Coated positive electrode material and preparation method thereof, secondary battery and positive electrode, and electrical device

Abstract

This application relates to the technical field of battery electrode materials, specifically to a coated positive electrode material, a preparation method thereof, a battery positive electrode, a secondary battery, and an electrical device. The coated positive electrode material comprises a positive electrode material substrate, a coprecipitated layer located on the surface of the positive electrode material substrate, and a passivation layer located on the surface of the coprecipitated layer. The substrate comprises a doping layer adjacent to the coprecipitated layer, the doping layer having a thickness of ≤50 nm, and the coprecipitated layer comprising a transition metal phosphate and a transition metal oxide. The preparation method of the present application is rapid and efficient, and the resulting coated positive electrode material can be used to prepare secondary batteries, improving the battery's cycle stability and rate performance.

Description

Technical Field

[0001] The present application relates to the technical field of battery electrode materials, and in particular to a coated positive electrode material and a preparation method thereof, a secondary battery and a positive electrode, and an electrical device. Background Art

[0002] Lithium-ion batteries have the advantages of long life, safe use, high temperature resistance, large capacity, no memory effect, small size and light weight. They have been widely used in many fields. In the field of electric vehicles, which is the most widely used, the cycle life performance of the battery is an important indicator for evaluating the performance of batteries and materials. The development of secondary batteries with long cycle performance is also the current development trend.

[0003] Among the existing cathode material systems, ternary materials are widely used due to their high specific energy density and good cycle performance. As the battery is charged and discharged, especially under extreme operating conditions, the cycle performance of the cathode material in the battery will be greatly attenuated. The main factors include: (1) in extreme environments, the drastic shrinkage of the unit cell after delithiation leads to the continuous growth of cracks at the grain boundaries, resulting in the collapse and decay of the crystal structure; (2) the electrode / electrolyte interface reaction leads to the dissolution of the surface metal, causing the surface lattice to restructure and form inactive rock salt phase and spinel phase, which has an adverse effect on the structure and cycle performance of the material.

[0004] In order to improve the stability of battery electrode structure, inhibit the generation of cracks at grain boundaries and reduce the interface reaction between electrode and electrolyte, the metal oxide doping method is usually used to solid-phase dope and coat the materials with inert nano inorganic oxides (such as aluminum oxide, magnesium oxide, titanium oxide and zinc oxide). However, the doping and coating methods of existing large-scale technologies have the following shortcomings: (1) Conventional simple oxide doping can inhibit the shrinkage of unit cells to a certain extent, but cannot inhibit the continuous growth of grain boundary cracks; (2) The nano oxide coating layer of conventional solid-phase process is an insulator, which causes continuous structural degradation and performance attenuation of the interface, thereby reducing the cycle performance and rate performance of the material.

[0005] Application Contents

[0006] Based on this, the purpose of this application includes providing a coated positive electrode material that can be used to prepare secondary battery positive electrodes, secondary batteries and electrical devices, and can effectively improve the cycle performance and rate performance of the prepared batteries.

[0007] The first aspect of the present application provides a coated positive electrode material, comprising a positive electrode material substrate, a coprecipitation layer located on the surface of the positive electrode material substrate, and a passivation layer located on the surface of the coprecipitation layer;

[0008] wherein the substrate comprises a doping layer adjacent to the coprecipitate, and the thickness of the doping layer is ≤50 nm;

[0009] The components of the coprecipitation layer include transition metal phosphate and transition metal oxide.

[0010] In some embodiments of the present application, in the coated positive electrode material, components of the doping layer include the transition metal phosphate and the transition metal oxide.

[0011] In some embodiments of the present application, in the coated positive electrode material, the doping layer has a micro-support structure.

[0012] In some embodiments of the present application, in the coated positive electrode material, the passivation layer has a porous structure.

[0013] In some embodiments of the present application, in the coated positive electrode material, the transition metal phosphate is M1 a N1 b (PO4)3, wherein M1 and N1 are different and independently selected from Ni, Co, Mn, Zr, Bi, Zn, La, Al, Ti, Ge, W or Sr, 0≤a<10, 0≤b<10, a and b are not 0 at the same time;

[0014] The transition metal oxide is M2 c N2 d O2, M2 and N2 are different and independently selected from Ni, Co, Mn, Zr, Bi, Zn, La, Al, Ti, Ge, W or Sr, 0≤c<10, 0≤d<10, c and d are not 0 at the same time.

[0015] In some embodiments of the present application, the coated positive electrode material has one or more of the following characteristics:

[0016] (1) M1 and N1 are different and independently selected from Al, Ge, W, Sr, Zr or Ti;

[0017] (2) M2 and N2 are different and independently selected from Al, Ge, W, Sr, Zr or Ti;

[0018] (3)0≤a<3, 0≤b<4, 0≤c<3, 0≤d<4.

[0019] In some embodiments of the present application, the material of the passivation layer is compound C m N n , where 0<m<5, 0<n<5, and m and n are integers.

[0020] In some embodiments of the present application, the coated positive electrode material has at least one of the following characteristics:

[0021] (1) In the XRD spectrum of the coated positive electrode material, the diffraction peak intensity ratio between the (003) plane and the (104) plane is 003 / I 104 Satisfy 1.40<I 003 / I 104 ≤1.60;

[0022] (2) The lattice parameter c of the coated positive electrode material satisfies the following relationship:

[0023] The second aspect of the present application provides a method for preparing a coated positive electrode material, comprising the following steps:

[0024] S100: Mixing the precursor, phosphate and water, and adjusting the pH to 4-7 to prepare a base solution;

[0025] S200: adding a transition metal salt solution to the base solution, causing metal cations in the transition metal salt solution to react with at least two anions in the base solution to form a co-precipitate that is coated on the precursor to produce a first coating material;

[0026] S300: mixing the first coating material and lithium salt, and performing a first calcination to obtain a first calcined material;

[0027] S400: mixing the first calcined material, a carbon source, and a nitrogen source, and performing a second calcination to obtain a coated positive electrode material;

[0028] The coated positive electrode material comprises a positive electrode material matrix, a coprecipitation layer located on the surface of the positive electrode material matrix, and a passivation layer located on the surface of the coprecipitation layer;

[0029] Wherein, the substrate includes a doping layer adjacent to the co-precipitated layer, and the thickness of the doping layer is ≤50nm;

[0030] The components of the coprecipitation layer include transition metal phosphate and transition metal oxide.

