Positive electrode active materials and their preparation methods, positive electrode sheets, secondary batteries and electrical devices

Abstract

This application provides a positive electrode active material and its preparation method, a positive electrode sheet, a secondary battery, and an electrical device. The positive electrode active material comprises core-shell particles, each comprising an inner core and a shell layer. The inner core contains a first positive electrode material, and the shell layer contains a second positive electrode material. The first positive electrode material comprises materials with the general formula Li. a1 Ni b1 M1 c1 The material for O2, M1 includes one or more of Mn, Co, Al, Mg, Ti, Zr, and W, where 0.9 ≤ a1 ≤ 1.2, and b1 + c1 = 1; the second cathode material includes materials with the general formula Li. a2 Ni b2 M2 c2 The material for O2, M2 includes one or more of Mn, Al, Sr, Nb, and Y, with 0.9 ≤ a2 ≤ 1.2 and b2 + c2 = 1; where c2 and c1 satisfy: c2 - c1 ≥ 0.05. The aforementioned positive electrode active material has a high nickel content and high thermal stability.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a positive electrode active material and its preparation method, a positive electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0003] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in various fields such as power tools, electric bicycles, electric motorcycles, and electric vehicles. Due to the significant advancements in lithium-ion battery technology, higher requirements have been placed on its energy density, cycle performance, and safety performance.

[0004] Ultra-high nickel cathode materials (nickel content ≥80%) can give batteries higher capacity and improve energy density. However, ultra-high nickel cathode materials have poor thermal stability and are easily affected by changes in the battery's own temperature, decomposing to produce oxygen and releasing a large amount of heat, which can easily lead to thermal runaway. In particular, when ultra-high nickel cathode materials are used in cylindrical batteries, the remaining space inside the winding is small, making thermal runaway or even explosion more likely. Summary of the Invention

[0005] To achieve the above objectives, the first aspect of this application provides a positive electrode active material with high nickel content and high thermal stability, a method for preparing the same, as well as a positive electrode sheet, a secondary battery, and an electrical device containing the positive electrode active material.

[0006] In a first aspect, this application provides a positive electrode active material comprising core-shell particles, the core-shell particles comprising an inner core and a shell layer, the inner core comprising a first positive electrode material, the shell layer comprising a second positive electrode material;

[0007] The first cathode material includes materials with the general formula Li a1 Ni b1 M1 c1 The material of O2, M1 includes one or more of Mn, Co, Al, Mg, Ti, Zr and W, 0.9≤a1≤1.2, b1+c1=1;

[0008] The second cathode material includes materials with the general formula Li a2 Ni b2 M2 c2 The material of O2, M2 includes one or more of Mn, Al, Sr, Nb and Y, 0.9≤a2≤1.2, b2 +c2=1;

[0009] Where c2 and c1 satisfy: c2-c1≥0.05.

[0010] The aforementioned positive electrode active material, based on the core-shell structure, can form a stable material surface structure by rationally configuring the element ratio in the core and shell layers of the positive electrode material, reducing surface lattice oxygen loss, thereby effectively improving the thermal stability of the material and giving it better high-temperature cycling performance. As a result, the positive electrode active material as a whole has high capacity and energy density as well as good high-temperature cycling stability.

[0011] In some implementations, c2 and c1 satisfy: 0.05 ≤ c2 - c1 ≤ 0.3.

[0012] In some embodiments, the second positive electrode material satisfies one or more of the following characteristics:

[0013] (1) 0.6 ≤ b2 ≤ 0.92;

[0014] (2) 0.05≤c2≤0.4;

[0015] (3) 0.9≤a2≤1.02.

[0016] In some embodiments, the first cathode material satisfies one or more of the following characteristics:

[0017] (1) 0.8 ≤ b1 ≤ 1;

[0018] (2) 0 ≤ c1 ≤ 0.2;

[0019] (3) 0.95≤a1≤1.05.

[0020] In some embodiments, the thickness of the shell is 0.1 μm to 3 μm.

