Positive electrode active material, method for preparing the same, and positive electrode sheet, secondary battery, and electric device comprising the same

Abstract

The application provides a positive electrode active material, a preparation method thereof, a positive electrode sheet comprising the same, a secondary battery, and an electric device. The positive electrode active material comprises a core and a shell covering the core, the core comprises Li m A x Mn 1‑y B y P 1‑z C z O 4‑n D n , the shell comprises a phosphate MPO4, a borate X a B b O c , and carbon, and the shell comprises one or more coating layers, each coating layer independently comprises one or more of the phosphate MPO4, the borate X a B b O c , and carbon. The positive electrode active material provided by the application can make the secondary battery have a higher energy density and also have improved cycle performance, safety performance, and / or rate performance.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a positive electrode active material, its preparation method, and a positive electrode sheet containing the same, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the application and promotion of rechargeable batteries, their safety performance has received increasing attention. Lithium manganese phosphate has become one of the most popular cathode active materials due to its advantages such as high capacity, good safety performance, and abundant raw material sources. However, lithium manganese phosphate is prone to manganese ion dissolution during charging, leading to rapid capacity decay. Summary of the Invention

[0003] The purpose of this application is to provide a positive electrode active material, a method for preparing the same, and a positive electrode sheet, a secondary battery, and an electrical device comprising the same, which enables the secondary battery using the positive electrode active material to have a high energy density while also improving cycle performance, safety performance, and / or rate performance.

[0004] The first aspect of this application provides a positive electrode active material with a core-shell structure, comprising a core and a shell enclosing the core, wherein the core comprises Li m A x Mn 1-y B y P 1-z C z O 4-n D nThe A element comprises one or more elements selected from Groups IA, IIA, IIIA, IIB, VB, and VIB, and optionally includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W. The B element comprises one or more elements selected from Groups IA, IIA, IIIA, IVA, VA, IIB, IVB, VB, VIB, and VIIIB, and optionally includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge. The C element comprises one or more elements selected from Groups IIIA, IVA, VA, and VIA, and optionally includes one element selected from B (boron), S, Si, and N. The core may contain one or more elements, wherein D comprises one or more elements selected from groups VIA and VIIA, and optionally one or more elements selected from S, F, Cl, and Br; m is selected from the range of 0.900 to 1.100, and optionally from the range of 0.900 to 1.006; x is selected from the range of 0 to 0.100, and optionally from the range of 0.001 to 0.005; y is selected from the range of 0.001 to 0.500, and optionally from the range of 0.100 to 0.450; z is selected from the range of 0.001 to 0.100; n is selected from the range of 0 to 0.100, and optionally from the range of 0.001 to 0.005; and the core is electrically neutral; the shell comprises phosphate MPO4, borate X a B b O c And carbon, and the shell comprises one or more coating layers, each coating layer independently comprising phosphate MPO4, borate X a B b O c The elements are selected from one or more of carbon, wherein M comprises one or more metallic elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA, and lanthanides, and optionally includes one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al; X comprises one or more metallic elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA, and lanthanides, and optionally includes one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al; a is selected from the range of 1 to 4; b is selected from the range of 1 to 7; c is selected from the range of 2 to 12; and the values ​​of a, b, and c satisfy the following condition: making borate X a B b O c Maintain electrical neutrality.

[0005] This application, through specific elemental doping and surface coating of lithium manganese phosphate, effectively suppresses the dissolution of manganese ions during the lithium insertion / extraction process while promoting lithium ion migration. Therefore, positive electrode sheets and secondary batteries using the positive electrode active material of this application can achieve higher energy density while also improving cycle performance, safety performance, and / or rate performance.

[0006] In any embodiment of this application, the shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer, wherein the third coating layer comprises carbon, and the first coating layer comprises phosphate MPO4, and the second coating layer comprises borate X. a B b O c Or the first coating layer includes borate X a B b O c The second coating layer comprises phosphate MPO4. Optionally, the first coating layer comprises phosphate MPO4, and the second coating layer comprises borate X. a B b O c Therefore, positive electrode sheets and electrical devices such as secondary batteries using the positive electrode active material of this application can have improved cycle performance, safety performance, and / or rate performance.

[0007] In any embodiment of this application, the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, optionally from 1% to 5% by weight, based on the weight of the core. This effectively utilizes the function of the first coating layer without affecting the kinetic performance of the secondary battery due to an excessively thick coating layer.

