CN113764630A - Positive electrode material and preparation method and application thereof - Google Patents

Positive electrode material and preparation method and application thereof Download PDF

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CN113764630A
CN113764630A CN202010490267.9A CN202010490267A CN113764630A CN 113764630 A CN113764630 A CN 113764630A CN 202010490267 A CN202010490267 A CN 202010490267A CN 113764630 A CN113764630 A CN 113764630A
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positive electrode
electrode material
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matrix
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韩晓燕
焦晓朋
李世彩
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BYD Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a positive electrode material, a preparation method and application thereofxCoyMn1‑x‑y‑zMzO2The compound is shown in the specification, wherein M is a doped metal element, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 0.2, x + y + z is more than or equal to 0 and less than or equal to 1, and x, y and z are not 0 at the same time; the coating layer is Li2CO3. Hair brushThe positive electrode material is prepared by adding Li on the surface of the substrate2Conversion of O to Li2CO3To improve the stability of the material in air, Li2CO3Decomposition of the produced Li+When the metal oxide is diffused to the negative electrode, the energy density of the whole battery is improved, and the cycle performance of the battery is improved. Meanwhile, the preparation method of the anode material provided by the invention is simple, the production cost is low, and the large-scale industrial production is easy to realize.

Description

Positive electrode material and preparation method and application thereof
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a positive electrode material and a preparation method and application thereof.
Background
With the rapid development of new energy automobiles, the market demands for the energy density and the service life of power lithium ion batteries are increasingly improved. As an important component of a lithium ion battery system, a positive electrode material with high energy density and long cycle life is in great market demand. Having alpha-NaFeO2Layered structure nickel-rich ternary material LiNixCoyMn1-x-yO2(x is not less than 0.8) is bonded with LiNiO2、LiCoO2And LiMnO2The characteristics of the three anode materials, high energy density, long cycle life, high safety and the like are achieved, and the anode materials are widely concerned by researchers.
However, the high nickel cathode material still has some problems at present, which limits the large-scale application of the high nickel cathode material on power batteries. Among them, the high nickel anode material has high residual alkali, which makes the material have serious gas generation problem and affects the material pulping and coating process. The components and the content of the residual lithium on the surface of the high-nickel cathode material are gradually changed along with the time and the storage condition, and the surface residual lithium component of the initially synthesized cathode high-nickel material is Li because the cathode high-nickel material is subjected to a high-temperature heat treatment process2O, surface Li with the change of storage time and storage condition of high nickel material in air2The O may be gradually converted to other Li-containing components, such as surface Li under storage conditions with high moisture content2O reacts with moisture in the air to form LiOH, and the formed LiOH also reacts with CO in the air with the increase of the storage time2Reaction to form Li2CO3。
At present, a common method for removing residual alkali on the surface of a high-nickel cathode material is a water washing method, but the water washing process can cause the crystal structure on the surface of the cathode material to change, so that the first charge-discharge efficiency and the cycle performance of the cathode material are influenced.
In view of this, it is necessary to provide a cathode material and a preparation method thereof, which are simple in operation, effectively reduce surface residual lithium, and improve the stability and cycle performance of the material.
Disclosure of Invention
The invention aims to solve the problems of chemical delithiation, crystal structure damage and material cycle performance reduction of a lithium ion battery anode material in the prior art after surface residual lithium is removed, and provides an anode material, a preparation method and application thereof.
In order to achieve the above object, a first aspect of the present invention provides a positive electrode material, which includes a substrate and a coating layer on a surface of the substrate, wherein the substrate is a LiNi represented by the general formulaxCoyMn1-x-y-zMzO2The compound is shown in the specification, wherein M is a doped metal element, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 0.2, x + y + z is more than or equal to 0 and less than or equal to 1, and x, y and z are not 0 at the same time; the coating layer is Li2CO3。
Preferably, the weight ratio of the substrate to the coating layer is 100: 0.1-10.