[0031] In some embodiments of the present application, in the preparation method, in step S300:

[0032] Part of the co-precipitated constituent elements of the first coating material penetrate from the surface to the core to obtain a first calcined material.

[0033] In some embodiments of the present application, the preparation method has one or more of the following characteristics:

[0034] (1) The particle size of the precursor is 4 μm to 15 μm;

[0035] (2) The first calcination conditions include: calcination in an oxygen or air atmosphere at 500°C to 1000°C;

[0036] (3) The second calcination conditions include: calcination in a protective gas atmosphere at 200° C. to 800° C.;

[0037] (4) The speed of adding the metal salt solution to the base liquid is 0.4 mL / min to 0.6 mL / min.

[0038] In some embodiments of the present application, in the preparation method, the transition metal salt solution includes a first metal salt and a second metal salt; the first metal salt includes metals M1 and N1; the second metal salt includes metals M2 and N2; wherein M1, M2, N1 and N2 are as defined in the first aspect of the present application;

[0039] The step S200 includes: dissolving the first metal salt in a solvent to prepare a first metal salt solution; adding the first metal salt solution to the base liquid, whereby metal cations in the first metal salt solution react with phosphates in the base liquid to obtain a first precipitate;

[0040] dissolving the second metal salt in a solvent to prepare a second metal salt solution; adjusting the pH to 8 to 12 with an alkaline solution, adding the second metal salt solution, and reacting the metal cations in the second metal salt solution with the hydroxide in the base solution to obtain a second precipitate;

[0041] The first precipitate and the second precipitate form a co-precipitate, which is in situ coated on the precursor to obtain a first coating material.

[0042] In some embodiments of the present application, the preparation method has one or more of the following characteristics:

[0043] (1) The mass ratio of the precursor, the first metal salt and the second metal salt is 1:(0.001-0.05):(0.001-0.05);

[0044] (2) the concentration of metal cations in the first metal salt solution is 0.001 to 0.1 mol / L, the concentration of metal cations in the second metal salt solution is 0.001 to 0.1 mol / L, and the total concentration of metal cations in the first metal salt solution and the second metal salt solution is 0.001 to 0.02 mol / L;

[0045] (3) The concentration of phosphate in the base solution is 0.005 mol / L to 0.5 mol / L;

[0046] (4) The mass ratio of the precursor to the alkaline solution is 1:(1-50), and the concentration of the alkaline solution is 0.1 mol / L-10 mol / L.

[0047] In some embodiments of the present application, in the preparation method, in step S400:

[0048] The first calcined material, the carbon source and the nitrogen source are mixed and subjected to a second calcination to form a porous passivation layer on the first coating material to prepare a coated positive electrode material.

[0049] In some embodiments of the present application, in the preparation method, the mass ratio of the first coating material, the carbon source and the nitrogen source is 1:(0.001-0.01):(0.0013-0.02).

[0050] In some embodiments of the present application, the preparation method has one or more of the following characteristics:

[0051] (1) The phosphate is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate and potassium dihydrogen phosphate;

[0052] (2) The lithium salt is one or more of lithium carbonate, lithium hydroxide and lithium acetate;

[0053] (3) The carbon and nitrogen source is one or more of urea, uric acid and hydrazine hydrate.

[0054] The third aspect of the present application provides a battery positive electrode, the active material of which is the coated positive electrode material provided in the first aspect of the present application, or the coated positive electrode material prepared by the preparation method provided in the second aspect of the present application.

[0055] The fourth aspect of the present application provides a secondary battery, comprising the battery positive electrode provided by the third aspect of the present application.

[0056] The fifth aspect of the present application provides an electrical device, comprising the secondary battery provided in the fourth aspect of the present application.

[0057] The coated positive electrode material of the present application includes a positive electrode material substrate, a coprecipitated layer located on the surface of the positive electrode material substrate, and a passivation layer located on the surface of the coprecipitated layer. The substrate includes a doping layer adjacent to the coprecipitated layer. The doping layer is a derivative structure formed by the penetration of components of the coprecipitated layer into the surface of the positive electrode material substrate. It has micro-regions with an olivine structure and can form a skeletal support to inhibit the generation and growth of cracks at the grain boundaries caused by unit cell shrinkage after delithiation. It can also inhibit the lattice distortion caused by the migration of metal ions and oxygen ions during the cycle process and suppress the formation of surface rock salt phase and spinel phase hybrid phases. The lithium ion conductivity of the passivation layer of the coated positive electrode material is much higher than that of the conventional inorganic oxide coating which is close to the insulating state, thereby improving the cycle and rate performance of the material. When used as a positive electrode material for lithium-ion batteries, on the one hand, it can form an effective and stable electrode / electrolyte interface, reduce corrosion and structural damage at the material interface, reduce DCR growth, and improve the cycle and rate performance of the material. On the other hand, the passivation layer has a porous structure, good compatibility with the electrolyte, increases the wettability of the electrode, and can remain intact during the electrode rolling process.

[0058] The preparation method of the present application is to first form a coating structure and then introduce lithium salt for calcination. A co-precipitation layer is first formed on the precursor by a suitable method, and then calcined (primary calcination) by adding lithium salt to introduce lithium element into the core and react with the precursor to form a positive electrode material matrix. During the calcination process, all or part of the constituent elements of the co-precipitation layer penetrate into the core to achieve shallow surface doping and form an olivine structure micro-region. Then, the first calcined material, carbon source and nitrogen source are calcined (secondary calcination) to form a porous passivation layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. It should also be noted that the drawings are all drawn in a simplified form and are only used to assist in explaining the present invention conveniently and clearly. The various dimensions of each component shown in the drawings are arbitrarily shown and may be accurate or not drawn according to the actual scale. For example, in order to make the illustration clearer, the dimensions of the components are appropriately exaggerated in some places in the drawings. Unless otherwise specified, the components in the figures are not drawn to scale. The present invention does not limit every dimension of each component.

[0060] In the following description, the same reference numerals denote the same parts.