[0021] In some embodiments, the core-shell particle further includes an intermediate layer disposed between the inner core and the shell, the intermediate layer comprising a third cathode material, the third cathode material comprising a material of the general formula Li. a3 Ni b3 M2 c3 M3 d3 The material containing O2, M3 includes one or more of Zr, Ti, W, Mo, Ta, Sn, Se, and Sb, where 0.9 ≤ a3 ≤ 1.2 and b3 + c3 + d3 = 1. By introducing the element-doped intermediate layer, lattice oxygen can be effectively confined, playing a blocking role in the event of shell structure failure, reducing lattice oxygen migration, thereby improving the thermal stability of the material and enhancing its cycling performance.

[0022] In some embodiments, the third cathode material satisfies one or more of the following characteristics:

[0023] (1) 0.8 ≤ b3 ≤ 0.9;

[0024] (2) 0 ≤ c3 ≤ 0.1;

[0025] (3) 0.02≤d3≤0.1.

[0026] In some embodiments, the thickness of the intermediate layer is 0.1 μm to 1 μm.

[0027] In some embodiments, the core-shell particles have a Dv50 of 6 μm to 15 μm.

[0028] A second aspect of this application provides a method for preparing the positive electrode active material described in the first aspect, comprising the following steps:

[0029] According to the general formula Li a1 Ni b1 M1 c1 O2 is mixed with Ni salt, M1 salt and a first solvent to prepare a first precursor solution;

[0030] According to the general formula Li a2 Ni b2 M2 c2 O2 is mixed with Ni salt, M2 salt and a second solvent to prepare a second precursor solution;

[0031] The precursor of the core-shell particles was prepared by precipitation using the first precursor solution and the second precursor solution.

[0032] The precursor is mixed with lithium salt and sintered to prepare the positive electrode active material.

[0033] In some embodiments, the preparation method further includes preparation according to the general formula Li a3 Ni b3 M2 c3 M3 d3 The steps include preparing a third precursor solution by mixing O2 with Ni salt, salt of M2, salt of M3 and a third solvent, and preparing the precursor of the core-shell particles by precipitation of the third precursor solution with the first precursor solution and the second precursor solution.

[0034] In some embodiments, the precursor for preparing the core-shell particles by precipitation has one or more of the following characteristics:

[0035] (1) The precipitant used includes one or more of sodium hydroxide, sodium carbonate, potassium carbonate and potassium hydroxide;

[0036] (2) The complexing agents used include one or more of ammonia, ammonium chloride, ammonium sulfate, urea, citric acid and ethylenediaminetetraacetic acid;

[0037] (3) The reaction pH is controlled at 11~14;

[0038] (4) The reaction temperature is 40℃~80℃.

[0039] In some embodiments, sintering has one or more of the following characteristics:

[0040] (1) The sintering temperature is 400℃~800℃;

[0041] (2) The sintering time is 8h~18h;

[0042] (3) The heating rate is 0.5℃ / min to 5℃ / min;

[0043] (4) The atmosphere is air or O2 atmosphere.

[0044] A third aspect of this application provides a positive electrode sheet, 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.

[0045] A fourth aspect of this application provides a secondary battery, including the positive electrode sheet described in the third aspect.

[0046] In some embodiments, the secondary battery is a cylindrical battery.

[0047] A fifth aspect of this application provides an electrical device comprising one or more of the positive electrode sheet described in the third aspect and the secondary battery described in the fourth aspect. Attached Figure Description

[0048] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0049] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0050] Figure 2 for Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0051] Figure 3This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0052] Explanation of reference numerals in the attached figures:

[0053] 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0054] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0055] 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 this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0056] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be independently included or excluded, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0057] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0058] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0059] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0060] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0061] In this application, open-ended technical features or solutions described using terms such as "containing," "including," or "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members."

[0062] In this application, unless otherwise specified, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0063] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0064] In this application, CP+SEM / EDS can be used to analyze the internal structure and elemental distribution of the material. CP can be used to obtain the cross-section of the positive electrode active material, and combined with SEM / EDS, the elemental distribution can be observed.

