CN113871589B - Lithium-rich manganese-based positive electrode material coated by molten salt-assisted lithium titanate and preparation method thereof - Google Patents
Lithium-rich manganese-based positive electrode material coated by molten salt-assisted lithium titanate and preparation method thereof Download PDFInfo
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 132
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 132
- 239000011572 manganese Substances 0.000 title claims abstract description 77
- 229910052748 manganese Inorganic materials 0.000 title claims abstract description 70
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 title claims abstract description 64
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 46
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 title claims abstract description 41
- 150000003839 salts Chemical class 0.000 title claims abstract description 40
- 238000002360 preparation method Methods 0.000 title claims abstract description 10
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims abstract description 45
- 239000004408 titanium dioxide Substances 0.000 claims abstract description 18
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims abstract description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 13
- 238000010438 heat treatment Methods 0.000 claims abstract description 12
- 238000002156 mixing Methods 0.000 claims abstract description 12
- 238000001035 drying Methods 0.000 claims abstract description 9
- 239000010405 anode material Substances 0.000 claims abstract description 8
- 239000000126 substance Substances 0.000 claims abstract description 8
- 239000011247 coating layer Substances 0.000 claims abstract description 7
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 7
- 238000001914 filtration Methods 0.000 claims abstract description 4
- 238000002844 melting Methods 0.000 claims abstract description 4
- 230000008018 melting Effects 0.000 claims abstract description 4
- 238000005406 washing Methods 0.000 claims abstract description 4
- 238000000576 coating method Methods 0.000 claims description 31
- 239000011248 coating agent Substances 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 14
- 238000006243 chemical reaction Methods 0.000 claims description 13
- 239000012153 distilled water Substances 0.000 claims description 12
- 238000000034 method Methods 0.000 claims description 12
- 239000002245 particle Substances 0.000 claims description 8
- 239000000376 reactant Substances 0.000 claims description 5
- 239000011734 sodium Substances 0.000 claims description 5
- 239000013078 crystal Substances 0.000 claims description 3
- 229910052751 metal Inorganic materials 0.000 claims description 3
- 239000002184 metal Substances 0.000 claims description 3
- 238000004321 preservation Methods 0.000 claims description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims description 2
- 229910002651 NO3 Inorganic materials 0.000 claims description 2
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 2
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 claims description 2
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 2
- 238000011534 incubation Methods 0.000 claims description 2
- 229910052700 potassium Inorganic materials 0.000 claims description 2
- 239000011591 potassium Substances 0.000 claims description 2
- 229910052708 sodium Inorganic materials 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 64
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 abstract description 11
- 239000001301 oxygen Substances 0.000 abstract description 11
- 229910052760 oxygen Inorganic materials 0.000 abstract description 11
- 238000000227 grinding Methods 0.000 abstract description 7
- 239000011164 primary particle Substances 0.000 abstract description 7
- 239000003792 electrolyte Substances 0.000 abstract description 3
- 238000007086 side reaction Methods 0.000 abstract description 2
- 229910052723 transition metal Inorganic materials 0.000 abstract description 2
- 238000009835 boiling Methods 0.000 abstract 1
- 238000004090 dissolution Methods 0.000 abstract 1
- 230000002035 prolonged effect Effects 0.000 abstract 1
- 239000012429 reaction media Substances 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 13
- 239000000047 product Substances 0.000 description 12
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 9
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 7
- 229910001416 lithium ion Inorganic materials 0.000 description 7
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 6
- 229910010413 TiO 2 Inorganic materials 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000012512 characterization method Methods 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- 229910052593 corundum Inorganic materials 0.000 description 4
- 239000010431 corundum Substances 0.000 description 4
- 230000000630 rising effect Effects 0.000 description 4
- 238000000967 suction filtration Methods 0.000 description 4
- 238000003786 synthesis reaction Methods 0.000 description 4
- 239000010406 cathode material Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 229910001386 lithium phosphate Inorganic materials 0.000 description 3
- 230000014759 maintenance of location Effects 0.000 description 3
- 229920000767 polyaniline Polymers 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 239000011163 secondary particle Substances 0.000 description 3
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical compound [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 0.000 description 3
- 229910013553 LiNO Inorganic materials 0.000 description 2
- 150000001463 antimony compounds Chemical class 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000001354 calcination Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 238000005303 weighing Methods 0.000 description 2