[0061] Figure 1 Schematic diagram of the structure of the coated positive electrode material prepared in one embodiment of the present application ( Figure 1 A) and local schematic diagram ( Figure 1 Middle B);

[0062] Figure 2 This is a scanning electron microscope image (SEM image) of the coated positive electrode material prepared in Example 1 of the present application;

[0063] Figure 3 X-ray diffraction patterns (XRD patterns) of the coated positive electrode materials prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 of the present application;

[0064] Figure 4 A comparison chart of cycle tests of batteries prepared with the coated positive electrode materials prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 of the present application;

[0065] Explanation of reference numerals: 100 positive electrode material matrix; 110 positive electrode material matrix core; 120 doping layer; 200 outer coating layer; 210 coprecipitation layer; 220 passivation layer. DETAILED DESCRIPTION

[0066] The present application will be further described below in conjunction with the embodiments, examples and accompanying drawings. It should be understood that these examples are intended only to illustrate the present application and are not intended to limit the scope of the present application. In addition, it should be understood that after reading the content taught in this application, those skilled in the art may make various changes or modifications to the present application, and these equivalent forms also fall within the scope of protection of the claims appended hereto.

[0067] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0068] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0069] In this application, "micro-support structure" refers to the support structure formed by the superficial doping of transition metal phosphate in this application. For example, it can be a transition metal phosphate in the coating layer on the surface of the positive electrode material matrix, which penetrates into the core under the intervention of certain external forces (such as calcination).

[0070] The terms "and / or", "or / and", and "and / or" used herein include any one of two or more related listed items, and also include any and all combinations of the related listed items, wherein the any and all combinations include any combination of two related listed items, any more related listed items, or all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that in this application, the technical solution undoubtedly includes technical solutions connected by "logical AND" and technical solutions connected by "logical OR". For example, "A and / or B" includes three parallel solutions: A, B, and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, the technical solution of all being connected by "logical OR"), and also includes any and all combinations of A, B, C, and D, that is, the combination of any two or any three of A, B, C, and D, and also includes the four-item combination of A, B, C, and D (that is, the technical solution of all being connected by "logical AND").

[0071] Herein, "preferred", "better", "better", etc. are only used to describe implementation methods or examples with better effects. It should be understood that they do not constitute limitations on the scope of protection of this application.

[0072] In this application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0073] In this application, the terms "first", "second", "third", "fourth", "fifth", etc. in "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", "the fifth aspect", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or quantity, nor should they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", "fifth", etc. only serve the purpose of non-exhaustive enumeration and description, and should be understood not to constitute a closed limitation on quantity.

[0074] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0075] In this application, when referring to a numerical interval (i.e., a numerical range), unless otherwise specified, the optional numerical distribution within the above numerical interval is considered continuous and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval refers only to integers within the numerical interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0076] Unless otherwise specified, the temperature parameters in this application allow for both constant temperature treatment and temperature fluctuations within a certain temperature range. It should be understood that the constant temperature treatment allows for temperature fluctuations within the accuracy range of instrument control. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are permitted.

[0077] In this application, weight can be mass units known in the chemical industry, such as μg, mg, g, and kg.

[0078] In this application, unless otherwise specified, the size, particle size, and diameter generally refer to the average value.

[0079] In a first aspect of the present application, a coated positive electrode material is provided, which has a special coating structure, can effectively reduce the dissolution of transition metals, reduce the increase in cycle DCR, and improve the high-temperature storage and cycle performance of the material.

[0080] In some embodiments of the present application, the coated positive electrode material includes a positive electrode material substrate, a coprecipitation layer located on the surface of the positive electrode material substrate, and a passivation layer located on the surface of the coprecipitation layer;

[0081] Wherein, the substrate includes a doping layer adjacent to the co-precipitated layer; preferably, the thickness of the doping layer is ≤50 nm;

[0082] The components of the coprecipitation layer include transition metal phosphate and transition metal oxide.

[0083] In some embodiments, the structure of the coated cathode material is as follows Figure 1 As shown in A. Among them, Figure 1 A includes a positive electrode material matrix 100 and an outer coating layer 200. The positive electrode material matrix 100 includes a matrix core 110 and a doping layer 120. The outer coating layer 200 includes a co-precipitation layer 210 and a passivation layer 220. The positive electrode material matrix 100 and the outer coating layer 200 together constitute a coated positive electrode material.

[0084] In some embodiments, the distribution of the micro-support structures in the junction doping layer of the coated positive electrode material is as follows: Figure 1 As shown in B. For example, Figure 1 Middle B includes micro-regions of olivine structure.

[0085] In some embodiments, the doping layer is a derivative structure formed by the penetration of the constituent elements of the coprecipitated layer into the near-surface of the cathode material matrix. Furthermore, the doping layer comprises a transition metal phosphate and a transition metal oxide. The doping layer of the coated cathode material of the present application can effectively inhibit crystal cracking caused by unit cell shrinkage during cycling and prevent lattice distortion caused by the formation of impurity phases such as rock salt phase and spinel phase in the surface sublayer.

[0086] In some embodiments, the doping layer has a micro-support structure. Furthermore, the micro-support structure includes an olivine structure. The characteristics of the olivine structure can refer to lithium iron phosphate, and the structural elements are LiO6 octahedron, MO6 octahedron and PO4 tetrahedron. Lithium iron phosphate has a stable structure and can improve the cycle performance of the electrode when used as a positive electrode material. However, the electronic conductivity and ionic conductivity of lithium iron phosphate are low, resulting in poor rate performance of the battery. The doping layer of the coated electrode material of the present application has a micro-support structure, which can play a stabilizing role without affecting the conductivity of the material.

[0087] Furthermore, the (total) thickness of the doping layer is preferably 5 to 50 nm. If the thickness of the doping layer is less than 5 nm, it is possible that the doping layer cannot effectively play the function of isolating the electrode and the electrolyte interface reaction. If the thickness of the doping layer exceeds 50 nm, it will cause the material to have an unstable phase interface, and the capacity is not conducive to achieving the optimal electrochemical performance of the material. For example, the thickness of the doping layer can be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, and other point values ​​within the above numerical range can be selected, which will not be repeated here.

[0088] In some embodiments, the transition metal phosphate is M1 a N1 b (PO4)3, wherein M1 and N1 are different and independently selected from Ni, Co, Mn, Zr, Bi, Zn, La, Al, Ti, Ge, W or Sr, 0≤a<10, 0≤b<10, a and b are not 0 at the same time.

[0089] In some embodiments, M1 and N1 are different and independently selected from Al, Ge, W, Sr, Zr, or Ti.

[0090] In some embodiments, the transition metal oxide is M2 c N2 dO2, M2 and N2 are different and independently selected from Ni, Co, Mn, Zr, Bi, Zn, La, Al, Ti, Ge, W or Sr, 0≤c<10, 0≤d<10, c and d are not 0 at the same time.

[0091] In some embodiments, M2 and N2 are different and independently selected from Al, Ge, W, Sr, Zr, or Ti.

