Positive electrode active material and preparation method therefor, positive electrode sheet, secondary battery, and electric device

Abstract

A positive electrode active material and a preparation method therefor, a positive electrode sheet, a secondary battery (1), and an electric device (2). The positive electrode active material comprises core-shell particles, each core-shell particle comprises an inner core and a shell layer, the inner core comprises a first positive electrode material, and the shell layer comprises a second positive electrode material. The first positive electrode material comprises a material represented by the general formula, i.e., Lia1Nib1M1c1O2, wherein M1 comprises one or more of Mn, Co, Al, Mg, Ti, Zr, and W, 0.9≤a1≤1.2, and b1+c1=1; the second positive electrode material comprises a material represented by the general formula, i.e., Lia2Nib2M2c2O2, wherein M2 comprises one or more of Mn, Al, Sr, Nb, and Y, 0.9≤a2≤1.2, and b2+c2=1; c2 and c1 satisfy: c2-c1≥0.05. The positive electrode active material has high nickel content and high thermal stability.

Description

Positive electrode active material and preparation method thereof, positive electrode sheet, secondary battery and electrical device

[0001] Related applications

[0002] This application claims priority to Chinese patent application number 2024103546247, filed on March 26, 2024, entitled “Positive electrode active material and preparation method thereof, positive electrode sheet, secondary battery and electrical device,” the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode active material and a preparation method thereof, a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0004] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0005] In recent years, the application of lithium-ion batteries has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, and electric vehicles. As lithium-ion batteries have achieved significant development, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0006] Ultra-high nickel cathode materials (nickel content ≥80%) can give batteries higher capacity and improve energy density. However, ultra-high nickel cathode materials themselves have poor thermal stability and are easily affected by changes in the battery's own temperature, decomposing to produce oxygen and release large amounts of heat, which can easily lead to thermal runaway. This is especially true when ultra-high nickel cathode materials are used in cylindrical batteries, where the internal winding space is small, making thermal runaway and even explosion more likely. Summary of the Invention

[0007] In order to achieve the above objectives, the first aspect of the present application provides a positive electrode active material with high nickel content and high thermal stability and a preparation method thereof, as well as a positive electrode sheet, a secondary battery and an electrical device containing the positive electrode active material.

[0008] In a first aspect of the present application, a positive electrode active material is provided, comprising a core-shell particle, wherein the core-shell particle comprises an inner core and a shell layer, wherein the inner core comprises a first positive electrode material, and the shell layer comprises a second positive electrode material;

[0009] The first cathode material includes a general formula of Li a1 Ni b1 M1 c1O2 material, M1 includes one or more of Mn, Co, Al, Mg, Ti, Zr and W, 0.9≤a1≤1.2, b1+c1=1;

[0010] The second positive electrode material includes a general formula of Li a2 Ni b2 M2 c2 O2 material, M2 includes one or more of Mn, Al, Sr, Nb and Y, 0.9≤a2≤1.2, b2+c2=1;

[0011] Among them, c2 and c1 satisfy: c2-c1≥0.05.

[0012] The above-mentioned positive electrode active material, based on the core-shell structure, rationally configures the element ratios in the core and shell positive electrode materials, which can form a stable material surface structure, reduce surface lattice oxygen loss, and thus effectively improve the thermal stability of the material, so that the material has better high-temperature cycle performance. In this way, the positive electrode active material as a whole has a higher capacity and energy density as well as better high-temperature cycle stability.

[0013] In some embodiments, c2 and c1 satisfy: 0.05≤c2-c1≤0.3.

[0014] In some embodiments, the second cathode material satisfies one or more of the following characteristics:

[0015] (1)0.6≤b2≤0.92;

[0016] (2) 0.05≤c2≤0.4;

[0017] (3)0.9≤a2≤1.02.

[0018] In some embodiments, the first cathode material satisfies one or more of the following characteristics:

[0019] (1)0.8≤b1≤1;

[0020] (2)0≤c1≤0.2;

[0021] (3)0.95≤a1≤1.05.

[0022] In some embodiments, the shell layer has a thickness of 0.1 μm to 3 μm.

