Core-shell structured positive electrode active materials and their preparation methods, positive electrode sheets, secondary batteries, battery modules, battery packs and electrical devices.

Abstract

This application provides a core-shell structured positive electrode active material, a method for preparing the positive electrode active material, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device; the positive electrode active material includes Li... m A x Mn 1‑y B y P 1‑z C z O 4‑n D n The core, the core-encapsulating crystalline pyrophosphate M a P2O7 and oxide M′ b O c The first coating layer and the carbon-containing second coating layer covering the first coating layer. The positive electrode active material of this application can reduce the generation of Li / Mn antisite defects, reduce manganese dissolution and reduce lattice change rate, improve the capacity of secondary batteries, and improve the cycle performance, high-temperature storage performance and safety performance of secondary batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode active material with a core-shell structure, a preparation method of the positive electrode active material, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and a power utilization device. BACKGROUND

[0002] In recent years, with the increasingly wide application range of secondary batteries, secondary batteries are widely used in energy storage power supply systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Due to the great development of secondary batteries, higher requirements are put forward for their energy density, cycle performance and safety performance, etc. As the existing positive electrode active material of secondary batteries, lithium manganese phosphate is prone to produce Li / Mn anti-site defects in the charging and discharging process, and manganese leaching is serious, which affects the specific capacity of the secondary battery and leads to poor safety performance and cycle performance of the secondary battery. SUMMARY

[0003] The present application is carried out in view of the above-mentioned problems, and aims to provide a positive electrode active material with a core-shell structure, a preparation method of the positive electrode active material, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and a power utilization device, to solve the problems that the existing lithium manganese phosphate positive electrode active material is prone to produce Li / Mn anti-site defects in the charging and discharging process, and manganese leaching is serious, thereby solving the problems of low capacity, poor safety performance and cycle performance of the secondary battery, etc.

[0004] To achieve the above-mentioned purpose, the present application provides a positive electrode active material with a core-shell structure in the first aspect, which comprises a core and a shell covering the core,

[0005] The core contains Li m A x Mn 1-y B y P 1-z C z O 4-n D nwherein m is selected from any value in the range of 0.5-1.2, optionally from any value in the range of 0.9-1.1, x is selected from any value in the range of 0.001-0.5, optionally from any value in the range of 0.001-0.1, y is selected from any value in the range of 0.001-0.5, z is selected from any value in the range of 0.001-0.2, optionally from any value in the range of 0.001-0.1, n is selected from any value in the range of 0.001-0.5, optionally from any value in the range of 0.001-0.1, A is one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, optionally one or more elements selected from Al, Mg, Nb, Mo and W, B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements selected from Ti, V, Fe, Ni, Mg and Co, C is one or more elements selected from B, S, Si and N, optionally one or more elements selected from S, Si and N, and D is one or more elements selected from S, F, Cl and Br, optionally one or more elements selected from F, Cl and Br;

[0006] The shell comprises a first cladding layer cladding the core and a second cladding layer cladding the first cladding layer;

[0007] wherein the first cladding layer comprises a crystalline pyrophosphate salt M a P2O7and an oxide M' b O c wherein a is greater than 0 and less than or equal to 4, optionally greater than 0 and less than or equal to 3, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, optionally one or more elements selected from Li and Fe, M' is one or more elements selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanides and Sb, optionally one or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce, more optionally one or more elements selected from Mg, Al, V, Cu, Zn, Zr and W;

[0008] The second cladding layer comprises carbon.

[0009] The inventors of the present application found in actual operation that the lithium manganese phosphate positive electrode active material is prone to Li / Mn anti-site defects during deep charge and discharge, and manganese dissolution is relatively serious. The dissolved manganese is reduced to metallic manganese after migrating to the negative electrode. The generated metallic manganese acts as a "catalyst" to catalyze the decomposition of the SEI film (solid electrolyte interphase) on the surface of the negative electrode, and the by-products generated are part of the gas, which is easy to cause the battery to swell, affecting the safety performance of the secondary battery, and the other part is deposited on the surface of the negative electrode, hindering the passage of lithium ions in and out of the negative electrode, causing the impedance of the secondary battery to increase, affecting the kinetic performance and cycle performance of the battery. In addition, to make up for the loss of the SEI film, the electrolyte and active lithium inside the battery are continuously consumed, which has an irreversible impact on the capacity retention rate of the secondary battery.

[0010] Therefore, the present applicant unexpectedly found that by doping specific elements in specific amounts at the Li, Mn, P, and O positions of the compound LiMnPO4, coating the surface of the compound with a first coating layer containing crystalline pyrophosphate and an oxide, and coating the surface of the first coating layer with a second coating layer containing carbon to obtain a positive electrode active material, the generation of Li / Mn anti-site defects can be greatly reduced, manganese dissolution can be reduced, and the lattice change rate can be reduced, thereby improving the capacity of the secondary battery, and improving the cycle performance, high-temperature storage performance, and safety performance of the secondary battery.

[0011] Unless otherwise specified, the chemical formula Li m A x Mn 1-y B y P 1-z C z O 4-n D n When A is two or more elements, the above limitation on the value range of x is not only a limitation on the stoichiometric number of each element as A, but also a limitation on the sum of the stoichiometric numbers of each element as A. For example, when A is two or more elements A1, A2, …, An, the stoichiometric numbers x1, x2, …, xn of A1, A2, …, An, respectively, each fall within the value range of x limited by the present application, and the sum of x1, x2, …, xn also falls within the value range. Similarly, for the case where B, C, and D are two or more elements, the limitation on the value range of the stoichiometric number of B, C, and D in the present application also has the above meaning.

[0012] Unless otherwise specified, the chemical formula M aIn P2O7, when M is two or more elements, the above-mentioned limitation on the value range of a is not only a limitation on the stoichiometric number of each element as M, but also a limitation on the sum of the stoichiometric numbers of each element as M. For example, when M is two or more elements M1, M2, …, Mn, the stoichiometric numbers a1, a2, …, an of M1, M2, …, Mn, respectively, each need to fall within the value range of a limited by the present application, and the sum of a1, a2, …, an also needs to fall within the value range. Similarly, for the chemical formula M' in M'P2O7, when M' is two or more elements, the above-mentioned limitation on the value range of b is also of the above-mentioned meaning. b O c In the case where M' in M'P2O7 is two or more elements, the above-mentioned limitation on the value range of b in the present application also has the above-mentioned meaning.

[0013] In any embodiment of the first aspect, the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal direction (111) is 26.41°-32.57°.

[0014] Optionally, the interplanar spacing of the pyrophosphate in the first coating layer is 0.300-0.310 nm; and / or,

[0015] Optionally, the included angle of the crystal direction (111) of the pyrophosphate in the first coating layer is 29.00°-30.00°.

[0016] When the interplanar spacing of the pyrophosphate and the included angle of the crystal direction (111) in the first coating layer are within the above-mentioned ranges, impurity phases in the coating layer can be effectively avoided, thereby improving the capacity of the material, and improving the cycle performance and rate performance of the secondary battery.

[0017] In any embodiment of the first aspect, x is any value within the range of 0.001-0.005; and / or,

[0018] y is any value within the range of 0.01-0.5, and optionally any value within the range of 0.25-0.5; and / or,

[0019] z is any value within the range of 0.001-0.005; and / or,

[0020] n is any value within the range of 0.001-0.005.

[0021] In this way, x, y, z, and n are within the above-mentioned ranges, which can further reduce the generation of Li / Mn antisite defects, reduce manganese elution, and reduce the lattice change rate, thereby further improving the capacity of the secondary battery, and improving the cycle performance, high-temperature storage performance, and safety performance of the secondary battery.

[0022] In any embodiment of the first aspect, the ratio of 1-y to y in the core is 1 to 4, optionally 1.5 to 3. Here, y represents the sum of the stoichiometric coefficients of the Mn-doped elements. When the above conditions are met, the energy density and cycle performance of the secondary battery made from the positive electrode active material can be further improved.

[0023] In any embodiment of the first aspect, the ratio of m to x in the core is from 1 to 1200, optionally from 9 to 1100, and more preferably from 190 to 998. Here, x represents the sum of the stoichiometric coefficients of the Li-site doping elements. When the above conditions are met, the energy density and cycle performance of the secondary battery made of the positive electrode active material can be further improved.

[0024] In any embodiment of the first aspect, the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally 4-5.6% by weight, based on the kernel weight.

[0025] When the coating amount of the first coating layer is within the above range, it can further suppress manganese dissolution and further promote lithium ion transport, maintain the low impedance of the secondary battery, and improve the kinetic performance of the secondary battery.

[0026] In any embodiment of the first aspect, the weight ratio of pyrophosphate to oxide in the first coating layer is 1:3 to 3:1, optionally 1:3 to 1:1.

[0027] A suitable ratio of pyrophosphate and oxide is beneficial to fully exert their synergistic effect, which can further suppress manganese dissolution while maintaining a low impedance in the secondary battery.

[0028] In any embodiment of the first aspect, the crystallinity of the pyrophosphate in the first coating layer is 10% to 100%, optionally 50% to 100%.

[0029] In the first coating layer of the lithium manganese phosphate cathode active material of this application, the presence of pyrophosphate with a certain degree of crystallinity helps maintain the structural stability of the first coating layer and reduces lattice defects. This is beneficial in two ways: firstly, it helps to fully utilize the role of pyrophosphate in inhibiting manganese dissolution; secondly, it helps to reduce the content of surface impurities and lower the valence state of surface oxygen, thereby reducing interfacial side reactions between the cathode material and the electrolyte, reducing electrolyte consumption, and improving the cycle performance and safety performance of the secondary battery.

[0030] In any embodiment of the first aspect, the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the kernel weight.