- 229910008555 Li1.2Mn0.6Ni0.2O2 Inorganic materials 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- 238000003917 TEM image Methods 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 150000001462 antimony Chemical class 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000009831 deintercalation Methods 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000000921 elemental analysis Methods 0.000 description 1
- 230000003301 hydrolyzing effect Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000002354 inductively-coupled plasma atomic emission spectroscopy Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 239000010416 ion conductor Substances 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000033116 oxidation-reduction process Effects 0.000 description 1
- SOQBVABWOPYFQZ-UHFFFAOYSA-N oxygen(2-);titanium(4+) Chemical compound [O-2].[O-2].[Ti+4] SOQBVABWOPYFQZ-UHFFFAOYSA-N 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 239000012466 permeate Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M potassium chloride Inorganic materials [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
- 235000012431 wafers Nutrition 0.000 description 1
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
- H01M4/364—Composites as mixtures
-
- 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
- H01M4/362—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
- 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
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- 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
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
Lithium-rich manganese-based positive electrode material coated by molten salt-assisted lithium titanate and preparation method thereof, wherein chemical formula of lithium-rich manganese-based positive electrode material is Li 2 TiO 3 @Li 1+ x M 1‑y O 2 0 < x < y < 1, M comprises Mn and Ni, mn and Co or Mn, co and Ni in combination, and the mass fraction of lithium titanate is 0.25% -5%. The preparation method comprises the steps of mixing the lithium-rich material with titanium dioxide and low-melting-point salt, grinding and heating to a temperature above the melting point and below the boiling point of the salt, melting the system, dissolving the titanium dioxide, reacting with the lithium-rich material, washing with water, filtering and drying to obtain the lithium titanate coated lithium-rich manganese-based anode material. According to the invention, molten salt is used as a reaction medium, a uniform lithium titanate coating layer is generated on the surface of primary particles of the lithium-rich manganese-based positive electrode material, so that the side reaction of active oxygen and electrolyte is inhibited, the dissolution loss of transition metal elements is reduced, the cycle life of the lithium-rich positive electrode material is prolonged, the voltage attenuation is reduced, and the lithium-rich manganese-based positive electrode material has high practical value.
Description
Technical Field
The invention belongs to the technical field of lithium ion battery anode materials, and particularly relates to a coating method of a lithium-rich manganese-based anode material.
Background
The development of lithium ion battery technology is greatly affected by cobalt-based and nickel-based positive electrodesThe limitations of materials with low specific capacity and high cost are stringent to demand positive electrode materials with high specific energy and long cycle life. Lithium-rich manganese-based cathode materials (Li 1+x M 1-x O 2 M=mn, co, ni, etc.) has a value exceeding 300mAh g -1 Theoretical specific capacity of (C) and approximately 1000Wh kg -1 Is a high energy density. However, the oxidation-reduction reversibility of lattice oxygen is low, and the first-cycle charging process has obvious oxygen release problem, so that the coulomb efficiency of the material is low and the cycle stability is poor. And secondly, oxygen release accelerates the phase change of the material structure, so that the deintercalation of lithium ions is blocked. In addition, the release of active oxygen can cause the gas production of the battery pack and the decomposition of electrolyte, so that the potential safety hazard is high. Therefore, oxygen release is an important factor affecting the structural stability of the lithium-rich material, and is important for protecting and modifying the surface of the material.
In order to inhibit the oxygen release problem of the lithium-rich manganese-based material, a coated modification strategy is often adopted to prevent oxygen molecules from overflowing and stabilize the surface of the lithium-rich material. For example, CN 112510200A discloses a lithium phosphate-polyaniline double-layer coated lithium-rich manganese-based cathode material, which is prepared by a multi-step method, depositing lithium phosphate on the surface of a lithium-rich material in the calcination process, mixing the lithium-rich material coated with lithium phosphate with polyaniline solution, and drying to obtain an organic-inorganic double-coating lithium-rich material, wherein lithium phosphate and polyaniline can respectively promote the transmission of lithium ions and electrons, and the coating can reduce the release of transition metal and oxygen, so that the cycle performance of the material is improved. CN 113200571A discloses a lithium-rich manganese-based positive electrode material coated with an antimony compound on the surface, which is prepared by mixing and hydrolyzing an antimony salt solution and a lithium-rich material, filtering, washing, drying and calcining the initially coated material to finally obtain an electrochemically active antimony compound coating layer.