[0023] In some embodiments, the core-shell particle further comprises an intermediate layer disposed between the inner core and the shell layer, wherein the intermediate layer comprises a third cathode material, wherein the third cathode material comprises a general formula of Li a3 Ni b3 M2 c3M3 d3 The material of O2, M3 includes one or more of Zr, Ti, W, Mo, Ta, Sn, Se, and Sb, 0.9≤a3≤1.2, and b3+c3+d3=1. The introduction of the element-doped intermediate layer can effectively bind lattice oxygen, play a blocking role when the shell structure fails, reduce lattice oxygen migration, thereby improving the thermal stability of the material and enhancing cycling performance.

[0024] In some embodiments, the third cathode material satisfies one or more of the following characteristics:

[0025] (1) 0.8≤b3≤0.9;

[0026] (2)0≤c3≤0.1;

[0027] (3)0.02≤d3≤0.1.

[0028] In some embodiments, the thickness of the intermediate layer is 0.1 μm to 1 μm.

[0029] In some embodiments, the Dv50 of the core-shell particles is 6 μm to 15 μm.

[0030] The second aspect of the present application provides a method for preparing the positive electrode active material according to the first aspect, comprising the following steps:

[0031] According to the general formula Li a1 Ni b1 M1 c1 O2 mixes Ni salt, M1 salt and a first solvent to prepare a first precursor solution;

[0032] According to the general formula Li a2 Ni b2 M2 c2 O2 mixes Ni salt, M2 salt and a second solvent to prepare a second precursor solution;

[0033] preparing the precursor of the core-shell particles by a precipitation method using the first precursor solution and the second precursor solution;

[0034] The precursor is mixed with lithium salt and sintered to prepare the positive electrode active material.

[0035] In some embodiments, the preparation method further comprises the following steps: a3 Ni b3 M2 c3 M3 d3O2 mixes Ni salt, M2 salt, M3 salt and a third solvent to prepare a third precursor solution, and prepares the precursor of the core-shell particles by precipitation method using the third precursor solution, the first precursor solution and the second precursor solution.

[0036] In some embodiments, the precursor of the core-shell particles prepared by precipitation method has one or more of the following characteristics:

[0037] (1) The precipitant used includes one or more of sodium hydroxide, sodium carbonate, potassium carbonate and potassium hydroxide;

[0038] (2) the complexing agent used includes one or more of ammonia, ammonium chloride, ammonium sulfate, urea, citric acid and ethylenediaminetetraacetic acid;

[0039] (3) The reaction pH is controlled at 11-14;

[0040] (4) The reaction temperature is 40°C to 80°C.

[0041] In some embodiments, the sintering has one or more of the following characteristics:

[0042] (1) The sintering temperature is 400℃~800℃;

[0043] (2) Sintering time is 8h~18h;

[0044] (3) The heating rate is 0.5℃ / min to 5℃ / min;

[0045] (4) The atmosphere is air or O2 atmosphere.

[0046] In a third aspect of the present application, a positive electrode plate is provided, comprising one or more of the positive electrode active materials described in the first aspect and the positive electrode active materials prepared by the preparation method described in the second aspect.

[0047] In a fourth aspect of the present application, a secondary battery is provided, comprising the positive electrode sheet described in the third aspect.

[0048] In some embodiments, the secondary battery is a cylindrical battery.

[0049] In a fifth aspect of the present application, an electrical device is provided, comprising one or more of the positive electrode sheet described in the third aspect and the secondary battery described in the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0051] FIG1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0052] FIG. 2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 1 .

[0053] FIG3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0054] Explanation of the accompanying symbols: 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Electric device. DETAILED DESCRIPTION

[0055] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0057] The "ranges" disclosed in this application can be defined in the form of lower limits and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this way can be inclusive or exclusive of the end values, any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4, and 5 are also listed, the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10," this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0058] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0059] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0060] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0061] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0062] In this application, open technical features or technical solutions described with words such as "contain," "include," and "includes" do not exclude additional members beyond the listed members unless otherwise specified, and can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may or may not include other members unless otherwise specified. This can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members."

[0063] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0064] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0065] In this application, CP+SEM / EDS can be used to analyze the internal structure and element distribution of the material. The cross-section of the positive electrode active material can be obtained through CP, and the element distribution can be observed in combination with SEM / EDS.