[0092] In some embodiments, 0≤a<3, 0≤b<4, 0≤c<3, 0≤d<4.

[0093] In some embodiments, the passivation layer has a porous structure. The passivation layer of the coated cathode material of the present application can inhibit electrode / electrolyte interface contact, reduce lattice defects caused by transition metal dissolution, reduce the increase in cycle DCR, and improve the high-temperature storage and cycling performance of the material.

[0094] In some embodiments, the material of the passivation layer is compound C m N n , wherein 0<m<5, 0<n<5, m and n are integers. Further, 1<m<4, 2<n<5.

[0095] Preferably, M1 is Al, N1 is selected from Ge, Ga or Ce, M1 and M2 are the same, N1 and N2 are the same, x is 0.6, y is 0.1, a is 1, b is 1, c is 0.3, d is 0.3, m is 3, and n is 4. This is beneficial for enhancing the bonding between the layers, providing a highly stable structural support, suppressing surface structural distortion, and improving the stability of the battery.

[0096] In some embodiments, in the XRD pattern of the coated positive electrode material, the diffraction peak intensity ratio between the (003) plane and the (104) plane is 003 / I 104 Satisfy 1.40<I 003 / I 104 ≤1.60.

[0097] In some embodiments, the lattice parameter c of the coated positive electrode material satisfies the following relationship:

[0098] In the second aspect of the present application, a method for preparing a coated positive electrode material is provided. The preparation method of the present application is different from the traditional technology. It first forms a coating structure and then introduces a lithium salt for calcination. Specifically, a coprecipitation layer is first formed on the precursor by a suitable method, and then a lithium salt is added for calcination (primary calcination). During the calcination process, the lithium element penetrates through the surface layer into the core, reacts with the precursor to form lithium nickel cobalt manganese oxide, and also reacts with some or all of the components of the coprecipitation layer to generate transition metal phosphates and transition metal oxides. In addition, some of the constituent elements of the coprecipitation penetrate from the surface to the core, forming a micro-support structure on the shallow surface of the positive electrode material matrix; then a carbon source and a nitrogen source are added and mixed and calcined (secondary calcination) to form a porous passivation layer on the first calcined material.

[0099] The preparation method of the second aspect of the present application can be used to prepare the coated positive electrode material of the first aspect of the present application, effectively improving the stability and rate performance of the material.

[0100] In some embodiments of the present application, the method for preparing the coated positive electrode material comprises the following steps:

[0101] S100: Mixing the precursor, phosphate and water, and adjusting the pH to 4-7 to prepare a base solution;

[0102] S200: adding a transition metal salt solution to the base solution, causing metal cations in the transition metal salt solution to react with at least two anions in the base solution to form a co-precipitate that is coated on the precursor to obtain a first coating material;

[0103] S300: mixing a first coating material and a lithium salt, and performing a first calcination to obtain a first calcined material;

[0104] S400: mixing the first calcined material, the carbon source and the carbon source, and performing a second calcination to obtain a coated positive electrode material; the coated positive electrode material includes a positive electrode material substrate, a coprecipitation layer located on the surface of the positive electrode material substrate, and a passivation layer located on the surface of the coprecipitation layer;

[0105] wherein the substrate includes a doping layer adjacent to the coprecipitated layer, and the thickness of the doping layer is ≤50 nm;

[0106] The components of the coprecipitation layer include transition metal phosphate and transition metal oxide.

[0107] In some embodiments, the precursor in step S100 is a ternary metal hydroxide (such as nickel cobalt manganese hydroxide). In step S200, the anions in the base solution (including phosphate and hydroxide) and the metal cations in the transition metal salt solution (including metal M1, M2, N1 and N2 cations) undergo precipitation reaction to form a coating layer on the surface of the precursor. The composition of the coating layer includes co-precipitation of phosphate and hydroxide. In step S300, in the presence of a lithium salt, the ternary metal hydroxide is calcined to convert it into lithium nickel cobalt manganese oxide, the hydroxide in the coating layer is converted into the corresponding oxide, and the components of the coating layer partially penetrate into the core to form a doping layer. In step S300, a carbon source and a nitrogen source are added for calcination to form a passivation layer covering the shell.

[0108] In some embodiments, the precursor is a ternary metal hydroxide, further a compound Ni x Co y Mn 1-x-y (OH)2, wherein 0<x<1, 0<y<1.

[0109] The precursor can be prepared according to conventional methods well known to those skilled in the art.

[0110] Illustratively, it can be prepared according to the following method: nickel salt, cobalt salt and manganese salt are dissolved in deionized water and mixed evenly to form a base liquid; under the protection of nitrogen atmosphere and stirring, an alkaline solution is introduced into the base liquid by a peristaltic pump for precipitation; the pH of the base liquid is controlled at 10.0-12.0 by ammonia water; and after precipitation, it is washed with deionized water.

[0111] Optionally, the total molar concentration of the metal salts in the base solution is 0.1 mol / L to 10 mol / L. For example, it can be 0.1 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 6 mol / L, 8 mol / L or 10 mol / L.

[0112] Optionally, the concentration of the alkaline solution is 0.1 mol / L to 10 mol / L. For example, it can be 0.1 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 6 mol / L, 8 mol / L or 10 mol / L.

[0113] Optionally, the precipitation reaction temperature is 20°C to 100°C. For example, the reaction temperature can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 95°C, or 100°C. Furthermore, the reaction time is 0.5h to 30h. For example, the reaction time can be 0.5h, 1h, 2h, 3h, 5h, 10h, 25h, 20h, 25h, or 30h.

[0114] In some embodiments, the particle size of the precursor is 4 μm to 15 μm, and can further be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc.

[0115] In some embodiments, a precursor, phosphate, and water are mixed and the pH is adjusted to 4 to 7 with an acid solution to prepare a base solution. Furthermore, the acid solution can be selected from an acetic acid solution, and further, the concentration of the acetic acid can be 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 5 mol / L, etc.

[0116] In some embodiments, the phosphate is a soluble phosphate. Further, the soluble phosphate is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, and the like.

[0117] In some embodiments, the concentration of phosphate in the base solution is 0.005 mol / L to 0.5 mol / L.

[0118] In some embodiments, the mass ratio of the precursor to the phosphate is 1:(0.001-0.1).

[0119] In some embodiments of the present application, in step S200, a transition metal salt solution is added to the base liquid, and the metal cations in the transition metal salt solution react with at least two anions in the base liquid to form a co-precipitate and coat the precursor to obtain a first coating material.

