CN114256457A - Lithium-rich manganese-based positive electrode material with homogeneous composite coating layer and preparation method thereof - Google Patents
Lithium-rich manganese-based positive electrode material with homogeneous composite coating layer and preparation method thereof Download PDFInfo
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- CN114256457A CN114256457A CN202111671583.7A CN202111671583A CN114256457A CN 114256457 A CN114256457 A CN 114256457A CN 202111671583 A CN202111671583 A CN 202111671583A CN 114256457 A CN114256457 A CN 114256457A
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- rich manganese
- positive electrode
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 104
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 104
- 239000011572 manganese Substances 0.000 title claims abstract description 102
- 229910052748 manganese Inorganic materials 0.000 title claims abstract description 95
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 title claims abstract description 94
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 50
- 239000011247 coating layer Substances 0.000 title claims abstract description 49
- 239000002131 composite material Substances 0.000 title claims abstract description 28
- 238000002360 preparation method Methods 0.000 title abstract description 8
- 239000000463 material Substances 0.000 claims abstract description 67
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 31
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 30
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 28
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 28
- 239000010416 ion conductor Substances 0.000 claims abstract description 26
- 238000000034 method Methods 0.000 claims abstract description 23
- 239000002345 surface coating layer Substances 0.000 claims abstract description 6
- VYFYYTLLBUKUHU-UHFFFAOYSA-N dopamine Chemical compound NCCC1=CC=C(O)C(O)=C1 VYFYYTLLBUKUHU-UHFFFAOYSA-N 0.000 claims description 108
- 239000011259 mixed solution Substances 0.000 claims description 72
- 229960003638 dopamine Drugs 0.000 claims description 54
- 239000000243 solution Substances 0.000 claims description 34
- 239000007787 solid Substances 0.000 claims description 29
- 238000000576 coating method Methods 0.000 claims description 23
- 238000003756 stirring Methods 0.000 claims description 23
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 23
- 239000011248 coating agent Substances 0.000 claims description 22
- 238000010438 heat treatment Methods 0.000 claims description 22
- LENZDBCJOHFCAS-UHFFFAOYSA-N tris Chemical compound OCC(N)(CO)CO LENZDBCJOHFCAS-UHFFFAOYSA-N 0.000 claims description 21
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 claims description 20
- 239000002994 raw material Substances 0.000 claims description 14
- UYLYBEXRJGPQSH-UHFFFAOYSA-N sodium;oxido(dioxo)niobium Chemical compound [Na+].[O-][Nb](=O)=O UYLYBEXRJGPQSH-UHFFFAOYSA-N 0.000 claims description 14
- 238000001035 drying Methods 0.000 claims description 13
- 238000001914 filtration Methods 0.000 claims description 13
- 238000005406 washing Methods 0.000 claims description 13
- 238000001816 cooling Methods 0.000 claims description 12
- 238000002156 mixing Methods 0.000 claims description 11
- 239000012298 atmosphere Substances 0.000 claims description 9
- 229910001386 lithium phosphate Inorganic materials 0.000 claims description 6
- 230000001681 protective effect Effects 0.000 claims description 6
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical compound [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 0.000 claims description 6
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 claims description 5
- 239000003792 electrolyte Substances 0.000 claims description 5
- MVGWWCXDTHXKTR-UHFFFAOYSA-J tetralithium;phosphonato phosphate Chemical compound [Li+].[Li+].[Li+].[Li+].[O-]P([O-])(=O)OP([O-])([O-])=O MVGWWCXDTHXKTR-UHFFFAOYSA-J 0.000 claims description 5
- 239000002253 acid Substances 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 4
- LWIHDJKSTIGBAC-UHFFFAOYSA-K tripotassium phosphate Chemical compound [K+].[K+].[K+].[O-]P([O-])([O-])=O LWIHDJKSTIGBAC-UHFFFAOYSA-K 0.000 claims description 4
- 150000001450 anions Chemical class 0.000 claims description 3
- FQENQNTWSFEDLI-UHFFFAOYSA-J sodium diphosphate Chemical compound [Na+].[Na+].[Na+].[Na+].[O-]P([O-])(=O)OP([O-])([O-])=O FQENQNTWSFEDLI-UHFFFAOYSA-J 0.000 claims description 3
- 229940048086 sodium pyrophosphate Drugs 0.000 claims description 3
- 235000019818 tetrasodium diphosphate Nutrition 0.000 claims description 3
- 239000001577 tetrasodium phosphonato phosphate Substances 0.000 claims description 3
- 239000004254 Ammonium phosphate Substances 0.000 claims description 2
- 229910013191 LiMO2 Inorganic materials 0.000 claims description 2
- LFVGISIMTYGQHF-UHFFFAOYSA-N ammonium dihydrogen phosphate Chemical compound [NH4+].OP(O)([O-])=O LFVGISIMTYGQHF-UHFFFAOYSA-N 0.000 claims description 2
- 229910000387 ammonium dihydrogen phosphate Inorganic materials 0.000 claims description 2
- 229910000148 ammonium phosphate Inorganic materials 0.000 claims description 2
- 235000019289 ammonium phosphates Nutrition 0.000 claims description 2
- 229910052804 chromium Inorganic materials 0.000 claims description 2
- -1 diamine hydrogen phosphate Chemical class 0.000 claims description 2
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 229910000473 manganese(VI) oxide Inorganic materials 0.000 claims description 2
- 229910052750 molybdenum Inorganic materials 0.000 claims description 2
- 235000019837 monoammonium phosphate Nutrition 0.000 claims description 2
- 229910052758 niobium Inorganic materials 0.000 claims description 2
- 229910000160 potassium phosphate Inorganic materials 0.000 claims description 2
- 235000011009 potassium phosphates Nutrition 0.000 claims description 2
- UKDIAJWKFXFVFG-UHFFFAOYSA-N potassium;oxido(dioxo)niobium Chemical compound [K+].[O-][Nb](=O)=O UKDIAJWKFXFVFG-UHFFFAOYSA-N 0.000 claims description 2
- 229910052707 ruthenium Inorganic materials 0.000 claims description 2
- 238000005245 sintering Methods 0.000 claims description 2
- 239000001488 sodium phosphate Substances 0.000 claims description 2
- 229910000162 sodium phosphate Inorganic materials 0.000 claims description 2
- 235000011008 sodium phosphates Nutrition 0.000 claims description 2
- RYCLIXPGLDDLTM-UHFFFAOYSA-J tetrapotassium;phosphonato phosphate Chemical compound [K+].[K+].[K+].[K+].[O-]P([O-])(=O)OP([O-])([O-])=O RYCLIXPGLDDLTM-UHFFFAOYSA-J 0.000 claims description 2