However, it is difficult to achieve uniform coating with the current conventional coating process, and it is more difficult to coat the primary particle surfaces in the particle aggregates because the coating process lacks the interaction of the reactant with the primary particles inside the lithium-rich material. From the perspective of the coating process, the interaction between the solids is the weakest, so that the mechanical mixing coating method is not easy to realize uniform coating; the reaction of gas with solid is uniform, but a specific closed reaction vessel is often required, and the operation is complicated. From the material point of view, the coating material can meet the lattice matching of the coating material and the lithium-rich material, and the coating material with lithium ion conductivity is rare. Therefore, a coating substance capable of uniformly coating the lithium-rich material is sought, and a high-efficiency and practical coating reaction is designed to protect the surface of the lithium-rich material, particularly the surface of primary particles, so that the method has important practical application significance.
Disclosure of Invention
The invention aims to solve the problems of oxygen release, capacity and voltage decay of a lithium-rich manganese-based positive electrode material, provides a strategy for coating the lithium-rich manganese-based positive electrode material by using lithium titanate, and adopts a simple and effective molten salt-assisted solid-liquid reaction coating technology to realize uniform coating of nano-level thickness lithium titanate on the surfaces of primary particles of the lithium-rich material, thereby prolonging the cycle life and multiplying power performance of the lithium-rich manganese-based material and inhibiting voltage decay. The method has obvious effect of improving the performance of the material, is simple and convenient to operate, has lower cost and has large-scale application prospect.
The technical scheme of the invention is as follows:
lithium-rich manganese-based positive electrode material coated by molten salt-assisted lithium titanate, and chemical formula composition is Li 2 TiO 3 @Li 1+x M 1-y O 2 Wherein x is more than 0 and less than y is more than 1, the metal M contains Mn and Ni, mn and Co or Mn, co and Ni, the mass fraction of lithium titanate is 0.25% -5% of the lithium-rich manganese-based positive electrode material, and the thickness of the coating layer is less than 20nm.
The preparation method of the lithium-rich manganese-based positive electrode material coated by the molten salt-assisted lithium titanate comprises the following steps of:
step one: uniformly mixing the lithium-rich manganese-based anode material with titanium dioxide and low-melting-point salt according to a certain proportion;
step two: heating the reactant and preserving the heat for a certain time to enable the coating reaction to occur;
step three: and washing the cooled reactant with distilled water to remove low-melting-point salt, filtering and drying to obtain the lithium titanate coated lithium-rich manganese-based positive electrode material.
Further, in the first step, the titanium dioxide crystal form is one or two of rutile type and anatase type, the grain size is between 5nm and 10 mu m, preferably anatase type, and the grain size is 10nm; the adding mass of the titanium dioxide is 0.25% -5%, preferably 1% of that of the lithium-rich manganese-based positive electrode material; the low-melting-point salt is one or more of chloride, nitrate and sulfate of lithium, sodium or potassium, and the addition mass is 20% -400%, preferably 200% of the lithium-rich manganese-based positive electrode material.
Further, in the second step, the heating atmosphere is air, and the heating rate is 2-20 ℃/min, preferably 5 ℃/min; the heat preservation temperature is 10-50 ℃ above the melting point of the salt; the incubation time is 5-60min, preferably 10min.
Further, in the third step, the distilled water is washed for more than 3 times, the drying temperature is 100-300 ℃, and the drying time is 30-180min.
The invention has the advantages and effects that:
1. lithium ion conductor lithium titanate (Li) 2 TiO 3 ) As the coating material, the interplanar spacing of the material is close to that of the lithium-rich material, and the material is compatible in structure, so that the coating layer is favorably combined with the positive electrode material body tightly, and the transmission of lithium ions is promoted.