[0120] Furthermore, the transition metal salt solution comprises metals M1, M2, N1, and N2, wherein M1, M2, N1, and N2 are as defined in the first aspect of the present application. Furthermore, the total molar concentration of M1 and N1 is 0.001 to 0.1 mol / L, and the total molar concentration of M2 and N2 is 0.001 to 0.1 mol / L.

[0121] In some embodiments, the transition metal salt solution includes a first metal salt and a second metal salt; the first metal salt includes metals M1 and N1; and the second metal salt includes metals M2 and N2.

[0122] In some embodiments, the mass ratio of the precursor, the first metal salt, and the second metal salt is 1:(0.001-0.05):(0.001-0.05).

[0123] In some embodiments, step S200 includes the following sub-steps:

[0124] S210: dissolving a first metal salt in a solvent to obtain a first metal salt solution; adding the first metal salt solution to the base solution, causing metal cations in the first metal salt solution to react with phosphates in the base solution to obtain a first precipitate;

[0125] S220: dissolving a second metal salt in a solvent to prepare a second metal salt solution; adjusting the pH to 8 to 12 with an alkaline solution, adding the second metal salt solution, and reacting the metal cations in the second metal salt solution with the hydroxide in the base solution to obtain a second precipitate;

[0126] S230: The first precipitate and the second precipitate form a co-precipitate, which is in situ coated on the precursor to obtain a first coating material.

[0127] In some embodiments, in step S210, the speed of adding the first metal salt solution to the base solution is 0.4 mL / min to 0.6 mL / min.

[0128] Furthermore, the addition method can be a method well known to those skilled in the art, such as adding by a constant speed peristaltic pump to effectively control the speed at which the metal elements are introduced into the base liquid to ensure that the thickness of the coating layer (phosphoric acid coating layer) is appropriate.

[0129] For example, the addition rate may be 0.4 mL / min, 0.45 mL / min, 0.5 mL / min, 0.55 mL / min, or 0.6 mL / min.

[0130] In some embodiments, the concentration of the metal cations in the first metal salt solution is 0.001 to 0.1 mol / L, and more specifically, the total molar concentration of M1 and N1 is 0.001 to 0.1 mol / L.

[0131] In some embodiments, the concentration of the metal cations in the second metal salt solution is 0.001 to 0.1 mol / L, and further, specifically, the total molar concentration of M2 and N2 is 0.001 to 0.1 mol / L.

[0132] Furthermore, the total concentration of metal cations in the first metal salt solution and the second metal salt solution is 0.001 to 0.02 mol / L.

[0133] In some embodiments, the mass ratio of the precursor to the alkaline solution is 1:(1-50), and further, the concentration of the alkaline solution is 0.1 mol / L to 10 mol / L. In some embodiments, the alkaline solution is aqueous ammonia, and further, the concentration of the aqueous ammonia can be 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 5 mol / L, etc.

[0134] In some embodiments, in step S220, the speed of adding the second metal salt solution is 0.4 mL / min to 0.6 mL / min.

[0135] Furthermore, the addition method can be a method well known to those skilled in the art, such as adding by a constant speed peristaltic pump to effectively control the speed at which the metal elements are introduced into the base liquid to ensure that the thickness of the coating layer (oxide coating layer) is appropriate.

[0136] For example, the addition rate can be 0.4 mL / min, 0.45 mL / min, 0.5 mL / min, 0.55 mL / min or 0.6 mL / min, etc. Other point values ​​within the above numerical range can be selected and will not be described here one by one.

[0137] In the present application, the transition metal salt solution (the first metal salt solution, the second metal salt solution) can be prepared according to conventional methods well known to those skilled in the art, and a soluble salt containing a metal element can be dissolved in water.

[0138] For example, M1 salt and N1 salt can be added to the aqueous solution in sequence. After they are completely dissolved, they are allowed to stand for 12 to 20 hours to ensure that the metal elements are evenly dispersed in the aqueous solution.

[0139] In the present application, the first coating material prepared in step S200 is further dried before the first calcination in step S300. The drying method can be a method well known to those skilled in the art, preferably dried in a rotary evaporator at 80°C for 5 hours.

[0140] In some embodiments, the lithium salt is one or more of lithium carbonate, lithium hydroxide, and lithium acetate. Furthermore, during the first calcination, the ratio of the lithium element in the lithium salt to the total molar number of transition metals in the precursor, i.e., Li / ME, is 1:(1.0-1.1). In some embodiments, the amount of lithium salt added is 0.01 wt% to 50 wt% of the core material.

[0141] In some embodiments of the present application, the temperature of the first calcination is 500-1000° C., further, the time of the first calcination is 5-30 hours, and further, the atmosphere of the first calcination is air or oxygen.

[0142] In some embodiments, the conditions of the first calcination include: calcining at 500° C. to 1000° C. in an oxygen or air atmosphere.

[0143] In some embodiments of the present application, the second calcination temperature is 200-800°C. For example, the calcination temperature can be 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, or 800°C. Furthermore, the second calcination time is 5-30 hours. For example, the calcination time can be 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, or 30 hours. Furthermore, the second calcination atmosphere is an inert atmosphere such as N2 or Ar.

[0144] In some embodiments, the second calcination conditions include: calcining at 200° C. to 800° C. in a protective gas atmosphere.

[0145] In some embodiments, in the XRD spectrum of the coated cathode material prepared by the preparation method of the present application, the diffraction peak intensity ratio between the (003) plane and the (104) plane is 003 / I 104 Satisfy 1.40<I 003 / I 104 ≤1.60.

[0146] In some embodiments, the lattice parameter c of the coated positive electrode material prepared by the preparation method of the present application satisfies the following relationship:

[0147] The third aspect of the present application provides a battery positive electrode, the active material of the battery positive electrode is the coated positive electrode material provided in the first aspect of the present application, or the coated positive electrode material prepared by the preparation method provided in the second aspect of the present application.