[0031] The carbon-containing layer, serving as the second coating layer, acts as a barrier, preventing direct contact between the positive electrode active material and the electrolyte, thereby reducing electrolyte corrosion and improving battery safety at high temperatures. Furthermore, its strong conductivity reduces internal resistance, thus improving the kinetic performance of the secondary battery. When the coating amount of the second layer is within the aforementioned range, it can further improve the kinetic and safety performance of the secondary battery while maintaining a high specific capacity of the positive electrode active material.

[0032] In any embodiment of the first aspect, in the positive electrode active material, A is any element selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; optionally, A is Mg or Nb; and / or,

[0033] B is at least two elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; optionally, B is at least two elements selected from Fe, Ti, V, Co, and Mg; more preferably, B is a combination of Fe and at least one element selected from Ti, V, Co, and Mg; and / or,

[0034] C is any element selected from B, S, Si, and N; optionally, C is S; and / or,

[0035] D is any element selected from S, F, Cl and Br, and optionally, D is F.

[0036] By selecting doping elements within the above-mentioned range, it is beneficial to enhance the doping effect. On the one hand, it further reduces the lattice change rate, thereby suppressing the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it is also beneficial to further reduce surface oxygen activity and reduce interfacial side reactions between the positive electrode active material and the electrolyte, thereby improving the cycle performance and high-temperature storage performance of the battery.

[0037] In any embodiment of the first aspect, the Li / Mn antisite defect concentration of the positive electrode active material is 4% or less, optionally 2% or less. In the positive electrode active material of this application, the Li / Mn antisite defect refers to the Li... + and Mn 2 + The positions of Li have been interchanged. + The transmission channel is a one-dimensional channel, Mn 2+ In Li + It is difficult to migrate in the transmission channel, therefore, the Mn of the inversion defect is difficult to migrate. 2+ It will hinder Li + The transport of Li / Mn antisite defects can be improved by controlling the specific capacity of the positive electrode active material and the rate performance of the secondary battery.

[0038] In any embodiment of the first aspect, the lattice change rate of the positive electrode active material before and after complete lithium insertion / extraction is 9.8% or less, optionally 6% or less, and more preferably 4% or less. The lithium insertion / extraction process of LiMnPO4 is a two-phase reaction. The interfacial stress between the two phases is determined by the magnitude of the lattice change rate; the smaller the lattice change rate, the smaller the interfacial stress. + The easier the transmission, the better. Therefore, reducing the lattice change rate of the core will be beneficial for enhancing Li. + This improves the transmission capacity, thereby enhancing the rate performance of secondary batteries.

[0039] In any embodiment of the first aspect, the surface oxygen valence state of the positive electrode active material is below -1.55, optionally below -1.88, and more preferably between -1.98 and -1.88. This is because the higher the valence state of oxygen in a compound, the stronger its electron-accepting ability, i.e., the stronger its oxidizing power. In the positive electrode active material of this application, by controlling the surface oxygen valence state at a low level, the reactivity of the positive electrode material surface can be reduced, the interfacial side reactions between the positive electrode active material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0040] In any embodiment of the first aspect, the compaction density of the positive electrode active material at 3 tons (T) is 1.89 g / cm³. 3 The above can be selected as 2.0g / cm 3 The above is optional, but 2.2 g / cm³ is also possible. 3 In conclusion, the higher the compaction density of the positive electrode active material, that is, the greater the weight of active material per unit volume, the more beneficial it is to improving the volumetric energy density of the secondary battery.

[0041] A second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0042] Steps for providing kernel materials: The kernel contains Li m A x Mn 1-y B y P 1-z C z O 4-n D nWherein, m is selected from any value in the range of 0.5-1.2, optionally from any value in the range of 0.9-1.1; x is selected from any value in the range of 0.001-0.5, optionally from any value in the range of 0.001-0.1; y is selected from any value in the range of 0.001-0.5; z is selected from any value in the range of 0.001-0.2, optionally from any value in the range of 0.001-0.1; n is selected from any value in the range of 0.001-0.5, optionally from any value in the range of 0.001-0.1; and A is selected from Zn, Al, Na, K, M. One or more elements selected from g, Nb, Mo and W, optionally one or more elements selected from Al, Mg, Nb, Mo and W; B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements selected from Ti, V, Fe, Ni, Mg and Co; C is one or more elements selected from B, S, Si and N, optionally one or more elements selected from S, Si and N; D is one or more elements selected from S, F, Cl and Br, optionally one or more elements selected from F, Cl and Br.

[0043] Coating step: Provides M containing pyrophosphate a P2O7 powder and containing carbon source and oxide M′ b O c A suspension containing core materials, including pyrophosphate M a P2O7 powder and containing carbon source and oxide M′ b O c The suspension is mixed and sintered to obtain a positive electrode active material, wherein a is greater than 0 and less than or equal to 4, or optionally greater than 0 and less than or equal to 3; b is greater than 0 and less than or equal to 2; c is greater than 0 and less than or equal to 5; M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, or optionally one or more elements selected from Li and Fe; and M′ is selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, and lanthanides. One or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce, and more preferably one or more elements selected from Mg, Al, V, Cu, Zn, Zr and W;

[0044] The positive electrode active material has a core-shell structure, comprising a core and a shell covering the core, wherein the core contains Li. m A x Mn 1-y B y P 1-z C z O 4-n D n The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer, the first coating layer containing crystalline pyrophosphate M. a P2O7 and oxide M′ b O c The second coating layer contains carbon.

[0045] As a result, the applicant unexpectedly discovered that by simultaneously doping specific elements in specific amounts at the Li, Mn, P, and O sites of the compound LiMnPO4, coating the surface of the compound with a first coating layer containing crystalline pyrophosphate and oxides, and then coating the surface of the first coating layer with a second coating layer containing carbon, a positive electrode active material can be obtained. This can greatly reduce the generation of Li / Mn antisite defects, reduce manganese dissolution, and lower the lattice change rate, thereby increasing the capacity of the secondary battery and improving the cycle performance, high-temperature storage performance, and safety performance of the secondary battery.

[0046] In any embodiment of the second aspect of this application, the step of providing the kernel material includes the following steps:

[0047] Step (1): Mix the manganese source, the source of element B, the acid, and an optional solvent to obtain a mixture;

[0048] Step (2): Mix the mixture with a lithium source, a phosphorus source, a source of element A, a source of element C, and a source of element D, and optionally a solvent, dry, and sinter to obtain a mixture containing Li. m A x Mn 1-y B y P 1-z C z O 4-n D n The core material.

[0049] In any embodiment of the second aspect of this application, step (1) is performed at 60°C-120°C; and / or, in step (1), the mixture is performed by stirring at a speed of 200-800 rpm.

[0050] In any embodiment of the second aspect of this application, in step (2), the mixing is carried out for 8-15 hours.

[0051] In any embodiment of the second aspect of this application, in step (2), sintering is carried out at 600°C-900°C for 6-14 hours.

[0052] In any embodiment of the second aspect of this application, the source of element A is one or more selected from the elemental form, oxide, phosphate, oxalate, carbonate, and sulfate of element A; and / or,

[0053] The source of element B is one or more selected from the elemental form, oxide, phosphate, oxalate, carbonate, and sulfate of element B; and / or,

[0054] The source of element C is one or more selected from sulfates, borates, nitrates, and silicates of element C; and / or,

[0055] The source of element D is one or more selected from the elemental form of element D and its ammonium salt.

[0056] In any embodiment of the second aspect of this application, pyrophosphate M is included. a P2O7 powder is prepared by the following steps:

[0057] Mix the source of element M, the phosphorus source, and an optional solvent to obtain a mixture. Adjust the pH of the mixture to 4-6, continue mixing, and then dry and sinter.

[0058] In any embodiment of the second aspect of this application, a preparation comprising pyrophosphate M is prepared. a In the process of preparing P2O7 powder, drying is performed at 100℃-300℃ for 4-8 hours, or optionally at 150℃-200℃; and / or sintering is performed at 500℃-800℃ under inert gas protection for 4-10 hours, or optionally at 650℃-800℃.

[0059] In any embodiment of the second aspect of this application, the sintering temperature in the coating step is 500-800℃ and the sintering time is 4-10h.

[0060] A third aspect of this application provides a positive electrode sheet, which 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 includes the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the preparation method of the second aspect of this application, and the content of the positive electrode active material in the positive electrode film layer is more than 10% by weight, based on the total weight of the positive electrode film layer.

[0061] In any embodiment of the third aspect of this application, the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, based on the total weight of the positive electrode film layer. This ensures that the secondary battery has high capacity, good cycle performance, high-temperature storage performance, and safety performance.

[0062] The fourth aspect of this application provides a secondary battery, including the positive electrode active material of the first aspect of this application, or the positive electrode active material prepared by the preparation method of the second aspect of this application, or the positive electrode sheet of the third aspect of this application.

[0063] The fifth aspect of this application provides a battery module, including the secondary battery of the fourth aspect of this application.

[0064] A sixth aspect of this application provides a battery pack that includes the battery module of the fifth aspect of this application.

[0065] A seventh aspect of this application provides an electrical device comprising at least one selected from the fourth aspect of this application, the fifth aspect of this application, and the sixth aspect of this application. Attached Figure Description

[0066] Figure 1 This is a schematic diagram of a core-shell structured positive electrode active material according to an embodiment of this application.

[0067] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0068] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0069] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0070] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0071] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0072] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0073] Explanation of reference numerals in the attached figures:

[0074] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 11 Core; 12 First covering layer; 13 Second covering layer. Detailed Implementation

[0075] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, the method for preparing the positive electrode active material, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the power supply device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0076] The "range" disclosed in this application is defined by 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 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 60-120 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 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 "ab" 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 "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0077] In this application, the terms "below a certain value" and "above a certain value" refer to the range defined by a certain value as the upper or lower limit.

[0078] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0079] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0080] 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) may 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.