2. The coating process is based on a molten salt-assisted solid-liquid reaction, nano titanium dioxide particles can be dissolved in the molten salt and fully contacted with the surface of the lithium-rich material, the solid-liquid reaction ensures the uniformity of a coating layer, and the operation is simple and convenient, thereby being beneficial to large-scale preparation.
3. The adopted molten salt process is not only suitable for monocrystal lithium-rich materials, but also suitable for secondary particle materials, molten salt can permeate into secondary particles in the reaction process and fully react with primary particles to obtain the lithium-rich materials with the surfaces coated with lithium titanate on the primary particles, so that the coating effect can be enhanced, and the oxygen loss on the surfaces of the lithium-rich materials and the side reaction with electrolyte can be inhibited.
Drawings
Fig. 1 is a schematic diagram of a preparation flow of a lithium-rich manganese-based positive electrode material coated with molten salt-assisted lithium titanate.
Fig. 2 is an SEM image of the lithium titanate coated lithium-rich manganese-based positive electrode material of example 2 and the comparative lithium-rich manganese-based material.
Fig. 3 is a TEM image of the lithium titanate coated lithium-rich manganese-based positive electrode material of example 2 and the comparative lithium-rich manganese-based material.
Fig. 4 is an XRD pattern of the lithium titanate coated lithium-rich manganese-based positive electrode material of example 2 and the comparative lithium-rich manganese-based material.
Fig. 5 is a graph showing the cycle performance of button half cells of example 2 and comparative example materials.
Fig. 6 is a graph of the rate performance of button half cells of example 2 and comparative example materials.
Detailed Description
For a further understanding of the present invention, the present invention is further described below with reference to the drawings, but the scope of the present invention is not limited thereby.
Example 1 Synthesis of a target chemical formula Li 2 TiO 3 @Li 1.2 Mn 0.6 Ni 0.2 O 2 (for the preparation scheme see FIG. 1)
Li is weighed according to the mass ratio of 100:150:150:2 1.2 Mn 0.6 Ni 0.2 O 2 LiCl, KCl and TiO 2 . Wherein TiO is 2 The particle size of the polymer is about 100 nm. Firstly, mixing and fully grinding LiCl and KCl in a dry environment, then adding the lithium-rich manganese-based anode material and titanium dioxide, mixing and uniformly grinding, and transferring the mixture into a corundum crucible for standby.
And heating and reacting the mixture of the lithium-rich manganese-based positive electrode material, the salt and the titanium dioxide by using a muffle furnace. The temperature rising rate is 20 ℃/min, the reaction is carried out for 20min at 800 ℃, and then the mixture of the coating product and the salt is obtained after natural cooling to room temperature.
Distilled water was added to the crucible and stirred until the block dissolved, the product was isolated by suction filtration, washed three times with distilled water and dried in a forced air oven at 150 ℃ for 3h. The obtained product is a lithium-rich manganese-based positive electrode material coated by 2% lithium titanate.
Example 2 Synthesis of the target chemical formula Li 2 TiO 3 @Li 1.08 Mn 0.54 Co 0.13 Ni 0.13 O 2 Is a material of (2)
Weighing Li according to the mass ratio of 100:200:1 1.08 Mn 0.54 Co 0.13 Ni 0.13 O 2 LiCl and TiO 2 . Wherein TiO is 2 The anatase type has a particle size of about 10 nm. And (3) uniformly mixing and grinding the lithium-rich manganese-based positive electrode material, the salt and the titanium dioxide in a dry environment, and transferring the mixture into a corundum crucible for standby.
And heating and reacting the mixture of the lithium-rich manganese-based positive electrode material, the salt and the titanium dioxide by using a muffle furnace. The temperature rising rate is 5 ℃/min, the reaction is carried out for 10min at 650 ℃, and then the mixture of the coating product and the salt is obtained after natural cooling to room temperature.
Distilled water was added to the crucible and stirred until the block dissolved, the product was isolated by suction filtration, washed three times with distilled water and dried in a forced air oven at 180 ℃ for 2h. The obtained product is a lithium-rich manganese-based positive electrode material coated by 1% lithium titanate.