[0066] One embodiment of the present application provides a positive electrode active material, including a core-shell particle, wherein the core-shell particle includes an inner core and a shell layer, wherein the inner core includes a first positive electrode material, and the shell layer includes a second positive electrode material;

[0067] The first cathode material includes a general formula of Li a1 Nib1 M1 c1 O2 material, M1 includes one or more of Mn, Co, Al, Mg, Ti, Zr and W, 0.9≤a1≤1.2, b1+c1=1;

[0068] The second positive electrode material includes a general formula of Li a2 Ni b2 M2 c2 O2 material, M2 includes one or more of Mn, Al, Sr, Nb and Y, 0.9≤a2≤1.2, b2+c2=1;

[0069] Among them, c2 and c1 satisfy: c2-c1≥0.05.

[0070] Research has found that the thermal decomposition / oxygen release of high-nickel materials first starts from the surface of the material. After the oxygen vacancies are formed, they will further promote the migration of lattice oxygen inside the material to the surface, forming a vicious cycle. Based on this, this application proposes to enhance the stability of the surface structure of high-nickel materials to reduce the phase change and oxygen release of the surface material structure. At the same time, the study also found that using a higher content of M2 elements in the shell can make the surface structure of high-nickel materials more stable, making it less likely for lattice oxygen oxidation and release to occur at high temperatures, and can delay the exothermic temperature of the material.

[0071] Based on this, the above-mentioned positive electrode active material, on the basis of the core-shell structure, rationally configures the element ratios in the positive electrode materials of the inner core and the shell, wherein the inner core adopts a high-nickel first positive electrode material and adopts less element doping to make the overall capacity and energy density of the positive electrode active material higher, and the shell adopts a second positive electrode material doped with an M2 element having a higher content than the inner core, which can form a stable material surface structure, reduce the surface lattice oxygen loss, thereby effectively improving the thermal stability of the material and making the material have better high-temperature cycle performance, so that the positive electrode active material as a whole has a higher capacity and energy density and better high-temperature cycle stability. In addition, the setting of the core-shell structure can also reduce the erosion of the electrolyte on the high-nickel first positive electrode material in the inner core, further improving the stability of the material.

[0072] It can be understood that the general formula of the first cathode material is Li a1 Ni b1 M1 c1 "M1 in O2 c1 "It can include two parts: traditional elements and stable structural elements. The stable structural elements can be added artificially or formed by the diffusion of elements in the middle layer and shell layer during the sintering process. Among them, traditional elements include one or more of Mn and Co, and stable structural elements include one or more of Al, Mg, Ti, Zr and W.

[0073] Specifically, the difference between c2 and c1 (c2-c1) includes, but is not limited to, 0.05, 0.08, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.2, 0.25, 0.3, or a range between any two of the foregoing. Further, c2 and c1 satisfy: 0.05≤c2-c1≤0.3.

[0074] In some examples, for the second positive electrode material, 0.6≤b2≤0.92. Specifically, the value of b2 includes, but is not limited to, 0.6, 0.65, 0.7, 0.72, 0.75, 0.8, 0.82, 0.85, 0.9, 0.92, or a range between any two of the foregoing.

[0075] In some examples, for the second positive electrode material, 0.05≤c2≤0.4. Specifically, the value of c2 includes, but is not limited to, 0.05, 0.1, 0.15, 0.18, 0.2, 0.25, 0.28, 0.3, 0.35, 0.4, or a range between any two of the foregoing.

[0076] In some examples, for the second positive electrode material, 0.9≤a2≤1.02. Specifically, the value of a2 includes, but is not limited to, 0.9, 0.95, 1, 1.02, or a range between any two of the foregoing.

[0077] In some examples, for the first cathode material, 0.8≤b1≤1. Specifically, the value of b1 includes, but is not limited to, 0.8, 0.85, 0.9, 0.92, 0.95, 1, or a range between any two of the foregoing.

[0078] In some examples, for the first cathode material, 0≤c1≤0.2. Specifically, the value of c1 includes, but is not limited to, 0, 0.01, 0.03, 0.04, 0.05, 0.07, 0.08, 0.1, 0.15, 0.2, or a range between any two of the foregoing.

