Composite-coated positive electrode material and preparation method therefor, positive electrode sheet, lithium-ion battery and electric device

Abstract

Provided in the present application are a composite-coated positive electrode material and a preparation method therefor, a positive electrode sheet, a lithium-ion battery and an electric device. The composite-coated positive electrode material comprises an inner core, a first coating layer that coats at least part of the surface of the inner core, and a second coating layer that coats at least part of the surface of the first coating layer, wherein the inner core comprises a lithium nickel manganese oxide; the first coating layer comprises a first coating material, the first coating material comprises one or more of nickel phosphate, manganese phosphate, lithium phosphate, lithium nickel phosphate and lithium manganese phosphate, the first coating material further comprises aluminum, and at least some aluminum atoms occupy nickel sites and / or manganese sites in the crystal structure of the lithium nickel manganese oxide; and the second coating layer comprises a second coating material, and the second coating material comprises lithium phosphate and at least one of lithium metaaluminate and aluminum oxide. The prepared positive electrode material has relatively high capacity and good cycle performance.

Description

Composite-coated positive electrode material, preparation method thereof, positive electrode sheet, lithium ion battery and electric device

[0001] The present application claims priority to the Chinese patent application No. 202411266040.0, filed on September 10, 2024, and titled "Composite-coated positive electrode material, preparation method thereof, positive electrode sheet, lithium ion battery and electric device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of lithium ion batteries, and in particular to a composite-coated positive electrode material, a preparation method thereof, a positive electrode sheet, a lithium ion battery and an electric device. BACKGROUND

[0003] Lithium ion batteries are one of the most widely used rechargeable batteries at present, and are widely used in mobile devices, electric vehicles and energy storage systems, etc. The positive electrode material plays an important role in the performance, safety and cost of lithium ion batteries. The theoretical discharge specific capacity of lithium nickel manganese oxide material with spinel structure can reach 146.7mA·h / g, and it has the advantages of high voltage platform, fast three-dimensional lithium ion diffusion channel, and abundant and relatively cheap, etc., so it becomes one of the most potential high-voltage positive electrode materials.

[0004] However, the lithium nickel manganese oxide material has the problem of poor cycle performance in the application process, which limits its further application. SUMMARY

[0005] Based on this, the present application provides a composite-coated positive electrode material, a preparation method thereof, a positive electrode sheet, a lithium ion battery and an electric device, to improve the cycle performance of the material.

[0006] The first aspect of the present application provides a composite-coated positive electrode material, comprising:

[0007] a core, the core comprising lithium nickel manganese oxide;

[0008] a first coating layer, coated on at least part of the surface of the core, the first coating layer comprising a first coating material, the first coating material comprising one or more of nickel phosphate, manganese phosphate, lithium phosphate, nickel lithium phosphate and manganese lithium phosphate, the first coating material further comprising aluminum elements, at least part of the aluminum elements occupying nickel element sites and / or manganese element sites of the crystal structure of the lithium nickel manganese oxide; and

[0009] a second coating layer, coated on at least part of the surface of the first coating layer, the second coating layer comprising a second coating material, the second coating material comprising (1) lithium phosphate, and (2) at least one of lithium met aluminate and aluminum oxide.

[0010] In some embodiments, the first coating material coats at least part of the surface of the lithium nickel manganese oxide, and the second coating material coats at least part of the surface of the first coating material.

[0011] In some embodiments, the mass ratio of aluminum element and phosphorus element contained in the first coating material is 3-10;

[0012] and / or the total mass of aluminum element and phosphorus element contained in the first coating material accounts for 0.05%-0.5% of the mass of the lithium nickel manganese oxide contained in the core; and / or

[0013] The first coating material further comprises one or more elements selected from Li, S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb and Bi.

[0014] In some embodiments, the total mass of aluminum element and phosphorus element contained in the second coating material accounts for 0.2%-1.5% of the mass of the lithium nickel manganese oxide contained in the core; and / or

[0015] The second coating material further comprises one or more elements selected from Li, S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb and Bi.

[0016] In some embodiments, the chemical formula of the lithium nickel manganese oxide is Li a Ni b Mn c M1dM2 e O 4-f , 0.95≤a≤1.1, 0.45<b<0.55, 1.4<c<1.6, 0≤d+e≤0.1, 0≤f≤0.1, M1 element comprises one or more elements selected from S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F and La, and M2 element comprises one or more elements selected from V, Nb, Mo, W, Ta, B, Sb and Bi.

[0017] In some embodiments, the composite-coated positive electrode material has one or more of the following characteristics (1)-(8):

[0018] (1) the volume average particle size Dv50 of the core is 4 μm-8 μm;

[0019] (2) the specific surface area of the core is 0.3 m 2 / g-0.7 m 2 / g;

[0020] (3) the specific surface area of the composite-coated cathode material is 0.3 m 2 / g-0.8 m 2 / g;

[0021] (4) the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the composite-coated cathode material at 0.33 C charging is > 50 mV;

[0022] (5) the percentage of the capacity of the electrochemical distribution curve of the composite-coated cathode material at 0.33 C charging in the 4.3 V to 3.8 V platform to the total discharge capacity is 5%-9%;

[0023] (6) the discharge capacity of the composite-coated cathode material at 0.33 C is > 130 mAh / g;

[0024] (7) the peak intensity ratio coefficient I 311 2 / (I 400 I 111 )<0.5 in the XRD diffraction pattern of the composite-coated cathode material, wherein I 311 is the diffraction intensity of the crystal face (311) in the XRD diffraction pattern, I 400 is the diffraction intensity of the crystal face (400) in the XRD diffraction pattern, and I 111 is the diffraction intensity of the crystal face (111) in the XRD diffraction pattern;

[0025] (8) the composite-coated cathode material is a single crystal particle and / or a quasi-single crystal particle.

[0026] The second aspect of the present application provides a preparation method of a composite-coated cathode material, comprising the following steps:

[0027] immersing the core in a solution containing a first aluminum source and a first phosphorus source for a preset time, filtering, and performing first calcination treatment on the obtained solid to form a first coating layer on at least part of the surface of the core to prepare an intermediate; or mixing the solution containing the first aluminum source and the first phosphorus source with the core for a preset time, removing the solvent by volatilization, and performing first calcination treatment on the remaining solid to form a first coating layer on at least part of the surface of the core to prepare an intermediate;

[0028] performing second calcination treatment on a mixture containing the intermediate, a second aluminum source, and a second phosphorus source to form a second coating layer on at least part of the surface of the first coating layer to prepare the composite-coated cathode material;

[0029] The inner core comprises lithium nickel manganese oxide; the first coating layer comprises a first coating material, the first coating material comprises one or more of nickel phosphate, manganese phosphate, lithium phosphate, lithium nickel phosphate and lithium manganese phosphate, and the first coating material further comprises aluminum elements, at least part of the aluminum elements occupy nickel element sites and / or manganese element sites of the crystal structure of the lithium nickel manganese oxide; the second coating layer comprises a second coating material, the second coating material comprises (1) lithium phosphate, and (2) at least one of lithium metavanadate and aluminum oxide.

[0030] In some embodiments, the preparation method comprises at least one of the following conditions:

[0031] (1) the first aluminum source comprises one or more of aluminum nitrate and its hydrate, aluminum dihydrogen phosphate and its hydrate, aluminum lactate and its hydrate, aluminum triethoxide, aluminum orthophosphate and aluminum pyrophosphate; optionally one or more of aluminum nitrate and its hydrate and aluminum triethoxide;

[0032] (2) the first phosphorus source comprises one or more of phosphoric acid, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, diphosphorus pentoxide, lithium dihydrogen phosphate, potassium dihydrogen phosphate, manganese dihydrogen phosphate and its hydrate, lithium monohydrogen phosphate, sodium monohydrogen phosphate, potassium monohydrogen phosphate, triethyl phosphate, trimethyl phosphate, aluminum dihydrogen phosphate and pyrophosphate; optionally one or more of phosphoric acid and trimethyl phosphate;

[0033] Optionally, the pyrophosphate comprises one or more of lithium pyrophosphate, sodium pyrophosphate, potassium pyrophosphate and aluminum pyrophosphate;

[0034] (3) the solvent used for preparing the solution comprising the first aluminum source and the first phosphorus source comprises one or more of ethanol, methanol, dimethyl phthalate and water;

[0035] (4) the temperature of the first calcination treatment is 600-900℃, the time is 2-12h, the heating rate is 1-5℃ / min, and the cooling rate is >2℃ / min;

[0036] Optionally, the temperature of the first calcination treatment is 700-800℃, and the time is 6-8h;

[0037] (5) the raw material during the first calcination treatment further comprises a first additive, the first additive and the filtered solid are subjected to the first calcination treatment together, and the first additive comprises one or more of Li, S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb and Bi elements;

[0038] (6) the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the 0.33C charged intermediate is greater than 50 mV;

[0039] (7) the second aluminum source comprises one or more of compounds containing Al-O bonds;

[0040] Optionally, the second aluminum source comprises one or more of aluminum hydroxide, aluminum oxide, lithium metaaluminate and sodium aluminate;

[0041] (8) the second phosphorus source comprises one or more of compounds containing P-O bonds;

[0042] Optionally, the second phosphorus source comprises one or more of lithium phosphate, monohydric lithium phosphate, dihydric lithium phosphate and lithium pyrophosphate;

[0043] (9) the temperature of the second calcination treatment is 200-450℃, the time is 0-12h, and the heating rate is 1-5℃ / min;

[0044] Optionally, the time of the second calcination treatment is 1-12h;

[0045] (10) the mixture subjected to the second calcination treatment further comprises a second additive, and the second additive comprises one or more of Li, S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb and Bi.

[0046] In some embodiments, the chemical formula of the lithium nickel manganese oxide is Li a Ni b Mn c M1 d M2 e O 4-f , 0.95≤a≤1.1, 0.45<b<0.55, 1.4<c<1.6, 0≤d+e≤0.1, 0≤f≤0.1, M1 comprises one or more of S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F and La, and M2 comprises one or more of V, Nb, Mo, W, Ta, B, Sb and Bi.