[0065] One embodiment of this application provides a positive electrode active material, including core-shell particles, wherein the core-shell particles include an inner core and a shell layer, the inner core containing a first positive electrode material, and the shell layer containing a second positive electrode material;

[0066] The first cathode material includes materials with the general formula Li a1 Ni b1 M1 c1 The material of O2, M1 includes one or more of Mn, Co, Al, Mg, Ti, Zr and W, 0.9≤a1≤1.2, b1+c1=1;

[0067] The second cathode material includes materials with the general formula Li a2 Ni b2 M2 c2 The material of O2, M2 includes one or more of Mn, Al, Sr, Nb and Y, 0.9≤a2≤1.2, b2 +c2=1;

[0068] Where c2 and c1 satisfy: c2-c1≥0.05.

[0069] Research has revealed that the thermal decomposition / oxygen release of high-nickel materials begins at the material surface. The formation of oxygen vacancies further promotes the migration of lattice oxygen from the material's interior to the surface, creating a vicious cycle. Based on this, this application proposes enhancing the stability of the surface structure of high-nickel materials to reduce phase transitions and oxygen release in the surface layer. The research also found that using a higher content of M2 element in the shell can further stabilize the surface structure of high-nickel materials, making them less prone to lattice oxygen oxidation and release at high temperatures, and delaying the material's exothermic temperature.

[0070] Based on this, the aforementioned positive electrode active material, with its core-shell structure, rationally configures the elemental ratios of the core and shell layers. The core uses a high-nickel first positive electrode material with fewer elemental doping elements, resulting in higher overall capacity and energy density. The shell layer uses a second positive electrode material with a higher M2 element doping content than the core, forming a stable surface structure and reducing surface lattice oxygen loss. This effectively improves the material's thermal stability and gives it better high-temperature cycling performance. Therefore, the overall positive electrode active material exhibits high capacity and energy density, as well as good high-temperature cycling stability. Furthermore, this core-shell structure reduces electrolyte erosion of the high-nickel first positive electrode material in the core, further improving the material's stability.

[0071] Understandably, the general formula of the first cathode material is Li a1 Ni b1 M1 c1 O2 "M1" 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 intermediate layer and shell layer during the sintering process. The traditional elements include one or more of Mn and Co, and the stable structural elements include one or more of Al, Mg, Ti, Zr and W.

[0072] 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 any two of the foregoing. Further, c2 and c1 satisfy: 0.05 ≤ c2-c1 ≤ 0.3.

[0073] In some examples, in the second cathode 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 any range between the two aforementioned values.

[0074] In some examples, in the second cathode 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 any range between the two aforementioned.

[0075] In some examples, in the second cathode 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 any two of the foregoing.

[0076] In some of these examples, in 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 any two of the foregoing.

[0077] In some of these examples, in 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 any two of the foregoing.

[0078] In some of these examples, in 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 any two of the foregoing.

[0079] In some examples, the thickness of the shell is 0.1 μm to 3 μm. Specifically, the thickness of the shell includes, but is 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 any range between the foregoing.

[0080] In some examples, the core-shell particle further includes an intermediate layer disposed between the inner core and the shell, the intermediate layer comprising a third cathode material, the third cathode material comprising the general formula Li a3 Ni b3 M2 c3 M3 d3 The O2 material, M3 includes one or more of Zr, Ti, W, Mo, Ta, Sn, Se, and Sb, with 0.9 ≤ a3 ≤ 1.2 and b3 + c3 + d3 = 1. By introducing the element-doped intermediate layer, lattice oxygen can be effectively confined, playing a blocking role when the shell structure fails, reducing lattice oxygen migration, thereby improving the thermal stability of the material and enhancing its cycling performance.

[0081] Understandably, the definition of M3 is the same as that of M3 in the shell. It can be added artificially, or it can be formed by the diffusion of M3 in the shell into the intermediate layer during the sintering process, thus forming elemental doping.

[0082] Specifically, in the third cathode material, the value of a3 includes, but is not limited to: 0.9, 1, 1.02, 1.1, 1.15, 1.2 or any two of the above.

[0083] In some examples, the third cathode material has a density of 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 any two of the foregoing.

[0084] In some examples, the third cathode material has a value of 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 any two of the foregoing.

[0085] In some examples, the third cathode material has a density of 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 any range between the two aforementioned values.

[0086] 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.

[0087] 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 any range between the foregoing. Further, the thickness of the intermediate layer is 9 μm to 12 μm.