[0079] In some examples, for the first cathode material, 0.95≤a1≤1.05. Specifically, the value of a1 includes, but is not limited to, 0.95, 0.98, 1, 1.02, 1.05, or a range between any two of the foregoing.

[0080] In some examples, the shell layer has a thickness of 0.1 μm to 3 μm. Specifically, the shell layer has a thickness including, but not limited to, 0.1 μm, 0.2 μm, 0.3 μm, 0.7 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.5 μm, 3 μm, or a range between any two of the foregoing.

[0081] In some examples, the core-shell particle further includes an intermediate layer disposed between the inner core and the shell layer, wherein the intermediate layer comprises a third cathode material, wherein the third cathode material comprises a cathode material having a general formula of Li a3 Ni b3 M2 c3 M3 d3 The material of O2, M3 includes one or more of Zr, Ti, W, Mo, Ta, Sn, Se, and Sb, 0.9≤a3≤1.2, and b3+c3+d3=1. The introduction of the element-doped intermediate layer can effectively bind lattice oxygen, play a blocking role when the shell structure fails, reduce lattice oxygen migration, thereby improving the thermal stability of the material and enhancing cycling performance.

[0082] It can be understood that the definition of M3 is the same as that of M3 in the shell layer. It can be artificially added, or M3 in the shell layer may diffuse into the middle layer during the sintering process to form element doping.

[0083] Specifically, in the third positive electrode material, the value of a3 includes but is not limited to: 0.9, 1, 1.02, 1.1, 1.15, 1.2 or a range between any two of the foregoing.

[0084] In some examples, in the third positive electrode material, 0.8≤b3≤0.9. Specifically, the value of b3 includes but is not limited to: 0.8, 0.85, 0.82, 0.88, 0.9, or a range between any two of the foregoing.

[0085] In some examples, in the third positive electrode material, 0≤c3≤0.1. Specifically, the value of c3 includes but is not limited to: 0, 0.02, 0.05, 0.07, 0.1, or a range between any two of the foregoing.

[0086] In some examples, in the third positive electrode material, 0.02≤d3≤0.18. Specifically, the value of d3 includes but is not limited to: 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, or a range between any two of the foregoing.

[0087] In some examples, the thickness of the intermediate layer is 0.1 μm to 1 μm. Specifically, the thickness of the intermediate layer includes, but is not limited to, 0.1 μm, 0.3 μm, 0.4 μm, 0.45 μm, 0.47 μm, 0.48 μm, 0.49 μm, 0.5 μm, 0.51 μm, 0.52 μm, 0.53 μm, 0.54 μm, 0.7 μm, 1 μm, or a range between any two of the foregoing.

[0088] In some examples, the Dv50 of the core-shell particles is 6 μm to 15 μm. Specifically, the thickness of the intermediate layer includes, but is not limited to, 6 μm, 9 μm, 9.1 μm, 9.3 μm, 9.5 μm, 9.6 μm, 9.7 μm, 9.8 μm, 9.9 μm, 10 μm, 10.1 μm, 10.2 μm, 10.3 μm, 10.4 μm, 10.5 μm, 11 μm, 12 μm, 13 μm, 15 μm, or a range between any two of the foregoing. Furthermore, the thickness of the intermediate layer is 9 μm to 12 μm.

[0089] Another example of the present application also provides a method for preparing a positive electrode active material, comprising the following steps:

[0090] According to the general formula Li a1 Ni b1 M1 c1 O2 mixes Ni salt, M1 salt and a first solvent to prepare a first precursor solution;

[0091] According to the general formula Li a2 Ni b2 M2 c2 O2 mixes Ni salt, M2 salt and a second solvent to prepare a second precursor solution;

[0092] preparing the precursor of the core-shell particles by a precipitation method using the first precursor solution and the second precursor solution;

[0093] The precursor is mixed with lithium salt and sintered to prepare the positive electrode active material.

[0094] In some examples, the method for preparing the positive electrode active material further comprises: a3 Ni b3 M2 c3 M3 d3 O2 mixes Ni salt, M2 salt, M3 salt and a third solvent to prepare a third precursor solution, and prepares the precursor of the core-shell particles by precipitation method using the third precursor solution, the first precursor solution and the second precursor solution.