[0047] In some embodiments, the preparation method of the core comprises:

[0048] mixing the nickel manganese precursor and the lithium salt and then performing a third calcination treatment, or mixing the nickel manganese precursor, the lithium salt and a third additive and then performing a third calcination treatment;

[0049] Optionally, the chemical formula of the nickel manganese precursor is Ni 0.25 Mn 0.75(OH)2, Ni 0.25 Mn 0.75 C2O4 and Ni 0.25 Mn 0.75 one or more of CO3;

[0050] Optionally, the nickel-manganese precursor comprises one or more of nickel-manganese hydroxide, nickel-manganese oxalate and nickel-manganese carbonate, and is optionally nickel-manganese hydroxide.

[0051] Optionally, the third additive comprises one or more of S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb and Bi.

[0052] Optionally, the lithium source comprises one or more of LiOH, Li2CO3, Li2SO4, LiCl and LiNO3, and is optionally one or more of LiOH and Li2CO3.

[0053] Optionally, the molar ratio of the total metal contained in the nickel-manganese precursor to the lithium element contained in the lithium source is 1:(0.5-0.55).

[0054] Optionally, the third calcination treatment has a temperature of 600-1000°C, a time of 5-30h, a temperature rising rate of 1-5°C / min, and an oxygen partial pressure in the calcination atmosphere of ≥10000Pa.

[0055] Optionally, the third calcination treatment has a temperature of 850-950°C and a time of 6-12h.

[0056] Optionally, the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the 0.33C charging of the core is less than 40mV or greater than 50mV.

[0057] The third aspect of the present application provides a positive electrode tab comprising the composite-coated positive electrode material of the first aspect of the present application or prepared by the preparation method of the second aspect of the present application.

[0058] The fourth aspect of the present application provides a lithium ion battery comprising the positive electrode tab of the third aspect of the present application.

[0059] The fifth aspect of the present application provides an electric device comprising the lithium ion battery of the fourth aspect of the present application.

[0060] The composite-coated positive electrode material comprises a composite coating layer composed of a first coating layer and a second coating layer. The first coating layer coating material contains aluminum elements which at least partially occupy the nickel element sites and / or manganese element sites of the crystal structure of the lithium nickel manganese oxide, thereby micro-doping the surface of the lithium nickel manganese oxide and enhancing the surface structure thereof. The phosphate contained in the first coating layer coating material forms a phosphate coating on the surface of the core, which can isolate the electrolyte while ensuring a certain ionic conductivity. The lithium phosphate contained in the second coating layer coating material can absorb acidic substances in the electrolyte, prevent the acidic substances from reacting with the surface of the positive electrode material, and reduce the crosstalk effect between the positive and negative electrode materials. The lithium metahydroxy aluminate and / or aluminum oxide contained in the second coating layer coating material can strongly absorb acidic substances in the electrolyte system. Therefore, the composite-coated positive electrode material provided in the present application effectively improves the capacity and cycle retention rate of the material and greatly reduces the impedance increase in the cycle by using a composite coating layer. BRIEF DESCRIPTION OF DRAWINGS

[0061] In order to more clearly illustrate the technical solutions in the embodiments of the present application, more completely understand the present application and its beneficial effects, the drawings needed to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0062] FIG. 1 is a scanning electron microscope image of the positive electrode material prepared in Example 1.

[0063] FIG. 2 is a scanning electron microscope image of the positive electrode material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0064] In order to facilitate the understanding of the present application, the present application will be more fully described below with reference to relevant embodiments. The following describes the preferred embodiments of the present application. However, the present application can be realized in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments of the present application, and are not intended to limit the present application.

[0066] The selection scope of the terms "and / or", "or / and", "and / or" used in the present application includes any one of two or more relevant listed items, and also includes any and all combinations of the relevant listed items, including any two relevant listed items, any more relevant listed items, or all relevant listed items. It should be noted that when at least two conjunctions selected from "and / or", "or / and", "and / or" are combined to connect at least three items, it should be understood that in the present application, the technical solution undoubtedly includes the technical solution connected by "logical and", and also undoubtedly includes the technical solution connected by "logical or".

[0067] In the present application, the technical features described in an open manner include both the closed technical solution consisting of the listed features and the open technical solution containing the listed features.

[0068] In the present application, if no special description is provided, the numerical range is considered to be continuous, and includes the minimum value and the maximum value of the range, and every value between the minimum value and the maximum value. Further, when the range refers to an integer, every integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges therein.

[0069] Only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and likewise any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individual disclosed point or single numerical value can itself be combined as a lower limit or an upper limit with any other point or single numerical value or with other lower limits or upper limits to form a range not explicitly recited.

[0070] In the present application, the temperature parameter, if not specifically limited, allows for constant temperature treatment, and also allows for treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuation within a range such as ±5°C, ±4°C, ±3°C, ±2°C, ±1°C is allowed.

[0071] In the present application, if not specifically limited, the size, particle size, diameter generally refers to the average value. In the present application, "particle size" and "particle size" have the same definition, both representing the average particle size of a sphere or a sphere-like object.

[0072] In the present application, the term "suitable" in "suitable combination", "suitable manner", "any suitable manner" and the like means that the technical solution of the present application can be implemented, the technical problem of the present application can be solved, and the intended technical effect of the present application can be achieved.

[0073] In the present application, the terms "further", "still further", "in particular" and the like are used for the purpose of description and represent differences in content, but should not be understood as limiting the scope of protection of the present application.

[0074] In the present application, the terms "optionally", "optional" and "optional" mean that it can or can not be present, i.e. it means that it is selected from either of the two parallel schemes "has" or "has not". If there are multiple "options" in a technical solution, and there is no special description, and there is no contradictory relationship or mutual restriction, each "option" is independent.

[0075] In the description of the application, the meaning of "multiple" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0076] If not specifically stated, all embodiments and optional embodiments of the present application can be combined to form new technical solutions. If not specifically stated, all technical features and optional technical features of the present application can be combined to form new technical solutions.

[0077] If not specifically stated, all steps of the present application can be performed in sequence or randomly, and preferably in sequence.

[0078] The basic chemical formula of the spinel-structured lithium nickel manganese oxide material mentioned in the present application is LiNi 0.5 Mn 1.5 O4(LNMO), is a lithium ion battery cathode material with a spinel structure mainly composed of nickel, manganese, lithium and oxygen elements.

[0079] The spinel-structured lithium nickel manganese oxide material is one of the most promising high-voltage cathode materials. The inventors have found that the lithium nickel manganese oxide material also encounters many problems in further application, such as dissolution of transition metals, Mn 3+The Jahn-Teller effect caused by disproportionation, irreversible phase transition on the surface, and side reactions with electrolyte at the interface under high voltage, etc. limit the further application of the lithium nickel manganese oxide positive electrode material. The intrinsic structural stability of the spinel material is strong, and the attenuation in the full battery is mainly caused by the positive and negative electrode cross-talk problem caused by the metal dissolution in the electrolyte. Based on the above problems, the lithium nickel manganese oxide material is coated with phosphorus-containing substances and aluminum-containing substances. The aluminum-containing substance can be micro-doped on the surface under calcination to enhance the surface structure, and at the same time, it is dispersed on the surface of the particle to absorb hydrogen fluoride decomposed from the electrolyte. The phosphorus-containing substance can form a phosphate coating on the surface, and the phosphate dispersed on the surface can absorb hydrogen fluoride and transition metal ions dissolved in the electrolyte. Through composite coating, the generation of HF in the electrolyte and the dissolution of transition metals are inhibited, and the cross-talk effect between the positive and negative electrode materials is reduced.

[0080] One or more embodiments of the present application provide a composite-coated positive electrode material, comprising a core, a first coating layer coated on at least part of the surface of the core, and a second coating layer coated on at least part of the surface of the first coating layer; the core comprises lithium nickel manganese oxide, the first coating layer comprises a first coating material, the first coating material includes one or more of nickel phosphate, manganese phosphate, lithium phosphate, nickel lithium phosphate, and manganese lithium phosphate, and the first coating material further includes aluminum elements, at least part of the aluminum elements occupying nickel element sites and / or manganese element sites of the crystal structure of the lithium nickel manganese oxide; the second coating layer comprises a second coating material, the second coating material includes (1) lithium phosphate, and (2) at least one of lithium metahydroxy aluminate and aluminum oxide.

[0081] It should be noted that the "lithium nickel manganese oxide" and "lithium nickel manganese oxide" in the context are not limited to LiNi 0.5 Mn 1.5 O4, as long as it is an oxide containing lithium elements, nickel elements and manganese elements, for example, an oxide containing lithium elements, nickel elements and manganese elements doped with other metal elements (such as transition metal elements), which is within the scope of protection of the present application.

[0082] The "first coating layer", "second coating layer", "first coating material", "second coating material", etc. mentioned in the context are only for description purposes and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implying the importance or quantity of the indicated technical features. Moreover, "first", "second", etc. only serve the purpose of non-exhaustive enumeration description and should be understood as not constituting a closed limitation on the quantity. Understandably, at least part of the aluminum elements in the first coating layer occupy nickel element sites and / or manganese element sites of the crystal structure of the lithium nickel manganese oxide, forming Al-O bonds.

[0083] The composite-coated positive electrode material provided in the embodiments of the present application comprises a composite coating layer composed of a first coating layer and a second coating layer. The first coating layer coating material contains aluminum elements which at least partially occupy the nickel element sites and / or manganese element sites of the crystal structure of the lithium nickel manganese oxide, thereby performing micro-doping on the surface of the lithium nickel manganese oxide and enhancing the surface structure thereof. The first coating layer coating material contains phosphate which forms a phosphate coating on the surface of the core, thereby ensuring a certain ionic conductivity while isolating the electrolyte. The second coating layer coating material contains lithium phosphate which can absorb acidic substances in the electrolyte, thereby preventing the acidic substances from reacting with the surface of the positive electrode material and reducing the cross-talk effect between the positive and negative electrode materials. The second coating layer coating material contains lithium metahydroxyaluminate and / or aluminum oxide which can strongly absorb acidic substances in the electrolyte system. Therefore, the composite-coated positive electrode material provided in the present application effectively improves the capacity and cycle retention rate of the material and greatly reduces the impedance increase in the cycle by adopting the composite coating layer.

[0084] It is understandable that the technical solutions of the present application do not exclude the core and / or the first coating layer and / or the second coating layer comprising other materials, especially the core further comprising other positive electrode materials and / or the first coating layer further comprising other coating materials and / or the second coating layer further comprising other coating materials.