[0088] Another example of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0089] According to the general formula Li a1 Ni b1 M1 c1 O2 is mixed with Ni salt, M1 salt and a first solvent to prepare a first precursor solution;

[0090] According to the general formula Li a2 Ni b2 M2 c2 O2 is mixed with Ni salt, M2 salt and a second solvent to prepare a second precursor solution;

[0091] The precursor of the core-shell particles was prepared by precipitation using the first precursor solution and the second precursor solution.

[0092] The precursor is mixed with lithium salt and sintered to prepare the positive electrode active material.

[0093] In some examples, the method for preparing the positive electrode active material further includes following the general formula Li a3 Ni b3 M2 c3 M3 d3 The steps include preparing a third precursor solution by mixing O2 with Ni salt, salt of M2, salt of M3 and a third solvent, and preparing the precursor of the core-shell particles by precipitation of the third precursor solution with the first precursor solution and the second precursor solution.

[0094] Understandably, the preparation method described above is similar to that of the aforementioned positive electrode active material, and will not be repeated here.

[0095] Without limitation, the salts of Ni, M1, M2, M3, and M4 can be one or more of the sulfates, nitrates, chlorides, fluorides, oxalates, and acetates of the corresponding elements.

[0096] Without limitation, the lithium salt may be one or more of LiOH•H2O, Li2CO3, Li2SO4, LiNO3, LiC2O4 and CH3COOLi.

[0097] Furthermore, in the process of preparing the precursor of the core-shell particles by precipitation:

[0098] In some of these examples, the precipitant used includes one or more of sodium hydroxide, sodium carbonate, potassium carbonate, and potassium hydroxide.

[0099] In some of these examples, the complexing agents used include one or more of ammonia, ammonium chloride, ammonium sulfate, urea, citric acid, and ethylenediaminetetraacetic acid (EDTA).

[0100] In some of these examples, the reaction pH was controlled between 11 and 14.

[0101] In some of these examples, the reaction temperature is 40°C to 80°C.

[0102] Furthermore, during the sintering process:

[0103] In some of these examples, the sintering temperature is 400℃~800℃.

[0104] In some of these examples, the sintering time is 8h to 18h.

[0105] In some of these examples, the heating rate is 0.5℃ / min to 5℃ / min.

[0106] In some of these examples, the atmosphere is air or an O2 atmosphere.

[0107] Another embodiment of this application provides a positive electrode sheet, comprising one or more of the positive electrode active material as described above and the positive electrode active material prepared by the preparation method as described above.

[0108] Another embodiment of this application provides a secondary battery, including the positive electrode sheet as described above.

[0109] In some of these examples, the secondary battery is a cylindrical battery.

[0110] Another embodiment of this application provides an electrical device, including one or more of the positive electrode sheet and the secondary battery described above.

[0111] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0112] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0113] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0114] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0115] 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 substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0116] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As a non-limiting example, the positive electrode active material may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries 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 include, but are not limited to, one or more of lithium cobalt oxides (such as LiCoO2), lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium manganese iron phosphate and carbon composites. 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 known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.8 Co 0.15 Al 0.05 O2.

[0117] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0118] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, 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.

[0119] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface or 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 5000 mPa·s to 25000 mPa·s. When coating the positive electrode slurry, the coating areal density per unit area (dry weight, minus solvent) can be 15 mg / cm³. 2 ~35mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 ~3.6g / cm 3 3.3g / cm³ is an option. 3 ~3.5g / cm 3 .

[0120] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0121] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0122] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0123] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. 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, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional 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.

[0124] In some embodiments, the negative electrode active material layer may optionally 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).

[0125] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. 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.

[0126] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0127] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes. 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 both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt%~60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s~10000mPa·s. When coating the negative electrode slurry, the coating unit areal density (dry weight, deducting solvent) can be 75g / m². 2 ~220g / m 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 ~ 1.8g / cm 3 .

[0128] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0129] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0130] 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 bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0131] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butene carbonate ( One or more of the following: 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.

[0132] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0133] 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), trifluoromethyl ethylene carbonate (TFPC), etc.

[0134] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0135] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven 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.