The second aspect of the present invention provides a method for preparing a positive electrode material, comprising the steps of:
(1) sequentially mixing and first sintering a matrix precursor, a lithium source and an optional metal compound to obtain a matrix;
(2) carrying out second sintering on the substrate to obtain a positive electrode material with a coating layer;
wherein the second sintering is carried out in the presence of CO2Is carried out in an atmosphere, wherein the CO is contained2In the atmosphere of CO2The content is 20-100 vol%.
Preferably, the matrix precursor is of the general formula NixCoyMn1-x-y(OH)2A metal hydroxide and/or of the formula AaObThe metal oxide is shown in the specification, wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, and x + y is more than or equal to 0 and less than or equal to 1; a is at least one of Ni, Co and Mn, a is an integer from 1 to 3, and b is an integer from 1 to 4.
The invention also provides a preparation method of the cathode material.
Compared with the prior art, the invention has the following advantages:
(1) the positive electrode material provided by the invention is prepared by using Li remained on the surface of a matrix2Conversion of O to Li2CO3So that a stable protective layer is formed on the surface of the material, thereby improving the stability of the material in the air;
(2) the anode material provided by the invention has Li under the condition of reaching a certain voltage during charging2CO3Decomposition of the produced Li+The active lithium is diffused to the negative electrode and can be embedded into a negative electrode material to form active lithium, so that the loss of the active lithium caused by the consumption of an SEI (solid electrolyte interphase) film of the negative electrode is supplemented, the energy density of the whole battery is improved, and the cycle performance of the battery is improved;
(3) the preparation method provided by the invention is simple, and the material can directly generate Li in situ in the heat treatment process2CO3The surface is coated, the production cost is low, and the large-scale industrial production is easy to realize.
Drawings
Fig. 1 is a TEM image of a positive electrode material P1 obtained in example 1;
fig. 2 is an XRD pattern of the positive electrode material P1 prepared in example 1;
FIG. 3 is a graph showing the first charge and discharge processes of QP-1 obtained in example 1 and QD-1 obtained in comparative example 1;
FIG. 4 is a graph showing the cycle characteristics of QP-1 cell prepared in example 1, QD-1 cell prepared in comparative example 1, and QD-2 cell prepared in comparative example 2.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a positive electrode material, which comprises a substrate and a coating layer on the surface of the substrate, wherein the substrate is LiNi with a general formulaxCoyMn1-x-y-zMzO2The compound is shown in the specification, wherein M is a doped metal element, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 0.2, x + y + z is more than or equal to 0 and less than or equal to 1, and x, y and z are not 0 at the same time; the coating layer is Li2CO3。
In the present invention, the doping metal element means a metal element other than lithium, nickel, cobalt and manganese without specific description, and preferably, the doping metal element is at least one selected from the group consisting of magnesium, iron, titanium, copper, zinc, aluminum, silicon, niobium, vanadium, zirconium, molybdenum, chromium, gallium and ruthenium.
In the present invention, x, y, and z are not 0 at the same time, which means that at least one of x, y, and z is not 0, that is: x is 0, y is not equal to 0, z is not equal to 0, x is 0, y is not equal to 0, z is 0, x is 0, y is 0, z is not equal to 0, x is not equal to 0, y is not equal to 0, z is 0.
In the present invention, the coating layer is coated on the surface of the matrix without any special description, that is, as shown in fig. 1, a TEM image of the positive electrode material P1 prepared in example 1 sequentially shows the matrix and the coating layer from the bottom right corner, that is: the anode material has a core-shell structure, wherein the core is a matrix, and the shell is a coating layer.
Considering the residual Li on the surface of the prior matrix material2O absorbs moisture in the air and is converted into LiOH, and LiOH is a strong alkaline substance and easily absorbs moisture in the air, so that the base material is sensitive and unstable to moisture in the air. In contrast, the positive electrode material of the present invention is obtained by mixing Li on the surface of a base material2O is converted to Li2CO3So that a stable protective layer is formed on the surface of the material, which is helpful for improving the quality of the materialStability of the material in air.