[0085] It should be noted that the core and / or the first coating layer and / or the second coating layer can further comprise other materials, but the content thereof should not make it the main component, thereby avoiding affecting the coating of the first coating material on the lithium nickel manganese oxide and the coating of the second coating material on the first coating material.

[0086] In some embodiments, the core mainly comprises or only contains the lithium nickel manganese oxide, the first coating layer mainly comprises or only contains the first coating material, and the second coating layer mainly comprises or only contains the second coating material.

[0087] In some embodiments, the first coating material of the first coating layer is directly coated on at least part of the surface of the lithium nickel manganese oxide of the core, and the second coating material of the second coating layer is directly coated on at least part of the surface of the first coating material of the first coating layer.

[0088] In some embodiments, the mass ratio of the aluminum element and the phosphorus element contained in the first coating material is 3-10; for example, it can be but is not limited to 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 or a range between any two of the above values. When the mass ratio of the aluminum element and the phosphorus element contained in the first coating material is in the above range, the phosphorus element will preferentially combine with the lithium element, and the aluminum element will not be combined with the phosphorus element to form aluminum phosphate, so that the aluminum element can effectively enter the crystal lattice.

[0089] As one possible implementation, the total mass of aluminum and phosphorus contained in the first coating material accounts for 0.05%-0.5% of the mass of the lithium nickel manganese oxide contained in the core; for example, it can be but is not limited to 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or a range between any two of the above values, etc. When the content of aluminum and phosphorus in the first coating material is within the above range, the corrosion phenomenon on the surface can be avoided due to the excessive addition of phosphorus.

[0090] In some optional embodiments, the first coating material further contains one or more elements selected from Li, S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb, and Bi.

[0091] As one possible implementation, the total mass of aluminum and phosphorus contained in the second coating material accounts for 0.2%-1.5% of the mass of the lithium nickel manganese oxide contained in the core; for example, it can be but is not limited to 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1.0%, 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, 1.5%, or a range between any two of the above values, etc. When the content of aluminum and phosphorus in the second coating material is within the above range, it is beneficial for the second coating material to absorb acidic substances in the electrolyte, while it will not cause the surface resistance of the material to rise or the capacity to decrease due to the excessive addition of non-active substances.

[0092] In some of the embodiments, the second coating material further contains one or more elements selected from Li, S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb, and Bi.

[0093] In some embodiments, the chemical formula of the lithium nickel manganese oxide is LiaNibMncM1dM2eO4-f, 0.95≤a≤1.1, 0.45<b<0.55, 1.4<c<1.6, 0≤d+e≤0.1, 0≤f≤0.1, M1 elements include one or more elements selected from S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, and La, and M2 elements include one or more elements selected from V, Nb, Mo, W, Ta, B, Sb, and Bi.

[0094] The doping of the M1 element is beneficial to improve the stability of the crystal structure of the lithium nickel manganese oxide, and the doping of the M2 element is beneficial to the crystal growth of the lithium nickel manganese oxide into a single crystal or a single crystal-like morphology.

[0095] It should be noted that the lithium nickel manganese oxide can also contain any possible impurity element with a mass ratio of less than 400 ppm, which is not specifically limited here.

[0096] In some embodiments, the volume average particle size Dv50 of the inner core is 4-8 μm; for example, it can be but is not limited to 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, or a range between any two of the above particle sizes, etc. When the volume average particle size of the inner core is in the above range, the electrochemical kinetics and the electrochemical stability of the material can be well balanced.

[0097] It should be noted that the volume average particle size Dv50 refers to the particle size corresponding to the cumulative volume particle size distribution percentage of 50% of the sample. It can be measured by a particle size distribution instrument.

[0098] As a possible embodiment, the specific surface area of the inner core is 0.3 m 2 / g-0.7 m 2 / g; for example, it can be but is not limited to 0.3 m 2 / g, 0.35 m 2 / g, 0.4 m 2 / g, 0.45 m 2 / g, 0.5 m 2 / g, 0.55 m 2 / g, 0.6 m 2 / g, 0.65 m 2 / g, 0.7 m 2 / g, or a range between any two of the above specific surface areas, etc. When the specific surface area of the inner core is in the above range, the electrochemical kinetics and the electrochemical stability of the material can be well balanced.

[0099] In some exemplary embodiments, the specific surface area of the composite-coated positive electrode material is 0.3 m 2 / g-0.8 m 2 / g; for example, it can be but is not limited to 0.3 m 2 / g, 0.35 m 2 / g, 0.4 m 2 / g, 0.45 m 2 / g, 0.5 m 2 / g, 0.55 m 2 / g, 0.6 m 2 / g, 0.65 m 20.7 m / g 2 0.75 m / g 2 0.8 m / g 2 0.9 m / g, or a range between any two of the above specific surface areas. When the specific surface area of the composite-coated cathode material is within the above range, the electrochemical kinetics and electrochemical stability of the material are well balanced.

[0100] In some embodiments, the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the composite-coated cathode material at 0.33 C charging is > 50 mV; thus, the cathode material has a structure with good crystallinity and high electronic conductivity.

[0101] In some embodiments, the percentage of the capacity of the electrochemical distribution curve of the composite-coated cathode material at 0.33 C charging in the 4.3 V to 3.8 V platform to the total discharge capacity is 5%-9%; for example, it can be, but is not limited to, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, or a range between any two of the above values, etc. Thus, the cathode material has high electronic conductivity and high reversible capacity.

[0102] In some embodiments, the 0.33 C discharge capacity of the composite-coated cathode material is > 130 mAh / g; thus, the cathode material has high reversible capacity and is suitable for use in various electrochemical energy storage devices.

[0103] As a possible embodiment, the peak intensity ratio coefficient I 311 2 / (I 400 I 111 )<0.5, I 311 is the diffraction intensity of the (311) crystal plane in the XRD diffraction pattern, I 400 is the diffraction intensity of the (400) crystal plane in the XRD diffraction pattern, I 111 is the diffraction intensity of the (111) crystal plane in the XRD diffraction pattern; thus, the cathode material has low ion mixing degree and good structural order.

[0104] In some embodiments, the composite-coated cathode material is a single crystal particle and / or a quasi-single crystal particle. When the cathode material is a single crystal particle and / or a quasi-single crystal particle, the cathode material has high electrochemical stability and rarely cracks due to volume deformation between grain boundaries.

[0105] It should be noted that the "quasi-single crystal particle" mentioned above and below refers to a crystal particle formed by aggregation of several or dozens of single crystal particles, and the number of grain boundaries thereof is much smaller than that of a polycrystal particle.

[0106] One or more embodiments of the present application provide a preparation method of a composite-coated positive electrode material, comprising the following steps:

[0107] After the core is immersed in a solution containing a first aluminum source and a first phosphorus source for a preset time, the core is filtered, and the obtained solid is subjected to a first calcination treatment to form a first coating layer on at least part of the surface of the core to prepare an intermediate; a mixture containing the intermediate, a second aluminum source and a second phosphorus source is subjected to a second calcination treatment to form a second coating layer on at least part of the surface of the first coating layer to prepare the composite-coated positive electrode material; wherein the core contains lithium nickel manganese oxide; the first coating layer contains a first coating material, the first coating material includes one or more of nickel phosphate, manganese phosphate, lithium phosphate, nickel lithium phosphate and manganese lithium phosphate, and the first coating material further includes aluminum elements, at least part of the aluminum elements occupying nickel element sites and / or manganese element sites of the crystal structure of the lithium nickel manganese oxide; the second coating layer contains a second coating material, the second coating material includes lithium phosphate and at least one of lithium metahydroxy aluminate and aluminum oxide.

[0108] It should be noted that the above and below mentioned "first calcination treatment", "second calcination treatment", "third calcination treatment", "first aluminum source", "second aluminum source", "first phosphorus source", "second phosphorus source" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implying the importance or quantity of the indicated technical features. Moreover, "first", "second", "third" and the like only serve the purpose of non-exhaustive enumeration description, and should be understood as not constituting a closed limitation on the quantity.

[0109] Understandably, in the preparation method provided by the embodiments of the present application, the coating is performed using a wet chemical method before the first calcination treatment, which greatly enhances the dispersion uniformity of the coating material (first aluminum source and first phosphorus source) on the surface. The first aluminum source can perform micro-doping on the surface of the lithium nickel manganese oxide during the first calcination treatment, enhancing the surface structure. The first phosphorus source can form a phosphate coating on the surface of the core during the calcination process, which can isolate the electrolyte while ensuring a certain ion conductivity. During the second calcination treatment, the second aluminum source and the second phosphorus source are added by dry mixing, and after calcination, the phosphate dispersed on the surface of the intermediate can absorb acidic substances in the electrolyte, preventing the acidic substances from reacting with the surface of the positive electrode material and reducing the cross-talk effect between the positive and negative electrode materials. The lithium metahydroxy aluminate and / or aluminum oxide dispersed on the surface of the intermediate can strongly absorb acidic substances in the electrolyte system. Therefore, the composite-coated positive electrode material prepared by the preparation method effectively improves the capacity and cycle retention rate of the material, and greatly reduces the impedance increase during the cycle.

[0110] It should be noted that the finished product prepared by the above preparation method can also be further processed and optimized as an intermediate, and the processing is not limited to adding other additives for further calcination, mixing other positive electrode materials or more other treatments. Further processing and optimization can also be added between the above first calcination treatment, and the processing is not limited to adding other additives for further calcination, mixing other positive electrode materials or more other treatments. Further processing and optimization can also be added between the above second calcination treatment, and the processing is not limited to adding other additives for further calcination, mixing other positive electrode materials or more other treatments.

[0111] After the core is immersed in the solution containing the first aluminum source and the first phosphorus source for a preset time and then filtered, the soluble impurities can be filtered out together with the solvent, and the purity of the reactant material is improved.

[0112] In some embodiments, the filtering method includes one or more of centrifugal filtration, pressure filtration, and suction filtration.