[0095] It can be understood that the above preparation method is similar to the above-mentioned positive electrode active material and will not be described in detail here.

[0096] Without limitation, the Ni salt, the salt of M1, the salt of M2, the salt of M3, the salt of M4, etc. can be one or more of sulfates, nitrates, chlorides, fluorides, oxalates and acetates of the corresponding elements.

[0097] Without limitation, the lithium salt may be one or more of LiOH·H2O, Li2CO3, Li2SO4, LiNO3, LiC2O4 and CH3COOLi.

[0098] Furthermore, in the process of preparing the precursor of the core-shell particles by precipitation method:

[0099] In some examples, the precipitant used includes one or more of sodium hydroxide, sodium carbonate, potassium carbonate, and potassium hydroxide.

[0100] In some examples, the complexing agent used includes one or more of ammonia, ammonium chloride, ammonium sulfate, urea, citric acid, and ethylenediaminetetraacetic acid (EDTA).

[0101] In some of these examples, the reaction pH was controlled to be between 11 and 14.

[0102] In some examples, the reaction temperature is 40°C to 80°C.

[0103] Furthermore, during the sintering process:

[0104] In some examples, the sintering temperature is 400°C to 800°C.

[0105] In some of these examples, the sintering time is 8 h to 18 h.

[0106] In some of the examples, the heating rate is 0.5°C / min to 5°C / min.

[0107] In some of these examples, the atmosphere is air or an O2 atmosphere.

[0108] Another embodiment of the present application provides a positive electrode plate, comprising one or more of the positive electrode active materials described above and the positive electrode active materials prepared by the preparation method described above.

[0109] Another embodiment of the present application provides a secondary battery, comprising the positive electrode sheet as described above.

[0110] In some examples, the secondary battery is a cylindrical battery.

[0111] Another embodiment of the present application provides an electrical device, comprising one or more of the positive electrode sheet and the secondary battery as described above.

[0112] The secondary battery and the electric device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0113] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0114] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0115] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0116] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0117] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0118] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0119] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000mPa·s to 25000mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15 mg / cm 2 ~35mg / cm 2 The compaction density of the positive electrode can be 3.0g / cm 3 ~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0121] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0122] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0123] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0124] In some of these embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0125] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0126] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0127] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0128] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s to 10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 ~220g / m 2 The compaction density of the negative electrode can be 1.0g / cm 3 ~1.8g / cm 3 .

[0129] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0130] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0131] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0132] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0133] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0134] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0135] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0136] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0137] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may optionally be 12 μm to 20 μm.

[0138] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0139] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0140] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0141] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0142] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0143] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 1 with a square structure as an example.

[0144] In some embodiments, referring to Figure 2, the outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to actual needs.

[0145] The secondary battery may be a battery module or a battery pack.

[0146] A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0147] In a battery module, multiple battery cells can be arranged in sequence along the length of the battery module. Of course, they can also be arranged in any other manner. Further, the multiple battery cells can be fixed by fasteners.

[0148] Optionally, the battery module may further include a housing having an accommodation space, wherein the plurality of battery cells are accommodated in the accommodation space.

[0149] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0150] A battery pack may include a battery box and multiple battery modules disposed within the box. The battery box comprises an upper case and a lower case. The upper case can be placed over the lower case to form an enclosed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0151] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0152] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0153] Figure 3 shows an example of an electric device 2. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0154] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0155] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0156] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0157] Example 1

[0158] This embodiment is the preparation of positive electrode active material, and the steps are as follows:

[0159] (1) Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate were mixed in a molar ratio of 90:6:4 and dissolved in pure water to obtain a first precursor salt solution having a total concentration of nickel ions, cobalt ions, and manganese ions of 2 mol / L.

[0160] (2) Nickel sulfate hexahydrate and manganese sulfate monohydrate were mixed in a molar ratio of 80:20 and dissolved in pure water to obtain a second precursor salt solution with a total concentration of nickel ions and manganese ions of 2 mol / L.