[0008] In any embodiment of this application, the coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, optionally from 1% to 5% by weight, based on the weight of the core. This further suppresses manganese ion dissolution while further promoting lithium ion and electron transport.

[0009] In any embodiment of this application, the coating amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, optionally from 2% to 5% by weight, based on the weight of the core. This effectively improves the specific capacity of the positive electrode active material.

[0010] In any embodiment of this application, the total coating amount of the first coating layer and the second coating layer is greater than 0 and less than or equal to 7% by weight, optionally from 4% to 5.6% by weight, based on the weight of the core. Therefore, the cycle performance, safety performance, and / or rate performance of the secondary battery can be further improved without sacrificing the specific capacity of the positive electrode active material.

[0011] In any embodiment of this application, the phosphate MPO4 and the borate X a B b O c The weight ratio is 1:3 to 3:1, and can be selected as 1:3 to 1:1. This is beneficial for leveraging the synergistic effect of phosphate and borate.

[0012] In any embodiment of this application, the interplanar spacing of the phosphate MPO4 is 0.345 nm to 0.358 nm, and the included angle of the crystal orientation (111) is 24.25° to 26.45°. This can further improve the cycle performance and rate performance of the secondary battery.

[0013] In any embodiment of this application, the crystallinity of the phosphate MPO4 is 10% to 100%, optionally 50% to 100%; and / or the borate X a B b O c The crystallinity is 10% to 100%, and can be selected as 50% to 100%. On the one hand, it is beneficial to give full play to the role of phosphate in reducing the content of surface impurities and lowering the valence state of surface oxygen. On the other hand, it is also beneficial to give full play to the role of borate in hindering the dissolution of manganese ions and promoting the transport of lithium ions and electrons, thereby reducing the interfacial side reactions between the positive electrode active material and the electrolyte, reducing the consumption of electrolyte, and improving the cycle performance and safety performance of secondary batteries.

[0014] In any embodiment of this application, in the core, the ratio of y to 1-y is 1:10 to 10:1, optionally 1:4 to 1:1. This further improves the energy density and cycle performance of the secondary battery.

[0015] In any embodiment of this application, in the core, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249. This further improves the energy density and cycle performance of the secondary battery.

[0016] In any embodiment of this application, in the core, B comprises one or more elements selected from Fe, Ti, V, Ni, Co, and Mg, and optionally includes at least two elements selected from Fe, Ti, V, Ni, Co, and Mg. This further reduces surface oxygen activity and inhibits the dissolution of manganese ions.

[0017] In any embodiment of this application, b:c is 1:3.

[0018] In any embodiment of this application, the Li / Mn antisite defect concentration of the positive electrode active material is 4% or less, optionally 2% or less. This improves the specific capacity and rate performance of the positive electrode active material.

[0019] In any embodiment of this application, the lattice change rate of the positive electrode active material is 8% or less, optionally 4% or less. This improves the rate performance of the secondary battery.

[0020] In any embodiment of this application, the surface oxygen valence state of the positive electrode active material is below -1.88, and can be selected as -1.98 to -1.88. This can improve the cycle performance and high-temperature storage performance of the secondary battery.

[0021] In any embodiment of this application, the compaction density of the positive electrode active material at 3 tons is 2.0 g / cm³. 3 The above can be selected as 2.2g / cm. 3 The above. This is beneficial for improving the volumetric energy density of secondary batteries.

[0022] The second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps of providing a core material and a coating step.

[0023] Steps for providing kernel material: The kernel includes Li m A x Mn 1-y B y P 1-z C z O 4-n D nThe A element comprises one or more elements selected from Groups IA, IIA, IIIA, IIB, VB, and VIB, and optionally includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W. The B element comprises one or more elements selected from Groups IA, IIA, IIIA, IVA, VA, IIB, IVB, VB, VIB, and VIIIB, and optionally includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge. The C element comprises one or more elements selected from Groups IIIA, IVA, VA, and VIA, and optionally includes elements selected from B (boron), S, ... One or more elements selected from Si and N, wherein D includes one or more elements selected from groups VIA and VIIA, optionally including one or more elements selected from S, F, Cl and Br, wherein m is selected from the range of 0.900 to 1.100, optionally from the range of 0.900 to 1.006, wherein x is selected from the range of 0 to 0.100, optionally from the range of 0.001 to 0.005, wherein y is selected from the range of 0.001 to 0.500, optionally from the range of 0.100 to 0.450, wherein z is selected from the range of 0.001 to 0.100, wherein n is selected from the range of 0 to 0.100, optionally from the range of 0.001 to 0.005, and wherein the core is electrically neutral.