[0113] One or more embodiments of the present application provide a preparation method of a composite-coated positive electrode material, including the following steps: mixing a solution containing a first aluminum source and a first phosphorus source with a core for a preset time, then removing the solvent by volatilization, and performing a first calcination treatment on the remaining solid to form a first coating layer on at least part of the surface of the core, thereby preparing an intermediate; performing a second calcination treatment on a mixture containing the intermediate, a second aluminum source and a second phosphorus source to form a second coating layer on at least part of the surface of the first coating layer, thereby preparing a composite-coated positive electrode material; wherein the core contains lithium nickel manganese oxide; the first coating layer contains a first coating material, the first coating material includes one or more of nickel phosphate, manganese phosphate, lithium phosphate, nickel lithium phosphate and manganese lithium phosphate, and the first coating material further includes aluminum elements, at least part of the aluminum elements occupying the nickel element sites and / or the manganese element sites of the crystal structure of the lithium nickel manganese oxide; the second coating layer contains a second coating material, the second coating material includes lithium phosphate and at least one of lithium meta-aluminate and aluminum oxide.

[0114] Understandably, in the preparation method provided by the embodiments of the present application, the wet chemical method is used for coating before the first calcination treatment, which greatly enhances the dispersion uniformity of the coating material (the first aluminum source and the first phosphorus source) on the surface. The first aluminum source can perform micro-doping on the surface of the lithium nickel manganese oxide during the first calcination treatment, enhancing the surface structure. The first phosphorus source can form a phosphate coating on the surface of the core during the calcination process, isolating the electrolyte while ensuring a certain ion conductivity. During the second calcination treatment, the second aluminum source and the second phosphorus source are added by dry mixing. After calcination, the phosphate dispersed on the surface of the intermediate body can absorb acidic substances in the electrolyte, preventing the acidic substances from reacting with the surface of the positive electrode material and reducing the cross-talk effect between the positive and negative electrode materials. The lithium metaliuate and / or aluminum oxide dispersed on the surface of the intermediate body can strongly absorb acidic substances in the electrolyte system. Therefore, the composite-coated positive electrode material prepared by the preparation method effectively improves the capacity and cycle retention rate of the material and greatly reduces the impedance increase during the cycle.

[0115] It should be noted that the finished product prepared by the above preparation method can also be further processed and optimized as an intermediate. The processing is not limited to adding other additives for further calcination, mixing other positive electrode materials, or more other treatments. Further processing and optimization can also be added between the above first calcination treatment. The processing is not limited to adding other additives for further calcination, mixing other positive electrode materials, or more other treatments. Further processing and optimization can also be added between the above second calcination treatment. The processing is not limited to adding other additives for further calcination, mixing other positive electrode materials, or more other treatments.

[0116] The above method of mixing the solution containing the first aluminum source and the first phosphorus source with the core can include pouring into the core under stirring, spraying the solution on the core under stirring, or using a flowing solution to wash the core, without limitation.

[0117] The compositions and properties of the lithium nickel manganese oxide, the first coating material, and the second coating material, as well as the structure and properties of the core and the prepared positive electrode material, are described above, and will not be repeated in the method.

[0118] In some exemplary embodiments, the preset time mentioned above and below can be 30s-300s. For example, it can be, but is not limited to, 30s, 60s, 120s, 180s, 240s, 300s, or a range between any two of the above times, etc.

[0119] As one possible embodiment, the first aluminum source includes one or more of aluminum nitrate and its hydrate, aluminum dihydrogen phosphate and its hydrate, aluminum lactate and its hydrate, aluminum triethoxide, aluminum orthophosphate, and aluminum pyrophosphate.

[0120] In some alternative embodiments, the first aluminum source comprises one or more of aluminum nitrate and hydrates thereof and aluminum triethoxide.

[0121] In some exemplary embodiments, the first phosphorus source comprises one or more of phosphoric acid, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, diphosphorus pentoxide, lithium dihydrogen phosphate, potassium dihydrogen phosphate, manganese dihydrogen phosphate and hydrates thereof, lithium monohydrogen phosphate, sodium monohydrogen phosphate, potassium monohydrogen phosphate, triethyl phosphate, trimethyl phosphate, aluminum dihydrogen phosphate, and pyrophosphates.

[0122] In some alternative embodiments, the first phosphorus source comprises one or more of phosphoric acid and trimethyl phosphate. As one possible embodiment, the pyrophosphate comprises one or more of lithium pyrophosphate, sodium pyrophosphate, potassium pyrophosphate, and aluminum pyrophosphate.

[0123] In some embodiments, the solvent employed in formulating the solution comprising the first aluminum source and the first phosphorus source comprises one or more of ethanol, methanol, dimethyl phthalate, and water.

[0124] In some embodiments, the first calcination process has a temperature of 600°C to 900°C; for example, but not limited to, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, or a range between any two of the foregoing temperatures.

[0125] In some alternative embodiments, the first calcination process has a temperature of 700°C to 800°C and a time of 6h to 8h.

[0126] In some alternative embodiments, the first calcination process has a temperature of 700°C to 800°C and a time of 6h to 8h.

[0127] As one possible embodiment, the first calcination process has a ramp rate of 1°C / min to 5°C / min; for example, but not limited to, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, or a range between any two of the foregoing ramp rates.

[0128] It is to be understood that the temperature, time, and ramp rate of the first calcination process can be combined in any suitable manner, and each can be selected from any of the temperatures, times, and ramp rates described herein for the first calcination process.

[0129] When the temperature, time and heating rate of the first calcination process are within the above ranges, the gas generated by the lithium salt or precursor can be effectively dissipated while ensuring a short time for heating.

[0130] In some exemplary embodiments, the cooling rate of the first calcination process is > 2°C / min.

[0131] In some embodiments, the raw material for the first calcination process further comprises a first additive, the first additive and the filtered solid are subjected to the first calcination process together, and the first additive comprises one or more elements selected from Li, S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb and Bi.

[0132] In some embodiments, the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the 0.33C charged intermediate is greater than 50 mV; thus, the material has a structure with better crystallinity and higher electronic conductivity.

[0133] In some embodiments, the second aluminum source comprises one or more compounds containing Al-O bonds.

[0134] As a possible embodiment, the second aluminum source comprises one or more of aluminum hydroxide, aluminum oxide, lithium metaaluminate and sodium aluminate.

[0135] In some embodiments, the second phosphorus source comprises one or more compounds containing P-O bonds.

[0136] In some alternative embodiments, the second phosphorus source comprises one or more of lithium phosphate, monohydric lithium phosphate, dihydric lithium phosphate and lithium pyrophosphate.

[0137] In some embodiments, the temperature of the second calcination process is 200°C-450°C; for example, it can be but is not limited to 200°C, 250°C, 300°C, 350°C, 400°C, 450°C or a range between any two of the above temperatures, etc.

[0138] As a possible embodiment, the time of the second calcination process is 0h-12h; for example, it can be but is not limited to 0h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h or a range between any two of the above times, etc. It should be noted that when the time of the second calcination process is 0h, it means that the mixture of the intermediate, the second aluminum source and the second phosphorus source is only mixed without calcination, which also has a certain improvement effect.

[0139] In some alternative embodiments, the time of the second calcination process is 1h-12h.

[0140] In some exemplary embodiments, the second calcination process has a heating rate of 1-5°C / min; for example, it can be, but is not limited to, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, or a range between any two of the above heating rates.

[0141] It should be noted that the temperature, time and heating rate of the second calcination process can be combined in any suitable manner, and each of them can be selected from any of the temperatures, times and heating rates of the second calcination process described herein.

[0142] When the temperature, time and heating rate of the second calcination process are within the above ranges, respectively, the coating additive can effectively bind to the surface of the material while not adversely affecting the electrochemical performance.

[0143] In some alternative embodiments, the mixture subjected to the second calcination process further comprises a second additive, and the second additive comprises one or more elements selected from Li, S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb and Bi.

[0144] In some embodiments, the lithium nickel manganese oxide has a chemical formula of Li a Ni b Mn c M1 d M2 e O 4-f , 0.95≤a≤1.1, 0.45<b<0.55, 1.4<c<1.6, 0≤d+e≤0.1, 0≤f≤0.1, M1 includes one or more elements selected from S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F and La, and M2 includes one or more elements selected from V, Nb, Mo, W, Ta, B, Sb and Bi.

[0145] In some embodiments, the preparation method of the core comprises: mixing the nickel-manganese precursor and the lithium salt, and then performing a third calcination process; or mixing the nickel-manganese precursor, the lithium salt and a third additive, and then performing a third calcination process.

[0146] In some embodiments, the nickel-manganese precursor has a chemical formula of Ni 0.25 Mn 0.75 (OH)2, Ni 0.25 Mn 0.75 C2O4 and Ni 0.25 Mn 0.75 CO3.

[0147] In some embodiments, the nickel-manganese precursor comprises one or more of nickel-manganese hydroxide, nickel-manganese oxalate, and nickel-manganese carbonate.

[0148] As one possible embodiment, the nickel-manganese precursor is nickel-manganese hydroxide.

[0149] In some embodiments, the third additive comprises one or more elements of S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb, and Bi.

[0150] It should be noted that the above and below mentioned "first additive", "second additive", "third additive" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implying the importance or quantity of the indicated technical features. Moreover, "first", "second", "third" and the like only serve the purpose of non-exhaustive enumeration description, and should be understood as not constituting a closed limitation on the quantity.

[0151] In some optional embodiments, the lithium source comprises one or more of LiOH, Li2CO3, Li2SO4, LiCl, and LiNO3, which can be one or more of LiOH and Li2CO3.

[0152] In some of the embodiments, the molar ratio of the total metal contained in the nickel-manganese precursor to the lithium element contained in the lithium source is 1:(0.5-0.55); for example, it can be but is not limited to 1:0.5, 1:0.51, 1:0.52, 1:0.53, 1:0.54, 1:0.55, or a range between any two of the above molar ratios, etc.

[0153] In some optional embodiments, the temperature of the third calcination treatment is 600-1000°C; for example, it can be but is not limited to 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, or a range between any two of the above temperatures, etc.

[0154] In some optional embodiments, the temperature of the third calcination treatment is 850-950°C.

[0155] As one possible embodiment, the time of the third calcination treatment is 5-30h; for example, it can be but is not limited to 5h, 8h, 10h, 13h, 15h, 18h, 20h, 23h, 25h, 28h, 30h, or a range between any two of the above times, etc.

[0156] In some optional embodiments, the time of the third calcination treatment is 6-12h. In some optional embodiments, the time of the third calcination treatment is 6-12h.