[0161] (3) Nickel sulfate hexahydrate, manganese sulfate monohydrate, and zirconium sulfate were mixed in a molar ratio of 85:10:5 and dissolved in pure water to obtain a third precursor salt solution with a total concentration of nickel ions, manganese ions, and zirconium ions of 2 mol / L.

[0162] (4) Add 20 L of pure water to a 100 L reactor, start stirring, maintain the temperature at 50 °C, add an appropriate amount of precipitant solution (4 mol / L NaOH aqueous solution), and adjust the pH of the solution in the reactor to 10-13.

[0163] (5) Under stirring conditions, the first precursor salt solution, the precipitant solution (4 mol / L NaOH aqueous solution), and the complexing agent solution (2 mol / L ammonia aqueous solution) are added to the reactor at a certain rate so that the salt solution undergoes a coprecipitation reaction in the presence of the precipitant and the complexing agent. During the reaction, the ammonia concentration and pH in the reactor are kept unchanged until the particle size Dv50 in the reactor reaches the set value.

[0164] (6) Then stop pumping the first precursor salt solution, and add the third precursor salt solution, precipitant solution (4 mol / L NaOH aqueous solution), and complexing agent solution (2 mol / L ammonia aqueous solution) into the reactor at a certain rate, keeping the ammonia concentration and pH in the reactor unchanged until the particle size Dv50 in the reactor reaches the set value.

[0165] (7) Subsequently, the second precursor salt solution is stopped from being pumped in, and the second precursor salt solution, precipitant solution (4 mol / L NaOH aqueous solution), and complexing agent solution (2 mol / L ammonia aqueous solution) are added to the reactor at a certain rate, while maintaining the ammonia concentration and pH in the reactor unchanged, until the Dv50 particle size of the particles in the reactor reaches the set value. After a period of reaction, the ternary cathode material precursor is obtained by centrifugation, washing, filtration, and drying.

[0166] (8) The ternary cathode material precursor was fully mixed with the lithium source Li2CO3, and then calcined at 500°C for 5 hours and then at 700°C for 12 hours in an air atmosphere to obtain a cathode active material. The ratio of the molar amount of the lithium element in the lithium source to the total molar amount of the metal elements in the ternary cathode material precursor was 1.02:1.

[0167] The preparation of the positive electrode active materials of Examples 2-5 is the same as that of Example 1, with the main difference being that the type of the first positive electrode material and / or the second material is changed to change the difference between c2 and c1.

[0168] The preparation of the positive electrode active materials of Examples 6-9 is the same as that of Example 1, with the main difference being that different first positive electrode materials and / or second materials are used.

[0169] The preparation of the positive electrode active materials of Examples 10-14 is the same as that of Example 1, with the main difference being that the thickness of the shell layer is changed while the thickness of the intermediate layer and the Dv50 of the core-shell particles are kept substantially unchanged.

[0170] The preparation of the positive electrode active material of Example 15 is the same as that of Example 1, with the main difference being that step (7) is not performed, i.e., no intermediate layer is provided, while the shell thickness and the core-shell particle Dv50 are kept substantially unchanged.

[0171] The preparation of the positive electrode active materials of Examples 16-18 is the same as that of Example 1, with the main difference being that the type of the third positive electrode material is changed.

[0172] The preparation of the positive electrode active materials of Examples 19-20 is the same as that of Example 1, with the main difference being that the thickness of the intermediate layer is changed while the thickness of the shell layer and the Dv50 of the core-shell particles are kept substantially unchanged.

[0173] The preparation of the positive electrode active materials of Examples 21-24 is the same as that of Example 1, with the main difference being that the Dv50 of the core-shell particles is changed while the thickness of the shell layer and the thickness of the intermediate layer are kept substantially unchanged.

[0174] The preparation of the positive electrode active material of Example 25 is the same as that of Example 1, with the main difference being that the type of the second material is changed and Al element is used as M2 doping.

[0175] The preparation of the positive electrode active material of Comparative Example 1 is the same as that of Example 1, with the main difference being that the type of the second material is changed so that the difference between c2 and c1 is 0.9.

[0176] The preparation of the positive electrode active material of Comparative Example 2 is the same as that of Example 1, with the main difference being that the type of the second material is changed and the doping element M2 is not used.