[0148] In some embodiments, the doping layer of the coated positive electrode material includes phosphate and oxide. The phosphate and oxide in the doping layer form olivine micro-regions in the shallow surface layer of the core, forming a skeleton support, which inhibits the generation and growth of cracks at the grain boundaries caused by the shrinkage of the unit cell after delithiation. The oxide can also inhibit the lattice distortion caused by the migration of metal ions and oxygen ions during the cycle, and inhibit the formation of surface rock salt phase and spinel phase hybrid phases. The lithium ion conductivity of the nitride passivation layer is much higher than that of the conventional inorganic oxide coating close to the insulating state, which improves the cycle and rate performance of the material. When used as a positive electrode material for lithium-ion batteries, on the one hand, it can form an effective and stable electrode / electrolyte interface, reduce corrosion and structural damage at the material interface, reduce DCR growth, and improve the cycle and rate performance of the material. On the other hand, the passivation layer has a porous structure, good compatibility with the electrolyte, increases the wettability of the electrode, and can remain intact during the electrode rolling process.

[0149] The fourth aspect of the present application provides a secondary battery, comprising the battery positive electrode provided by the third aspect of the present application.

[0150] For example, the secondary battery can be a lithium-ion battery, a lithium-sulfur battery, or a lithium-air battery. Furthermore, the secondary battery is a lithium-ion battery. Optionally, the secondary battery includes an electrolyte, a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet includes a positive electrode active material that can embed or deintercalate lithium ions, a conductive agent, a current collector, and a binder that combines the positive electrode active material and the conductive agent with the current collector; the negative electrode sheet includes a negative electrode active material that can embed or deintercalate lithium ions, a conductive agent, a current collector, and a binder that combines the negative electrode active material and the conductive agent with the current collector. Preferably, the positive electrode active material is the coated positive electrode material provided in the first aspect of the present application, or the coated positive electrode material prepared by the preparation method provided in the second aspect of the present application.

[0151] The fifth aspect of the present application provides an electrical device, comprising the secondary battery provided in the fourth aspect of the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device.

[0152] By way of example, electrical devices may include mobile devices (e.g., mobile phones, laptop computers, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0153] For example, the power-consuming device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0154] The following are some specific examples.

[0155] For experimental parameters not specified in the following specific examples, reference is made to the guidance given in this application document, and reference may also be made to experimental manuals in the art or other experimental methods known in the art, or to the experimental conditions recommended by the manufacturer.

[0156] The raw materials and reagents involved in the following specific examples can be obtained commercially, or can be prepared by those skilled in the art according to known methods.

[0157] 1. Preparation of positive electrode materials

[0158] Example 1

[0159] Prepare the positive electrode material S1 by the following preparation steps:

[0160] (1) 50g of precursor (Ni 0.6 Co 0.1 Mn 0.3(OH)2, particle size of 4 μm), 1 g of phosphate (ammonium dihydrogen phosphate) was added to water (200 mL), the pH was adjusted to 6.5 with acetic acid, the mixture was stirred for 1 h, and the mixture was allowed to stand for 12 h to prepare a base solution.

[0161] (2) providing a first metal salt solution as follows: dissolving 0.1151 g of aluminum chloride and 0.2784 g of germanium chloride in 20 mL of deionized water, stirring for 1 h to dissolve, and allowing to stand for 12 h;

[0162] A second metal salt solution was provided as follows: 0.1001 g of aluminum chloride and 0.1580 g of germanium chloride were dissolved in 20 mL of deionized water, stirred for 1 h to dissolve, and allowed to stand for 12 h;

[0163] The first metal salt solution was passed into the base liquid at 0.5 mL / min for in-situ coating (first coating) to obtain the first coating material. The pH was adjusted to 8.5 with ammonia water, and then the second metal salt solution was continued to be passed into the base liquid at 0.5 mL / min (second coating) to obtain the second coating material (solid).

[0164] (3) The obtained solid was dried (80°C, 8h), added with lithium salt mixture (mixed lithium carbonate, Li / ME=1.05), and calcined at 940°C in an oxygen atmosphere for 15h (primary sintering) to obtain a single-fired material.

[0165] (4) 20 g of the calcined material and 0.2 g of urea were mixed and calcined at 480 °C for 12 h in an Ar atmosphere.

[0166] Example 2

[0167] The positive electrode material S2 was prepared by a method substantially the same as that of Example 1-1, except that:

[0168] In step (2), a first metal salt solution is provided as follows: 0.1151 g of aluminum chloride and 0.2784 g of gallium acetate are dissolved in 20 mL of deionized water, stirred for 1 h to dissolve, and allowed to stand for 12 h;

[0169] The second metal salt solution was provided as follows: 0.1001 g of aluminum sulfate and 0.1580 g of gallium chloride were dissolved in 20 mL of deionized water, stirred for 1 hour to dissolve, and allowed to stand for 12 hours.

[0170] Example 3

[0171] The positive electrode material S3 was prepared by a method substantially the same as that of Example 1-1, except that:

[0172] In step (2), a first metal salt solution is provided as follows: 0.1151 g of aluminum nitrate and 0.2784 g of cerium chloride are dissolved in 20 mL of deionized water, stirred for 1 h to dissolve, and allowed to stand for 12 h;

[0173] The second metal salt solution was provided as follows: 0.1001 g of aluminum nitrate and 0.1580 g of cerium chloride were dissolved in 20 mL of deionized water, stirred for 1 hour to dissolve, and allowed to stand for 12 hours.

[0174] Comparative Example 1

[0175] Prepare the positive electrode material D1 by the following preparation steps:

[0176] Provide precursor (Ni 0.6 Co 0.1 Mn 0.3 (OH)2, particle size 4 μm); the precursor and lithium hydroxide were mixed at a Li / (Ni+Mn+Co) molar ratio of 1.04, and calcined at 940°C for 15 hours in an oxygen atmosphere to prepare a calcined material. The calcined material was calcined at 450°C for 15 hours in an Ar atmosphere.

[0177] Comparative Example 2

[0178] Prepare the positive electrode material D2 by the following preparation steps:

[0179] (1) The precursor (Ni 0.6 Co 0.1 Mn 0.3 (OH)2, particle size of 4 μm) and lithium hydroxide are mixed in a Li / (Ni+Mn+Co) molar ratio of 1.04, and calcined at 940°C for 15 h in an oxygen atmosphere to obtain a fired material.

[0180] (2) 2.5 kg of the calcined material and 8 g of nano-alumina were mixed and calcined at 450 °C in an air atmosphere for 15 h.

[0181] Comparative Example 3

[0182] The positive electrode material D3 was prepared by the following preparation steps:

[0183] (1) The precursor (Ni 0.6 Co 0.1 Mn 0.3 (OH)2, particle size of 4 μm) and lithium carbonate are mixed in a Li / (Ni+Mn+Co) molar ratio of 1.04, and calcined at 930°C for 15 h in an oxygen atmosphere to obtain a fired material.