[0081] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0082] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0083] Unless otherwise specified, in this application, the median particle size D v 50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for the positive electrode active material. In this application, the median particle size Dv of the positive electrode active material... 50 Particle size can be determined using laser diffraction particle size analysis. For example, according to standard GB / T 19077-2016, a laser particle size analyzer (e.g., MalvernMaster Size 3000) can be used for determination.

[0084] Unless otherwise specified, in this application, the term "cladding layer" refers to a material layer covering the core, which may completely or partially cover the core. The use of "cladding layer" is for ease of description only and is not intended to limit the invention. Similarly, the term "cladding layer thickness" refers to the thickness of the material layer covering the core in the radial direction of the core.

[0085] Unless otherwise specified, in this application, the term "source" refers to a compound that is the source of a certain element. For example, the types of "sources" include, but are not limited to, carbonates, sulfates, nitrates, elements, halides, oxides, and hydroxides.

[0086] [Rechargeable Battery]

[0087] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0088] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0089] [Positive electrode active material]

[0090] This application provides a positive electrode active material with a core-shell structure, comprising a core and a shell covering the core.

[0091] The kernel includes Li m A x Mn 1-y B y P 1-z C z O 4-n D n Wherein, m is selected from any value in the range of 0.5-1.2, optionally from any value in the range of 0.9-1.1; x is selected from any value in the range of 0.001-0.5, optionally from any value in the range of 0.001-0.1; y is selected from any value in the range of 0.001-0.5; z is selected from any value in the range of 0.001-0.2, optionally from any value in the range of 0.001-0.1; n is selected from any value in the range of 0.001-0.5, optionally from any value in the range of 0.001-0.1; and A is selected from Zn, Al, Na, K, M. One or more elements selected from g, Nb, Mo and W, optionally one or more elements selected from Al, Mg, Nb, Mo and W; B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements selected from Ti, V, Fe, Ni, Mg and Co; C is one or more elements selected from B, S, Si and N, optionally one or more elements selected from S, Si and N; D is one or more elements selected from S, F, Cl and Br, optionally one or more elements selected from F, Cl and Br.

[0092] The shell includes a first covering layer that covers the core and a second covering layer that covers the first covering layer;

[0093] The first coating layer contains crystalline pyrophosphate M.a P2O7 and oxide M′ b O c Wherein, a is greater than 0 and less than or equal to 4, or optionally greater than 0 and less than or equal to 3; b is greater than 0 and less than or equal to 2; c is greater than 0 and less than or equal to 5; M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, or optionally one or more elements selected from Li and Fe; and M′ is one or more elements selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanides, and Sb. The element may optionally be one or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce, and more preferably one or more elements selected from Mg, Al, V, Cu, Zn, Zr and W;

[0094] The second coating layer contains carbon.

[0095] like Figure 1 As shown, the core-shell structured positive electrode active material of this application includes a core 11, a first coating layer 12 covering the core 11, and a second coating layer 13 covering the first coating layer 12. The core 11 comprises Li... m A x Mn 1-y B y P 1- z C z O 4-n D nIn the core 11, lattice change rate is reduced by Li and Mn doping; Mn doping can also effectively reduce surface activity, thereby suppressing Mn dissolution and interfacial side reactions between the positive electrode active material and the electrolyte; P-site doping makes the Mn-O bond length change rate faster, reducing the small polaron migration barrier of the material, which is beneficial to electronic conductivity; O-site doping has a good effect on reducing interfacial side reactions; P-site and O-site doping also affect the Mn dissolution and kinetic performance of antisite defects; therefore, doping reduces the concentration of antisite defects in the material, improves the kinetic performance and specific capacity of the material, and can also change the morphology of the particles, thereby increasing the compaction density. The first coating layer 12 includes crystalline pyrophosphate and oxide; since the migration barrier of transition metals in pyrophosphate is high (>1eV), the dissolution of transition metals can be effectively suppressed; while oxides have high structural stability and low surface activity, therefore, oxide coating can effectively reduce interfacial side reactions, thereby improving the high-temperature cycling and high-temperature storage performance of the battery. Furthermore, since the second coating layer 13 is a carbon-containing layer, it can effectively improve the conductivity and desolvation capability of the positive electrode active material. In addition, the "barrier" effect of the second coating layer 13 can further hinder the migration of manganese ions into the electrolyte and reduce the corrosion of the active material by the electrolyte. Therefore, the positive electrode active material of this application, through elemental doping and surface coating of lithium manganese phosphate, can reduce the generation of Li / Mn antisite defects, effectively suppress Mn dissolution during the lithium insertion / extraction process, and simultaneously promote lithium ion migration, thereby improving the rate performance of the cell and enhancing the cycle performance, high-temperature performance, and safety performance of the secondary battery. It should be noted that the positions of the main characteristic peaks of the positive electrode active material of this application are basically consistent with those of the pre-doped LiMnPO4, indicating that the doped lithium manganese phosphate positive electrode active material has no impurity phase, and the improvement in secondary battery performance mainly comes from elemental doping, rather than impurity phase.

[0096] In some implementations, Li m A x Mn 1-y B y P 1-z C z O 4-n D n The entire system remains electrically neutral.

[0097] Unless otherwise stated, the chemical formula Li m A x Mn 1-y B y P 1-z C z O 4-n D nIn this context, when A comprises two or more elements, the aforementioned limitation on the range of x values ​​applies not only to the stoichiometric coefficient of each element representing A, but also to the sum of the stoichiometric coefficients of all elements representing A. For example, when A comprises two or more elements A1, A2...An, the stoichiometric coefficients x1, x2...xn of each of A1, A2...An must each fall within the range of x values ​​defined in this application, and the sum of x1, x2...xn must also fall within this range. Similarly, for the case where B, C, and D comprise two or more elements, the limitation on the range of stoichiometric coefficients of B, C, and D in this application also has the aforementioned meaning.

[0098] Unless otherwise stated, the chemical formula M a In P₂O₇, when M consists of two or more elements, the aforementioned limitation on the range of values ​​for 'a' applies not only to the stoichiometric coefficient of each element as M, but also to the sum of the stoichiometric coefficients of all elements as M. For example, when M consists of two or more elements M₁, M₂, ..., Mₙ, the stoichiometric coefficients a₁, a₂, ..., an of each of M₁, M₂, ..., Mₙ must each fall within the range of values ​​for 'a' defined in this application, and the sum of a₁, a₂, ..., an must also fall within this range. Similarly, for the chemical formula M′... b O c When M′ contains two or more elements, the limitation on the numerical range of the stoichiometric coefficient b of M′ in this application also has the above meaning.

[0099] In some implementations, when A is one, two, three, or four elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W, A x For Q x1 H x2 E x3 K x4 Where x1 + x2 + x3 + x4 = x, and x1, x2, x3, and x4 are all positive numbers and not all zero simultaneously. Q, H, E, and K are each independently selected from Zn, Al, Na, K, Mg, Nb, Mo, and W. Optionally, one of x1, x2, x3, and x4 is zero, and the others are not zero; more alternatively, two of x1, x2, x3, and x4 are zero, and the others are not zero; still alternatively, three of x1, x2, x3, and x4 are zero, and the others are not zero. Kernel Li m A x Mn 1-y B y P 1-z C z O 4-n D nIn this process, it is advantageous to dope one, two, three or four of the aforementioned A elements at the Li site, and optionally, to dope one, two or three of the aforementioned A elements; in addition, it is advantageous to dope one or two B elements at the Mn site, one or two C elements at the phosphorus site, and one or two D elements at the O site, which is beneficial to make the doped elements uniformly distributed.

[0100] In some implementations, the values ​​of m, x, y, z, and n satisfy the condition that the entire kernel remains electrically neutral.

[0101] Kernel Li m A x Mn 1-y B y P 1-z C z O 4-n D n In this system, the value of m is influenced by the valence states of A, B, C, and D, as well as the values ​​of x, y, z, and n, to ensure the overall system remains electrically neutral. If the value of m is too small, the lithium content of the entire core system will decrease, affecting the specific capacity of the material. The values ​​of x, y, z, and n limit the total amount of all dopants. If the doping amount is too low, the dopants will not have an effect; if y exceeds 0.5, the Mn content in the system will be low, affecting the voltage plateau of the material. C is doped at the P site. Since the PO tetrahedron is relatively stable, and a large z value would affect the stability of the material, the z value is limited to 0.001-0.2.

[0102] Furthermore, maintaining the electrical neutrality of the entire core system ensures that defects and impurities in the cathode active material are minimized. If an excess of transition metal (such as manganese) exists in the cathode active material, due to the relatively stable structure of the material system itself, the excess transition metal is likely to precipitate as elemental form or form impurities within the crystal lattice. Maintaining electrical neutrality minimizes such impurities. In addition, ensuring the electrical neutrality of the system can, in some cases, generate lithium vacancies in the material, thereby improving the material's kinetic performance.

[0103] By controlling the process (e.g., thoroughly mixing and grinding materials from various sources), it is possible to ensure that each element is uniformly distributed in the crystal lattice and that no aggregation occurs. The main characteristic peak positions in the XRD pattern of element-doped lithium manganese phosphate are consistent with those of undoped LiMnPO4, indicating that no impurity phase was introduced during the doping process. Therefore, the improvement in core performance mainly comes from element doping, rather than impurity phases. After preparing the cathode active material, the inventors of this application used focused ion beam (FIB) to cut the middle region of the prepared cathode active material particles. Testing using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) revealed that the elements were uniformly distributed and no aggregation occurred.

[0104] In some implementations, the values ​​of a, b, and c satisfy the following condition: making M a P2O7 and M′ b O c Maintain electrical neutrality.

[0105] In some embodiments, the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°;

[0106] Optionally, the interplanar spacing of the pyrophosphate in the first coating layer is 0.300-0.310 nm (e.g., 0.303 nm); and / or,

[0107] Optionally, the included angle of the crystal orientation (111) of the pyrophosphate in the first coating layer is 29.00°-30.00° (e.g., 29.496°).