[0177] The parameters of the positive electrode active materials of Examples 1-25 and Comparative Examples 1-2 are summarized in Table 1-2 below.

[0178] Preparation Example 1

[0179] 1) Preparation of positive electrode sheet

[0180] The positive electrode active material, conductive carbon black SP and binder PVDF prepared in Example 1 were dispersed in a solvent NMP at a weight ratio of 98:1:1 and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on both sides of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained, wherein the coating amount per unit area on both sides was 0.27 g / 1540.25 mm 2 .

[0181] 2) Preparation of negative electrode sheet

[0182] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene butadiene rubber, and conductive agent acetylene black were mixed in a mass ratio of 97:1:1:1, and deionized water was added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated on both sides of the copper foil; the copper foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain a negative electrode sheet, wherein the coating amount per unit area on both sides was 0.17g / 1540.25mm 2 .

[0183] 3) Isolation film

[0184] A 12μm thick polypropylene isolation film was selected.

[0185] 4) Preparation of electrolyte

[0186] The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with the volume ratio of EC, EMC, and DEC being 20:20:60. In an argon atmosphere glove box with a water content of <10 ppm, fully dried lithium salt LiPF6 is dissolved in the organic solvent and mixed thoroughly to obtain an electrolyte solution. The concentration of the lithium salt is 1 mol / L.

[0187] 5) Preparation of batteries

[0188] The positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, with the isolation film placed between the positive and negative electrode sheets to serve as an isolation. After winding into a square bare battery cell, an aluminum-plastic film is placed in it. After baking at 80°C to remove water, 10g of the corresponding non-aqueous electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a finished battery with a capacity of 4000mAh is obtained.

[0189] The secondary batteries of Preparation Examples 2-25 and the secondary batteries of Comparative Examples 1-2 were prepared in a similar manner to the secondary battery of Preparation Example 1, but using the positive electrode active materials of the corresponding examples.

[0190] Table 1

[0191] Table 2

[0192] Test example:

[0193] (1) Exothermic temperature DSC test

[0194] 1. Fully charge the battery to 4.25V at 0.33C, then charge at a constant voltage of 4.25V until the current is ≤0.05mA. Then disassemble the battery and remove the positive electrode.

[0195] 2. Weigh the empty crucible in an indoor environment (the default is a high-pressure sealed crucible);

[0196] 3. The crucible and the positive electrode sample are transferred to the glove box, and the electrode is punched into a disc (5 mm in diameter) and placed in the crucible;

[0197] 4. Add electrolyte dropwise;

[0198] 5. Seal the crucible, transfer it out of the glove box, and weigh it. The difference between the two masses minus the weight of the substrate is the sample weight.

[0199] 6. Test: the test temperature range is 35℃~1000℃, and the temperature rise rate is 10℃ / min.

[0200] (2) Fully electric 25 / 45℃ cycle performance test

[0201] At a constant temperature of 25°C or 45°C, charge the battery at 2.8-4.25V at 1C to 4.25V, then charge at 4.25V at constant voltage until the current is ≤ 0.05mA. Let it stand for 5 minutes, then discharge the battery at 1C to 2.8V. The capacity is recorded as Dn (n=0, 1, 2...). Repeat the previous process until the capacity decays to 80%.

[0202] The test results are shown in Table 3 below:

[0203] Table 3

[0204] Comparison between the examples and the comparative examples shows that the present application can achieve better room temperature and high temperature cycle performance and better material thermal stability by rationally arranging the positive electrode materials in each layer. Furthermore, comparison between Example 1 and Example 15 shows that the provision of an intermediate layer can further improve room temperature and high temperature cycle performance and improve material thermal stability.

[0205] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0206] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A positive electrode active material comprising a core-shell particle, wherein the core-shell particle comprises an inner core and a shell, wherein the inner core comprises a first positive electrode material and the shell comprises a second positive electrode material; The first cathode material includes a general formula of Li a1 Ni b1 M1 c1 O2 material, M1 includes one or more of Mn, Co, Al, Mg, Ti, Zr and W, 0.9≤a1≤1.2, b1+c1=1; The second positive electrode material includes a general formula of Li a2 Ni b2 M2 c2 O2 material, M2 includes one or more of Mn, Al, Sr, Nb and Y, 0.9≤a2≤1.2, b2+c2=1; in, c2 and c1 satisfy: c2-c1≥0.