[0136] In some embodiments, the thickness of the isolation membrane is 6μm to 40μm, and optionally 12μm to 20μm.

[0137] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0138] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0139] In some embodiments, the outer packaging of the secondary battery can be a rigid 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 pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0140] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0141] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0142] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 1.

[0143] In some of these embodiments, reference is made to Figure 2 The outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The secondary battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to actual needs.

[0144] Secondary batteries can be battery modules or battery packs.

[0145] A battery module includes at least one battery cell. The number of battery cells 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.

[0146] In a battery module, multiple battery cells can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these battery cells can be secured using fasteners.

[0147] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells are housed.

[0148] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0149] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0150] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may 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.

[0151] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0152] Figure 3 Here is an example of an electrical device 2. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0153] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0154] 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 embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0155] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0156] Example 1

[0157] This embodiment describes the preparation of the positive electrode active material, and the steps are as follows:

[0158] (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 with a total concentration of nickel ions, cobalt ions, and manganese ions of 2 mol / L.

[0159] (2) Mix nickel sulfate hexahydrate and manganese sulfate monohydrate in a molar ratio of 80:20 and dissolve them in pure water to obtain a second precursor salt solution with a total concentration of nickel ions and manganese ions of 2 mol / L.

[0160] (3) Mix nickel sulfate hexahydrate, manganese sulfate monohydrate and zirconium sulfate in a molar ratio of 85:10:5 and dissolve them 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.

[0161] (4) Add 20L of pure water to a 100L reactor, turn on the stirrer, keep the temperature at 50℃, add an appropriate amount of precipitant solution (4mol / L NaOH aqueous solution), and adjust the pH of the solution in the reactor to 10-13.

[0162] (5) Under stirring conditions, the first 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 so that the salt solution undergoes a co-precipitation reaction in the presence of precipitant and complexing agent. During the reaction, the ammonia concentration and pH in the reactor are kept constant until the particle size Dv50 in the reactor reaches the set value.

[0163] (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) to 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.

[0164] (7) Subsequently, the pumping of the second precursor salt solution was stopped, and the second precursor salt solution, precipitant solution (4 mol / L NaOH aqueous solution), and complexing agent solution (2 mol / L ammonia aqueous solution) were added to the reactor at a certain rate, keeping the ammonia concentration and pH in the reactor constant until the particle size Dv50 in the reactor reached the set value. After reacting for a period of time, the precursor of the ternary cathode material was obtained by centrifugation, washing, filtration, and drying.

[0165] (8) The ternary cathode material precursor was thoroughly mixed with the lithium source Li2CO3 and calcined at 500°C for 5 h in an air atmosphere, followed by calcination at 700°C for 12 h to obtain the cathode active material. The molar ratio of Li element in the lithium source to the total molar ratio of metal elements in the ternary cathode material precursor was 1.02:1.

[0166] The preparation of the positive electrode active materials in Examples 2-5 is the same as in Example 1, the main difference being that the types of the first positive electrode material and / or the second material are changed to change the difference between c2 and c1.

[0167] The preparation of the positive electrode active materials in Examples 6-9 is the same as in Example 1, the main difference being that different first positive electrode materials and / or second materials are used.

[0168] The preparation of the positive electrode active materials in Examples 10-14 is the same as in Example 1, the main difference being that the thickness of the shell layer is changed, while the thickness of the intermediate layer and the core-shell particle Dv50 are kept basically unchanged.

[0169] The preparation of the positive electrode active material in Example 15 is the same as in Example 1, except that step (7) is not performed, that is, no intermediate layer is set, while the shell thickness and the core-shell particle Dv50 are kept basically unchanged.

[0170] The preparation of the positive electrode active materials in Examples 16-18 is the same as in Example 1, the main difference being that the type of the third positive electrode material is changed.

[0171] The preparation of the positive electrode active material in Examples 19-20 is the same as in Example 1, the main difference being that the thickness of the intermediate layer is changed, while the thickness of the shell layer and the core-shell particle Dv50 are kept basically unchanged.