[0108] When the interplanar spacing and the angle between the crystal orientation (111) of the pyrophosphate in the first coating layer are within the above range, impurity phases in the coating layer can be effectively avoided, thereby improving the specific capacity of the material and enhancing the cycle performance and rate performance of the secondary battery.

[0109] In some implementations, x is any value in the range of 0.001-0.005; and / or,

[0110] y is any value in the range of 0.01-0.5, optionally any value in the range of 0.25-0.5; and / or,

[0111] z is any value in the range of 0.001-0.005; and / or,

[0112] n is any value in the range of 0.001 to 0.005.

[0113] Therefore, within the above ranges, x, y, z, and n can further reduce the generation of Li / Mn antisite defects, reduce manganese dissolution, and lower the lattice change rate, thereby further improving the capacity of the secondary battery and enhancing its cycle performance, high-temperature storage performance, and safety performance.

[0114] In some implementations, the ratio of 1-y to y in the core is 1 to 4, optionally 1.5 to 3. Here, y represents the sum of the stoichiometric coefficients of the Mn-doped elements. When the above conditions are met, the energy density and cycle performance of the secondary battery made from the positive electrode active material can be further improved.

[0115] In some implementations, the ratio of m to x in the core is from 1 to 1200, optionally from 9 to 1100, and more preferably from 190 to 998. Here, x represents the sum of the stoichiometric coefficients of the Li-site doping elements. When the above conditions are met, the energy density and cycle performance of the secondary battery made from the positive electrode active material can be further improved.

[0116] In some implementations, the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally 4-5.6% by weight, based on the kernel weight.

[0117] When the coating amount of the first coating layer is within the above range, it can further suppress manganese dissolution and further promote lithium ion transport, maintain the low impedance of the secondary battery, and improve the kinetic performance of the secondary battery.

[0118] In some embodiments, the weight ratio of pyrophosphate to oxide in the first coating layer is 1:3 to 3:1, optionally 1:3 to 1:1.

[0119] A suitable ratio of pyrophosphate and oxide is beneficial to fully exert their synergistic effect, which can further suppress manganese dissolution while maintaining a low impedance in the secondary battery.

[0120] In some embodiments, the thickness of the first coating layer is 1-100 nm. This results in a higher migration barrier for the transition metal within the first coating layer, effectively reducing its dissolution. The oxides in the coating layer exhibit high stability, effectively mitigating interfacial side reactions and thus improving the material's high-temperature stability.

[0121] In some implementations, the thickness of the second coating layer is 1-100 nm.

[0122] In some embodiments, the crystallinity of the pyrophosphate in the first coating layer is 10% to 100%, optionally 50% to 100%.

[0123] In the first coating layer of the lithium manganese phosphate cathode active material of this application, the presence of pyrophosphate with a certain degree of crystallinity helps maintain the structural stability of the first coating layer and reduces lattice defects. This is beneficial in two ways: firstly, it helps to fully utilize the role of pyrophosphate in inhibiting manganese dissolution; secondly, it helps to reduce the content of surface impurities and lower the valence state of surface oxygen, thereby reducing interfacial side reactions between the cathode material and the electrolyte, reducing electrolyte consumption, and improving the cycle performance and safety performance of the secondary battery.

[0124] In some embodiments, the crystallinity of the first coating layer pyrophosphate of the positive electrode active material can be tested by conventional techniques in the art, such as density method, infrared spectroscopy, differential scanning calorimetry and nuclear magnetic resonance absorption method, or by, for example, X-ray diffraction.

[0125] A specific method for testing the crystallinity of the first coating layer pyrophosphate of a positive electrode active material using X-ray diffraction may include the following steps:

[0126] A certain amount of positive electrode active material powder is taken, and the total scattering intensity is measured by X-rays. It is the sum of the scattering intensities of all matter in space. It is only related to the intensity of the primary rays, the chemical structure of the positive electrode active material powder, and the total number of electrons participating in diffraction, i.e., the mass, and is independent of the order state of the sample. Then, crystalline scattering and non-crystalline scattering are separated from the diffraction pattern. The crystallinity is the ratio of the scattering of the crystalline part to the total scattering intensity.

[0127] It should be noted that, in some embodiments, the crystallinity of the pyrophosphate in the coating layer can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature and sintering time.

[0128] In some implementations, the second coating layer has a coating amount greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the kernel weight.

[0129] The carbon-containing layer, serving as the second coating layer, acts as a barrier, preventing direct contact between the positive electrode active material and the electrolyte, thereby reducing electrolyte corrosion and improving battery safety at high temperatures. Furthermore, its strong conductivity reduces internal resistance, thus improving the kinetic performance of the secondary battery. When the coating amount of the second layer is within the aforementioned range, it can further improve the kinetic and safety performance of the secondary battery while maintaining a high specific capacity of the positive electrode active material.

[0130] In some embodiments, in the positive electrode active material, A is any element selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; optionally, A is Mg or Nb; and / or,

[0131] B is at least two elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; optionally, B is at least two elements selected from Fe, Ti, V, Co, and Mg; more preferably, B is a combination of Fe and at least one element selected from Ti, V, Co, and Mg; and / or,

[0132] C is any element selected from B, S, Si, and N; optionally, C is S; and / or,

[0133] D is any element selected from S, F, Cl and Br, and optionally, D is F.

[0134] By selecting doping elements within the above-mentioned range, it is beneficial to enhance the doping effect. On the one hand, it further reduces the lattice change rate, thereby suppressing the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it is also beneficial to further reduce surface oxygen activity and reduce interfacial side reactions between the positive electrode active material and the electrolyte, thereby improving the cycle performance and high-temperature storage performance of the battery.

[0135] In some embodiments, the concentration of Li / Mn antisite defects in the positive electrode active material is 4% or less, optionally 2% or less. In the positive electrode active material of this application, Li / Mn antisite defects refer to the Li / Mn antisite defects in the LiMnPO4 lattice. + and Mn 2+ The positions of Li have been interchanged. + The transmission channel is a one-dimensional channel, Mn 2+ In Li + It is difficult to migrate in the transmission channel, therefore, the Mn of the inversion defect is difficult to migrate. 2+ It will hinder Li + The transport of Li / Mn antisite defects can be improved by controlling the specific capacity of the cathode active material and the rate performance of the secondary battery by keeping the concentration of antisite defects at a low level. In this application, the concentration of antisite defects can be determined, for example, according to JIS K 0131-1996.

[0136] In some embodiments, the lattice change rate of the positive electrode active material before and after complete lithium insertion / extraction is less than 9.8%, optionally less than 6%, and more preferably less than 4%. The lithium insertion / extraction process of LiMnPO4 is a two-phase reaction. The interfacial stress between the two phases is determined by the magnitude of the lattice change rate; the smaller the lattice change rate, the smaller the interfacial stress. + The easier the transmission, the better. Therefore, reducing the lattice change rate of the core will be beneficial for enhancing Li. + This improves the transmission capacity, thereby enhancing the rate performance of the secondary battery. The lattice change rate can be measured using methods known in the art, such as X-ray diffraction (XRD).

[0137] In some embodiments, the surface oxygen valence state of the positive electrode active material is below -1.55, optionally below -1.88, and more preferably between -1.98 and -1.88. This is because the higher the valence state of oxygen in a compound, the stronger its electron-accepting ability, i.e., the stronger its oxidizing power. In the positive electrode active material of this application, by controlling the surface oxygen valence state at a low level, the reactivity of the positive electrode material surface can be reduced, the interfacial side reactions between the positive electrode active material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery. The surface oxygen valence state can be measured by methods known in the art, such as by electron energy loss spectroscopy (EELS).

[0138] In some embodiments, the compaction density of the positive electrode active material at 3 tons (T) is 1.89 g / cm³. 3 The above can be selected as 2.0g / cm 3 The above is optional, but 2.2 g / cm³ is also possible. 3 The higher the compaction density of the positive electrode active material, i.e., the greater the weight of active material per unit volume, the more beneficial it is to improving the volumetric energy density of the secondary battery. In this application, the compaction density can be measured, for example, according to GB / T 24533-2009.

[0139] In some embodiments, the average discharge voltage of the positive electrode active material is 3.5V or higher, and the discharge specific capacity is 140mAh / g or higher; alternatively, the average discharge voltage is 3.6V or higher, and the discharge specific capacity is 145mAh / g or higher.

[0140] Although the average discharge voltage of undoped LiMnPO4 is above 4.0V, its discharge specific capacity is low, usually less than 120mAh / g, and therefore its energy density is low. By adjusting the lattice change rate through doping, its discharge specific capacity can be greatly improved, and the overall energy density can be significantly increased with a slight decrease in average discharge voltage.

[0141] In some implementations, m is selected from any value in the range of 0.97-1.01.

[0142] In some implementations, x is selected from any value in the range of 0.001 to 0.005.

[0143] In some implementations, y is selected from any value in the range of 0.25-0.5.

[0144] In some implementations, a is any value in the range of 1-4, for example, a is 1, 2, 3, or 4.

[0145] In some implementations, b is any value in the range of 1-2, for example, b is 1 or 2.

[0146] In some implementations, c is any value in the range of 1-5, and can be any value in the range of 1-3, for example, c is 1, 2, 3, 4, 5.