[0024] Coating steps: Provide phosphate MPO4 and borate X respectively. a B b O c A coating solution containing a carbon source is prepared, and the core material is added to the coating solution and mixed. The mixture is then sintered to obtain a positive electrode active material. The positive electrode active material has a core-shell structure, comprising the core and a shell covering the core. The shell comprises phosphate MPO4 and borate X. a B b O c And carbon, and the shell comprises one or more coating layers, each coating layer independently comprising phosphate MPO4, borate X a B b O cThe elements are selected from one or more of carbon, wherein M comprises one or more metallic elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA, and lanthanides, and optionally includes one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al; X comprises one or more metallic elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA, and lanthanides, and optionally includes one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al; a is selected from the range of 1 to 4; b is selected from the range of 1 to 7; c is selected from the range of 2 to 12; and the values ​​of a, b, and c satisfy the following condition: making borate X a B b O c Maintain electrical neutrality.

[0025] In any embodiment of this application, the step of providing the core material includes the following steps: Step (1): mixing and stirring a source of manganese, a source of element B and an acid in a container to obtain manganese salt particles doped with element B; Step (2): mixing the manganese salt particles doped with element B with a source of lithium, a source of phosphorus, a source of element C, a source of optional element A and a source of optional element D in a solvent to obtain a slurry, and sintering it under an inert gas atmosphere to obtain the core material.

[0026] In any embodiment of this application, step (1) is performed at a temperature of 20°C to 120°C, or optionally 25°C to 80°C.

[0027] In any embodiment of this application, the stirring in step (1) is carried out at 500 rpm to 700 rpm for 60 minutes to 420 minutes, or optionally 120 minutes to 360 minutes.

[0028] By controlling the reaction temperature, stirring rate, and mixing time during doping, the doping elements can be evenly distributed, and the crystallinity of the sintered material can be higher, thereby improving the specific capacity and rate performance of the positive electrode active material.

[0029] In any embodiment of this application, the source of element A is selected from one or more of element A's simple substance, carbonate, sulfate, halide, nitrate, organic acid salt, oxide and hydroxide.

[0030] In any embodiment of this application, the source of element B is selected from one or more of element B as a simple substance, carbonate, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide.

[0031] In any embodiment of this application, the source of element C is selected from one or more of element C, sulfates, halides, nitrates, organic acid salts, oxides, hydroxides, and inorganic acids of element C.

[0032] In any embodiment of this application, the source of element D is selected from one or more of the element D in its elemental form and ammonium salt.

[0033] By selecting the sources of each dopant element within the above range, the performance of the positive electrode active material can be effectively improved.

[0034] In any embodiment of this application, the sintering in step (2) is sintering at 600°C to 800°C for 4 to 10 hours in an inert gas or a mixture of inert gas and hydrogen atmosphere.

[0035] In any embodiment of this application, the coating step includes, in an optional order, the steps of coating phosphate MPO4 and coating borate X. a B b O c The steps and the steps of coating carbon.

[0036] Optionally, in any embodiment of this application, the first coating step is the step of coating phosphate MPO4, and the second coating step is the step of coating borate X. a B b O c The third coating step is a carbon coating step, thereby obtaining a positive electrode active material with a core-shell structure, which includes the core and a shell covering the core. The shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer. The first coating layer includes phosphate MPO4, and the second coating layer includes borate X. a B b O c The third coating layer contains carbon.

[0037] In any embodiment of this application, the step of coating with phosphate MPO4 includes the following steps: providing a coating solution containing phosphate MPO4, adding the material to be coated to the coating solution, mixing evenly, drying, and then sintering to obtain a material coated with phosphate MPO4.

[0038] In any embodiment of this application, the coated borate X a B b O c The steps include the following: providing borate X a B b O cThe coating solution is prepared, and then the material to be coated is added to the coating solution, mixed evenly, dried, and then sintered to obtain borate X. a B b O c The covering material.