The cathode material provided by the invention is stable in air, and simultaneously converts residual lithium on the surface of a matrix material into Li2CO3And Li2CO3When the anode material is charged, the following decomposition can be carried out when a certain voltage is reached: li2CO3→2Li++CO2+x1O2+(0.5-x)O2+2e-Wherein, in the step (A),1O2is singlet oxygen, and lithium carbonate is decomposed during charging to generate partial singlet oxygen1O2The activity of the singlet oxygen is strong,1O2the electrolyte can be quickly consumed by reaction, and active lithium can not be consumed by diffusion to the negative electrode. Thus, Li2CO3Li formed during decomposition+When the active lithium is diffused to the negative electrode, the active lithium can be normally embedded into the negative electrode material to form active lithium, so that the loss of the active lithium caused by the consumption of the SEI film of the negative electrode is supplemented, the energy density of the whole battery is improved, and the cycle performance of the battery is improved.
In the present invention, the substrate has a wide range of choices as long as the substrate satisfies the above general formula. Preferably, the matrix is of the general formula LiNixCoyMn1-x-y-zMzO2Compounds of the formula (I) in which 0.5 < x < 1, 0 < y < 0.5, 0 < z < 0.1, 0 < x + y + z < 1, for example LiNi0.55Co0.15Mn0.3O2、LiNi0.65Co0.1Mn0.25O2、LiNi0.9Co0.05Mn0.05O2(ii) a Further preferably, the matrix is of the general formula LiNixCoyMn1-x-y-zMzO2Compounds of the formula (I) in which 0.6. ltoreq. x < 1, 0 < y < 0.4, 0. ltoreq. z < 0.05, 0 < x + y + z < 1, for example LiNi0.6Co0.1Mn0.3O2、LiNi0.8Co0.1Mn0.1O2、LiNi0.7Co0.15Mn0.15O2。
According to a preferred embodiment of the invention, said baseThe body is selected from LiNi0.8Co0.15Al0.05O2、LiNi0.8Co0.1Mn0.1O2、LiNi0.6Co0.2Mn0.2O2、LiNi0.4Co0.3Mn0.3O2、LiNi0.7Co0.3O2、LiNi0.6Mn0.4O2、LiNi0.9Co0.05Al0.05O2And LiCoO2At least one of them, the present invention is not limited thereto, as long as the above general formula is satisfied.
According to the invention, the particle size D50 of the matrix is preferably 0.5 to 40 μm, preferably 2 to 20 μm, wherein the particle size of the matrix is determined by laser diffraction.
In the present invention, the selection of the matrix particle size is mainly based on the comprehensive consideration of the specific surface area and the rate capability of the material, and the material with relatively small matrix particle size has a large specific surface area, which may cause many side reactions between the matrix material and the electrolyte, but the material with small particle size has good rate capability. On the contrary, the material with larger particle size has small specific surface area, so the side reaction between the material and the electrolyte is less, and the material cycle performance is improved. However, the large particle size material has a problem of poor rate capability. Therefore, by comprehensively considering these two factors, a preferable range of the particle size of the material matrix is determined under the condition that both the rate capability and the cycle capability of the material satisfy practical applications.
Preferably, the thickness of the coating layer is 1 to 1000nm, preferably 10 to 500nm, wherein the thickness of the coating layer is measured by transmission electron microscopy.
In the present invention, the preferable thickness of the coating layer can ensure a good coating effect, and also consider the influence on the rate capability of the matrix material and the specific capacity of the material. Li2CO3The electronic conductivity of the cladding layer is poor, and the excessively thick thickness can cause the polarization of the positive electrode material to be too large when the positive electrode material is charged for the first time. When the coating layer is too thin, the complete coating effect cannot be ensured.
According to a preferred embodiment of the present invention,the weight ratio of the substrate to the coating layer is 100: 0.1 to 10, preferably 100: 0.2-5. With the preferred weight ratio, on the one hand, the residual Li on the surface of the material can be ensured2Conversion of all O to Li2CO3On the other hand, the proportion of active lithium consumed by the SEI film generation of the negative electrode in the first charging process of the negative electrode material matched with the positive electrode is mainly considered, so that Li in the surface coating layer of the positive electrode material2CO3The effective active lithium provided by the decomposition can just supplement the active lithium consumed by SEI, thereby achieving the effect of improving the energy density of the battery prepared by the cathode material provided by the patent.