[0184] (2) 2.5 kg of the calcined material and 10 g of nano-gallium oxide were mixed and calcined at 450° C. in an air atmosphere for 15 h.

[0185] Comparative Example 4

[0186] The positive electrode material D4 was prepared by the following preparation steps:

[0187] (1) The precursor (Ni 0.6 Co 0.1 Mn 0.3 (OH)2, particle size of 4 μm) and lithium carbonate are mixed in a Li / (Ni+Mn+Co) molar ratio of 1.04, and calcined at 930°C for 15 h in an oxygen atmosphere to obtain a fired material.

[0188] (2) 2.5 kg of the calcined material, 10 g of nano-germanium oxide and 12 g of aluminum oxide were mixed and calcined at 450° C. in an air atmosphere for 15 h.

[0189] 2. Scanning electron microscopy (SEM) observations and results

[0190] The morphology of the cathode material obtained in Example 1 was characterized using a scanning electron microscope. Figure 2 As shown, it can be seen that there is an obvious coating layer structure on the surface of the material, and the overall coating effect of C3N4 is good.

[0191] 3. Performance test of cathode materials

[0192] The positive electrode materials prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 of the present application were respectively subjected to performance tests.

[0193] The test parameters are: 2.8-4.4V voltage, 0.5C / 1C rate.

[0194] The test method is: using an X-ray diffraction instrument (Bruker D8, scanning range 10-80°, scanning speed: 2° / min), the X-ray diffraction patterns (XRD patterns) of the positive electrode materials prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 after different numbers of cycles are measured.

[0195] Figure 3 The XRD comparison diagram after 50 cycles is shown in Figure 2. Figure 3 It can be seen that no impurity peak appears after 50 cycles of the samples prepared according to the methods of Examples 1-2 and Comparative Examples 1-2, indicating that the phosphate and oxide doping of Al and Ge and the C3N4 coating do not change the crystal structure of the material. At the same time, the structure of the material has good stability and no structural abnormality occurs.

[0196] Table 1 shows the XRD refinement results of the materials obtained in Examples 1-2 and Comparative Examples 1-4.

[0197] According to Table 1, the doped materials (Example 1, Example 2) 003 / I 104 The value is 1.562 / 1.568, which is significantly higher than that of the unmodified sample (Comparative Example 1, I 003 / I104 Value is 1.405) or samples modified by conventional method (Comparative Example 2, I 003 / I 104 The value is 1.457). The Li / Ni mixing of the sample is reduced after surface phosphate and oxide doping. After Al and Ge doping, the metal vacancies in the lattice are filled to form a strong skeleton effect, which inhibits the formation of NiO rock salt phase and further inhibits Li / Ni mixing.

[0198] According to Table 1, it can be found that after 50 cycles at a voltage of 2.8V to 4.4V and a rate of 0.5C / 1C, the I 003 / 104 The value is greater than that of comparative examples 1 to 4, the unit cell parameters c, a, c / a and unit cell volume values ​​are increased, and the unit cell volume is increased, which is beneficial to Li + Diffusion in the bulk phase can reduce the cycle DCR. This is based on the substitution of Al and Ge for transition metal vacancies, and their bond energy is higher than that of Ni / Co / Mn and O elements, which is conducive to enhancing the stability of the layered structure and inhibiting the formation of rock salt phase. On the other hand, the coating can stabilize the electrode / electrolyte interface and inhibit Ni 4+ The reaction with the electrolyte alleviates the corrosion of HF in the electrolyte on the positive electrode material and inhibits the formation of oxygen vacancies.

[0199] Table 1 XRD refinement data of samples of Examples 1 to 2 and Comparative Examples 1 to 4

[0200]

[0201]

[0202] 4. Battery performance test made of positive electrode materials

[0203] The positive electrode materials prepared in each embodiment and comparative example were subjected to cycle and rate tests at 25°C and 45°C. The test methods are as follows:

[0204] The positive electrode materials were assembled into button cells, wherein the electrode material: conductive carbon black = 90:10 wt%, the solvent was NMP, and the battery electrode surface density was 1.8 mg / cm 2 , at a voltage of 2.8-4.4V and 25°C, after charging and discharging for one cycle at a rate of 0.1C / 0.1C, then charging and discharging at rates of 0.5C / 0.1C, 0.5C / 0.2C, 0.5C / 0.5C, and 0.5C / 1C, and then at a rate of 0.5C / 1C at 25°C and 45°C for 50 cycles, the test results are shown in Table 2 below:

[0205] Table 2

[0206]

[0207] As can be seen from the data in the table above, compared with the comparative example, the electrochemical performance of the material is improved after phosphate and oxide doping and C3N4 coating. The positive electrode material (coated positive electrode material) provided by this application has a charge and discharge capacity that is about 2 to 5 mAh / g higher than that of the comparative example, and the rate performance is also significantly improved. The cycle performance and rate performance of the coated modified positive electrode material at 45°C are significantly improved (as shown in Tables 2 and Figure 4 , which shows that the coated positive electrode material prepared by the preparation method of the embodiment of the present application has a core-shell structure coating layer that can form an effective and stable interface layer, reducing the interface reaction of the electrode / electrolyte. At the same time, the coating layer has high lithium ion conductivity and lithium ion storage function, which significantly improves the initial discharge capacity and rate performance of the material.

[0208] In summary, the coated positive electrode material prepared in the present application is used as a positive electrode material for lithium-ion batteries. The core-shell structured phosphate / hydroxide co-precipitation grown in situ on the surface of the precursor realizes shallow doping of phosphate and oxide after sintering, inhibiting the crystal cracks caused by unit cell shrinkage during the cycle and preventing the lattice distortion caused by the formation of impurities such as rock salt phase and spinel phase in the surface sublayer; and further nitride coating inhibits the electrode / electrolyte interface contact, reduces the lattice defects caused by transition metal dissolution, reduces the increase in cycle DCR, and improves the high-temperature storage and cycle performance of the material.

[0209] All documents mentioned in this application are cited as references in this application, just as each document is cited as reference separately. Unless they conflict with the application purpose and / or technical solution of this application, the cited documents involved in this application are cited in their entirety and for all purposes. When cited documents are involved in this application, the definitions of relevant technical features, terms, nouns, phrases, etc. in the cited documents are also cited. When cited documents are involved in this application, the examples and preferred embodiments of the cited relevant technical features may also be incorporated into this application as references, but are limited to the ability to implement this application. It should be understood that when the cited content conflicts with the description in this application, the present application shall prevail or be adaptively amended according to the description in this application.

