface coated with the lithium iron phosphate through a coating reaction.
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