[0039] In any embodiment of this application, the carbon coating step includes the following steps: providing a coating liquid containing a carbon source, then adding the material to be coated into the coating liquid, mixing evenly, drying, and then sintering to obtain a carbon-coated material.

[0040] In any embodiment of this application, the coating solution containing phosphate MPO4 is prepared by the following method: adding the source of element M and the source of phosphorus to a solvent, stirring evenly to obtain a mixture, and then heating the mixture to 60°C to 120°C and holding for 2 hours to 8 hours to obtain the coating solution.

[0041] In any embodiment of this application, the borate X is included. a B b O c The coating solution was prepared by the following method: the source of element X and the source of boron were added to the solvent and stirred evenly to obtain the coating solution.

[0042] In any embodiment of this application, the sintering in the step of coating phosphate MPO4 is performed at 500°C to 800°C for 4 to 10 hours.

[0043] In any embodiment of this application, the coated borate X a B b O c The sintering in the step is sintering at 300°C to 500°C for 2 to 10 hours.

[0044] In any embodiment of this application, the sintering in the carbon coating step is sintering at 500°C to 800°C for 4 to 10 hours.

[0045] By controlling the sintering temperature and time during coating, the specific capacity and rate performance of the positive electrode active material can be further improved.

[0046] 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 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, optionally from 90% to 99.5% by weight, based on the total weight of the positive electrode film layer.

[0047] The positive electrode sheet of this application, when used in secondary batteries, can improve the energy density, cycle performance, safety performance, and / or rate performance of secondary batteries.

[0048] 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 method of the second aspect of this application, or the positive electrode sheet of the third aspect of this application.

[0049] The fifth aspect of this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0050] The positive electrode sheet, secondary battery, and electrical device of this application include the positive electrode active material of this application, and therefore have at least the same advantages as the positive electrode active material. Attached Figure Description

[0051] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0052] Figure 1 This is a schematic diagram of one embodiment of the battery cell of this application.

[0053] Figure 2 This is an exploded view of one embodiment of the battery cell of this application.

[0054] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0055] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0056] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0057] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0058] Figure 7 This is a comparison diagram of the XRD pattern of the core of the positive electrode active material prepared in Example 1-1 and the standard XRD pattern of lithium manganese phosphate (00-033-0804).

[0059] The accompanying drawings are not necessarily drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Individual battery cell, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0060] The following detailed description, with appropriate reference to the accompanying drawings, discloses the positive electrode active material, its preparation method, and embodiments of the positive electrode sheet, secondary battery, and power-consuming device comprising the same. 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0061] 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.

[0062] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0063] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0064] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates 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.

[0065] 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.

[0066] 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).

[0067] In this document, the median particle size Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% in the material. In this application, the median particle size Dv50 of the material can be determined using laser diffraction particle size analysis. For example, it can be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000) in accordance with standard GB / T19077-2016.

[0068] In this document, the term "cladding layer" refers to a layer of material 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. Furthermore, each cladding layer may be a complete or partial cover. Similarly, the term "thickness of cladding layer" refers to the thickness of the material layer covering the core in the radial direction of the core.

[0069] In this document, 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.

[0070] In this article, the terms "multiple", "various", and "multi-layered" refer to two, two kinds, or more than two layers.

[0071] In this article, “about” refers to a range of values, specifically the range of ±10% of that value.

[0072] The inventors of this application discovered in practical operation that manganese ion dissolution is severe in lithium manganese phosphate (LiMnPO4) positive electrode active materials during deep charge-discharge processes. Although existing technologies have attempted to coat lithium manganese phosphate with lithium iron phosphate to reduce interfacial side reactions, this coating cannot prevent the dissolved manganese ions from migrating into the electrolyte. After migrating to the negative electrode, the dissolved manganese ions are reduced to metallic manganese. This generated metallic manganese acts as a "catalyst," catalyzing the decomposition of the SEI film (solid electrolyte interphase) on the negative electrode surface. Some of the byproducts are gases, which can easily cause battery expansion and affect the safety performance of the secondary battery. Others deposit on the negative electrode surface, obstructing the channels for lithium ions to enter and exit the negative electrode, increasing the impedance of the secondary battery and affecting its kinetic performance. Furthermore, to replenish the lost SEI film, the active lithium ions in the electrolyte and inside the battery are continuously consumed, thus irreversibly affecting the capacity retention rate of the secondary battery.