The second aspect of the present invention provides a method for preparing a positive electrode material, comprising the steps of:
(1) sequentially mixing and first sintering a matrix precursor, a lithium source and an optional metal compound to obtain a matrix;
(2) carrying out second sintering on the substrate to obtain a positive electrode material with a coating layer;
wherein the second sintering is carried out in the presence of CO2Is carried out in an atmosphere, wherein the CO is contained2In the atmosphere of CO2The content is 20-100 vol%.
According to the present invention, preferably, the matrix precursor is of the general formula NixCoyMn1-x-y(OH)2A metal hydroxide and/or of the formula AaObThe metal oxide is shown, wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, x + y is more than or equal to 0 and less than or equal to 1, A is selected from at least one of Ni, Co and Mn, a is selected from an integer of 1-3, and b is selected from an integer of 1-4; further preferably, the matrix precursor is of the general formula NixCoyMn1-x-y(OH)2The metal hydroxide shown.
According to a preferred embodiment of the present invention, when the matrix is a poly lithium acid, the matrix precursor is of the general formula NixCoyMn1-x-y(OH)2The metal hydroxides shown, for example: the matrix is LiNi0.8Co0.1Mn0.1O2The matrix precursor is Ni0.8Co0.1Mn0.1(OH)2(ii) a When the matrix is monobasic lithium acid, the matrix precursor is shown as a general formula AaObThe metal oxides shown, for example: the matrix is LiCoO2The matrix precursor is Co3O4。
Further preferably, the general formula NixCoyMn1-x-y(OH)20.5 < x < 1, 0 < y < 0.5, 0 < x + y < 1, e.g. Ni0.55Co0.15Mn0.3(OH)2、Ni0.65Co0.1Mn0.25(OH)2、Ni0.9Co0.05Mn0.05(OH)2。
More preferably, the general formula NixCoyMn1-x-y(OH)2In which 0.6. ltoreq. x < 1, 0 < y < 0.4, 0 < x + y < 1, e.g. Ni0.6Co0.1Mn0.3(OH)2、Ni0.8Co0.1Mn0.1(OH)2、Ni0.7Co0.15Mn0.15(OH)2。
According to a preferred embodiment of the invention, the matrix precursor is selected from Ni0.8Co0.1Mn0.1(OH)2、Ni0.6Co0.2Mn0.2(OH)2、Ni0.4Co0.3Mn0.3(OH)2、Ni0.7Co0.3(OH)2、Ni0.842Co0.158(OH)2、Ni0.947Co0.053(OH)2、Ni0.6Mn0.4(OH)2And Co3O4At least one of (1).
In the present invention, the source of the matrix precursor has a wide range of choice, and may be obtained commercially or by preparation, and the present invention is not limited thereto.
According to the present invention, it is preferred that the particle diameter D50 of the matrix precursor, as measured by laser diffraction, is 0.5 to 45 μm, preferably 2 to 25 μm.
In the present inventionThe lithium source may be selected from a wide range of sources as long as it contains elemental lithium, preferably the lithium source is selected from lithium hydroxide and/or lithium carbonate, preferably lithium carbonate. The lithium source described in the examples is LiOH H2O is an example, but the present invention is not limited thereto.
Preferably, the metal compound is selected from compounds containing at least one element of magnesium, iron, titanium, copper, zinc, aluminum, silicon, niobium, vanadium, zirconium, molybdenum, chromium, gallium and ruthenium, and the metal compound is present in the form of hydroxide, oxide, carbonate, acetate, nitrate, chloride, nitrate, for example, the metal compound is selected from at least one of aluminum oxide, magnesium oxide, iron nitrate, copper acetate and zinc sulfate, but the present invention is not limited thereto.
In the invention, the metal compound is added to modify the base material in a doping way, so that the structural stability of the material in a circulation process and a high lithium removal state is improved, and the high-temperature storage, circulation and safety performance of the material are improved.