[0147] [Preparation method of positive electrode active material]

[0148] This application provides a method for preparing a positive electrode active material, including the following steps:

[0149] Steps for providing kernel materials: The kernel contains Li m A x Mn 1-y B y P 1-zC z O 4-n D n Wherein, m is selected from any value in the range of 0.5-1.2, optionally from any value in the range of 0.9-1.1; x is selected from any value in the range of 0.001-0.5, optionally from any value in the range of 0.001-0.1; y is selected from any value in the range of 0.001-0.5; z is selected from any value in the range of 0.001-0.2, optionally from any value in the range of 0.001-0.1; n is selected from any value in the range of 0.001-0.5, optionally from any value in the range of 0.001-0.1; and A is selected from Zn, Al, Na, K, M. One or more elements selected from g, Nb, Mo and W, optionally one or more elements selected from Al, Mg, Nb, Mo and W; B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements selected from Ti, V, Fe, Ni, Mg and Co; C is one or more elements selected from B, S, Si and N, optionally one or more elements selected from S, Si and N; D is one or more elements selected from S, F, Cl and Br, optionally one or more elements selected from F, Cl and Br.

[0150] Coating step: Provides M containing pyrophosphate a P2O7 powder and containing carbon source and oxide M′ b O c A suspension containing core materials, including pyrophosphate M a P2O7 powder and containing carbon source and oxide M′ b O cThe suspension is mixed and sintered to obtain a positive electrode active material, wherein a is greater than 0 and less than or equal to 4, or optionally greater than 0 and less than or equal to 3; b is greater than 0 and less than or equal to 2; c is greater than 0 and less than or equal to 5; M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, or optionally one or more elements selected from Li and Fe; and M′ is selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, and lanthanides. One or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce, and more preferably one or more elements selected from Mg, Al, V, Cu, Zn, Zr and W;

[0151] The positive electrode active material has a core-shell structure, comprising a core and a shell covering the core, wherein the core contains Li. m A x Mn 1-y B y P 1-z C z O 4-n D n The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer, the first coating layer containing crystalline pyrophosphate M. a P2O7 and oxide M′ b O c The second coating layer contains carbon. The definitions of A, B, C, D, M, M′, m, x, y, z, n, a, b, and c are as described above.

[0152] As a result, the applicant unexpectedly discovered that by simultaneously doping specific elements in specific amounts at the Li, Mn, P, and O sites of the compound LiMnPO4, coating the surface of the compound with a first coating layer containing crystalline pyrophosphate and oxides, and then coating the surface of the first coating layer with a second coating layer containing carbon, a positive electrode active material can be obtained. This can greatly reduce the generation of Li / Mn antisite defects, reduce manganese dissolution, and lower the lattice change rate, thereby increasing the capacity of the secondary battery and improving the cycle performance, high-temperature storage performance, and safety performance of the secondary battery.

[0153] In some implementations, the step of providing the core material includes the following steps:

[0154] Step (1): Mix the manganese source, the source of element B, the acid, and an optional solvent to obtain a mixture;

[0155] Step (2): Mix the mixture with a lithium source, a phosphorus source, a source of element A, a source of element C, and a source of element D, and optionally a solvent, dry, and sinter to obtain a mixture containing Li. m A x Mn 1-y B y P 1-z C z O 4-n D n The core material.

[0156] In some embodiments, step (1) is performed at 60°C-120°C, or optionally at 70°C-120°C (e.g., about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C or about 120°C); and / or, in step (1), mixing is performed by stirring at a speed of 200-800 rpm (e.g., 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm), optionally for 1-9 hours (more preferably 3-7 hours, e.g., about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours or about 9 hours).

[0157] In some embodiments, in step (2), the mixing is carried out for 8-15 hours (e.g., about 8 hours, about 9 hours, about 10 hours, about 11 hours, about 12 hours, about 13 hours, about 14 hours, or about 15 hours), optionally at a temperature of 20-120°C, optionally at 40-120°C (e.g., about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C, or about 120°C).

[0158] When the temperature and time during the core particle preparation process are within the above range, the obtained core and the positive electrode active material made from it have fewer lattice defects, which is beneficial to suppress manganese dissolution, reduce interfacial side reactions between the positive electrode active material and the electrolyte, and thus improve the cycle performance and safety performance of the secondary battery.

[0159] In some embodiments, in step (2), mixing is performed at a pH of 3.5-6, optionally at a pH of 4-6, and more preferably at a pH of 4-5. It should be noted that the pH can be adjusted in this application using methods commonly used in the art, for example, by adding an acid or a base.

[0160] In some alternative embodiments, the mixture obtained in step (1) is filtered, dried, and ground to obtain a particle size D. v50 refers to manganese salt particles doped with element B with a wavelength of 50-200 nm. The manganese salt particles doped with element B are used in step (2) to mix with lithium source, phosphorus source, source of element A, source of element C and source of element D and optional solvent.

[0161] In some embodiments, optionally, in step (2), the molar ratio of the mixture or manganese salt particles doped with element B to the lithium source and phosphorus source is 1:0.4-2.1:0.1-2.1, optionally about 1:0.4-0.5:0.1-1.

[0162] In some embodiments, in step (2), sintering is performed at 600-900°C for 4-10 hours; optionally, sintering can be performed at about 650°C, about 700°C, about 750°C, about 800°C, about 850°C or about 900°C for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; optionally, sintering is performed under an inert gas or a mixture of inert gas and hydrogen atmosphere; more preferably, the protective atmosphere is a mixture of 70-90 vol% nitrogen and 10-30 vol% hydrogen; the sintering temperature and sintering time can be within any range of the above values, which can improve the crystallinity of the core, reduce the generation of impurity phases, maintain a certain particle size of the core, thereby improving the specific capacity and compaction density of the positive electrode active material, and improving the overall performance of the secondary battery, including rate performance.

[0163] In some alternative implementations, in step (2), drying is performed using a spray drying device.

[0164] In some alternative implementations, in step (2), grinding is performed simultaneously with mixing.

[0165] In some embodiments, pyrophosphate M is included. a P2O7 powder is prepared by the following steps:

[0166] Mix the source of element M, the phosphorus source, and an optional solvent to obtain a mixture. Adjust the pH of the mixture to 4-6, continue mixing, and then dry and sinter.

[0167] In some embodiments, preparation is carried out containing pyrophosphate M a In the process of preparing P2O7 powder, drying is performed at 100℃-300℃ for 4-8 hours, or optionally at 150℃-200℃; and / or sintering is performed at 500℃-800℃ under inert gas protection for 4-10 hours, or optionally at 650℃-800℃.

[0168] In some embodiments, the sintering temperature in the coating step is 500-800℃, and the sintering time is 4-10h.

[0169] The preparation method of this application does not have any particular restrictions on the source of materials. The source of a certain element may include one or more of the element's elemental form, sulfate, halide, nitrate, phosphate, oxalate, carbonate, oxide and hydroxide, provided that the source can achieve the purpose of the preparation method of this application.

[0170] In some embodiments, the source of element A is selected from one or more of the following: elemental form, oxide, phosphate, oxalate, carbonate, and sulfate; and / or,

[0171] The source of element B is one or more selected from the elemental form, oxide, phosphate, oxalate, carbonate, and sulfate of element B; and / or,

[0172] The source of element C is one or more selected from sulfates, borates, nitrates, and silicates of element C; and / or,

[0173] The source of element D is one or more selected from the elemental form of element D and its ammonium salt.

[0174] In some embodiments, the source of element M is one or more selected from elemental form, carbonate, sulfate, halide, nitrate, organic acid salt, oxide and hydroxide of element M.

[0175] In some embodiments, the source of element M' is one or more selected from elemental form, carbonate, sulfate, halide, nitrate, organic acid salt, oxide and hydroxide of element M'.

[0176] The amount of source added for each of elements A, B, C, D, M, and M' depends on the target doping amount, and the ratio of the amount of lithium source, manganese source, and phosphorus source used conforms to the stoichiometric ratio.

[0177] In this application, the manganese source can be any manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the manganese source can be one or more selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0178] In this application, the acid may be one or more organic acids selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, silicic acid, siliceous acid, and organic acids such as oxalic acid. In some embodiments, the acid is a dilute organic acid with a concentration of 60% by weight or less.

[0179] In this application, the lithium source may be any lithium-containing material known in the art that can be used to prepare lithium manganese phosphate. As an example, the lithium source may be one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0180] In this application, the phosphorus source may be any phosphorus-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the phosphorus source may be one or more selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0181] In this application, as an example, the carbon source is one or more selected from starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0182] [Positive electrode plate]

[0183] This application provides a positive electrode sheet, which 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 includes the aforementioned positive electrode active material or a positive electrode active material prepared by the aforementioned preparation method, and the content of the positive electrode active material in the positive electrode film layer is more than 10% by weight, based on the total weight of the positive electrode film layer.

[0184] In some embodiments, the content of the positive electrode active material in the positive electrode film is 90-99.5% by weight, based on the total weight of the positive electrode film. This ensures that the secondary battery has high capacity, good cycle performance, high-temperature storage performance, and safety performance.

[0185] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0186] In some embodiments, the positive electrode film may also include other positive electrode active materials known in the art for use in batteries. As an example, the positive electrode active material may include at least one of the following: lithium-containing phosphates with an olivine structure and their 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-containing phosphates with an olivine structure include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites.

[0187] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0188] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0189] [Negative electrode plate]

[0190] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0191] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0192] 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 substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0193] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one 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 be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one 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.

[0194] In some embodiments, the negative electrode film layer may optionally include a binder. As an example, the binder may be selected from at least one 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).

[0195] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0196] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0197] 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 (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0198] [Electrolytes]

[0199] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0200] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0201] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0202] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, 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.

[0203] In some embodiments, the electrolyte may optionally include additives. As examples, 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.

[0204] [Isolation membrane]

[0205] 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.

[0206] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can 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 can be the same or different, without particular limitation.

[0207] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0208] 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.

[0209] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0210] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0211] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 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 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0212] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0213] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0214] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0215] 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, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0216] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0217] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack 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 (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0218] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0219] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0220] [Example]

[0221] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially. Unless otherwise specified, the content of each component in the embodiments of this invention is based on the mass of the component excluding crystallization water.