[0172] The preparation of the positive electrode active materials in Examples 21-24 is the same as in Example 1, the main difference being: the core-shell particle Dv50 is changed, while the thickness of the shell layer and the thickness of the intermediate layer are kept basically unchanged.

[0173] The preparation of the positive electrode active material in Example 25 is the same as in Example 1, except that the type of the second material is changed and Al element is used as M2 dopant.

[0174] The preparation of the positive electrode active material in Comparative Example 1 is the same as in Example 1, except that the type of the second material is changed so that the difference between c2 and c1 is 0.9.

[0175] The preparation of the positive electrode active material in Comparative Example 2 is the same as in Example 1, except that the type of the second material is changed and doping element M2 is not used.

[0176] The parameters of the positive electrode active materials of Examples 1-25 and Comparative Examples 1-2 are summarized in Table 1-2 below.

[0177] Preparation Example 1

[0178] 1) Preparation of positive electrode sheet

[0179] The positive electrode active material, conductive carbon black SP, and binder PVDF prepared in Example 1 were dispersed in NMP solvent at a weight ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was uniformly 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 mm². 2 .

[0180] 2) Preparation of negative electrode sheet

[0181] Graphite (negative electrode active material), sodium carboxymethyl cellulose (thickener), styrene-butadiene rubber (binder), and acetylene black (conductive agent) were mixed in a mass ratio of 97:1:1:1. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was then uniformly coated onto both sides of a copper foil. After the copper foil was dried at room temperature, it was transferred to a 120°C oven and dried for 1 hour. The foil was then cold-pressed and slit to obtain the negative electrode sheet, with a coating weight of 0.17 g / 1540.25 mm² on both sides. 2 .

[0182] 3) Separating membrane

[0183] A 12μm thick polypropylene separator membrane was selected.

[0184] 4) Preparation of electrolyte

[0185] The organic solvent was a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a volume ratio of EC:20:20:60. Thoroughly dried lithium salt LiPF6 was dissolved in the organic solvent and mixed thoroughly in an argon-atmosphere glove box with a water content of <10 ppm to obtain the electrolyte. The concentration of the lithium salt was 1 mol / L.

[0186] 5) Battery manufacturing

[0187] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. After being wound into a square bare cell, it is placed in an aluminum-plastic film, baked at 80°C to remove water, and then 10g of the corresponding non-aqueous electrolyte is injected and sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, a finished battery with a capacity of 4000mAh is obtained.

[0188] The preparation methods of the secondary batteries in Examples 2-25 and Comparative Examples 1-2 are similar to those in Example 1, but the corresponding positive electrode active materials are used.

[0189] Table 1

[0190]

[0191] Table 2

[0192]

[0193] Test example:

[0194] (1) Exothermic temperature DSC test

[0195] 1. Charge the full battery to 4.25V at 0.33C, and then charge it at a constant voltage of 4.25V until the current is ≤0.05mA. After that, disassemble the battery and remove the positive electrode.

[0196] 2. Weigh the empty crucible in an indoor environment (default is a high-pressure sealed crucible).

[0197] 3. Transfer the crucible and positive electrode sample to the glove box, punch out circular electrode sheets (5mm in diameter), and place them into the crucible;

[0198] 4. Add electrolyte dropwise;

[0199] 5. Seal the crucible, transfer it out of the glove box, weigh it, and subtract the weight of the substrate from the difference between the two weights to get the sample weight.

[0200] 6. Testing: The test temperature range is 35℃~1000℃, and the temperature rise rate is 10℃ / min.

[0201] (2) All-electric 25 / 45℃ cycle performance test

[0202] In a constant temperature environment of 25℃ or 45℃, charge at 1C to 4.25V at 2.8~4.25V, then charge at constant voltage at 4.25V until the current is ≤0.05mA, let stand for 5 minutes, and then discharge at 1C to 2.8V. The capacity is recorded as Dn (n=0, 1, 2...). Repeat the above process until the capacity decays to 80%.

[0203] The test results are shown in Table 3 below:

[0204] Table 3

[0205]

[0206] A comparison between the embodiments and comparative examples shows that, by rationally setting the cathode materials in each layer, this application can achieve better room temperature and high temperature cycling performance, and the material thermal stability is better. Furthermore, a comparison between Embodiment 1 and Embodiment 15 shows that by setting an intermediate layer, the room temperature and high temperature cycling performance can be further improved, and the material thermal stability is better.