According to a preferred embodiment of the present invention, when the matrix precursor is of the general formula NixCoyMn1-x-y(OH)2The molar ratio of the matrix precursor, the lithium source and the metal compound is 0.8-1: 1.01-1.1: 0-0.2, e.g., 1: 1.05: 0. 0.95: 1.06: 0.05, 0.9: 1.07: 0.1, 0.85: 1.08: 0.15, 0.8: 1.09: 0.2 and 1: 1.1: 0, and any molar ratio therebetween, more preferably 0.9 to 1: 1.05-1.1: 0 to 0.1, more preferably 0.95 to 1: 1.05-1.09: 0 to 0.05, wherein the lithium source is Li+The metal compound is calculated by metal elements.
According to a preferred embodiment of the present invention, when the matrix precursor is AaObThe molar ratio of the lithium source to the metal compound in the matrix precursor is 0.8-1: 1.01-1.1: 0-0.2, e.g., 1: 1.05: 0. 0.95: 1.06: 0.05, 0.9: 1.07: 0.1, 0.85: 1.08: 0.15, 0.8: 1.09: 0.2 and 1: 1.1: 0, and any molar ratio therebetween, more preferably 0.9 to 1: 1.05-1.1:0 to 0.1, more preferably 0.95 to 1: 1.05-1.09: 0 to 0.05, wherein the matrix precursor is represented by Ab+In terms of Li, the lithium source+The metal compound is calculated by metal elements.
In the present invention, there is a wide range of selection of the manner and conditions of the mixing, which may be a means conventionally used in the art, as long as the matrix precursor, the lithium source, and the metal compound are uniformly mixed.
In the present invention, there is a wide range of choices for the first sintering as long as the uniformly mixed matrix precursor, lithium source, and metal compound are converted into a matrix. Preferably, the first sintering is performed in an oxygen-containing atmosphere, wherein the content of oxygen in the oxygen-containing atmosphere is greater than or equal to 99.5 vol%, preferably an oxygen atmosphere. The optimal conditions are adopted, so that the residual lithium LiO on the surface of the matrix is reduced2Contact with water in the air, and further influence the structural stability of the matrix.
In the present invention, there is a wide selection of conditions for the first sintering, and preferably, the first sintering comprises a primary sintering and a secondary sintering, wherein the conditions for the primary sintering comprise: the temperature is 300-600 ℃, preferably 350-550 ℃; the time is 0.5 to 5 hours, preferably 1 to 4 hours; the conditions of the secondary roasting comprise: the temperature is 600-1000 ℃, preferably 650-850 ℃; the time is 8-25h, preferably 10-20 h. The preferred conditions for the first sintering are used to favor the formation of a complete and well-crystallized crystal structure.
According to a preferred embodiment of the invention, after mixing a matrix precursor and a lithium source in a certain molar ratio, the matrix precursor and the lithium source are firstly calcined at 600 ℃ of 300-5 h and then at 1000 ℃ of 600-25 h in an oxygen atmosphere to obtain the matrix.
In the present invention, the CO-containing component is not particularly limited2The atmosphere being CO2An atmosphere having a content of not less than 20% by volume. Preferably, the CO is contained2The atmosphere may be CO2Gas, which may also be CO2Mixed gas of gas and other gases, provided that CO is present2The content is more than or equal to 20 percent by volume.
In the present invention, there is a wide selection range of conditions for the second sintering, including: 80-300 ℃, preferably 150-250 ℃; the time is 0.5-10h, preferably 1-8 h. And the preferable second sintering condition is adopted, so that residual lithium on the surface is effectively converted into a lithium carbonate coating layer, the stability of the positive electrode material in the air is improved, and the sensitivity to moisture is reduced.
According to a preferred embodiment of the invention, the CO is2And sintering the substrate at 80-300 ℃ for 0.5-10h in the atmosphere to obtain the cathode material with the coating layer.
According to a preferred embodiment of the invention, the CO is2And air, wherein CO2The content is more than or equal to 20 percent by volume, and the matrix is sintered for 0.5 to 10 hours at the temperature of 80 to 300 ℃ to obtain the anode material with the coating layer.
In the present invention, the general formula of the substrate, the particle size of the substrate, the thickness of the coating layer, and the weight ratio of the substrate to the coating layer are defined as above, and the detailed description thereof is omitted.
The invention also provides a preparation method of the cathode material.