- 229910052718 tin Inorganic materials 0.000 claims description 2
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 claims description 2
- 229910052720 vanadium Inorganic materials 0.000 claims description 2
- 229910052726 zirconium Inorganic materials 0.000 claims description 2
- 230000008569 process Effects 0.000 abstract description 12
- 230000000694 effects Effects 0.000 abstract description 7
- 150000002500 ions Chemical class 0.000 abstract description 6
- 239000010406 cathode material Substances 0.000 abstract description 5
- 239000011159 matrix material Substances 0.000 abstract description 4
- 238000005580 one pot reaction Methods 0.000 abstract description 2
- 239000012528 membrane Substances 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 22
- 239000008367 deionised water Substances 0.000 description 21
- 229910021641 deionized water Inorganic materials 0.000 description 21
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 20
- 239000010410 layer Substances 0.000 description 13
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 12
- 238000005303 weighing Methods 0.000 description 10
- 230000005540 biological transmission Effects 0.000 description 9
- 239000012299 nitrogen atmosphere Substances 0.000 description 9
- 230000014759 maintenance of location Effects 0.000 description 8
- 239000007858 starting material Substances 0.000 description 8
- KLARSDUHONHPRF-UHFFFAOYSA-N [Li].[Mn] Chemical compound [Li].[Mn] KLARSDUHONHPRF-UHFFFAOYSA-N 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 239000010405 anode material Substances 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 6
- 238000006116 polymerization reaction Methods 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 5
- 239000000047 product Substances 0.000 description 5
- 229910019142 PO4 Inorganic materials 0.000 description 4
- 238000011065 in-situ storage Methods 0.000 description 4
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 4
- 229910052808 lithium carbonate Inorganic materials 0.000 description 4
- 229920000447 polyanionic polymer Polymers 0.000 description 4
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 3
- 239000013590 bulk material Substances 0.000 description 3
- 229910017052 cobalt Inorganic materials 0.000 description 3
- 239000010941 cobalt Substances 0.000 description 3
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 3
- 230000001351 cycling effect Effects 0.000 description 3
- 229910000388 diammonium phosphate Inorganic materials 0.000 description 3
- 235000019838 diammonium phosphate Nutrition 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 229910052596 spinel Inorganic materials 0.000 description 3
- 239000011029 spinel Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 239000005696 Diammonium phosphate Substances 0.000 description 2
- QXZUUHYBWMWJHK-UHFFFAOYSA-N [Co].[Ni] Chemical compound [Co].[Ni] QXZUUHYBWMWJHK-UHFFFAOYSA-N 0.000 description 2
- 239000007853 buffer solution Substances 0.000 description 2
- 238000003763 carbonization Methods 0.000 description 2
- 238000006243 chemical reaction 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
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 2
- XPPKVPWEQAFLFU-UHFFFAOYSA-J diphosphate(4-) Chemical compound [O-]P([O-])(=O)OP([O-])([O-])=O XPPKVPWEQAFLFU-UHFFFAOYSA-J 0.000 description 2
- 235000011180 diphosphates Nutrition 0.000 description 2
- 230000001965 increasing effect Effects 0.000 description 2
- INHCSSUBVCNVSK-UHFFFAOYSA-L lithium sulfate Chemical compound [Li+].[Li+].[O-]S([O-])(=O)=O INHCSSUBVCNVSK-UHFFFAOYSA-L 0.000 description 2
- 238000011056 performance test Methods 0.000 description 2
- 239000010452 phosphate Substances 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 229940048084 pyrophosphate Drugs 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 238000003786 synthesis reaction Methods 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 description 1
- 208000019901 Anxiety disease Diseases 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910010092 LiAlO2 Inorganic materials 0.000 description 1
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- 239000007983 Tris buffer Substances 0.000 description 1
- 239000006230 acetylene black Substances 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910003481 amorphous carbon Inorganic materials 0.000 description 1
- 230000036506 anxiety Effects 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000000872 buffer Substances 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 238000005087 graphitization Methods 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000005764 inhibitory process Effects 0.000 description 1
- MRVHOJHOBHYHQL-UHFFFAOYSA-M lithium metaphosphate Chemical group [Li+].[O-]P(=O)=O MRVHOJHOBHYHQL-UHFFFAOYSA-M 0.000 description 1
- 238000003760 magnetic stirring Methods 0.000 description 1
- 238000010907 mechanical stirring Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000002120 nanofilm Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 229920001690 polydopamine Polymers 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
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Classifications
-
- 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
- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
-
- 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
Abstract
Provides a lithium-rich manganese-based positive electrode material with a multifunctional homogeneous composite coating layer and a preparation method thereof. The lithium-rich manganese-based positive electrode material comprises a lithium-rich manganese-based material and a homogeneous composite coating layer, and is characterized in that the homogeneous composite coating layer is composed of a fast ion conductor and a three-dimensional carbon grid, and the fast ion conductor is uniformly loaded in the three-dimensional carbon grid and is crossed and interconnected to form the homogeneous composite surface coating layer. Namely, the lithium-rich manganese-based cathode material loads a fast ion conductor with high lithium ion conduction efficiency in a high-conductivity three-dimensional carbon network to form a specific continuous lithium ion and electron channel, thereby synchronously improving the ion conduction and the electron conduction of a matrix material and simultaneously effectively reducing the interface impedance. In addition, the preparation method can obtain the homogeneous membrane by adopting one-step reaction, and has the advantages of simple process flow, mild conditions and outstanding effect.