[0073] After extensive research, the inventors discovered that the problems of severe manganese ion dissolution and high surface reactivity in lithium manganese phosphate cathode active materials may be due to the delithiation of Mn. 3+ The Jiang-Taylor effect and Li + This is caused by changes in channel size. To address this, the inventors modified lithium manganese phosphate to obtain a positive electrode active material that can significantly reduce manganese ion dissolution and lattice change rate, thereby exhibiting good cycle performance, safety performance, and / or rate performance.

[0074] Positive electrode active material

[0075] Specifically, the first aspect of this application proposes a positive electrode active material with a core-shell structure, comprising a core and a shell covering the core.

[0076] The kernel includes Li m A x Mn 1-y B y P 1-z C z O 4-n D nThe A includes one or more elements selected from families IA, IIA, IIIA, IIB, VB, and VIB; the B includes one or more elements selected from families IA, IIA, IIIA, IVA, VA, IIB, IVB, VB, VIB, and VIIIB; the C includes one or more elements selected from families IIIA, IVA, VA, and VIA; the D includes one or more elements selected from families VIA and VIIA; the m is selected from the range of 0.900 to 1.100; the x is selected from the range of 0 to 0.100; the y is selected from the range of 0.001 to 0.500; the z is selected from the range of 0.001 to 0.100; the n is selected from the range of 0 to 0.100; and the kernel is electrically neutral.

[0077] The shell comprises phosphate MPO4 and borate X. a B b O c And carbon, and the shell comprises one or more coating layers, each coating layer independently comprising phosphate MPO4, borate X a g b O c And one or more of carbon, wherein M comprises one or more metallic elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, wherein X comprises one or more metallic elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, wherein a is selected from the range of 1 to 4, wherein b is selected from the range of 1 to 7, wherein c is selected from the range of 2 to 12, and wherein the values ​​of a, b and c satisfy the following condition: making borate X a B b O c Maintain electrical neutrality.

[0078] Unless otherwise stated, in the above chemical formulas, when A consists of two or more elements, the limitation on the range of x values ​​described above applies not only to the stoichiometric coefficient of each element as A, but also to the sum of the stoichiometric coefficients of all elements as A. For example, when A consists of 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 consist of two or more elements, the limitation on the range of stoichiometric coefficients of B, C, and D in this application also has the above meaning.

[0079] The lithium manganese phosphate cathode active material of this application has a core-shell structure, with the core comprising Li... m A x Mn1-y B y P 1-z C z O 4- n D n The core, doped with element B at the Mn site of lithium manganese phosphate, helps reduce the lattice change rate of lithium manganese phosphate during lithium insertion / extraction, improves the structural stability of the lithium manganese phosphate cathode active material, significantly reduces manganese ion dissolution, and lowers the oxygen activity on the particle surface. Element C, doped at the P site, helps change the ease of Mn-O bond length changes, thereby lowering the lithium ion migration barrier, promoting lithium ion migration, and improving the rate performance of the secondary battery. Element A, doped at the Li site, also helps reduce the lattice change rate of lithium manganese phosphate during lithium insertion / extraction. Element D, doped at the O site, helps reduce interfacial side reactions. The shell comprises phosphate MPO4 and borate X. a B b O c Carbon. Phosphates possess excellent lithium-ion conductivity and can reduce surface lithium impurities. Borates possess excellent lithium-ion and electron conductivity, and can reduce surface lithium impurities and inhibit manganese ion dissolution, thereby reducing interfacial side reactions and lowering gas production, thus improving cycle performance. Carbon can effectively improve the conductivity and desolvation capability of cathode active materials.

[0080] Therefore, by performing specific element doping and surface coating on lithium manganese phosphate, this application can effectively suppress the dissolution of manganese ions during the lithium insertion / extraction process, while promoting the migration of lithium ions, thereby improving the cycle performance, safety performance, and / or rate performance of secondary batteries.

[0081] It should be noted that the core of the positive electrode active material in this application is basically consistent with the position of the main characteristic peaks before LiMnPO4 doping, indicating that the core of the doped lithium manganese phosphate positive electrode active material in this application has no impurity phase, and the improvement of the secondary battery performance mainly comes from element doping, rather than impurity phase.

[0082] In some embodiments, the shell comprises multiple coating layers, and each coating layer independently comprises phosphate MPO4 and borate X. a B b O c And one or more of carbon.