In the present invention, the positive electrode material has a substrate and a coating layer, and the substrate is made to contain CO2And performing second sintering in the atmosphere to effectively utilize residual lithium on the surface of the substrate, so that the structural stability of the anode material is improved, a certain lithium supplement effect is achieved, the energy density of the battery is improved, and the cycle performance of the material is improved.
The present invention will be described in detail below by way of examples.
The particle size of the matrix is measured by a laser diffraction method;
the thickness of the coating layer was measured by transmission electron microscopy.
The parameters of the positive electrode materials obtained in examples 1 to 9 and comparative examples 1 to 3 are shown in table 1.
Example 1
(1) Ni with a particle size of 10 μm0.8Co0.1Mn0.1(OH)2With LiOH. H2O is in a ratio of 1: 1.05 mol ratio, and performing first sintering in an oxygen atmosphere to obtain a matrix, wherein the conditions of the first sintering comprise: roasting at 450 ℃ for 3h, and then roasting at 780 for 15 h;
(2) placing the matrix in CO2And performing second sintering in gas to obtain a positive electrode material P1, wherein the conditions of the second sintering comprise: sintering at 200 ℃ for 2 h.
As shown in fig. 1, the TEM image of the positive electrode material P1 is shown in fig. 1, and as can be seen from fig. 1, the TEM image of the positive electrode material P1 sequentially shows a substrate (dark color) and a cladding layer (light color) from the lower right corner to the upper left corner, that is: the positive electrode material P1 has a core-shell structure.
The XRD pattern of the positive electrode material P1 is shown in fig. 2, and it can be seen from fig. 2 that the positive electrode material P1 contains LiNi0.8Co0.1Mn0.1O2Diffraction peak, also containing Li2CO3Diffraction peaks.
Example 2
(1) Ni with a particle size of 10 μm0.8Co0.1Mn0.1(OH)2With LiOH. H2O is in a ratio of 1: 1.05 mol ratio, and performing first sintering in an oxygen atmosphere to obtain a matrix, wherein the conditions of the first sintering comprise: roasting at 450 ℃ for 3h, and then roasting at 780 for 15 h;
(2) placing the matrix in CO2And air, wherein CO is2The content was 20 vol%, and a positive electrode material P2 was obtained, wherein the conditions of the second sintering included: sintering at 200 ℃ for 6 h.
Example 3
(1) Ni with a particle size of 10 μm0.8Co0.1Mn0.1(OH)2With LiOH. H2O is in a ratio of 1: 1.08 mixing the components in a molar ratio, and performing first sintering in an oxygen atmosphere to obtain a matrix, wherein the conditions of the first sintering comprise: roasting at 450 ℃ for 3h, and then roasting at 780 for 15 h;
(2) placing the matrix in CO2And air, wherein CO is2The content was 20 vol%, and a positive electrode material P3 was obtained, wherein the conditions for the second sintering were as followsComprises the following steps: sintering at 200 ℃ for 6 h.
Example 4
(1) Ni with a particle size of 10 μm0.6Co0.2Mn0.2(OH)2With LiOH. H2O is in a ratio of 1: 1.05 mol ratio, and performing first sintering in an oxygen atmosphere to obtain a matrix, wherein the conditions of the first sintering comprise: roasting at 450 ℃ for 3h, and then roasting at 780 for 15 h;
(2) placing the matrix in CO2And air, wherein CO is2The content was 50 vol%, and a positive electrode material P4 was obtained, wherein the conditions of the second sintering included: sintering at 150 deg.C for 5 h.
Example 5
(1) Co with a particle size of 5 μm3O4With LiOH. H2O is in a ratio of 1: 3.1 mixing the components in a molar ratio, and performing first sintering in an oxygen atmosphere to obtain a matrix, wherein the conditions of the first sintering comprise: firstly roasting at 450 ℃ for 3h, and then roasting at 950 ℃ for 15 h;
(2) placing the matrix in CO2And air, wherein CO is2The content was 50 vol%, and a positive electrode material P5 was obtained, wherein the conditions of the second sintering included: sintering at 150 deg.C for 5 h.