Example 3 Synthesis of a target chemical formula Li 2 TiO 3 @Li 1.2 Mn 0.6 Co 0.2 O 2 Is a material of (2)
Weighing Li according to a mass ratio of 100:100:0.5 1.2 Mn 0.6 Co 0.2 O 2 、KNO 3 And TiO 2 . Wherein TiO is 2 The anatase type has a particle size of about 100 nm. And (3) uniformly mixing and grinding the lithium-rich manganese-based positive electrode material, the salt and the titanium dioxide in a dry environment, and transferring the mixture into a corundum crucible for standby.
And heating and reacting the mixture of the lithium-rich manganese-based positive electrode material, the salt and the titanium dioxide by using a muffle furnace. The temperature rising rate is 10 ℃/min, the reaction is carried out for 40min at 700 ℃, and then the mixture of the coating product and the salt is obtained after natural cooling to the room temperature.
Distilled water was added to the crucible and stirred until the block dissolved, the product was isolated by suction filtration, washed three times with distilled water and dried in a forced air oven at 200 ℃ for 1h. The obtained product is a lithium-rich manganese-based positive electrode material coated with 0.5% of lithium titanate.
Example 4 Synthesis of the target chemical formula Li 2 TiO 3 @Li 1.11 Mn 0.49 Ni 0.29 Co 0.11 O 2 Is a material of (2)
Li is weighed according to the mass ratio of 100:50:50:3 1.11 Mn 0.49 Ni 0.29 Co 0.11 O 2 、LiNO 3 、Na 2 SO 4 And TiO 2 . Wherein TiO is 2 The anatase type has a particle size of about 2 μm. LiNO is firstly carried out in a dry environment 3 And Na (Na) 2 SO 4 Mixing and grinding fully, adding the lithium-rich manganese-based anode material and titanium dioxide, mixing and grinding uniformly, and transferring the mixture into a corundum crucible for standby.
And heating and reacting the mixture of the lithium-rich manganese-based positive electrode material, the salt and the titanium dioxide by using a muffle furnace. The temperature rising rate is 20 ℃/min, the reaction is carried out for 5min at 880 ℃, and then the mixture of the coating product and the salt is obtained after natural cooling to room temperature.
Distilled water was added to the crucible and stirred until the block dissolved, the product was isolated by suction filtration, washed three times with distilled water and dried in a forced air oven at 180 ℃ for 2h. The obtained product is a 3% lithium titanate coated lithium-rich manganese-based positive electrode material.
Comparative example
The spherical secondary particle lithium-rich manganese-based positive electrode material without surface coating in example 2 was used as a positive electrode material, and a battery was assembled and tested for electrochemical performance.
Test case
(1) Characterization of materials: elemental analysis (for Li) was performed on the lithium titanate-coated lithium-rich manganese-based cathode material prepared in example 2 using ICP-AES 2 TiO 3 The coating amount was 1.14%. SEM characterization was performed on the lithium titanate coated lithium-rich manganese-based material prepared in example 2 and the comparative example material, and the results are shown in fig. 2. TEM characterization was performed on the lithium titanate coated lithium-rich manganese-based material prepared in example 2 and the comparative example material, as shown in FIG. 3, wherein a lithium titanate coating layer of about 7nm exists on the surface of the example material, and the surface of the comparative example material is smooth. Coating the lithium titanate prepared in example 2XRD characterization is carried out on the lithium-rich manganese-based material and the comparative material, as shown in figure 4, the two patterns are in accordance with the R-3m space group structure except the superlattice peak at 20-30 degrees, no obvious impurity peak appears, and the molten salt auxiliary coating method adopted by the invention has no influence on the bulk structure of the lithium-rich material, and the purity of the synthesized material is higher.
(2) And (3) battery assembly: the lithium titanate coated lithium-rich manganese-based material prepared in example 2 and the comparative example material are respectively mixed with Super P and PVDF according to a mass ratio of 8:1:1, slurried and coated, vacuum dried and cut into wafers with the diameter of 10mm, and a half cell is assembled by taking a metal lithium sheet as a negative electrode.