[0083] In some embodiments, the shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer, the third coating layer comprising carbon, and the first coating layer comprising phosphate MPO4, and the second coating layer comprising borate X. a B b O cOr the first coating layer includes borate X a B b O c The second coating layer comprises phosphate MPO4.

[0084] In some embodiments, the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, optionally from 1% to 5% by weight, based on the weight of the core.

[0085] In some embodiments, the amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, optionally from 1% to 5% by weight, based on the weight of the core.

[0086] When the coating amount of the first and / or second coating layers is within the above-mentioned range, it can reduce the content of impure lithium, suppress manganese ion dissolution, and promote the transport of lithium ions and electrons. Furthermore, it can further improve the cycle performance and storage performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material. It can effectively avoid the following situations: if the coating amount of the first and / or second coating layers is too small, the suppression of manganese ion dissolution may be insufficient, and the improvement in lithium ion and electron transport performance may not be significant; if the coating amount of the first and / or second coating layers is too large, the overall coating layer may be too thick, increasing battery impedance and affecting the kinetic performance of the secondary battery. Additionally, since the coating layer does not provide capacity, excessive coating will reduce the specific capacity of the positive electrode active material.

[0087] In some embodiments, optionally, the total coating amount of the first coating layer and the second coating layer is greater than 0 and less than or equal to 7% by weight, optionally from 4% to 5.6% by weight, based on the weight of the core. This allows for further improvement in the cycle performance, safety performance, and / or rate performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0088] In some embodiments, the coating amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, optionally from 1% to 6% by weight, and more preferably from 2% to 5% by weight, based on the weight of the core. The carbon-containing layer, as the third coating layer, functions as a "barrier," preventing direct contact between the positive electrode active material and the electrolyte, thereby reducing electrolyte erosion of the positive electrode active material and improving the safety performance of the secondary battery at high temperatures. On the other hand, it possesses strong conductivity, reducing battery impedance and thus improving the kinetic performance of the secondary battery. However, due to the low specific capacity of carbon materials, excessive use of the third coating layer may reduce the overall specific capacity of the positive electrode active material. Therefore, when the coating amount of the third coating layer is within the aforementioned range, the kinetic and safety performance of the secondary battery can be further improved without sacrificing the specific capacity of the positive electrode active material.

[0089] In some embodiments, optionally, the first coating layer comprises phosphate MPO4, and the second coating layer comprises borate X. a B b O c The third coating layer contains carbon.

[0090] The first coating layer may include phosphate, which has excellent lithium-ion conductivity and can reduce surface lithium content. The second coating layer may include borate, which has excellent lithium-ion and electron conductivity, and can reduce surface lithium content and inhibit manganese ion dissolution. This reduces interfacial side reactions and gas production, improving cycle performance. Furthermore, borate is chosen as the second coating layer primarily because it has lower surface activity compared to phosphate, further reducing surface lithium content, electrolyte decomposition, and manganese ion dissolution. The third coating layer is a carbon-containing layer, effectively improving the conductivity and desolvation capability of the positive electrode active material. Moreover, being the outermost layer, the third coating layer acts as a barrier, further hindering manganese ion migration into the electrolyte and reducing electrolyte erosion of the positive electrode active material. Therefore, positive electrode sheets using the positive electrode active material of this application, as well as electrical devices such as secondary batteries, can have improved cycle performance, safety performance, and / or rate performance.

[0091] In some embodiments, the first coating layer comprises phosphate MPO4, and the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, optionally from 1% to 5% by weight, more preferably from 1% to 3% by weight, based on the weight of the core. When the coating amount of the first coating layer is within the above range, it can reduce the content of impure lithium, suppress manganese ion dissolution, and promote lithium ion transport. It can also effectively avoid the following situations: if the coating amount of the first coating layer is too small, it may lead to insufficient suppression of manganese ion dissolution, and the improvement of lithium ion transport performance may not be significant; if the coating amount of the first coating layer is too large, it may lead to an excessively thick coating layer, increasing battery impedance and affecting the kinetic performance of the secondary battery.