[0210] The various technical features of the above-mentioned implementation modes and examples can be combined in any appropriate manner. In order to make the description concise, not all possible combinations of the various technical features in the above-mentioned implementation modes and examples are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the description in this specification.

[0211] The embodiments described above only express several implementation methods of the present application, but they should not be understood as limiting the scope of the patent application. It should be pointed out that, for those of ordinary skill in the art, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. In addition, it should be understood that after reading the above-mentioned teaching content of the present application, those skilled in the art can make various changes or modifications to the present application, and the equivalent forms obtained also fall within the scope of protection of the present application. It should also be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the scope of protection of the claims attached to the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims, and the description and drawings may be used to explain the contents of the claims.

Claims

1. A coated positive electrode material, characterized in that: It comprises a positive electrode material matrix, a coprecipitation layer located on the surface of the positive electrode material matrix, and a passivation layer located on the surface of the coprecipitation layer; Wherein, the substrate includes a doping layer adjacent to the co-precipitated layer, and the thickness of the doping layer is ≤50nm; The components of the coprecipitation layer include transition metal phosphate and transition metal oxide; the molecular formula of the transition metal phosphate is M1 a N1 b (PO4)3, wherein M1 and N1 are different and independently selected from aluminum, germanium, gallium or cerium; 0≤a<3, 0≤b<4, a and b are not both 0; the molecular formula of the transition metal oxide is M2 c N2 d O2, M2 and N2 are different and independently selected from aluminum, germanium, gallium or cerium; 0≤c<3, 0≤d<4, c and d are not 0 at the same time; The doping layer is a derivative structure formed by the components of the coprecipitation layer penetrating into the surface of the positive electrode material matrix; the doping layer has a micro-support structure; In the XRD spectrum of the coated positive electrode material, the diffraction peak intensity ratio between the (003) plane and the (104) plane is 003 / I 104 Satisfy 1.40<I 003 / I 104 ≤1.60; The lattice parameter c of the coated positive electrode material satisfies the following relationship:

2. The coated positive electrode material according to claim 1, characterized in that: The doping layer comprises the transition metal phosphate and the transition metal oxide.

3. The coated positive electrode material according to claim 1, characterized in that: The passivation layer has a porous structure.

4. The coated positive electrode material according to any one of claims 1 to 3, characterized in that: The material of the passivation layer is compound C m N n , where 0<m<5, 0<n<5, and m and n are integers.

5. A method for preparing the coated positive electrode material according to any one of claims 1 to 4, characterized in that: The steps include: S100: Mixing the precursor, phosphate and water, and adjusting the pH to 4-7 to prepare a base solution; S200: adding a transition metal salt solution to the base solution, causing metal cations in the transition metal salt solution to react with at least two anions in the base solution to form a co-precipitate that is coated on the precursor to produce a first coating material; S300: mixing the first coating material and lithium salt, and performing a first calcination, so that some of the co-precipitated constituent elements of the first coating material penetrate from the surface to the core to obtain a first calcined material; S400: mixing the first calcined material, a carbon source and a nitrogen source, and performing a second calcination to obtain the coated positive electrode material.

6. The preparation method according to claim 5, characterized in that Have one or more of the following characteristics: (1) The particle size of the precursor is 4 μm to 15 μm; (2) The first calcination conditions include: calcination in an oxygen or air atmosphere at 500°C to 1000°C; (3) The second calcination conditions include: calcination in a protective gas atmosphere at 200° C. to 800° C.; (4) The speed of adding the metal salt solution to the base liquid is 0.4 mL / min to 0.6 mL / min.

7. The preparation method according to claim 5 or 6, characterized in that: The transition metal salt solution includes a first metal salt and a second metal salt; the first metal salt includes metals M1 and N1; the second metal salt includes metals M2 and N2; wherein M1, M2, N1 and N2 are as defined in claim 1; The step S200 includes: dissolving the first metal salt in a solvent to prepare a first metal salt solution; adding the first metal salt solution to the base liquid, whereby metal cations in the first metal salt solution react with phosphates in the base liquid to obtain a first precipitate; dissolving the second metal salt in a solvent to prepare a second metal salt solution; adjusting the pH to 8 to 12 with an alkaline solution, adding the second metal salt solution, and reacting the metal cations in the second metal salt solution with the hydroxide in the base solution to obtain a second precipitate; The first precipitate and the second precipitate form a co-precipitate, which is in situ coated on the precursor to obtain a first coating material.

8. The preparation method according to claim 7, characterized in that Have one or more of the following characteristics: (1) The mass ratio of the precursor, the first metal salt and the second metal salt is 1:(0.001-0.05):(0.001-0.05); (2) the concentration of metal cations in the first metal salt solution is 0.001 to 0.1 mol / L, the concentration of metal cations in the second metal salt solution is 0.001 to 0.1 mol / L, and the total concentration of metal cations in the first metal salt solution and the second metal salt solution is 0.001 to 0.02 mol / L; (3) The concentration of phosphate in the base solution is 0.005 mol / L to 0.5 mol / L; (4) The mass ratio of the precursor to the alkaline solution is 1:(1-50), and the concentration of the alkaline solution is 0.1 mol / L-10 mol / L.

9. The preparation method according to claim 5 or 6, characterized in that: In step S400: The first calcined material, the carbon source and the nitrogen source are mixed and subjected to a second calcination to form a porous passivation layer on the first coating material to prepare a coated positive electrode material.

10. The preparation method according to claim 9, characterized in that The mass ratio of the first coating material, the carbon source and the nitrogen source is 1:(0.001-0.01):(0.0013-0.02).

11. The preparation method according to claim 5 or 6, characterized in that: Have one or more of the following characteristics: (1) The phosphate is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate and potassium dihydrogen phosphate; (2) The lithium salt is one or more of lithium carbonate, lithium hydroxide and lithium acetate; (3) The carbon and nitrogen source is one or more of urea, uric acid and hydrazine hydrate.

12. A positive electrode of a battery, characterized in that: The active material of the battery positive electrode is the coated positive electrode material according to any one of claims 1 to 4, or the coated positive electrode material prepared by the preparation method according to any one of claims 5 to 11.

13. A secondary battery, characterized in that: The battery positive electrode according to claim 12 is included.

14. An electrical device, characterized in that: The secondary battery according to claim 13 is included.

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