Description
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a lithium-rich manganese-based positive electrode material with a multifunctional homogeneous composite coating layer and a preparation method thereof.
Background
Mileage anxiety, safety and cost are major bottlenecks that restrict the development of electric vehicle technology, with positive electrode materials being their important contributing factors.
The lithium-rich manganese-based positive electrode material is considered to be the preferred positive electrode material of the next generation of high specific energy battery due to the advantages of high specific capacity (more than 250mAh/g), low cost, good thermal stability and the like. The lithium-rich manganese-based cathode material mainly uses an environment-friendly manganese element, has low nickel-cobalt content, even can not contain cobalt, effectively avoids the problem of nickel-cobalt resources, simultaneously, compared with cobalt and nickel, manganese is low in price and rich in reserves, according to data of the national geological survey bureau 2015, the reserve of manganese ore in China accounts for 7.7% of the global reserve, and nickel ore and cobalt ore respectively account for 3.7% and 1.1% of the global reserve.
However, lithium-rich materials have a low lithium ion diffusion coefficient, resulting in poor rate performance and charge-discharge cycling processMetal ions in the alloy migrate and are gradually converted into a spinel structure from a layered structure, so that the specific capacity and the discharge voltage are gradually attenuated. Research shows that the structural phase change of the lithium-rich manganese-based material gradually extends from the surface layer to the bulk phase. Therefore, a stable surface structure is important to construct, and a proper surface coating layer can provide a rapid transmission channel for lithium ions/electrons and isolate direct contact between electrolyte and a positive electrode material, so that the battery performance is prevented from being deteriorated by reaction of the electrolyte and the positive electrode material. Like Li3PO4、Li2SO4、LiAlO2And the like, which are also the current popular cladding materials due to better lithium ion transmission efficiency. However, the single-structure clad layer cannot simultaneously improve the ion conductivity and the electron conductivity of the base material, so researchers developed a series of multi-layer clad layers.
Such as:
chinese patent application CN113308080A discloses a double-coated lithium-rich material, wherein the coating layer is a lithium metaphosphate base and a vulcanized carbon layer in sequence, and the cycle performance and rate capability of the material are obviously improved.
Chinese patent application CN113078315A discloses a lithium-rich manganese-based material coated by two conductive layers, which has a structure comprising a lithium-rich core, a spinel lithium manganate coating layer and a nitrogen-doped graphitized carbon coating layer from inside to outside in sequence, wherein the spinel lithium manganate has a higher lithium ion transmission capability, the nitrogen-doped graphitized carbon coating layer can effectively improve the electron transmission capability of the material, and the material has the characteristics of high capacity, high multiplying power and high cycle.
Although the multilayer coating can improve ion conduction, electron conduction or enhance interface stability, the increase of the coating means the increase of the interface, and the interface impedance is increased accordingly, and generally, a single coating only has one property, that is, the increase of the ion conduction and the inhibition of electron transmission may hinder the electron transmission, and affect the conductivity, and vice versa, for example, the conductivity of the carbon layer is good, but the lithium ion transmission capability is relatively poor. In addition, the multilayer coating means that the synthesis process is more complicated, the bonding strength between the coating layers is difficult to ensure, and the separation of the coating layers from the base material may occur along with the circulation process, thereby deteriorating the performance.
Therefore, a new lithium-rich manganese-based positive electrode material and a preparation method thereof are needed to solve the above technical problems.
Disclosure of Invention
Therefore, aiming at the defects of the prior art, the invention provides a lithium-rich manganese-based positive electrode material with a multifunctional homogeneous composite coating layer and a preparation method thereof.
The invention provides a lithium-rich manganese-based positive electrode material with a multifunctional homogeneous composite coating layer, which comprises a lithium-rich manganese-based material and a surface coating layer and is characterized in that the homogeneous composite coating layer is composed of fast ion conductors and three-dimensional carbon grids, and the fast ion conductors are uniformly loaded in the three-dimensional carbon grids and are crossed and interconnected to form the homogeneous composite surface coating layer.
Wherein the chemical general formula of the lithium-rich manganese-based material is xLi2MnO3·(1-x)LiMO2Wherein x is more than or equal to 0.1 and less than or equal to 0.9, and M is one or more of Ni, Co, Mn, Cr, Fe, Ti, Mo, Ru, V, Nb, Zr and Sn.
Wherein, the fast ion conductor is any one of lithium phosphate, lithium niobate and lithium pyrophosphate.
Wherein the thickness of the homogeneous composite coating layer is 5-50nm, and the content of the fast ion conductor is more than 0-10 mol% of the content of the lithium-rich manganese-based material.
The invention also provides a preparation method of the lithium-rich manganese-based positive electrode material with the multifunctional homogeneous composite coating layer, which is characterized by comprising the following steps of:
(1) adding a certain amount of lithium-rich manganese-based material and tris (hydroxymethyl) aminomethane into deionized water to form a mixed solution A;
(2) dissolving a certain amount of dopamine and a coating raw material in deionized water to form a solution B;
(3) mixing the solution B and the solution A under the stirring condition to form a mixed solution C, adjusting the pH value of the mixed solution C to be 8-10, preferably 8.5-9.5 by using acid, stirring for 10-24 hours continuously, and then filtering, washing and drying to obtain a solid D;
(4) and (3) placing the solid D in a sintering furnace, carrying out heat treatment in a protective atmosphere, and cooling to obtain the lithium-rich manganese-based positive electrode material with the multifunctional surface coating layer.