[0092] In some embodiments, the second coating layer comprises borate X a B b O c Furthermore, the coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, optionally from 1% to 5% by weight, and more preferably from 2% to 5% by weight, based on the weight of the core. When the coating amount of the second coating layer is within the above range, it can further suppress the dissolution of manganese ions, while further promoting the transport of lithium ions and electrons. It can effectively avoid the following situations: if the coating amount of the second coating layer is too small, the suppression of manganese ion dissolution may be insufficient, and the improvement in lithium ion and electron transport performance may not be significant; if the coating amount of the second coating layer is too large, the coating layer may be too thick, increasing battery impedance and affecting the kinetic performance of the secondary battery. Also, since the coating layer does not provide capacity, excessive coating will reduce the specific capacity of the positive electrode active material. Therefore, when the coating amount of the second coating layer is within the above range, the cycle performance and storage performance of the secondary battery can be further improved without sacrificing the specific capacity of the positive electrode active material.

[0093] In some embodiments, optionally, the phosphate MPO4 and the borate X a B b O c The weight ratio is 1:3 to 3:1, and can be selected as 1:3 to 1:1. A suitable ratio of phosphate and borate is beneficial to give full play to their synergistic effect, which can effectively inhibit the dissolution of manganese ions and reduce the content of surface impurities and side reactions at the interface.

[0094] In the kernel, m is selected from the range of 0.900 to 1.100, for example, m can be 0.900, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, 1.000, 1.001, 1.002, 1.003, 1.004, 1.005, or 1.006. Optionally, m is selected from the range of 0.900 to 1.006.

[0095] In the kernel, x is selected from the range of 0 to 0.100, for example, 0, 0.001, 0.005. Optionally, x is selected from the range of 0.001 to 0.1, or 0.001 to 0.005.

[0096] In the kernel, y is selected from the range of 0.001 to 0.500, for example, y can be 0.100, 0.200, 0.250, 0.300, 0.350, 0.400, or 0.450. Optionally, y is selected from the range of 0.100 to 0.450.

[0097] In the kernel, z is selected from the range of 0.001 to 0.100, for example, z can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, or 0.100.

[0098] In the kernel, n is selected from the range of 0 to 0.100, for example, 0, 0.001, 0.005, 0.08, 0.1. Optionally, n is selected from the range of 0.001 to 0.1, or 0.001 to 0.005.

[0099] The x is selected from the range of 0 to 0.100, and the n is selected from the range of 0 to 0.100, meaning that the Li and O sites of lithium manganese phosphate may or may not be doped.

[0100] In some embodiments, x may optionally be selected from the range of 0.001 to 0.100, i.e., element A is doped at the Li site of lithium manganese phosphate.

[0101] In some embodiments, n may optionally be selected from the range of 0.001 to 0.100, i.e., element D is doped at the O site of lithium manganese phosphate.

[0102] In some embodiments, x may optionally be selected from the range of 0.001 to 0.100, and n may be selected from the range of 0.001 to 0.1, meaning that both the Li and O sites of lithium manganese phosphate are simultaneously doped.

[0103] In some embodiments, optionally, in the core, the ratio of y to 1-y is 1:10 to 10:1, optionally 1:4 to 1:1. 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 can be further improved.

[0104] In some embodiments, optionally, in the core, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249. Here, y represents the sum of the stoichiometric coefficients of the p-site dopants. When the above conditions are met, the energy density and cycle performance of the secondary battery can be further improved.

[0105] In some embodiments, optionally, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W. By selecting the Li-site doping element within the above range, the lattice change rate can be further reduced, thereby further improving the rate performance of the secondary battery.

[0106] In some embodiments, optionally, B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; more preferably, B includes one or more elements selected from Fe, Ti, V, Ni, Co, and Mg; and even more preferably, B includes at least two elements selected from Fe, Ti, V, Ni, Co, and Mg. Simultaneous doping of two or more of the above-mentioned elements at the Mn site in the lithium manganese phosphate cathode active material is beneficial to enhancing the doping effect. On the one hand, it further reduces the lattice change rate, thereby suppressing the dissolution of manganese ions and reducing the consumption of electrolyte and active lithium ions. On the other hand, it also helps to further reduce surface oxygen activity, reducing interfacial side reactions between the cathode active material and the electrolyte, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0107] In some embodiments, C may optionally include one or more elements selected from B (boron), S, Si, and N. By selecting the p-site doping element within the above range, the rate performance of the secondary battery can be further improved.

[0108] In some embodiments, the D may optionally include one or more elements selected from S, F, Cl and Br. By selecting the doping element at the O site within the above range, the side reactions at the interface can be further reduced and the high-temperature stability of the secondary battery can be improved.