[0157] In some exemplary embodiments, the third calcination process has a temperature rising rate of 1-5℃ / min; for example, it can be, but is not limited to, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, or a range between any two of the above temperature rising rates.

[0158] It should be noted that the temperature, time and temperature rising rate of the third calcination process can be combined in any suitable manner, and each of them can be selected from any of the temperature, time and temperature rising rate of the third calcination process described herein.

[0159] In some of the embodiments, the oxygen partial pressure in the calcination atmosphere of the third calcination process is ≥10000 Pa.

[0160] In some embodiments, the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the 0.33C charging of the core is less than 40mV or greater than 50mV. Thus, the core of the material has good crystallinity.

[0161] One or more embodiments of the present application provide a positive electrode sheet comprising the composite-coated positive electrode material provided by the present application or prepared by the preparation method provided by the present application.

[0162] One or more embodiments of the present application provide a lithium ion battery comprising the positive electrode sheet described above.

[0163] The lithium ion battery of the present application comprises the composite-coated positive electrode material described above, has high capacity and initial efficiency, and has excellent cycle performance.

[0164] One or more embodiments of the present application provide an electric device comprising the lithium ion battery described above. The electric device can be an electric vehicle, an electric bicycle, an electric two-wheeled vehicle, an electric vehicle power system, an energy storage system, or a mobile storage device, etc., without limitation.

[0165] The electric device of the present application comprises the lithium ion battery provided by the present application, and thus at least has the same advantages as the lithium ion battery.

[0166] The technical solutions of the present application are described in detail below in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and do not limit the scope of the present application. If the experimental methods are not specified in the following examples, the instructions given in the present application are preferred, and the experimental methods can also be performed according to the experimental manuals or conventional conditions in the art, or according to the conditions suggested by the manufacturers, or according to the known experimental methods in the art.

[0167] In the following specific examples, the amount of raw material components are described in terms of measurement parameters, which can have minor variations within the range of weighing accuracy, unless otherwise specified. The temperature and time parameters are allowed to have acceptable variations due to the accuracy of the instruments or the accuracy of the operation.

[0168] I. Preparation of the positive electrode material

[0169] Example 1

[0170] Step S1, Ni 0.25 Mn 0.75 (OH)2(nickel-manganese precursor, Dv50 of 4 pm), Li2CO3(lithium source) were mixed in a molar ratio of 1:0.2625, and then 1000 ppm Y2O3, 1000 ppm Al(OH)3, 1000 ppm SiO2, 500 ppm MoO3, and 500 ppm Ta2O5 were added based on the mass of the finally prepared core, and mixed in a high-speed mixer at a speed of 1000 rpm for 40 min. After sufficient mixing, a mixture was obtained. The mixture was calcined at 600°C for 4 h in an air atmosphere, and then the temperature was increased to 950°C for calcination for 10 h. The calcined product was crushed, sieved, washed with water, and dried to obtain the core Li 1.013 Ni 0.496 Mn 1.488 Y 0.002 Al 0.007 Si 0.006 Mo 0.001 Ta 0.0005 O 3.983 .

[0171] Step S2, the core was immersed in an ethanol solution of aluminum triethoxide (first aluminum source) and triethyl phosphate (first phosphorus source), in which the addition amounts of Al and P elements were 0.2 wt% and 0.05 wt%, respectively, based on the mass of the core, and mixed under strong stirring for 15 min. After the solid powder was separated by centrifugal filtration, it was vacuum dried at 60°C for 2 h, and then 0.05 wt% of TiO2 was added and mixed in a high-speed mixer at a speed of 700 rpm for 20 min. After uniform mixing, it was calcined at 700°C for 6 h to obtain an intermediate.

[0172] Step S3, aluminum oxide (second aluminum source) and lithium phosphate (second phosphorus source) were added to the intermediate, in which the addition amounts of Al and P elements were 0.3 wt% and 0.2 wt%, respectively, based on the mass of the intermediate, and mixed in a high-speed mixer at a speed of 700 rpm for 20 min. After uniform mixing, it was calcined at 450°C for 6 h to obtain the finished lithium nickel-manganese phosphate positive electrode material.

[0173] Example 2

[0174] The preparation method of Example 2 and the preparation method of Example 1 differ in that the temperature at which the calcination treatment is performed in step S2 of Example 2 is 750°C, and the others are the same. Step S2 in Example 2 is as follows:

[0175] Step S2, the inner core is immersed in an ethanol solution of aluminum triethoxide (first aluminum source) and triethyl phosphate (first phosphorus source), wherein the addition amount of Al and P elements is 0.2wt% and 0.05wt% respectively based on the mass of the inner core, mixed under strong stirring for 15min, the solid powder is separated by centrifugal filtration, then vacuum dried at 60°C for 2h, then 0.05wt% of TiO2 is added, mixed in a high-speed mixer, the rotation speed of the high-speed mixer is 700rpm, the mixing time is 20min, after uniform mixing, calcined at 750°C for 6h, to obtain the intermediate.

[0176] Example 3

[0177] The preparation method of Example 3 and the preparation method of Example 1 differ in that the addition amount of Al and P elements in step S2 of Example 3 is 0.4wt% and 0.1wt% respectively, and the others are the same. Step S2 in Example 3 is as follows:

[0178] Step S2, the inner core is immersed in an ethanol solution of aluminum triethoxide (first aluminum source) and triethyl phosphate (first phosphorus source), wherein the addition amount of Al and P elements is 0.4wt% and 0.1wt% respectively based on the mass of the inner core, mixed under strong stirring for 15min, the solid powder is separated by centrifugal filtration, then vacuum dried at 60°C for 2h, then 0.05wt% of TiO2 is added, mixed in a high-speed mixer, the rotation speed of the high-speed mixer is 700rpm, the mixing time is 20min, after uniform mixing, calcined at 700°C for 6h, to obtain the intermediate.

[0179] Example 4

[0180] The preparation method of Example 4 and the preparation method of Example 1 differ in that the first phosphorus source and the first aluminum source used in step S2 of Example 4 are different, and the others are the same. Step S2 in Example 4 is as follows:

[0181] Step S2, the core was immersed into an ethanol solution of aluminum dihydrogen phosphate and aluminum nitrate, in which the added amounts of Al and P elements were 0.2wt% and 0.05wt% respectively based on the mass of the core, mixed under strong stirring for 15min, after the solid powder was separated by centrifugal filtration and vacuum dried at 60℃ for 2h, 0.05wt% of TiO2 was added and mixed in a high-speed mixer at a speed of 700rpm for 20min, and then the intermediate was obtained after being calcined at 700℃ for 6h.

[0182] Example 5

[0183] The preparation method of Example 5 and the preparation method of Example 1 are different in that the temperature for calcination in Step S1 of Example 5 is 940℃; and the way of removing the solvent in Step S2 of Example 5 is different, and the others are the same. Steps S1 and S2 of Example 5 are as follows respectively.

[0184] Step S1, Ni 0.25 Mn 0.75 (OH)2(nickel-manganese precursor, Dv50 is 4μm), Li2CO3(lithium source) were mixed according to the molar ratio of 1:0.2625, and then 1000ppm Y2O3, 1000ppm Al(OH)3, 1000ppm SiO2, 500ppm MoO3 and 500ppm Ta2O5 were added based on the mass of the finally prepared core, and mixed in a high-speed mixer at a speed of 1000rpm for 40min, and then the mixture was obtained after being mixed sufficiently. The mixture was calcined at 600℃ for 4h in an air atmosphere, and then the temperature was increased to 940℃ for 10h to obtain a calcined product. After crushing, sieving, washing and drying, the Li 1.015 Ni 0.496 Mn 1.488 Y 0.002 Al 0.007 Si 0.006 Mo 0.001 Ta 0.0005 O 3.989 .

[0185] Step S2, the core was immersed into an ethanol solution of aluminum dihydrogen phosphate and aluminum nitrate, in which the added amounts of Al and P elements were 0.2wt% and 0.05wt% respectively based on the mass of the core, mixed under strong stirring for 15min, after the solid powder was separated by centrifugal filtration and vacuum dried at 60℃ for 2h, 0.05wt% of TiO2 was added and mixed in a high-speed mixer at a speed of 700rpm for 20min, and then the intermediate was obtained after being calcined at 700℃ for 6h.

[0186] Example 6

[0187] The preparation method of Example 6 is different from the preparation method of Example 1 in that the addition amounts of Al and P elements in step S2 of Example 6 are 0.4wt% and 0.1wt% respectively, and the addition amounts of Al and P elements in step S3 of Example 6 are 0.6wt% and 0.4wt% respectively, and the others are the same. Steps S2 and S3 of Example 6 are as follows respectively:

[0188] Step S2, the core is immersed into an ethanol solution of aluminum triethoxide (first aluminum source) and triethyl phosphate (first phosphorus source), wherein the addition amounts of Al and P elements are 0.4wt% and 0.1wt% respectively based on the mass of the core, mixed under strong stirring for 15min, the solid powder is separated by centrifugal filtration, and then vacuum dried at 60℃ for 2h, then 0.05wt% of TiO2 is added, mixed in a high-speed mixer, the rotation speed of the high-speed mixer is 700rpm, and the mixing time is 20min, after uniform mixing, calcined at 700℃ for 6h to obtain an intermediate.

[0189] Step S3, aluminum oxide (second aluminum source) and lithium phosphate (second phosphorus source) are added to the intermediate, wherein the addition amounts of Al and P elements are 0.6wt% and 0.4wt% respectively based on the mass of the intermediate, the rotation speed of the high-speed mixer is 700rpm, and the mixing time is 20min, after uniform mixing, calcined at 450℃ for 6h to obtain the finished lithium nickel manganese oxide positive electrode material.

[0190] Example 7

[0191] The preparation method of Example 7 is different from the preparation method of Example 1 in that the molar ratio of the nickel-manganese precursor and the lithium source in step S1 of Example 7 is different, and the types of additives are different, and the others are the same. Step S1 of Example 7 is as follows:

[0192] Step S1, Ni 0.25 Mn 0.75 (OH)2 (nickel-manganese precursor, Dv50 is 4μm), Li2CO3 (lithium source) are mixed according to the molar ratio of 1:0.265, then 2000ppm ZrO2, 1000ppm TiO2, 1000ppm La2O3, 500ppm WO3 and 500ppm B2O3 are added based on the mass of the finally prepared core, mixed in a high-speed mixer, the rotation speed of the high-speed mixer is 1000rpm, and the mixing time is 40min, and the mixture is obtained after sufficient mixing. The mixture is calcined at 600℃ for 4h in an air atmosphere, and then the temperature is increased to 950℃ for calcination for 10h to obtain a calcined product. After crushing, sieving, washing and drying, the core Li is obtained.1.011 Ni 0.496 Mn 1.488 Zr 0.004 Ti 0.004 La 0.001 W 0.0005 B 0.008 O 3.982 .