05.

2. The positive electrode active material according to claim 1, wherein c2 and c1 satisfy: 0.05≤c2-c1≤0.

3.

3. The positive electrode active material according to claim 1 or 2, wherein The second positive electrode material satisfies one or more of the following characteristics: (1)0.6≤b2≤0.92； (2)0.05≤c2≤0.4； (3)0.9≤a2≤1.02。 4. The positive electrode active material according to any one of claims 1 to 3, wherein The first positive electrode material satisfies one or more of the following characteristics: (1)0.8≤b1≤1； (2)0≤c1≤0.2； (3)0.95≤a1≤1.05。 5. The positive electrode active material according to any one of claims 1 to 4, wherein The thickness of the shell layer is 0.1 μm to 3 μm.

6. The positive electrode active material according to any one of claims 1 to 5, wherein The core-shell particle further comprises an intermediate layer disposed between the inner core and the shell layer, wherein the intermediate layer comprises a third positive electrode material, wherein the third positive electrode material comprises a general formula of Li a3 Ni b3 M2 c3 M3 d3 The material of O2, M3 includes one or more of Zr, Ti, W, Mo, Ta, Sn, Se and Sb, 0.9≤a3≤1.2, b3+c3+d3=1.

7. The positive electrode active material according to claim 6, wherein The third positive electrode material satisfies one or more of the following characteristics: (1)0.8≤b3≤0.9； (2)0≤c3≤0.1； (3)0.02≤d3≤0.1。 8. The positive electrode active material according to claim 6 or 7, wherein The thickness of the intermediate layer is 0.1 μm to 1 μm.

9. The positive electrode active material according to any one of claims 1 to 8, wherein The Dv50 of the core-shell particles is 6 μm to 15 μm.

10. The method for preparing the positive electrode active material according to any one of claims 1 to 9, comprising the following steps: According to the general formula Li a1 Ni b1 M1 c1 O2 mixes Ni salt, M1 salt and a first solvent to prepare a first precursor solution; According to the general formula Li a2 Ni b2 M2 c2 O2 mixes Ni salt, M2 salt and a second solvent to prepare a second precursor solution; preparing the precursor of the core-shell particles by a precipitation method using the first precursor solution and the second precursor solution; The precursor is mixed with lithium salt and sintered to prepare the positive electrode active material.

11. The method for preparing a positive electrode active material according to claim 10, wherein: Also includes the general formula Li a3 Ni b3 M2 c3 M3 d3 O2 mixes Ni salt, M2 salt, M3 salt and a third solvent to prepare a third precursor solution, and prepares the precursor of the core-shell particles by precipitation method using the third precursor solution, the first precursor solution and the second precursor solution.

12. The method for preparing a positive electrode active material according to claim 10 or 11, wherein: The precursor of the core-shell particles prepared by precipitation method has one or more of the following characteristics: (1) The precipitant used includes one or more of sodium hydroxide, sodium carbonate, potassium carbonate and potassium hydroxide; (2) the complexing agent used includes one or more of ammonia, ammonium chloride, ammonium sulfate, urea, citric acid and ethylenediaminetetraacetic acid; (3) The reaction pH is controlled at 11-14; (4) The reaction temperature is 40°C to 80°C.

13. The method for preparing a positive electrode active material according to any one of claims 10 to 12, wherein: Sintering has one or more of the following characteristics: (1) The sintering temperature is 400℃~800℃; (2) Sintering time is 8h~18h; (3) The heating rate is 0.5℃ / min to 5℃ / min; (4) The atmosphere is air or O2 atmosphere.

14. A positive electrode sheet comprising one or more of the positive electrode active material according to any one of claims 1 to 9 and the positive electrode active material prepared by the preparation method according to any one of claims 10 to 13.

15. A secondary battery comprising the positive electrode sheet according to claim 14. The secondary battery according to claim 15 , which is a cylindrical battery.

17. An electrical device comprising one or more of the positive electrode sheet according to claim 14 and the secondary battery according to any one of claims 15 to 16.

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