Example 6
(1) Ni with a particle size of 5 μm0.8Co0.1Mn0.1(OH)2With LiOH. H2O is in a ratio of 1: 1.08 mixing the components in a molar ratio, and performing first sintering in an oxygen atmosphere to obtain a matrix, wherein the conditions of the first sintering comprise: roasting at 450 ℃ for 3h, and then roasting at 780 for 15 h;
(2) placing the matrix in CO2And air, wherein CO is2The content was 20 vol%, and a positive electrode material P6 was obtained, wherein the conditions of the second sintering included: sintering at 200 ℃ for 6 h.
Example 7
The procedure is as in example 1, except that Ni is added0.8Co0.1Mn0.1(OH)2Replacement by Ni0.7Co0.3(OH)2To obtain a positive electrode material P7.
Example 8
The procedure is as in example 1, except that MgO, in which Ni is present, is added in step (1)0.8Co0.1Mn0.1(OH)2：LiOH·H2O: the molar ratio of MgO is 0.98: 1.05: 0.02, a positive electrode material P8 was obtained.
Example 9
The method of example 1 was followed except that the conditions for the first sintering were replaced with: and roasting for 18h at 780 to obtain the cathode material P9.
Comparative example 1
According to the method of example 1, except that the matrix obtained in the step (1) is added into deionized water and stirred for 1 hour, and then the mixture is filtered and dried to obtain the cathode material D1.
Comparative example 2
The procedure of example 1 was repeated, except that the step (2) was omitted and the substrate obtained in the step (1) was used as a positive electrode material D2.
Comparative example 3
The procedure is as in example 1, except that Ni is added0.8Co0.1Mn0.1(OH)2With LiOH. H2Replacing the molar ratio of O by 1: 1, a positive electrode material D3 was obtained.
TABLE 1
Figure BDA0002520693950000131
Note: the molar ratio refers to the molar ratio of the matrix precursor to the lithium source; the particle size refers to the particle size D50 of the matrix; the weight ratio refers to the weight ratio of the substrate to the coating layer.
As can be seen from the data in Table 1, compared with comparative examples 1-3, the positive electrode material prepared by the method provided by the invention has a core-shell structure, namely the positive electrode material comprises a substrate and a coating layer on the surface of the substrate, and the coating layer is Li2CO3。
Test example
The positive electrode materials (P1-P9 and D1-D3) obtained in examples 1-9 and comparative examples 1-3 were subjected to charge and discharge performance tests.
Manufacturing a battery: the anode material, the conductive agent and the binder are mixed according to the mass ratio of 100: 3: 3, taking graphite as a negative electrode, wherein the mass ratio of the active material to the conductive agent to the binder is 100: 2: 3, and the ratio of the capacity of the anode material (graphite) to the capacity of the cathode material is 1.06: 1. the electrolyte adopts 1mol/L LiPF6EC of (1): DEC: DMC cells (QP1-9 and QD1-3) were made with a volume ratio of EC, DEC and DMC of 1: 1: 1, cell design capacity 2800 mAh.
And (3) testing conditions are as follows: during the first charging, the battery with the ternary material as the anode is charged to 4.4V at a constant current and constant voltage of 0.1C rate, discharged to 3V, and then circulated at a rate of 1C between 2.8 and 4.3V. Against LiCoO2If the material is a positive battery, the battery is charged to 4.48V at constant current and constant voltage under 0.1C multiplying power, the battery is discharged to 3V, the subsequent battery cycle is cycled between 2.8V and 4.48V at 1C multiplying power, and the test results are listed in Table 2.
Wherein, the first charge and discharge processes of the battery QP-1 prepared in example 1 and the battery QD-1 prepared in comparative example 1 are shown in FIG. 3.