[0193] Example 8

[0194] The preparation method of Example 8 and the preparation method of Example 7 differ in that the temperature of the calcination treatment in step S2 of Example 8 is different, and the others are the same. Steps S1 and S2 of Example 8 are as follows, respectively:

[0195] Step S2, the inner core is immersed into an ethanol solution of aluminum triethoxide (first aluminum source) and triethyl phosphate (first phosphorus source), wherein the addition amount of Al and P elements is 0.2wt% and 0.05wt% respectively based on the mass of the inner core, mixed under strong stirring for 15min, the solid powder is separated by centrifugal filtration, then vacuum dried at 60℃ for 2h, 0.05wt% of TiO2 is added, mixed in a high-speed mixer, the rotation speed of the high-speed mixer is 700rpm, the mixing time is 20min, after uniform mixing, calcined at 750℃ for 6h, to obtain the intermediate.

[0196] Example 9

[0197] The preparation method of Example 9 and the preparation method of Example 7 differ in that the addition amount of Al and P elements in step S2 of Example 9 is 0.4wt% and 0.1wt% respectively, and the others are the same. Step S2 of Example 9 is as follows:

[0198] Step S2, the inner core is immersed into an ethanol solution of aluminum triethoxide (first aluminum source) and triethyl phosphate (first phosphorus source), wherein the addition amount of Al and P elements is 0.4wt% and 0.1wt% respectively based on the mass of the inner core, mixed under strong stirring for 15min, the solid powder is separated by centrifugal filtration, then vacuum dried at 60℃ for 2h, 0.05wt% of TiO2 is added, mixed in a high-speed mixer, the rotation speed of the high-speed mixer is 700rpm, the mixing time is 20min, after uniform mixing, calcined at 700℃ for 6h, to obtain the intermediate.

[0199] Example 10

[0200] The preparation method of Example 10 and the preparation method of Example 7 differ in that the types of the first phosphorus source and the first aluminum source used in step S2 of Example 10 are different, and the others are the same. Step S2 of Example 10 is as follows:

[0201] Step S2, the inner core was immersed into an ethanol solution of aluminum dihydrogen phosphate and aluminum nitrate, in which the added amounts of Al and P elements were 0.2wt% and 0.05wt% respectively based on the mass of the inner core, mixed under strong stirring for 15min, after the solid powder was separated by centrifugal filtration, vacuum dried at 60°C for 2h, then 0.05wt% of TiO2 was added, mixed in a high-speed mixer, the rotation speed of the high-speed mixer was 700rpm, the mixing time was 20min, after uniform mixing, calcined at 700°C for 6h, to obtain an intermediate.

[0202] Example 11

[0203] The preparation method of Example 11 and the preparation method of Example 7 are different in that the way of removing the solvent in step S2 of Example 11 is different, and the others are the same. Step S2 of Example 11 is as follows:

[0204] Step S2, the inner core was immersed into an ethanol solution of aluminum dihydrogen phosphate and aluminum nitrate, in which the added amounts of Al and P elements were 0.2wt% and 0.05wt% respectively based on the mass of the inner core, mixed under strong stirring for 15min, after the solid powder was separated by centrifugal filtration, vacuum dried at 60°C for 2h, then 0.05wt% of TiO2 was added, mixed in a high-speed mixer, the rotation speed of the high-speed mixer was 700rpm, the mixing time was 20min, after uniform mixing, calcined at 700°C for 6h, to obtain an intermediate.

[0205] Example 12

[0206] The preparation method of Example 12 and the preparation method of Example 7 are different in that the added amounts of Al and P elements in step S2 of Example 12 are 0.4wt% and 0.1wt% respectively, and the added amounts of Al and P elements in step S3 of Example 12 are 0.6wt% and 0.4wt% respectively, and the others are the same. Step S2 and step S3 of Example 12 are as follows respectively:

[0207] Step S2, the inner core was immersed into an ethanol solution of aluminum dihydrogen phosphate and aluminum nitrate, in which the added amounts of Al and P elements were 0.2wt% and 0.05wt% respectively based on the mass of the inner core, mixed under strong stirring for 15min, after the solid powder was separated by centrifugal filtration, vacuum dried at 60°C for 2h, then 0.05wt% of TiO2 was added, mixed in a high-speed mixer, the rotation speed of the high-speed mixer was 700rpm, the mixing time was 20min, after uniform mixing, calcined at 700°C for 6h, to obtain an intermediate.

[0208] Step S3, adding aluminum oxide (second aluminum source) and lithium phosphate (second phosphorus source) to the intermediate, wherein the addition amounts of Al and P elements are 0.6 wt% and 0.4 wt% respectively based on the mass of the intermediate, the speed of the high-speed mixer is 700 rpm, the mixing time is 20 min, after uniform mixing, calcining at 450°C for 6 h, to obtain the finished lithium nickel manganese oxide positive electrode material.

[0209] Example 13

[0210] The preparation method of Example 13 and the preparation method of Example 1 are different in that no additive is added in the preparation of the core in step S1 of Example 13, and the others are the same. Step S1 of Example 13 is as follows:

[0211] Step S1, mixing Ni 0.25 Mn 0.75 (OH)2 (nickel-manganese precursor, Dv50 is 4 μm), Li2CO3 (lithium source) according to the molar ratio of 1:0.2625, and placing them in a high-speed mixer for mixing, the speed of the high-speed mixer is 1000 rpm, the mixing time is 40 min, and after sufficient mixing, a mixture is obtained. The mixture is calcined at 600°C for 4 h in an air atmosphere, and then the temperature is increased to 950°C for calcining for 10 h, to obtain a calcined product. After crushing, sieving, water washing and drying, Li 1.016 Ni 0.5 Mn 1.5 O 3.991 .

[0212] Comparative Example 1

[0213] The preparation method of Comparative Example 1 and the preparation method of Example 1 are different in that no phosphorus source and aluminum source are used to prepare the coating layer in Comparative Example 1, and Comparative Example 1 is as follows:

[0214] Step S1, mixing Ni 0.25 Mn 0.75 (OH)2 (nickel-manganese precursor, Dv50 is 4 μm), Li2CO3 (lithium source) according to the molar ratio of 1:0.2625, and then adding 1000 ppm Y2O3, 1000 ppm Al(OH)3, 1000 ppm SiO2, 500 ppm MoO3 and 500 ppm Ta2O5 based on the mass of the finally prepared core, and placing them in a high-speed mixer for mixing, the speed of the high-speed mixer is 1000 rpm, the mixing time is 40 min, and after sufficient mixing, a mixture is obtained. The mixture is calcined at 600°C for 4 h in an air atmosphere, and then the temperature is increased to 950°C for calcining for 10 h, to obtain a calcined product. After crushing, sieving, water washing and drying, Li 1.013 Ni 0.496 Mn1.488 Y 0.002 Al 0.007 Si 0.006 Mo 0.001 Ta 0.0005 O 3.983 .

[0215] Step S2, 0.05wt% of TiO2 was added to the inner core in terms of the mass of the inner core, and mixed in a high-speed mixer at a speed of 700 rpm for 20 min. After uniform mixing, the intermediate was calcined at 700℃ for 6h to obtain the intermediate.

[0216] Step S3, the intermediate was calcined at 450℃ for 6h to obtain the positive electrode material product.

[0217] Comparative Example 2

[0218] The difference between the preparation method of Comparative Example 2 and the preparation method of Example 1 is that no first phosphorus source and first aluminum source is used in the coating of Step S2 of Comparative Example 2, and the others are the same. Comparative Example 2 is as follows:

[0219] Step S1, Ni 0.25 Mn 0.75 (OH)2(nickel-manganese precursor, Dv50 is 4μm), Li2CO3(lithium source) were mixed according to the molar ratio of 1:0.2625, then 1000ppm Y2O3, 1000ppm Al(OH)3, 1000ppm SiO2, 500ppm MoO3 and 500ppm Ta2O5 were added in terms of the mass of the finally prepared inner core, and mixed in a high-speed mixer at a speed of 1000 rpm for 40 min. After sufficient mixing, a mixture was obtained. The mixture was calcined at 600℃ for 4h in an air atmosphere, and then the temperature was increased to 950℃ for 10h to obtain a calcined product. After crushing, sieving, washing and drying, Li 1.013 Ni 0.496 Mn 1.488 Y 0.002 Al 0.007 Si 0.006 Mo 0.001 Ta 0.0005 O 3.983 .

[0220] Step S2, 0.05wt% of TiO2 was added to the inner core in terms of the mass of the inner core, and mixed in a high-speed mixer at a speed of 700 rpm for 20 min. After uniform mixing, the intermediate was calcined at 700℃ for 6h to obtain the intermediate.

[0221] Step S3, adding aluminum trioxide (second aluminum source) and lithium phosphate (second phosphorus source) to the intermediate, wherein the added amounts of Al and P elements are 0.3wt% and 0.2wt% respectively based on the mass of the intermediate, the speed of the high-speed mixer is 700rpm, the mixing time is 20min, after uniform mixing, calcining at 450℃ for 6h, obtaining the finished positive electrode material.

[0222] Comparative Example 3

[0223] The difference between the preparation method of Comparative Example 3 and the preparation method of Example 1 is that no second phosphorus source and second aluminum source are used in the coating of Step S3 of Comparative Example 3, and the others are the same. Comparative Example 3 is as follows:

[0224] Step S1, mixing Ni 0.25 Mn 0.75 (OH)2 (nickel-manganese precursor, Dv50 is 4μm), Li2CO3 (lithium source) according to the molar ratio of 1:0.2625, then adding 1000ppm Y2O3, 1000ppm Al(OH)3, 1000ppm SiO2, 500ppm MoO3 and 500ppm Ta2O5 based on the mass of the finally prepared core, placing in a high-speed mixer, the speed of the high-speed mixer is 1000rpm, the mixing time is 40min, after sufficient mixing, obtaining a mixture. Placing the mixture in an air atmosphere and calcining at 600℃ for 4h, then increasing the temperature to 950℃ and calcining for 10h, obtaining a calcined product, after crushing, sieving, washing with water and drying, obtaining Li 1.013 Ni 0.496 Mn 1.488 Y 0.002 Al 0.007 Si 0.006 Mo 0.001 Ta 0.0005 O 3.983 .