[0222] The sources of raw materials involved in the preparation examples and embodiments of this application are as follows:

[0223]

[0224]

[0225] Example 1-1

[0226] Step S1: Preparation of doped manganese oxalate

[0227] 1.3 mol MnSO4·H2O and 0.7 mol FeSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was then transferred to a reaction vessel, and 10 L of deionized water and 2 mol oxalic acid dihydrate were added. The mixture was heated to 80 °C and then stirred at 600 rpm for 6 hours until the reaction was terminated (no more bubbles were generated), yielding a suspension of Fe-doped manganese oxalate. The suspension was filtered, and the filter cake was dried at 120 °C and ground to obtain a particle size D. v 50 consists of Fe-doped manganese oxalate particles of approximately 100 nm.

[0228] Step S2: Preparation of Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 kernel

[0229] 1 mol of Fe-doped manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 0.005 mol of sucrose were added to 20 L of deionized water. The mixture was then transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation at 250 °C for 4 hours to obtain particles. The particles were sintered at 700 °C for 10 hours under a nitrogen (90% v / v) + hydrogen (10% v / v) protective atmosphere to obtain the core material. The elemental composition of the core material was determined using inductively coupled plasma atomic emission spectrometry (ICP), and the core chemical formula is as shown above.

[0230] Step S3: Prepare lithium iron pyrophosphate powder

[0231] 4.77 g lithium carbonate, 7.47 g ferrous carbonate, 14.84 g ammonium dihydrogen phosphate, and 1.3 g oxalic acid dihydrate were dissolved in 50 ml deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react completely. The resulting solution was then heated to 80 °C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain a powder. The powder was sintered at 650 °C under a nitrogen atmosphere for 8 hours, and after naturally cooling to room temperature, it was ground to obtain Li₂FeP₂O₇ powder.

[0232] Step S4: Prepare a suspension containing aluminum oxide and sucrose.

[0233] 4.71g of nano-sized Al2O3 (particle size approximately 20nm) and 3.73g of sucrose (in C 12 H 22 O 11 Add (the same amount below) to 150 ml of deionized water, stir for 6 hours to mix thoroughly, then heat the mixture to 120°C and maintain that temperature for 6 hours to obtain a suspension containing aluminum oxide and sucrose.

[0234] Step S5: Preparation of the two coating layers

[0235] 157.21g of the above-mentioned core and 1.57g of the above-mentioned lithium iron pyrophosphate (Li2FeP2O7) powder were added to the suspension containing aluminum oxide and sucrose prepared in the previous step. After stirring and mixing evenly, the mixture was transferred to a vacuum oven and dried at 150°C for 6 hours. The product was then dispersed by sand milling. After dispersion, the product was sintered at 700°C for 6 hours in a nitrogen atmosphere to obtain double-layer coated lithium manganese phosphate.

[0236] Examples 1-2 to 1-59 and Comparative Examples 1 to 12

[0237] The positive electrode active materials of Examples 1-2 to 1-59 and Comparative Examples 1 to 12 were prepared using a method similar to that of Examples 1-1. The differences in the preparation of the positive electrode active materials are shown in Tables 1-4.

[0238] Among them, Comparative Examples 1-9 do not involve steps S3-S5; Comparative Example 10 does not involve step S4; Comparative Example 11 does not involve step S3.

[0239]

[0240]

[0241]

[0242]

[0243]

[0244]

[0245]

[0246]

[0247]

[0248]

[0249]

[0250]

[0251]

[0252]

[0253]

[0254]

[0255]

[0256]

[0257]

[0258]

[0259]

[0260]

[0261]

[0262] Example 2-1

[0263] Except for step S3 in preparing lithium iron pyrophosphate (Li2FeP2O7) powder, where the sintering temperature in the powder sintering step is 550°C and the sintering time is 1 h to control the crystallinity of Li2FeP2O7 to 30%, the other conditions are the same as in Examples 1-1.

[0264] Example 2-2

[0265] Except for step S3 in preparing lithium iron pyrophosphate (Li2FeP2O7) powder, where the sintering temperature in the powder sintering step is 550°C and the sintering time is 2h to control the crystallinity of Li2FeP2O7 to 50%, the other conditions are the same as in Examples 1-1.

[0266] Example 2-3

[0267] Except for step S3 in preparing lithium iron pyrophosphate (Li2FeP2O7) powder, where the sintering temperature in the powder sintering step is 600°C and the sintering time is 3h to control the crystallinity of Li2FeP2O7 to 70%, the other conditions are the same as in Examples 1-1.

[0268] Examples 2-4

[0269] Except for step S3 in preparing lithium iron pyrophosphate (Li2FeP2O7) powder, where the sintering temperature in the powder sintering step is 500°C to control the crystallinity of Li2FeP2O7 to 10%, the other conditions are the same as in Examples 1-1.

[0270] Preparation of positive electrode tab

[0271] The double-layer coated lithium manganese phosphate positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) prepared above were added to N-methylpyrrolidone (NMP) at a weight ratio of 92:2.5:5.5, and stirred until homogeneous to obtain the positive electrode slurry. Then, the positive electrode slurry was prepared at a ratio of 0.280 g / 1540.25 mm. 2 The material is evenly coated onto aluminum foil, then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0272] Preparation of negative electrode tab

[0273] Artificial graphite (anode active material), superconducting carbon black (Super-P) (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) were dissolved in deionized water at a mass ratio of 95%:1.5%:1.8%:1.7%. After thorough mixing, a negative electrode slurry with a viscosity of 3000 mPa·s and a solid content of 52% was obtained. The negative electrode slurry was coated onto a 6 μm thick copper foil current collector, then baked at 100℃ for 4 hours to dry it, and finally rolled to obtain a compacted density of 1.75 g / cm³. 3 The negative electrode sheet.

[0274] Separator film

[0275] Polypropylene film is used.

[0276] Preparation of electrolyte

[0277] Ethylene carbonate, dimethyl carbonate, and 1,2-propanediol carbonate were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the mixture to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0278] Preparation of full cell

[0279] The obtained positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to obtain a bare cell. The bare cell is placed in an outer packaging, injected with the electrolyte, and sealed to obtain a full battery (hereinafter also referred to as "full battery").

[0280] Preparation of button cell

[0281] The prepared positive electrode active material, PVDF, and acetylene black were added to NMP at a weight ratio of 90:5:5, and stirred in a drying chamber to form a slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet. The coating amount was 0.2 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 .

[0282] A lithium sheet is used as the negative electrode, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC) in a volume ratio of 1:1:1 is used as the electrolyte. Together with the positive electrode sheet prepared above, they are assembled into a coin cell (hereinafter also referred to as "coin cell") in a coin cell box.

[0283] Property test of positive active material

[0284] 1. Determination of the core chemical formula and composition of different coating layers:

[0285] High spatial resolution characterization of the internal microstructure and surface structure of the positive electrode active material was performed using spherical aberration electron microscopy (ACSTEM). Combined with three-dimensional reconstruction technology, the core chemical formula and the composition of the first and second coating layers of the positive electrode active material were obtained.

[0286] 2. Initial capacity test of button cells:

[0287] At a voltage of 2.5–4.3V, the button cell prepared above is charged to 4.3V at 0.1C, and then charged at 4.3V at a constant voltage until the current is less than or equal to 0.05mA. After standing for 5 minutes, it is discharged to 2.0V at 0.1C. The discharge capacity at this time is the initial specific capacity, denoted as D0.

[0288] 3. Average discharge voltage (V) test of coin cells:

[0289] The coin cells prepared above were placed in a constant temperature environment of 25°C for 5 minutes, discharged at 0.1C to 2.5V, placed in a constant temperature environment for 5 minutes, charged at 0.1C to 4.3V, and then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. After being placed in a constant temperature environment for 5 minutes, they were discharged at 0.1C to 2.5V. The discharge capacity at this time is the initial specific capacity, denoted as D0, and the discharge energy is the initial energy, denoted as E0. The average discharge voltage V of the coin cells is E0 / D0.

[0290] 4. Full battery gas expansion test at 60°C:

[0291] The prepared full cell was stored at 60°C at 100% state of charge (SOC). The open-circuit voltage (OCV) and internal resistance (IMP) of the cell were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. The full cell was removed after every 48 hours of storage, allowed to stand for 1 hour, and then the OCV and IMP were measured. After cooling to room temperature, the cell volume was measured using the displacement method. The displacement method involves first measuring the cell's weight F1 separately using a balance with automatic unit conversion, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the experiment, the weight F2 of the battery cell and the buoyancy F of the battery cell are measured at this time. 浮 That is, F1-F2, and then according to Archimedes' principle, F 浮 =ρ×g×V 排 The cell volume V is calculated to be V = (F1 - F2) / (ρ × g).

[0292] Based on the OCV and IMP test results, the batteries in all embodiments maintained a SOC of over 99% throughout the entire experiment until the end of storage.

[0293] After 30 days of storage, the cell volume was measured, and the percentage increase in cell volume after storage was calculated relative to the cell volume before storage.

[0294] In addition, measure the residual capacity of the battery cell. Charge the full battery at 1C to 4.3V within the range of 2.5V to 4.3V, then charge it at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, and record the charging capacity at this point as the residual capacity of the battery cell.

[0295] 5. Cyclic performance test of the entire battery at 45°C:

[0296] Under constant temperature conditions of 45℃ and at a voltage range of 2.5–4.3V, the prepared full battery was charged at 1C to 4.3V, and then charged at a constant voltage of 4.3V until the current was less than or equal to 0.05mA. After resting for 5 minutes, it was discharged at 1C to 2.5V, and the discharge capacity at this point was recorded as D0. The aforementioned charge-discharge cycle was repeated until the discharge capacity decreased to 80% of D0. The number of cycles completed at this point was recorded.