Wherein, in the step (3), the acid is hydrochloric acid.
In the step (1), the adding amount of the lithium-rich manganese-based material is such that the mass percentage of the lithium-rich manganese-based material in the mixed solution A is more than 0-10%, and the adding amount of the tris (hydroxymethyl) aminomethane is such that the concentration of the tris (hydroxymethyl) aminomethane in the mixed solution A is 0-1 mol/L.
In the step (2), the adding amount of the dopamine is controlled so that the mass ratio of the dopamine to the lithium-rich manganese-based material in the mixed solution A is greater than 0-0.5.
In the step (2), the raw material of the coating material comprises one or more of ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, potassium phosphate, sodium phosphate, potassium niobate, sodium niobate, potassium pyrophosphate and sodium pyrophosphate.
In the step (2), the usage amount of the coating raw materials is as follows: the ratio of the mole number of the anions in the raw materials of the coating material to the mole number of the lithium-rich manganese-based material added into the mixed solution A in the step (1) is>0 to 0.1, and more preferably 0.01 to 0.05, wherein the molar number of anions in the raw material for the coating is the molar number of acid groups, for example, NaNbO for the coating3Is NbO3 -Calculated as moles of NH in the coating4H2PO4In other words PO4 6-Calculated by the number of moles of (c).
In the step (3), the stirring manner is one or more of mechanical stirring and magnetic stirring, and the stirring temperature is room temperature.
In the step (4), the protective atmosphere includes a reducing atmosphere or an inert atmosphere, and may be one of argon, helium, nitrogen, and hydrogen.
Wherein, in the step (4), the heat treatment condition is that the temperature is raised to 500-1000 ℃ at the heating rate of 3-10 ℃/min, and the temperature is preserved for 3-15 hours.
The invention also provides a lithium ion battery which comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the lithium-rich manganese-based positive electrode material with the multifunctional homogeneous composite coating layer.
From the above, the technical scheme adopted by the invention is as follows: adding a lithium-rich manganese-based material and tris (hydroxymethyl) aminomethane into deionized water, controlling the pH range of the mixed solution to be 8-10, preparing an aqueous solution containing dopamine and a soluble coating raw material, uniformly mixing the two mixed solutions, continuously stirring, filtering, washing and drying after a certain time to form a solid C. And (3) placing the C in a muffle furnace for heat treatment under protective atmosphere to obtain the lithium-rich manganese-based positive electrode material with the multifunctional homogeneous coating layer.
The mechanism of the invention is as follows: and a trace amount of lithium carbonate remains on the surface of the lithium-rich manganese-based material, the lithium carbonate on the surface is dissolved when the lithium-rich manganese-based material is placed in a polyanion aqueous solution, and the dissolved lithium ions and the polyanion in the solution generate a water-insoluble lithium fast ion conductor (lithium phosphate, lithium niobate, lithium tantalate, lithium pyrophosphate and the like) in situ. On the other hand, lithium carbonate is dissolved in an aqueous solution to be alkaline (pH is more than 8), and when dopamine contacts air under a weakly alkaline condition (pH is more than 8.5), the dopamine can be polymerized on the solid surface to form a polydopamine nano-film, and particularly, self-polymerization reaction is easier to occur in a hydrochloric acid solution of tris (hydroxymethyl) aminomethane. Adding dopamine into a polyanion-containing lithium-rich manganese-based material aqueous solution, controlling process conditions to synchronously carry out the formation of a lithium fast ion conductor and the polymerization reaction of the dopamine, and forming a homogeneous lithium fast ion conductor/dopamine film on the surface of the lithium-rich manganese-based material. Furthermore, dopamine is used as a carbon source and is subjected to heat treatment in a protective atmosphere, the dopamine is carbonized to form a three-dimensional carbon network structure, and in-situ carbonization is helpful for enhancing the bonding strength of the carbon network and the fast ion conductor as well as the bonding strength of the carbon network and the matrix material.
Therefore, the invention has the following beneficial technical effects:
(1) according to the invention, a homogeneous composite coating layer is designed and constructed on the surface of a lithium-rich material, and a fast ion conductor with high lithium ion conduction efficiency is loaded in a high-conductivity three-dimensional carbon network to form a specific continuous lithium ion and electron channel, as shown in figure 1, so that the ion conduction and the electron conduction of a matrix material are synchronously improved. Compared with the conventional multilayer coating, the method effectively reduces the interface impedance and avoids the problems of poor transmission capability of electrons in the fast plasma coating layer and lithium ions in the conductive coating layer.
(2) The surface of the lithium-rich manganese-based material is remained with trace lithium carbonate, lithium ions are dissolved in the aqueous solution of the lithium-rich manganese-based material and are alkaline, dopamine and specific polyanion (which reacts with lithium to form insoluble fast ion conductor) are simultaneously added into the aqueous solution of the lithium-rich material to form a film when the dopamine is contacted with air under the alkalescent condition, the formation of the fast ion conductor and the polymerization of the dopamine are simultaneously carried out by controlling the process conditions, and a homogeneous and compact fast ion conductor/dopamine coating layer can be formed. The method combines the characteristics of the lithium-rich manganese-based surface, the dopamine property, the fast ion conductor property and the like, can obtain a homogeneous film by adopting one-step reaction, and has the advantages of simple process flow, mild conditions and outstanding effect.
(3) The dopamine has multiple functions, firstly, a homogeneous film is formed on the surface of a lithium-rich manganese-based material by utilizing the autopolymerization reaction of the dopamine, and then the homogeneous film is used as a carbon source, the dopamine is carbonized into a three-dimensional amorphous carbon network structure through heat treatment in a protective atmosphere, compared with the traditional coating process, in-situ polymerization and in-situ carbonization can obviously improve the bonding strength of a coating layer and a base material, the falling of the coating layer and the performance degradation caused by uneven stress in the circulating process are avoided, the circulating life of the material is obviously prolonged, the capacity retention rate of 600 weeks is improved to 89.1% from 49% of the original material to 72.1-76.1% after the coating by the conventional process.