As can be seen from FIG. 3, the discharge capacity of battery QP-1 is higher than that of battery QD-1 during the first charge. This is because: the cathode material P1 converted the excess lithium source into Li2CO3And Li2CO3The theoretical capacity is 725mAh/g, and the effective capacity which can be actually utilized is about 500 mAh/g. Thus, excess lithium source is converted to Li2CO3And is decomposed during the first constant voltage charge, reaction Li taking place2CO3→2Li++CO2+x1O2+(0.5-x)O2+2e-Effective active lithium is released because of Li2CO3Decomposition product to gaseous CO2No longer able to intercalate lithium, therefore Li2CO3The lithium ion battery can be used as a lithium supplement agent to supplement active lithium provided by a positive electrode consumed for negative electrode SEI generation in the first charging process, and is beneficial to improving the battery capacity and the energy density of the battery. Li2CO3On different base materials, because the base materials have different decomposition catalytic properties to the base materials, the catalyst is used for the decomposition of the base materialsSo that there is a difference in decomposition potential. Current research indicates that Li2CO3The decomposition potential at the nickel-containing anode is slightly lower than that of the other anodes, and thus there is a difference between the charging voltages of different materials.
Among them, the cycle characteristics of QP-1 obtained in example 1, QD-1 obtained in comparative example 1 and QD-2 obtained in comparative example 2 are shown in FIG. 4.
As can be seen from fig. 4, the cycle performance of the battery made of the cathode material provided by the present invention is significantly improved.
TABLE 2
Figure BDA0002520693950000151
As can be seen from the data in table 2, the capacity retention rate of the battery manufactured by using the positive electrode material P1 provided by the present patent after 200 cycles is 95.9%, whereas the capacity retention rate of the battery QD-1 manufactured by using the material in the comparative example D1 after 200 cycles is 94.3%, and the capacity retention rate of the battery QD-2 manufactured by using the material in the comparative example D2 after 200 cycles is 80.9%. The positive electrode material proposed in this patent is due to Li on the surface thereof2CO3Active lithium is decomposed on the surface of the positive electrode and released, and the active lithium can be used for compensating active lithium loss caused by the generation of a graphite SEI film of the negative electrode, so that the cycle performance of the battery can be improved.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims (10)

1. The cathode material is characterized by comprising a substrate and a coating layer on the surface of the substrate, wherein the substrate is of a general formulaLiNixCoyMn1-x-y-zMzO2The compound is shown in the specification, wherein M is a doped metal element, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 0.2, x + y + z is more than or equal to 0 and less than or equal to 1, and x, y and z are not 0 at the same time; the coating layer is Li2CO3。
2. The positive electrode material according to claim 1, wherein the doping metal element is at least one selected from the group consisting of magnesium, iron, titanium, copper, zinc, aluminum, silicon, niobium, vanadium, zirconium, molybdenum, chromium, gallium, and ruthenium.
3. The positive electrode material according to claim 1 or 2, wherein the particle diameter D50 of the matrix is 0.5 to 40 μm.
4. The positive electrode material according to claim 1 or 2, wherein the thickness of the clad layer is 1 to 1000 nm.
5. The positive electrode material according to claim 1 or 2, wherein a weight ratio of the base body to the clad layer is 100: 0.1-10.
6. A preparation method of a positive electrode material is characterized by comprising the following steps:
(1) sequentially mixing and first sintering a matrix precursor, a lithium source and an optional metal compound to obtain a matrix;
(2) carrying out second sintering on the substrate to obtain a positive electrode material with a coating layer;
wherein the second sintering is carried out in the presence of CO2Is carried out in an atmosphere, wherein the CO is contained2In the atmosphere of CO2The content is 20-100 vol%.
7. The method of claim 6, wherein the matrix precursor is of the general formula NixCoyMn1-x-y(OH)2A metal hydroxide and/or of the formula AaObThe metal oxide is shown, wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, x + y is more than or equal to 0 and less than or equal to 1, A is selected from at least one of Ni, Co and Mn, a is selected from an integer of 1-3, and b is selected from an integer of 1-4.
8. The method according to claim 6 or 7, wherein the particle diameter D50 of the matrix precursor is 0.5-45 μm.
9. The method according to claim 6 or 7, wherein the metal compound is selected from compounds containing at least one element selected from the group consisting of magnesium, iron, titanium, copper, zinc, aluminum, silicon, niobium, vanadium, zirconium, molybdenum, chromium, gallium, and ruthenium.
10. Use of the positive electrode material of any one of claims 1 to 5 and/or the positive electrode material produced by the method of any one of claims 6 to 9 in a lithium ion battery.
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