[0297] 6. Lattice change rate test:

[0298] Under a constant temperature environment of 25℃, the positive electrode active material sample prepared above was placed in an XRD (model Bruker D8 Discover) and tested at 1° / min. The test data was then organized and analyzed. Referring to the standard PDF card, the lattice constants a0, b0, c0 and v0 were calculated (a0, b0 and c0 represent the length of each aspect of the unit cell, and v0 represents the volume of the unit cell, which can be directly obtained from the XRD refinement results).

[0299] Using the above-described method for preparing coin cells, the positive electrode active material sample was prepared into a coin cell, and the coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. The positive electrode sheet from the coin cell was then removed and immersed in dimethyl carbonate (DMC) for 8 hours. After drying, the powder was scraped off, and particles with a diameter less than 500 nm were screened out. Samples were taken, and their cell volume v1 was calculated in the same manner as the fresh samples tested above. The lattice change rate (cell volume change rate) before and after complete lithium insertion / extraction is shown in the table.

[0300] 7. Li / Mn inverse defect concentration test:

[0301] The XRD results obtained from the "lattice change rate measurement method" are compared with the PDF (Powder Diffraction File) card of the standard crystal to determine the Li / Mn antisite defect concentration. Specifically, the XRD results obtained from the "lattice change rate measurement method" are imported into the General Structure Analysis System (GSAS) software to automatically obtain refined results, which include the occupancy of different atoms. The Li / Mn antisite defect concentration is then obtained by reading the refined results.

[0302] 8. Transition metal dissolution test:

[0303] The full battery, after being cycled at 45°C until its capacity decayed to 80%, was discharged at a 0.1C rate until the cutoff voltage of 2.0V. Then, the battery was disassembled, the negative electrode was removed, and 30 unit areas (1540.25 mm²) were randomly selected from the negative electrode. 2 The discs were tested using an Agilent ICP-OES730 inductively coupled plasma emission spectrometry (ICP). The amounts of Fe (if the Mn site of the positive electrode active material is doped with Fe) and Mn were calculated based on the ICP results, thus determining the amount of Mn (and Mn-doped Fe) dissolved after cycling. The testing standard was based on EPA-6010D-2014.

[0304] 9. Surface oxygen valence state test:

[0305] 5g of the positive electrode active material sample prepared above was used to prepare a coin cell according to the above method. The coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. Then, the positive electrode sheet of the coin cell was removed and immersed in dimethyl carbonate (DMC) for 8 hours. After drying, the powder was scraped off, and particles with a diameter of less than 500nm were screened out. The obtained particles were measured using electron energy loss spectroscopy (EELS, using a Talos F200S instrument) to obtain the energy loss near-edge structure (ELNES), which reflects the density of states and energy level distribution of the element. Based on the density of states and energy level distribution, the number of occupied electrons was calculated by integrating the valence band density of states data, thereby deducing the valence state of the surface oxygen after charging.

[0306] 10. Compacted density measurement:

[0307] Take 5g of the prepared positive electrode active material powder and place it in a compaction mold (CARVER mold, model 13mm, USA). Then place the mold on a compaction density instrument. Apply a pressure of 3T and read the thickness of the powder under pressure (thickness after depressurization; the area of ​​the container used for testing is 1540.25mm²) on the instrument. 2 The compaction density is calculated using ρ = m / v.

[0308] 11. X-ray diffraction method for testing the crystallinity of pyrophosphate and phosphate.

[0309] Take 5g of the positive electrode active material powder prepared above, and measure the total scattering intensity by X-rays. It is the sum of the scattering intensity of all matter in space. It is only related to the intensity of the primary rays, the chemical structure, and the total number of electrons participating in the diffraction, i.e., the mass, and is not related to the order state of the sample. Then, separate the crystalline scattering and non-crystalline scattering from the diffraction pattern. The crystallinity is the ratio of the scattering of the crystalline part to the total scattering intensity.

[0310] 12. Interplanar spacing and included angles

[0311] Take 1g of each of the above-prepared positive electrode active material powders into a 50mL test tube, and inject 10mL of 75% alcohol into the test tube. Then, stir and disperse the mixture thoroughly for 30 minutes. Then, use a clean disposable plastic pipette to take an appropriate amount of the above solution and drop it onto a 300-mesh copper grid. At this time, some powder will remain on the copper grid. Transfer the copper grid along with the sample to the TEM (Talos F200s G2) sample chamber for testing, obtain the original TEM test image, and save the original image format (xx.dm3).

[0312] Open the original image obtained from the TEM test in DigitalMicrograph software and perform a Fourier transform (the software will automatically complete this step after clicking) to obtain the diffraction pattern. Measure the distance from the diffraction spot to the center position in the diffraction pattern to obtain the interplanar spacing. The included angle is calculated according to the Bragg equation.

[0313] The results are shown in Table 5-9.

[0314]

[0315]

[0316]

[0317]

[0318]

[0319]

[0320]

[0321]

[0322]

[0323]

[0324] As can be seen from Examples 1-1 to 1-59 and Comparative Examples 1-9, the presence of the first coating layer is beneficial for reducing the concentration of Li / Mn antisite defects and the amount of Fe and Mn leaching after cycling in the obtained material, thereby increasing the coin capacity of the battery and improving its high-temperature storage performance, safety performance, and cycle performance. When other elements are doped at the Li, Mn, phosphorus, and oxygen sites, respectively, the lattice change rate, antisite defect concentration, and the amount of Fe and Mn leaching in the obtained material can be significantly reduced, thereby increasing the specific capacity and compaction density of the battery and improving its high-temperature storage performance, safety performance, and cycle performance.

[0325] As can be seen from Examples 1-33 to 1-36, as the amount of the first coating layer increases from 3.2% to 6.4%, the leaching of Fe and Mn after cycling gradually decreases, corresponding to improved high-temperature storage performance, safety performance, and cycle performance at 45°C, although the coin cell capacity slightly decreases. Optionally, the overall performance of the battery is optimal when the total amount of the first coating layer is 4-6.4% by weight.

[0326] Based on Examples 1-1 and 1-37 to 1-40, it can be seen that as the amount of the second coating layer increases from 1% to 6%, the leaching of Fe and Mn after cycling gradually decreases, corresponding to improved high-temperature storage performance, safety performance, and cycle performance at 45°C. However, the coin cell capacity decreases slightly. Optionally, when the total amount of the second coating layer is 3-5% by weight, the overall performance of the corresponding battery is optimal.

[0327] Based on Examples 1-1 and 1-41 to 1-44, it can be seen that when Li2FeP2O7 and Al2O3 are present in the first coating layer, especially when the weight ratio of Li2FeP2O7 to Al2O3 is 1:3 to 3:1, the battery performance is significantly improved.

[0328]

[0329]

[0330]

[0331]

[0332]

Claims

1. A positive electrode active material having a core-shell structure, comprising an inner core and a shell covering the inner core, The inner core comprises Li m A x Mn 1-y B y P 1-z C z O 4-n D n wherein, the m is selected from any value within a range of 0.5 to 1.2, the x is selected from any value within a range of 0.001 to 0.5, the y is selected from any value within a range of 0.001 to 0.5, the z is selected from any value within a range of 0.001 to 0.2, the n is selected from any value within a range of 0.001 to 0.5, the A is one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, the B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, the C is one or more elements selected from B, S, Si and N, and the D is one or more elements selected from S, F, Cl and Br; the shell comprises a first coating layer covering the inner core and a second coating layer covering the first coating layer; wherein the first coating layer comprises a crystalline pyrophosphate M a P2O7and an oxide M' b O c wherein a is greater than 0 and less than or equal to 4, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and M' is one or more elements selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanide series elements, and Sb. the second coating layer contains carbon.

2. The positive electrode active material according to claim 1, wherein the m is selected from any value within a range of 0.9 to 1.

1.

3. The positive electrode active material according to claim 1, wherein the x is selected from any value within a range of 0.001 to 0.

1.

4. The positive electrode active material according to claim 1, wherein the z is selected from any value within a range of 0.001 to 0.

1.

5. The positive electrode active material according to claim 1, wherein the n is selected from any value within a range of 0.001 to 0.

1.

6. The positive electrode active material according to claim 1, wherein the A is one or more elements selected from Al, Mg, Nb, Mo and W.

7. The positive electrode active material according to claim 1, wherein the B is one or more elements selected from Ti, V, Fe, Ni, Mg and Co.

8. The positive electrode active material according to claim 1, wherein the C is one or more elements selected from S, Si and N.

9. The positive electrode active material according to claim 1, wherein the D is one or more elements selected from F, Cl and Br.

10. The positive electrode active material according to claim 1, wherein the a is greater than 0 and less than or equal to 3.

11. The positive electrode active material according to claim 1, wherein the M is one or more elements selected from Li and Fe.

12. The positive electrode active material according to claim 1, wherein the M' is one or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce.

13. The positive electrode active material according to claim 1, wherein the M' is one or more elements selected from Mg, Al, V, Cu, Zn, Zr and W.

14. The positive electrode active material according to claim 1, wherein in the inner core, the ratio of 1-y to y is 1 to 4; and / or, the ratio of m to x is 1 to 1200.

15. The positive electrode active material according to claim 1, wherein in the inner core, the ratio of 1-y to y is 1.5 to 3; and / or, the ratio of m to x is 9 to 1100.

16. The positive electrode active material according to claim 1, wherein in the inner core, the ratio of m to x is 190 to 998.

17. The positive electrode active material according to claim 1, wherein the x is any value within a range of 0.001 to 0.005; and / or, the y is any value within a range of 0.01 to 0.5; and / or, the z is any value within a range of 0.001 to 0.005; and / or, the n is any value within a range of 0.001 to 0.

005.

18. The positive electrode active material according to claim 1, wherein the y is any value within a range of 0.25 to 0.

5.