Brief description of the drawings
Fig. 1 is a schematic structural diagram of a lithium-rich manganese-based positive electrode material with a multifunctional homogeneous composite coating layer according to the invention.
Fig. 2 shows the first charge and discharge curves of the batteries manufactured from the lithium-rich manganese-based positive electrode materials prepared in examples 1-2 and comparative example 1.
Fig. 3 shows rate performance of batteries manufactured from the lithium-rich manganese-based positive electrode materials prepared in examples 1-2 and comparative example 1.
Fig. 4 shows the cycle capacity retention rates of batteries manufactured from the lithium-rich manganese-based positive electrode materials prepared in examples 1-2 and comparative example 1.
Fig. 5 shows the medium voltage retention in discharge of batteries manufactured from the lithium-rich manganese-based positive electrode materials prepared in examples 1-2 and comparative example 1.
Detailed Description
The present invention will be described in further detail with reference to specific examples. It is to be understood that these examples are for illustration only and are not intended to limit the scope of the present invention. Furthermore, it should be understood that various changes and modifications can be made by those skilled in the art after reading the teaching of the present invention, and these equivalents also fall within the scope of the claims of the present application. The examples do not specify particular techniques or conditions, and are performed according to the techniques or conditions described in the literature in the field or according to the product specifications. The instruments and the like used by the manufacturer are not known, and conventional products can be purchased by regular distributors. The chemical raw materials used in the invention can be conveniently bought in domestic chemical product markets.
Example 1
5g of a lithium-manganese-rich base starting material (No. GM5, molecular formula Li) which was synthesized by this company1.2Mn0.52Ni0.13Co0.13O2) GM5 is added into 100mL deionized water to form a mixed solution A with the mass fraction of 5%, and a certain amount of tris (hydroxymethyl) aminomethane is added into the mixed solution A to ensure that the concentration of tris (hydroxymethyl) aminomethane is 0.1mol/L, and the mixture is uniformly stirred for later use; weighing a certain amount of dopamine and sodium niobate, dissolving the dopamine and sodium niobate in deionized water to form a solution B, enabling the mass ratio of the dopamine content in the solution B to the lithium-rich manganese-based material in the mixed solution A to be 0.2 and the molar ratio of the niobate to the lithium-rich manganese-based material in the mixed solution A to be 0.028, mixing the mixed solution A and the solution B to form a mixed solution C, adding a proper amount of hydrochloric acid to regulate the pH value of a system of the mixed solution C to be 8.5, stirring for 15 hours at room temperature, filtering, washing and drying the mixed solution C to obtain a solid D with a lithium niobate and dopamine homogeneous coating layer, placing the solid D in a muffle furnace to carry out heat treatment in a nitrogen atmosphere, preserving the heat for 5 hours at 750 ℃, and cooling to room temperature to obtain the product containing the niobateThe lithium/carbon network composite homogeneous coating layer lithium-rich manganese-based positive electrode material is marked as a positive electrode material 1.
Mixing the positive electrode material 1, acetylene black, polyvinylidene fluoride and N-methyl pyrrolidone to form slurry, and uniformly coating the slurry on the surface of an aluminum foil to obtain a positive electrode piece; and then, assembling the lithium ion battery in a glove box by taking a lithium sheet as a negative electrode sheet and taking a 1mol/L Ethylene Carbonate (EC) and dimethyl carbonate (DMC) solution of lithium hexafluorophosphate (the volume ratio of EC to DMC is 1: 1) as electrolyte to obtain the lithium ion battery.
The lithium ion battery is subjected to cycle performance test by using an electrochemical tester, the test temperature is 25 ℃, and the current density is 0.1C (1C is 200 mAg)-1) And testing the first charge-discharge performance of the battery within the charge-discharge voltage range of 4.8-2V. The rate performance of the cells was tested at 0.1C, 0.2C, 0.5C, 1C, 3C rates. The cycling performance was tested under a 1C/1C regime after a first 0.1C activation at 2.0-4.7V. The results are shown in tables 2 to 3.
Example 2
5g of a lithium-manganese-rich base starting material (No. GM5, molecular formula Li) which was synthesized by this company1.2Mn0.52Ni0.13Co0.13O2) GM5 is added into 100mL deionized water to form a mixed solution A with the mass fraction of 5%, and a certain amount of tris (hydroxymethyl) aminomethane is added into the mixed solution A to ensure that the concentration of tris (hydroxymethyl) aminomethane is 0.1mol/L, and the mixture is uniformly stirred for later use; weighing a certain amount of dopamine and sodium pyrophosphate, dissolving in deionized water to form a solution B, enabling the mass ratio of the dopamine content in the solution B to the lithium-rich manganese-based material in the mixed solution A to be 0.2 and the molar ratio of pyrophosphate to the lithium-rich manganese-based material in the mixed solution A to be 0.024, mixing the mixed solution A with the solution B to form a mixed solution C, adding a proper amount of hydrochloric acid to regulate the pH value of a system of the mixed solution C to be 8.5, stirring for 15 hours at room temperature, filtering, washing and drying the mixed solution C to obtain a solid D with a lithium pyrophosphate and dopamine homogeneous coating layer, placing the solid D in a muffle furnace to carry out heat treatment in a nitrogen atmosphere, preserving heat for 5 hours at 750 ℃, and cooling to room temperature to obtain the lithium-rich manganese-based anode material containing the lithium pyrophosphate/carbon network composite homogeneous coating layer, wherein the lithium-rich manganese-based anode material is marked as an anode material 2.
Lithium ion batteries were prepared and tested for performance as described in example 1 and the results are shown in tables 2-3.