(3) Performance test: at 0.2C (1c=250 mAh g -1 ) The assembled half cells were subjected to a cycle test at a rate of 2 to 4.8V, as shown in fig. 5, and the initial discharge capacity of 0.2C of the lithium titanate-coated lithium-rich manganese-based material prepared in example 2 was 259.8mAh g -1 Capacity after 50 cycles was 257.6mAhg -1 The capacity retention rate was 99.1%, and the initial discharge capacity of comparative example material 0.2C was 259.8mAh g -1 The capacity after 50 cycles is 233.8mAh g -1 The capacity retention rate is 90.0%, which indicates that the lithium titanate coated lithium-rich material prepared by the method has better capacity retention rate and cycle performance than uncoated lithium-rich material. As shown in FIG. 6, the discharge capacities of the lithium titanate coated lithium-rich manganese-based material prepared in example 2 at 0.1C, 1C and 5C are 275.9mAh g respectively -1 、217.0mAh g -1 And 148.0mAh g -1 The discharge capacity of the comparative example materials was 268.9mAh g, respectively -1 、203.0mAh g -1 And 142.5mAh g -1 This shows that the lithium titanate coated lithium-rich manganese-based material prepared by the method has better rate capability than the uncoated lithium-rich material.
The above embodiments are merely illustrative of the principles and embodiments, and are not intended to limit the invention, but any modifications, equivalents, improvements, etc. made to the invention without departing from the principles of the invention should be included in the scope of the invention.
Claims (6)
1. The preparation method of the lithium-rich manganese-based positive electrode material coated by the lithium titanate assisted by the molten salt is characterized by comprising the following steps of:
step one: uniformly mixing the lithium-rich manganese-based anode material with titanium dioxide and low-melting-point salt;
step two: heating the reactant and preserving heat to enable the coating reaction to occur;
step three: washing the cooled reactant with distilled water to remove low-melting-point salt, filtering and drying to obtain a lithium titanate coated lithium-rich manganese-based positive electrode material;
the chemical composition of the lithium titanate coated lithium-rich manganese-based positive electrode material is shown as a formula (I):
Li 2 TiO 3 @Li 1+x M 1-y O 2 (Ⅰ)；
wherein x is more than 0 and less than y is more than 1, and the metal M comprises Mn and Ni, mn and Co or Mn, co and Ni;
the titanium dioxide crystal form is one or two of rutile type and anatase type, and the particle size is between 5nm and 10 mu m; the adding mass of the titanium dioxide is 0.25% -5% of that of the lithium-rich manganese-based anode material; the low-melting-point salt is one or more of chloride, nitrate and sulfate of lithium, sodium or potassium, and the addition mass is 20-400% of the lithium-rich manganese-based positive electrode material.
2. The preparation method of the lithium-rich manganese-based positive electrode material coated by the molten salt-assisted lithium titanate according to claim 1, wherein the mass fraction of the lithium titanate is 0.25% -5% of that of the lithium-rich manganese-based positive electrode material, and the thickness of the coating layer is less than 20nm.
3. The method for preparing the lithium-rich manganese-based positive electrode material coated with the molten salt-assisted lithium titanate according to claim 1, wherein the titanium dioxide crystal form is anatase, and the particle size is 10nm; the adding mass of the titanium dioxide is 1% of that of the lithium-rich manganese-based positive electrode material; the addition mass of the low-melting-point salt is 200% of that of the lithium-rich manganese-based positive electrode material.
4. The method for preparing the lithium-rich manganese-based positive electrode material coated with the molten salt-assisted lithium titanate according to claim 1, wherein in the second step, the heating atmosphere is air, and the heating rate is 2-20 ℃/min; the heat preservation temperature is 10-50 ℃ above the melting point of the salt; the heat preservation time is 5-60min.
5. The method for preparing the lithium-rich manganese-based positive electrode material coated with the molten salt-assisted lithium titanate according to claim 4, wherein the heating rate is 5 ℃/min; the incubation time was 10min.
6. The method for preparing the lithium-rich manganese-based positive electrode material coated with the molten salt-assisted lithium titanate according to claim 1, wherein in the third step, distilled water is washed for more than 3 times, the drying temperature is 100-300 ℃, and the drying time is 30-180min.
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