19. The positive electrode active material according to claim 1, wherein The first coating layer has a coating amount of greater than 0% by weight and less than or equal to 7% by weight based on the weight of the core.

20. The positive electrode active material according to claim 1, wherein The first coating layer has a coating amount of 4-5.6% by weight based on the weight of the core.

21. The positive electrode active material according to claim 1, wherein, The weight ratio of the pyrophosphate and the oxide in the first coating layer is 1:3 to 3:

1.

22. The positive electrode active material according to claim 1, wherein The weight ratio of the pyrophosphate and the oxide in the first coating layer is 1:3 to 1:

1.

23. The positive electrode active material according to claim 1, wherein, The interplanar spacing of the pyrophosphate in the first coating layer is 0.300-0.310 nm.

24. The positive electrode active material according to claim 1, wherein The interplanar spacing of the pyrophosphate in the first coating layer is 0.300-0.310 nm.

25. The positive electrode active material according to claim 1, wherein The interplanar spacing of the pyrophosphate in the first coating layer is 0.300-0.310 nm.

26. The positive electrode active material according to claim 1, wherein, The crystallinity of the pyrophosphate in the first coating layer is 10% to 100%.

27. The positive electrode active material according to claim 1, wherein, The crystallinity of the pyrophosphate in the first coating layer is 50% to 100%.

28. The positive electrode active material according to claim 1, wherein, The second coating layer has a coating amount of greater than 0% by weight and less than or equal to 6% by weight based on the weight of the core.

29. The positive electrode active material according to claim 1, wherein, The second coating layer has a coating amount of 3-5% by weight based on the weight of the core.

30. The positive electrode active material according to claim 1, wherein, The A is any one element selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W; and / or, The B is at least two elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; and / or, The C is any one element selected from the group consisting of B, S, Si, and N; and / or, The D is any one element selected from the group consisting of S, F, Cl, and Br.

31. The positive electrode active material according to claim 1, wherein The A is Mg or Nb; and / or, The B is at least two elements selected from the group consisting of Fe, Ti, V, Co, and Mg; and / or, The C is S; and / or, The D is F.

32. The positive electrode active material according to claim 1, wherein The B is a combination of the Fe element and at least one element selected from the group consisting of Ti, V, Co, and Mg.

33. The positive electrode active material according to claim 1, wherein, The Li / Mn antisite defect concentration of the positive electrode active material is 4% or less.

34. The positive electrode active material according to claim 1, wherein, The Li / Mn antisite defect concentration of the positive electrode active material is 2% or less.

35. The positive electrode active material according to claim 1, wherein, The lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 9.8% or less.

36. The positive electrode active material according to claim 1, wherein, The lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 6% or less.

37. The positive electrode active material according to claim 1, wherein, The lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 4% or less.

38. The positive electrode active material according to claim 1, wherein, The surface oxygen valence state of the positive electrode active material is -1.55 or less.

39. The positive electrode active material according to claim 1, wherein, The surface oxygen valence state of the positive electrode active material is -1.88 or less.

40. The positive electrode active material according to claim 1, wherein, The surface oxygen valence state of the positive electrode active material is -1.98 to -1.

88.

41. The positive electrode active material according to any one of claims 1 to 40, wherein, The positive electrode active material has a compaction density of 1.89 g / cm 3 The above.

42. The positive electrode active material according to any one of claims 1 to 40, wherein, The positive electrode active material has a compaction density of 2.0 g / cm 3 The above.

43. The positive electrode active material according to any one of claims 1 to 40, wherein, The positive electrode active material has a compaction density of 2.2 g / cm 3 The above.

44. A method for producing a positive electrode active material, comprising the steps of: The step of providing a core material: the core comprises Li m A x Mn 1-y B y P 1-z C z O 4-n D n , wherein the m is selected from any value in the range of 0.5-1.2, the x is selected from any value in the range of 0.001-0.5, the y is selected from any value in the range of 0.001-0.5, the z is selected from any value in the range of 0.001-0.2, the n is selected from any value in the range of 0.001-0.5, the A is one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, the B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, the C is one or more elements selected from B, S, Si and N, and the D is one or more elements selected from S, F, Cl and Br. Coating step: Provides M containing pyrophosphate a P2O7 powder and containing carbon source and oxide M′ b O c A suspension containing the core material, including pyrophosphate M a P2O7 powder and containing carbon source and oxide M′ b O c The suspension is mixed and sintered to obtain a positive electrode active material, wherein a is greater than 0 and less than or equal to 4, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, and M′ is one or more elements selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanides and Sb; wherein the positive electrode active material has a core-shell structure including an inner core and a shell covering the inner core, the inner core comprising Li m A x Mn 1-y B y P 1-z C z O 4-n D n , the shell including a first coating layer covering the inner core and a second coating layer covering the first coating layer, the first coating layer comprising a crystalline pyrophosphate M a P2O7and an oxide M' b O c , the second coating layer comprising carbon.

45. The method of manufacturing according to claim 44, wherein, The m is selected from any numerical value within the range of 0.9 to 1.

1.

46. The method of manufacturing according to claim 44, wherein, The x is selected from any numerical value within the range of 0.001 to 0.

1.

47. The method of manufacturing according to claim 44, wherein, The z is selected from any numerical value within the range of 0.001 to 0.

1.

48. The method of manufacturing according to claim 44, wherein, The n is selected from any numerical value within the range of 0.001 to 0.

1.

49. The method of manufacturing according to claim 44, wherein, The A is selected from one or more elements among Al, Mg, Nb, Mo, and W.

50. The method of manufacturing according to claim 44, wherein, The B is selected from one or more elements among Ti, V, Fe, Ni, Mg, and Co.

51. The method of manufacturing according to claim 44, wherein, The C is selected from one or more elements among S, Si, and N.

52. The method of manufacturing according to claim 44, wherein, The D is selected from one or more elements among F, Cl, and Br.

53. The method of manufacturing according to claim 44, wherein, The a is greater than 0 and less than or equal to 3.

54. The method of manufacturing according to claim 44, wherein, The M is selected from one or more elements among Li and Fe.

55. The method of manufacturing according to claim 44, wherein, The M' is selected from one or more elements among Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La, and Ce.

56. The method of manufacturing of claim 44, wherein, The M' is selected from one or more elements among Mg, Al, V, Cu, Zn, Zr, and W.

57. The production method according to claim 44, wherein the step of providing a core material comprises the steps of: Step (1): mixing a manganese source, a source of element B, and an acid or mixing a manganese source, a source of element B, an acid, and a solvent to obtain a mixture; Step (2): mixing the mixture with a source of lithium, a source of phosphorus, a source of element A, a source of element C, and a source of element D, or mixing the mixture with a source of lithium, a source of phosphorus, a source of element A, a source of element C, and a source of element D, and a solvent, drying, sintering, to obtain a core material comprising Li m A x Mn 1- y B y P 1-z C z O 4-n D n D 58. The method of manufacturing according to claim 57, wherein, The step (1) is performed by mixing at 60°C to 120°C; and / or, in the step (1), the mixing is performed by stirring at a rotation speed of 200 to 800 rpm.

59. The method of manufacturing according to claim 57, wherein, In the step (2), the mixing is performed for 8 to 15 hours.

60. The method of manufacturing according to claim 57, wherein, In the step (2), the sintering is performed at 600°C to 900°C for 6 to 14 hours.

61. The method of manufacturing of claim 44, wherein, The source of element A is one or more selected from the group consisting of an elemental substance, an oxide, a phosphate, an oxalate, a carbonate, and a sulfate of element A; and / or, The source of element B is one or more selected from the group consisting of an elemental substance, an oxide, a phosphate, an oxalate, a carbonate, and a sulfate of element B; and / or, The source of element B is one or more selected from the group consisting of an elemental substance, an oxide, a phosphate, an oxalate, a carbonate, and a sulfate of element B; and / or, the source of the element C is one or more selected from the group consisting of sulfates, borates, nitrates and silicates of the element C; and / or, the source of the element D is one or more selected from the group consisting of elemental D and ammonium salts of the element D.

62. The preparation method of claim 44, wherein, The powder comprising pyrophosphate M a The powder comprising P2O7 is prepared by the following steps: the source of the element M is mixed with the source of phosphorus or the source of the element M, the source of phosphorus and the solvent are mixed to obtain a mixture, the pH of the mixture is adjusted to 4-6, and the mixture is continuously mixed, and then dried and sintered.

63. The method of manufacturing according to claim 62, wherein, The powder comprising pyrophosphate M a In the step of preparing the powder comprising pyrophosphate M P2O7, the drying is drying at 100-300°C for 4-8h; and / or, the sintering is sintering at 500-800°C under inert gas protection for 4-10h.

64. The method of manufacturing according to claim 63, wherein, The powder comprising pyrophosphate M a In the step of preparing the powder comprising pyrophosphate M P2O7, the drying is at 150-200°C; and / or, the sintering is at 650-800°C.

65. The preparation method of any one of claims 44-64, wherein, the sintering temperature in the coating step is 500-800°C, and the sintering time is 4-10h.

66. A positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material of any one of claims 1-43 or the positive electrode active material prepared by the preparation method of any one of claims 44-65, and the content of the positive electrode active material in the positive electrode film layer is 10% by weight or more based on the total weight of the positive electrode film layer.

67. The cathode sheet of Claim 66, wherein, The content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight based on the total weight of the positive electrode film layer.

68. A secondary battery comprising the positive electrode active material of any one of claims 1-43 or the positive electrode active material prepared by the preparation method of any one of claims 44-65 or the positive electrode sheet of claim 66 or 67.

69. A battery module comprising: The secondary battery of claim 68.

70. A battery pack, comprising: The battery module of claim 69.

71. An electrical device, comprising: At least one selected from the group consisting of the secondary battery of claim 68, the battery module of claim 69 and the battery pack of claim 70. The battery pack of claim 70.

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