Example 3
5g of a lithium-manganese-rich base starting material (No. GM5, molecular formula Li) which was synthesized by this company1.2Mn0.52Ni0.13Co0.13O2) GM5 is added into 100mL deionized water to form a mixed solution A with the mass fraction of 5%, and a certain amount of tris (hydroxymethyl) aminomethane is added into the mixed solution A to ensure that the concentration of tris (hydroxymethyl) aminomethane is 0.1mol/L, and the mixture is uniformly stirred for later use; weighing a certain amount of dopamine and diammonium phosphate, dissolving the dopamine and diammonium phosphate in deionized water to form a solution B, mixing the dopamine content in the solution B with the lithium-rich manganese-based material in the mixed solution A in a mass ratio of 0.2 and the molar ratio of phosphate radical to the lithium-rich manganese-based material in the mixed solution A of 0.028 to form a mixed solution C, adding a proper amount of hydrochloric acid to regulate the pH value of a system of the mixed solution C to be 8.5, stirring for 15 hours at room temperature, filtering, washing and drying the mixed solution C to obtain a solid D with a lithium phosphate and dopamine homogeneous coating layer, placing the solid D in a muffle furnace, carrying out heat treatment in a nitrogen atmosphere, preserving heat for 5 hours at 750 ℃, and cooling to room temperature to obtain the lithium-rich manganese-based positive electrode material containing the lithium phosphate/carbon network composite homogeneous coating layer, wherein the lithium-rich manganese-based positive electrode material is marked as a positive electrode material 3.
Lithium ion batteries were prepared and tested for performance as described in example 1 and the results are shown in tables 2-3.
Example 4
5g of a lithium-manganese-rich base starting material (No. GM5, molecular formula Li) which was synthesized by this company1.2Mn0.52Ni0.13Co0.13O2) Adding GM5 into 100mL of deionized water to form a mixed solution A with the mass fraction of 5%, and uniformly stirring for later use; weighing a certain amount of dopamine and sodium niobate, dissolving the dopamine and sodium niobate in deionized water to form a solution B, enabling the mass ratio of the dopamine content in the solution B to the lithium-rich manganese-based material in the mixed solution A to be 0.2 and the molar ratio of the niobate to the lithium-rich manganese-based material in the mixed solution A to be 0.028, mixing the mixed solution A and the solution B to form a mixed solution C, adding a proper amount of hydrochloric acid to regulate the pH value of a system of the mixed solution C to be 8.5, stirring for 15 hours at room temperature, and then filtering, washing and drying the mixed solution C to obtain the lithium-rich manganese-based lithium niobate lithium ion battery mixed lithium ion batteryAnd (3) placing the solid D with the lithium niobate and dopamine homogeneous coating layer into a muffle furnace, carrying out heat treatment in nitrogen atmosphere, keeping the temperature at 750 ℃ for 5 hours, and cooling to room temperature to obtain the lithium-rich manganese-based positive electrode material containing the lithium niobate/carbon network composite homogeneous coating layer, wherein the lithium-rich manganese-based positive electrode material is marked as a positive electrode material 4.
Lithium ion batteries were prepared and tested for performance as described in example 1 and the results are shown in tables 2-3.
Example 5
5g of a lithium-manganese-rich base starting material (No. GM5, molecular formula Li) which was synthesized by this company1.2Mn0.52Ni0.13Co0.13O2) Adding GM5 into 100mL of deionized water to form a mixed solution A with the mass fraction of 5%, adding a certain amount of tris (hydroxymethyl) aminomethane into the mixed solution A to enable the concentration of tris (hydroxymethyl) aminomethane to be 0.999mol/L, and uniformly stirring for later use; weighing a certain amount of dopamine and sodium niobate, dissolving in deionized water to form a solution B, enabling the mass ratio of the dopamine content in the solution B to the lithium-rich manganese-based material in the mixed solution A to be 0.2 and the molar ratio of the niobate to the lithium-rich manganese-based material in the mixed solution A to be 0.028, mixing the mixed solution A and the solution B to form a mixed solution C, adding a proper amount of hydrochloric acid to regulate the pH value of a system of the mixed solution C to be 8.5, stirring for 15 hours at room temperature, filtering, washing and drying the mixed solution C to obtain a solid D with a lithium niobate and dopamine homogeneous coating layer, placing the solid D in a muffle furnace to carry out heat treatment in a nitrogen atmosphere, preserving heat for 5 hours at 750 ℃, and cooling to room temperature to obtain the lithium-rich manganese-based positive electrode material containing the lithium niobate/carbon network composite homogeneous coating layer, wherein the lithium-rich manganese-based positive electrode material is marked as a positive electrode material 5.
Lithium ion batteries were prepared and tested for performance as described in example 1 and the results are shown in tables 2-3.
Example 6
5g of a lithium-manganese-rich base starting material (No. GM5, molecular formula Li) which was synthesized by this company1.2Mn0.52Ni0.13Co0.13O2) GM5 is added into 100mL deionized water to form a mixed solution A with the mass fraction of 5%, and a certain amount of tris (hydroxymethyl) aminomethane is added into the mixed solution A to ensure that the concentration is 0.1mol/L, and the mixture is uniformly stirred for later use(ii) a Weighing a certain amount of dopamine and sodium niobate, dissolving in deionized water to form a solution B, enabling the mass ratio of the dopamine content in the solution B to the lithium-rich manganese-based material in the mixed solution A to be 0.5 and the molar ratio of the niobate to the lithium-rich manganese-based material in the mixed solution A to be 0.028, mixing the mixed solution A and the solution B to form a mixed solution C, adding a proper amount of hydrochloric acid to regulate the pH value of a system of the mixed solution C to be 8.5, stirring for 15 hours at room temperature, filtering, washing and drying the mixed solution C to obtain a solid D with a lithium niobate and dopamine homogeneous coating layer, placing the solid D in a muffle furnace to carry out heat treatment in a nitrogen atmosphere, preserving heat for 5 hours at 750 ℃, and cooling to room temperature to obtain the lithium-rich manganese-based positive electrode material containing the lithium niobate/carbon network composite homogeneous coating layer, wherein the lithium-rich manganese-based positive electrode material is marked as a positive electrode material 6.