[0225] Step S2, immersing the core into an ethanol solution of aluminum triethoxide (first aluminum source) and triethyl phosphate (first phosphorus source), wherein the added amounts of Al and P elements are 0.2wt% and 0.05wt% respectively based on the mass of the core, mixing under strong stirring for 15min, separating the solid powder by centrifugal filtration, then vacuum drying at 60℃ for 2h, then adding 0.05wt% of TiO2, placing in a high-speed mixer, the speed of the high-speed mixer is 700rpm, the mixing time is 20min, after uniform mixing, calcining at 700℃ for 6h, obtaining an intermediate. Step S3, calcining the intermediate at 450℃ for 6h, obtaining the finished positive electrode material.

[0226] Comparative Example 4

[0227] The preparation method of Comparative Example 4 and the preparation method of Example 1 are different in that no first phosphorus source is used in the coating in step S2 of Comparative Example 4, and the rest are the same. Step S2 of Comparative Example 4 is specifically as follows:

[0228] Step S2, the core was immersed in an ethanol solution of aluminum triethoxide (first aluminum source), wherein the addition amount of Al element was 0.25wt% based on the mass of the core, mixed under strong stirring for 15 min, the solid powder was separated by centrifugal filtration, and then vacuum dried at 60°C for 2h, 0.05wt% of TiO2 was then added and mixed in a high-speed mixer, the rotation speed of the high-speed mixer was 700rpm, and the mixing time was 20 min, and the intermediate was obtained after being uniformly mixed and calcined at 700°C for 6h.

[0229] Comparative Example 5

[0230] The preparation method of Comparative Example 5 and the preparation method of Example 1 are different in that no first aluminum source is used in the coating in step S2 of Comparative Example 5, and the rest are the same. Step S2 of Comparative Example 5 is specifically as follows:

[0231] Step S2, the core was immersed in an ethanol solution of triethyl phosphate (first phosphorus source), wherein the addition amount of P element was 0.25wt% based on the mass of the core, mixed under strong stirring for 15 min, the solid powder was separated by centrifugal filtration, and then vacuum dried at 60°C for 2h, 0.05wt% of TiO2 was then added and mixed in a high-speed mixer, the rotation speed of the high-speed mixer was 700rpm, and the mixing time was 20 min, and the intermediate was obtained after being uniformly mixed and calcined at 700°C for 6h.

[0232] Comparative Example 6

[0233] The preparation method of Comparative Example 6 and the preparation method of Example 1 are different in that no second aluminum source is used in the coating in step S3 of Comparative Example 6, and the rest are the same. Step S3 of Comparative Example 6 is specifically as follows:

[0234] Step S3, lithium phosphate (second phosphorus source) was added to the intermediate, wherein the addition amount of P element was 0.5wt% based on the mass of the intermediate, the rotation speed of the high-speed mixer was 700rpm, and the mixing time was 20 min, and the positive electrode material finished product was obtained after being uniformly mixed and calcined at 450°C for 6h.

[0235] Comparative Example 7

[0236] The preparation method of Comparative Example 7 and the preparation method of Example 1 are different in that no second phosphorus source is used in the coating in step S3 of Comparative Example 7, and the rest are the same. Step S3 of Comparative Example 6 is specifically as follows:

[0237] Step S3, adding aluminum trioxide (second aluminum source) to the intermediate, wherein the added amount of Al element is 0.5wt% based on the mass of the intermediate, the speed of the high-speed mixer is 700 rpm, the mixing time is 20 min, after uniform mixing, calcining at 550℃ for 6h, to obtain the finished positive electrode material.

[0238] Comparative Example 8

[0239] The difference between the preparation method of Comparative Example 8 and the preparation method of Example 1 is that no wet chemical coating is used in the coating of Step S2 of Comparative Example 8, and the others are the same. Step S2 of Comparative Example 8 is as follows:

[0240] Step S2, adding aluminum trihydroxide (first aluminum source), triethyl phosphate (first phosphorus source) and TiO2 to the core, wherein the added amounts of Al and P elements are 0.2wt% and 0.05wt% respectively based on the mass of the core, and the added amount of TiO2 is 0.05wt%, placing in a high-speed mixer, the speed of the high-speed mixer is 700 rpm, the mixing time is 20 min, after uniform mixing, calcining at 700℃ for 6h, to obtain the intermediate.

[0241] Comparative Example 9

[0242] adding Ni 0.25 Mn 0.75 (OH)2 (nickel-manganese precursor, Dv50 is 4μm), Li2CO3 (lithium source) are mixed according to the molar ratio of 1:0.2625, then 1000ppm Y2O3, 1000ppm Al(OH)3, 1000ppm SiO2, 500ppm MoO3 and 500ppm Ta2O5 are added based on the mass of the finally prepared core, placing in a high-speed mixer, the speed of the high-speed mixer is 1000 rpm, the mixing time is 40 min, after sufficient mixing, to obtain the mixture. The mixture is calcined at 600℃ for 4h in an air atmosphere, and then the temperature is increased to 950℃ for calcining for 10h, to obtain the calcined product, after crushing, sieving, washing with water and drying, to obtain Li 1.013 Ni 0.496 Mn 1.488 Y 0.002 Al 0.007 Si 0.006 Mo 0.001 Ta 0.0005 O 3.983 .

[0243] The specific surface area of the positive electrode materials prepared in the above examples and comparative examples is tested by gas adsorption method, and the results are shown in Table 1.

[0244] The positive electrode material prepared in Example 1 and Comparative Example 1 was observed by scanning electron microscope, and the scanning electron microscope images (SEM images) of the positive electrode material in Example 1 and Comparative Example 1 are shown in Figures 1 and 2, respectively.

[0245] II. Battery performance test

[0246] The positive electrode material prepared in Example 1 was mixed with acetylene black and polyvinylidene fluoride at a mass ratio of 90:5:5, and then N-methyl pyrrolidone was added as a dispersant to grind into a slurry. Then the slurry was uniformly coated on one side of the surface of an aluminum foil, vacuum dried at 120°C for 10h, and the dried electrode sheet was rolled using a roll machine. The aluminum foil was cut into a circular electrode sheet with a diameter of 1.2cm using a slicing machine, and the loading amount of active material was controlled at 12mg / cm 2 A liquid battery was assembled in an argon atmosphere glove box, in which a lithium sheet with a diameter of 1.5cm was used as the negative electrode, a 12μm PP / PE film was used as the separator, and 10μL of 1mol / L LiPF6 electrolyte was added at the interface between the positive electrode sheet, lithium negative electrode and electrolyte. The CR2032 type button cell was assembled in an environment with a water partial pressure ≤0.1ppm and an oxygen partial pressure ≤0.1ppm.

[0247] The preparation method of the button cell in Examples 2-13 and Comparative Examples 1-9 was the same as that in Example 1.

[0248] The button cells prepared in each of the above examples and comparative examples were subjected to metal elution test, capacity test and cycle performance test, and the test conditions were LR 2032.

[0249] The cycle performance test method was as follows: the button cell was charged at 1C and discharged at 1C at 45°C for 50 cycles, and the voltage range was 3.5V-4.9V.

[0250] The capacity test method was as follows: the button cell was charged at 0.33C and discharged at 0.33C at 25°C for 1 cycle, and the voltage range was 3.5V-4.9V.

[0251] Metal elution test: the metal content in the electrolyte was tested by ICP after standing at 60°C for 7 days at 4.9V. The test results of each of the above examples and comparative examples are shown in Table 1.

[0252] Table 1

[0253] From the comparison of the results of Examples 1-13 and Comparative Examples 1-9, compared with Comparative Examples 1-9, Examples 1-13 have higher discharge specific capacity and cycle capacity retention rate and lower total metal elution amount. It shows that the composite coating layer provided by the application can effectively adsorb transition metal ions dissolved in the electrolyte, reducing the crosstalk effect between the positive and negative materials; the positive material of the application effectively improves the capacity and cycle retention rate of the material by adopting the composite coating layer, and greatly reduces the impedance increase in the cycle.

[0254] From the comparison of the results of Examples 1 and Comparative Example 1 in Table 1 and Figures 1-2, the positive material prepared in Comparative Example 1 has no coating on the surface, and after the positive material prepared in Example 1 forms a composite coating layer containing Al and P on the surface, the capacity is greatly increased, the initial coulombic efficiency is increased, the capacity retention rate is greatly increased, and the metal elution amount is greatly decreased. It shows that the composite coating has good effects of improving capacity, inhibiting cycle decay and inhibiting transition metal elution.

[0255] From the comparison of the results of Examples 1 and Comparative Examples 1-7, compared with Comparative Examples 1-7, the capacity and cycle retention rate in Example 1 are greatly improved, and the metal elution amount is greatly decreased; it shows that when the lithium nickel manganese oxide is coated with a composite coating, and each coating layer contains aluminum and phosphorus elements, the composite coating has good effects of improving capacity, inhibiting cycle decay and inhibiting transition metal elution.

[0256] From the comparison of the results of Examples 1 and Comparative Example 8, the application provides a preparation method, in step S2, wet chemical coating is performed before the calcination treatment, which can greatly enhance the dispersion uniformity of the coating material (phosphorus source and aluminum source) on the surface of the core, thereby further improving the performance of the prepared positive material.

[0257] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.

[0258] The above-described embodiments only express several embodiments of the application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which are within the scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A composite-coated cathode material, characterized by, The composite-coated positive electrode material has one or more of the following characteristics (1)-(10): (1) the first coating material coats at least part of the surface of the lithium nickel manganese oxide, and the second coating material coats at least part of the surface of the first coating material; (3) the volume average particle size Dv50 of the inner core is 4-8 μm; (6) the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging is > 50 mV; 2. The composite-coated cathode material of claim 1, wherein, (7) the percentage of the capacity of the 4.3 V to 3.8 V platform of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging to the total discharge capacity is 5%-9%; (8) the 0.33 C discharge capacity of the composite-coated positive electrode material is > 130 mAh / g; (10) the composite-coated positive electrode material is a single crystal particle and / or a single crystal-like particle.