[0207] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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.

[0208] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A positive electrode active material, characterized by, The 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 cathode material includes a material of a general formula of Li a1 Ni b1 M1 c1 O2, M1 includes one or more of Mn, Co, Al, Mg, Ti, Zr, and W, 0.9≤a1≤1.2, b1+c1=1, 0.8≤b1≤1, 0 The second cathode material includes a material of a general formula of Li a2 Ni b2 M2 c2 O2, M2 includes one or more of Mn, Al, Sr, Nb, and Y, 0.9≤a2≤1.2, b2 +c2=1, 0.6≤b2≤0.92, 0.05≤c2≤0.

4. Wherein, c2 and c1 satisfy: c2-c1≥0.05; The core-shell particle further includes an intermediate layer disposed between the inner core and the shell layer, the intermediate layer comprising a third cathode material, the third cathode material comprising a material of a general formula of Li a3 Ni b3 M2 c3 M3 d3 O2, M3 comprising one or more of Zr, Ti, W, Mo, Ta, Sn, Se, and Sb, 0.9 a3 b3 + c3 + d3 = 1, 0.8 b3 0 c3 0.02 d3 2. The positive electrode active material according to claim 1, characterized by c2 and c1 satisfy: 0.05≤c2-c1≤0.

3.

3. The positive electrode active material according to claim 1 or 2, characterized by The second positive electrode material satisfies: 0.9≤a2≤1.02。 4. The positive electrode active material according to any one of claims 1 to 3, characterized by The first positive electrode material satisfies: 0.95≤a1≤1.05。 5. The positive electrode active material according to any one of claims 1 to 4, characterized by The thickness of the shell layer is 0.1 μm~3 μm.

6. The positive electrode active material according to any one of claims 1 to 5, characterized by The thickness of the intermediate layer is 0.1 μm~1 μm.

7. The positive electrode active material according to any one of claims 1 to 6, characterized by The Dv50 of the core-shell particle is 6 μm ~15 μm.

8. The method of producing a positive electrode active material according to any one of claims 1 to 7, characterized by, The method comprises the following steps: According to general formula Li a1 Ni b1 M1 c1 O2mixing a Ni salt, a salt of M1, and a first solvent, to prepare a first precursor solution; According to general formula Li a2 Ni b2 M2 c2 O2mixing a Ni salt, a salt of M2, and a second solvent, to prepare a second precursor solution; The first precursor solution and the second precursor solution are used to prepare a precursor of the core-shell particle by a precipitation method; The precursor is mixed with a lithium salt, and sintered to prepare the positive electrode active material.

9. The method of producing a positive electrode active material according to claim 8, characterized by, Also included are compounds according to the general formula Li a3 Ni b3 M2 c3 M3 d3 O2mixing a Ni salt, a salt of M2, a salt of M3, and a third solvent, preparing a third precursor solution, and a step of precipitating the precursors of the core-shell particles from the first, second, and third precursor solutions.

10. The method for producing a positive electrode active material according to claim 8 or 9, characterized by, The preparation of the precursor of the core-shell particle by the precipitation method has one or more of the following characteristics: (1) The precipitator used comprises one or more of sodium hydroxide, sodium carbonate, potassium carbonate and potassium hydroxide; (2) The complexing agent used comprises one or more of ammonia, ammonium chloride, ammonium sulfate, urea, citric acid and ethylenediaminetetraacetic acid; (3) The reaction pH is controlled to be 11~14; (4) The reaction temperature is 40℃~80℃.

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

12. A positive electrode sheet characterized by comprising: One or more of the positive electrode active materials prepared by the preparation method of any one of claims 8~11.

13. A secondary battery characterized by comprising: The positive electrode sheet of claim 12.

14. The secondary battery according to claim 13, characterized by The secondary battery is a cylindrical battery.

15. An electrical device, comprising: One or more of the positive electrode sheet of claim 12 and the secondary battery of any one of claims 13~14. One or more of the positive electrode sheet of claim 12 and the secondary battery of any one of claims 13~14.

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