Lithium ion batteries were prepared and tested for performance as described in example 1 and the results are shown in tables 2-3.
Example 7
The temperature of the heat treatment of the solid C was raised to 1000 ℃ and the remaining conditions were the same as in example 1.
Example 8
The heat treatment time of the solid C was extended to 12 hours, and the remaining conditions were the same as in example 1.
Example 9
The pH of the mixed solution C system was adjusted to 8, and the other conditions were the same as in example 1.
Example 10
The pH of the mixed solution C system was adjusted to 10, and the other conditions were the same as in example 1.
Example 11
The amount of sodium niobate added to the solution B was changed to 0.91g, and the remaining conditions were kept the same as in example 1.
Table 1 below further lists some of the key process parameters in examples 1-11.
Comparative example 1
The lithium-rich manganese-based cathode material with the number of GM5, which was prepared by the synthesis technology of the same company, was used as the cathode material, and the lithium ion battery was prepared and tested for performance as described in example 1, with the results shown in tables 2-3.
Comparative example 2
Weighing a certain amount of sodium niobate, dissolving the sodium niobate in 100mL of deionized water to form a solution, adding 5g of an original material GM5 in the stirring process to ensure that the molar ratio of the niobate to the GM material is 0.028, filtering the mixture after stirring for 5 hours, washing and drying a precipitate to obtain a solid D of a lithium niobate coating layer, placing the solid D in a muffle furnace to carry out heat treatment in the air atmosphere, preserving the heat at 750 ℃ for 5 hours, and cooling to room temperature to obtain the lithium-rich manganese-based anode material containing the lithium niobate coating layer.
Comparative example 3
Weighing 1g of dopamine, dissolving the dopamine in 100mL of deionized water to form a solution, adding 5g of raw material GM5 in the stirring process, heating and stirring until the solution is completely evaporated to dryness to obtain a solid, placing the solid in a muffle furnace, carrying out heat treatment in a nitrogen atmosphere, keeping the temperature at 750 ℃ for 5 hours, and cooling to room temperature to obtain the carbon-coated lithium-rich manganese-based cathode material.
Comparative example 4
Weighing a certain amount of sodium niobate, dissolving the sodium niobate in 100mL of deionized water to form a solution, adding 5g of an original material GM5 in the stirring process to ensure that the molar ratio of the niobate to the GM material is 0.028, stirring for 5 hours, filtering the mixture, washing and drying the precipitate to obtain a solid C of the lithium niobate coating layer; adding the obtained solid C with the surface coated with lithium niobate and a certain amount of tris (hydroxymethyl) aminomethane into 100mL of deionized water to form a mixed solution A, wherein the concentration of tris (hydroxymethyl) aminomethane in the mixed solution A is 0.1mol/L, adding a certain amount of dopamine into the solution A to ensure that the mass ratio of the added dopamine to the originally added GM5 material is 0.2, adding a proper amount of hydrochloric acid to regulate and control the pH value of the system to be 8.5, stirring for 15 hours at room temperature, then filtering, washing and drying to obtain a solid D with an inner layer which is coated with lithium niobate and an outer layer which is coated with dopamine in multiple layers, placing the solid D into a muffle furnace to carry out heat treatment in a nitrogen atmosphere, preserving the heat for 5 hours at 750 ℃, and cooling to room temperature to obtain the lithium-rich manganese-based anode material with the inner layer coated with lithium niobate and the outer layer coated with carbon.
Comparative example 5
5g of a lithium-manganese-rich base starting material (No. GM5, molecular formula Li) which was synthesized by this company1.2Mn0.52Ni0.13Co0.13O2) GM5 is added into 100mL deionized water to form a mixed solution A with the mass fraction of 5%, and a certain amount of tris (hydroxymethyl) aminomethane is added into the mixed solution A to ensure that the concentration of tris (hydroxymethyl) aminomethane is 0.1mol/L, and the mixture is uniformly stirred for later use; weighing a certain amount of dopamine and sodium niobate, dissolving in deionized water to form a solution B, mixing the solution B with the lithium-rich manganese-based material in the mixed solution A to form a mixed solution C, adding a proper amount of hydrochloric acid to regulate the pH value of the mixed solution C to be 11.5, stirring for 15 hours at room temperature, filtering, washing and drying the mixed solution C to obtain a solid D, placing the solid D in a muffle furnace to carry out heat treatment in nitrogen atmosphere, preserving heat for 5 hours at 750 ℃, and cooling to room temperature to obtain the lithium-rich manganese-based anode material containing the lithium niobate coating.
Lithium ion batteries were prepared as described in example 1 using the lithium-rich manganese-based positive electrode materials prepared in examples 1 to 11 and comparative examples 1 to 5, and the performance thereof was tested, with the results shown in tables 2 and 3. In addition, fig. 2 to 5 show the first charge and discharge curves, rate performance, cycle capacity retention rate, and discharge medium voltage retention rate of batteries manufactured from the lithium-rich manganese-based positive electrode materials prepared in examples 1 to 2 and comparative example 1.
TABLE 2 Rate Properties of batteries prepared in examples 1-11 and comparative examples 1-5
TABLE 3 Cyclic and discharged Medium Voltage holding ratio of batteries prepared in examples 1 to 11 and comparative examples 1 to 5
From the performance test results of examples 1-3, it can be seen that when the raw material is one of soluble niobate, pyrophosphate and phosphate, the lithium-rich manganese-based positive electrode material with the surface being the fast ion conductor/carbon network homogeneous coating layer can be obtained by the method disclosed by the present invention, and compared with the original material (comparative example 1), the first coulombic efficiency, rate capability, capacity retention rate and voltage attenuation capability of the lithium-rich manganese-based positive electrode material are comprehensively and significantly improved.