3. The composite-coated cathode material of claim 1, wherein, The composite-coated positive electrode material has one or more of the following characteristics (1)-(10): (1) the first coating material coats at least part of the surface of the lithium nickel manganese oxide, and the second coating material coats at least part of the surface of the first coating material; 4. The composite-coated cathode material of any one of claims 1 to 3, wherein the coating layer comprises a lithium transition metal oxide. (3) the volume average particle size Dv50 of the inner core is 4-8 μm; (6) the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging is > 50 mV; (2) the lithium nickel manganese oxide has a chemical formula of Li a Ni b Mn c M1 d M2 e O 4-f , 0.95≤a≤1.1, 0.45<b<0.55, 1.4<c<1.6, 0≤d+e≤0.1, 0≤f≤0.1, the M1 element includes one or more elements of S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F and La, and the M2 element includes one or more elements of V, Nb, Mo, W, Ta, B, Sb and Bi; (7) the percentage of the capacity of the 4.3 V to 3.8 V platform of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging to the total discharge capacity is 5%-9%; (4) the specific surface area of the core is 0.3 m 2 / g-0.7 m 2 / g; (5) the specific surface area of the composite-coated positive electrode material is 0.3 m 2 / g-0.8 m 2 / g; (8) the 0.33 C discharge capacity of the composite-coated positive electrode material is > 130 mAh / g; (10) the composite-coated positive electrode material is a single crystal particle and / or a single crystal-like particle. The composite-coated positive electrode material has one or more of the following characteristics (1)-(10): (9) the peak intensity ratio coefficient I 311 2 / (I 400 I 111 )<0.5, wherein I 311 is the diffraction intensity of the crystal face (311) in the XRD diffraction pattern, I 400 is the diffraction intensity of the crystal face (400) in the XRD diffraction pattern, and I 111 is the diffraction intensity of the crystal face (111) in the XRD diffraction pattern. (1) the first coating material coats at least part of the surface of the lithium nickel manganese oxide, and the second coating material coats at least part of the surface of the first coating material; 5. A method for preparing a composite-coated cathode material, characterized by, (3) the volume average particle size Dv50 of the inner core is 4-8 μm; (6) the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging is > 50 mV; (7) the percentage of the capacity of the 4.3 V to 3.8 V platform of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging to the total discharge capacity is 5%-9%; (8) the 0.33 C discharge capacity of the composite-coated positive electrode material is > 130 mAh / g; (10) the composite-coated positive electrode material is a single crystal particle and / or a single crystal-like particle. The composite-coated positive electrode material has one or more of the following characteristics (1)-(10): (1) the first coating material coats at least part of the surface of the lithium nickel manganese oxide, and the second coating material coats at least part of the surface of the first coating material; (3) the volume average particle size Dv50 of the inner core is 4-8 μm; (6) the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging is > 50 mV; (7) the percentage of the capacity of the 4.3 V to 3.8 V platform of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging to the total discharge capacity is 5%-9%; (8) the 0.33 C discharge capacity of the composite-coated positive electrode material is > 130 mAh / g; (10) the composite-coated positive electrode material is a single crystal particle and / or a single crystal-like particle. The composite-coated positive electrode material has one or more of the following characteristics (1)-(10): (1) the first coating material coats at least part of the surface of the lithium nickel manganese oxide, and the second coating material coats at least part of the surface of the first coating material; (3) the volume average particle size Dv50 of the inner core is 4-8 μm; (6) the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging is > 50 mV; (7) the percentage of the capacity of the 4.3 V to 3.8 V platform of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging to the total discharge capacity is 5%-9%; (8) the 0.33 C discharge capacity of the composite-coated positive electrode material is > 130 mAh / g; (10) the composite-coated positive electrode material is a single crystal particle and / or a single crystal-like particle. The composite-coated positive electrode material has one or more of the following characteristics (1)-(10): (1) the first coating material coats at least part of the surface of the lithium nickel manganese oxide, and the second coating material coats at least part of the surface of the first coating material; (3) the volume average particle size Dv50 of the inner core is 4-8 μm; (6) the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging is > 50 mV; (7) the percentage of the capacity of the 4.3 V to 3.8 V platform of the electrochemical distribution curve of the composite-coated positive electrode material at 0.33 C charging to the total discharge capacity is 5%-9%; (8) the 0.33 C discharge capacity of the composite-coated positive electrode material is > 130 mAh / g; (10) the composite-coated positive electrode material is a single crystal particle and / or a single crystal-like particle. carrying out a second calcination treatment on the mixture containing the intermediate, the second aluminum source and the second phosphorus source to form a second coating layer on at least part of the surface of the first coating layer, to prepare the composite-coated cathode material; wherein the inner core contains lithium nickel manganese oxide; the first coating layer contains a first coating material, the first coating material includes one or more of nickel phosphate, manganese phosphate, lithium phosphate, nickel lithium phosphate and manganese lithium phosphate, and the first coating material further includes aluminum elements, at least part of the aluminum elements occupying nickel element sites and / or manganese element sites of the crystal structure of the lithium nickel manganese oxide; the second coating layer contains a second coating material, the second coating material includes lithium phosphate and at least one of lithium metaluminite and aluminum oxide.

6. The production method according to claim 5, wherein The preparation method includes at least one of the following conditions: (1) the first aluminum source includes one or more of aluminum nitrate and its hydrate, aluminum dihydrogen phosphate and its hydrate, aluminum lactate and its hydrate, aluminum triethoxide, aluminum orthophosphate and aluminum pyrophosphate; optionally one or more of aluminum nitrate and its hydrate and aluminum triethoxide; (2) the first phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, monohydrogen ammonium phosphate, diphosphorus pentoxide, lithium dihydrogen phosphate, potassium dihydrogen phosphate, manganese dihydrogen phosphate and its hydrate, lithium monohydrogen phosphate, sodium monohydrogen phosphate, potassium monohydrogen phosphate, triethyl phosphate, trimethyl phosphate, aluminum dihydrogen phosphate and pyrophosphate salt, and optionally one or more of phosphoric acid and trimethyl phosphate; optionally, the pyrophosphate salt includes one or more of lithium pyrophosphate, sodium pyrophosphate, potassium pyrophosphate and aluminum pyrophosphate; (3) the solvent used for preparing the solution containing the first aluminum source and the first phosphorus source includes one or more of ethanol, methanol, dimethyl phthalate and water; (4) the temperature of the first calcination treatment is 600-900℃, the time is 2-12h, the heating rate is 1-5℃ / min, and the cooling rate is >2℃ / min; optionally, the temperature of the first calcination treatment is 700-800℃, and the time is 6-8h; (5) the raw material during the first calcination treatment further includes a first additive, the first additive and the filtered solid are subjected to the first calcination treatment together, and the first additive contains one or more of Li, S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb and Bi; (6) the voltage difference between the two main peaks of the capacity differential curve of the electrochemical distribution curve of the 0.33C charge of the intermediate is greater than 50mV; (7) the second aluminum source includes one or more of compounds containing Al-O bonds; optionally, the second aluminum source includes one or more of aluminum hydroxide, aluminum oxide, lithium metaluminite and sodium aluminate; (8) the second phosphorus source includes one or more of compounds containing P-O bonds; optionally, the second phosphorus source includes one or more of lithium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate and lithium pyrophosphate; (9) the second calcination treatment has a temperature of 200-450℃, a time of 0-12h, and a temperature increase rate of 1-5℃ / min; Optionally, the second calcination treatment has a time of 1-12h. (10) the mixture subjected to the second calcination treatment further comprises a second additive, and the second additive comprises one or more of Li, S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb, and Bi.

7. The production method according to any one of claims 5 to 6, wherein The lithium nickel manganese oxide has a chemical formula of Li a Ni b Mn c M1 d M2 e O 4-f , 0.95≤a≤1.1, 0.45<b<0.55, 1.4<c<1.6, 0≤d+e≤0.1, 0≤f≤0.1, the M1 element includes one or more elements of S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F and La, and the M2 element includes one or more elements of V, Nb, Mo, W, Ta, B, Sb and Bi. Optionally, the preparation method of the core comprises: mixing the nickel-manganese precursor and the lithium source and then performing a third calcination treatment; or mixing the nickel-manganese precursor, the lithium source, and a third additive and then performing a third calcination treatment; Optionally, the nickel-manganese precursor has a chemical formula of Ni 0.25 Mn 0.75 (OH)2, Ni 0.25 Mn 0.75 C2O4, and Ni 0.25 Mn 0.75 CO3. Optionally, the nickel-manganese precursor comprises one or more of nickel-manganese hydroxide, nickel-manganese oxalate, and nickel-manganese carbonate, and is optionally nickel-manganese hydroxide. Optionally, the third additive comprises one or more of S, Y, Mg, Al, Ti, Zr, P, Sr, Si, F, La, V, Nb, Mo, W, Ta, B, Sb, and Bi. Optionally, the lithium source comprises one or more of LiOH, Li2CO3, Li2SO4, LiCl, and LiNO3, and is optionally one or more of LiOH and Li2CO3. Optionally, the molar ratio of the total metal in the nickel-manganese precursor to the lithium in the lithium source is 1:(0.5-0.55). Optionally, the third calcination treatment has a temperature of 600-1000℃, a time of 5-30h, a temperature increase rate of 1-5℃ / min, and an oxygen partial pressure in the calcination atmosphere of ≥10000Pa. Optionally, the third calcination treatment has a temperature of 850-950℃ and a time of 6-12h. Optionally, the capacity differential curve of the electrochemical distribution curve of the 0.33C charging of the core has a voltage difference between the two main peaks of less than 40mV or greater than 50mV.

8. A positive electrode sheet characterized by comprising: A composite-coated positive electrode material as claimed in any one of claims 1 to 4 or prepared by the preparation method as claimed in any one of claims 5 to 7.

9. A lithium-ion battery, characterized by A positive electrode sheet as claimed in claim 8.

10. An electrical device, characterized by A lithium ion battery as claimed in claim 9. A lithium ion battery as claimed in claim 9.

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