Example 4 is a buffer solution without tris, which has slightly lower electrochemical performance than example 1, but still significantly higher electrochemical performance than the comparative example, and illustrates that a dopamine/fast ion conductor homogeneous film can be formed without buffer, as long as the pH of the system is controlled within a suitable range. The above results show that the buffer solution is not an essential condition for the present invention, and the concentration of tris (hydroxymethyl) aminomethane is too high, which further affects the film forming effect and the electrochemical performance, and it can be seen from example 5 that the specific capacity and the cycle performance are both reduced to some extent.
In the invention, the dopamine is used as a carbon source, the addition amount of the dopamine is directly related to the thickness of a coating layer of a final finished product, and excessive addition amount causes the thickness of a carbon network structure to exceed an optimal value, but affects the lithium ion transmission efficiency, and as in example 6, the electrochemical performance is reduced to a certain extent.
Examples 7 and 8 prove that the heat treatment temperature and time are also key factors influencing the structure of the homogeneous coating layer and the performance of the whole material, the high temperature and the long time can cause the graphitization degree of the carbon network structure to be high on one hand, and can cause elements in the fast ion conductor to diffuse into the matrix material on the other hand, and finally can influence the performance of the material, and example 7 shows that the cycling performance of the material can be further improved by increasing the temperature moderately.
Examples 9-10 show that dopamine polymerization and fast ion conductor generation can occur within the system pH range of 8-10, and the system has certain performance improvement effect, but when the improvement effect is worse than that when the pH is 8.5, the circulating capacity retention rate and the voltage retention rate are both lower than those of example 1, but are obviously higher than those of the original material and the comparative example
Example 11 shows that if the amount of the added raw material of the coating is too much, the molar ratio of the raw material of the coating to the lithium-rich manganese-based material in this example is 0.095, which is close to the upper limit of the present invention, and the performance improvement effect is adversely affected, probably because lithium generated when the fast ion conductor is generated is derived from the bulk material, and if the lithium loss of the bulk material is too much, the structure of the bulk material is deteriorated, and the performance is affected.
Comparative example 1 is an uncoated GM5 starting material, comparative example 2 is a single-pack lithium niobate fast ion conductor, comparative example 3 is a single-pack carbon material, comparative example 4 is a multi-layer coated structure with an inner layer of lithium niobate and an outer layer of a carbon network, and comparative example 5 has a pH too high to allow dopamine polymerization and film formation, and it can be seen from tables 2 and 3 that the electrochemical performance of comparative examples 1-5 is significantly inferior to the examples.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (10)
1. The lithium-rich manganese-based positive electrode material is characterized in that the homogeneous composite coating layer is composed of fast ion conductors and three-dimensional carbon grids, and the fast ion conductors are uniformly loaded in the three-dimensional carbon grids and are crossed and interconnected to form the homogeneous composite surface coating layer.
2. The lithium-rich manganese-based positive electrode material according to claim 1, wherein the general chemical formula of the lithium-rich manganese-based material is xLi2MnO3·(1-x)LiMO2Wherein x is more than or equal to 0.1 and less than or equal to 0.9, and M is Ni, Co, Mn, Cr, Fe, TiOne or more of Mo, Ru, V, Nb, Zr and Sn; the fast ion conductor is any one of lithium phosphate, lithium niobate and lithium pyrophosphate.
3. The lithium-rich manganese-based positive electrode material according to claim 1 or 2, wherein the thickness of the homogeneous composite coating layer is 5-50nm and the fast ion conductor content is >0-10 mol% of the lithium-rich manganese-based material content.
4. The method for preparing the lithium-rich manganese-based positive electrode material with the multifunctional homogeneous composite coating layer according to claims 1 to 3, comprising the following steps:
(1) adding a certain amount of lithium-rich manganese-based material and tris (hydroxymethyl) aminomethane into water to form a mixed solution A;
(2) dissolving a certain amount of dopamine and a coating raw material in water to form a solution B;
(3) mixing the solution B and the solution A under the stirring condition to form a mixed solution C, adjusting the pH value of the mixed solution C to be 8-10 by using acid, stirring for a certain time, and then filtering, washing and drying to obtain a solid D;
(4) and (3) placing the solid D in a sintering furnace, carrying out heat treatment in a protective atmosphere, and cooling to obtain the lithium-rich manganese-based positive electrode material with the multifunctional homogeneous composite coating layer.
5. The method according to claim 4, wherein in the step (1), the lithium-rich manganese-based material is added in an amount such that the mass percentage of the lithium-rich manganese-based material in the mixed solution A is greater than 0-10%, and the tris (hydroxymethyl) aminomethane is added in an amount such that the concentration thereof in the mixed solution A is 0-1 mol/L.
6. The method according to claim 4, wherein in the step (2), the amount of dopamine added is controlled so that the mass ratio of dopamine to the lithium-rich manganese-based material in the mixed solution A is 0 to 0.5.
7. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 4, wherein in the step (2), the coating material comprises one or more of ammonium phosphate, diamine hydrogen phosphate, ammonium dihydrogen phosphate, potassium phosphate, sodium phosphate, potassium niobate, sodium niobate, potassium pyrophosphate, and sodium pyrophosphate.
8. The method for preparing the lithium-rich manganese-based positive electrode material according to claim 4, wherein in the step (2), the coating raw materials are used in the following amounts: the ratio of the mole number of the anions in the raw materials of the coating material to the mole number of the lithium-rich manganese-based material added into the mixed solution A in the step (1) is more than 0-0.1.
9. The method for preparing a lithium-rich manganese-based positive electrode material as claimed in claim 4, wherein in the step (4), the heat treatment temperature is 500-1000 ℃.
10. A lithium ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the lithium-rich manganese-based positive electrode material with the multifunctional homogeneous composite coating layer according to any one of claims 1 to 3.
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