[0109] In some embodiments, the M may optionally include one or more selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al.

[0110] In some embodiments, X may optionally include one or more selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al.

[0111] In some implementations, b:c can optionally be 1:3.

[0112] In some embodiments, optionally, the interplanar spacing of the phosphate MPO4 is 0.345 nm to 0.358 nm, and the included angle of the crystal orientation (111) is 24.25° to 26.45°. When the interplanar spacing and the included angle of the crystal orientation (111) of the phosphate MPO4 are within the above range, impurity phases in the coating layer can be effectively avoided, thereby improving the specific capacity of the positive electrode active material and improving the cycle performance and rate performance of the secondary battery.

[0113] In some embodiments, optionally, the crystallinity of the phosphate MPO4 is 10% to 100%, optionally 50% to 100%; and / or, the borate X a B b O c The crystallinity ranges from 10% to 100%, with a selectable range of 50% to 100%. Phosphates and borates with a certain degree of crystallinity are beneficial for maintaining the structural stability of the coating layer and reducing lattice defects. This is beneficial in two ways: firstly, it allows phosphates to fully utilize their ability to reduce surface lithium content and lower the valence state of surface oxygen; secondly, it allows borates to fully utilize their ability to inhibit manganese ion dissolution and promote lithium ion and electron transport. This reduces interfacial side reactions between the positive electrode active material and the electrolyte, reduces electrolyte consumption, and improves the cycle performance and safety performance of the secondary battery.

[0114] It should be noted that, in this application, the crystallinity of phosphates and borates can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature and sintering time. The crystallinity of phosphates and borates can be measured by methods known in the art, such as X-ray diffraction, density method, infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance absorption method.

[0115] In some embodiments, optionally, the Li / Mn antisite defect concentration of the positive electrode active material is 4% or less, and optionally 2% or less. Li / Mn antisite defects refer to the Li... + and Mn 2+ The positions of Li and Mn are interchanged. The Li / Mn antisite defect concentration refers to the concentration of Li / Mn antisite defects in the positive electrode active material. 2+ Interchangeable Li + Zhan Li + Percentage of the total. Due to Li + The transmission channel is a one-dimensional channel, Mn2+ 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 [materials / materials]. In the positive electrode active material of this application, by controlling the concentration of Li / Mn antisite defects to a low level, the specific capacity and rate performance of the positive electrode active material can be improved. In this application, the antisite defect concentration can be determined, for example, according to JIS K0131-1996.

[0116] In some embodiments, optionally, the lattice change rate of the positive electrode active material is below 8%, optionally below 6%, and more preferably below 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 secondary batteries.

[0117] In some embodiments, optionally, the average discharge voltage of the positive electrode active material is 3.5V or higher, and the specific discharge capacity is 140mAh / g or higher; alternatively, the average discharge voltage is 3.6V or higher, and the specific discharge capacity is 145mAh / g or higher. Although the average discharge voltage of undoped LiMnPO4 is above 4.0V, its specific discharge capacity is low, typically less than 120mAh / g, resulting in a low energy density for the secondary battery. By adjusting the lattice change rate through doping, its specific discharge capacity can be significantly increased, leading to a substantial increase in the overall energy density of the secondary battery even with a slight decrease in the average discharge voltage.

[0118] In some embodiments, optionally, the surface oxygen valence state of the positive electrode active material is below -1.88, and optionally 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 lithium manganese phosphate positive electrode active material of this application, by controlling the surface oxygen valence state at a low level, the reactivity of the positive electrode active 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.

[0119] In some embodiments, optionally, the compaction density of the positive electrode active material at 3 tons (T) is 2.0 g / cm³. 3 The above can be selected as 2.2g / cm. 3 The higher the compaction density of the positive electrode active material, i.e., the greater the weight of the 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 / T24533-2009.

[0120] Preparation method

[0121] The second aspect of this application provides a method for preparing the positive electrode active material of the first aspect of this application, which includes the following steps of providing a core material and a coating step.

[0122] Steps for providing kernel material: The kernel includes Li m A x Mn 1-y B y P 1-z C z O 4-n D n The A element comprises one or more elements selected from Groups IA, IIA, IIIA, IIB, VB, and VIB, and optionally includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W. The B element comprises one or more elements selected from Groups IA, IIA, IIIA, IVA, VA, IIB, IVB, VB, VIB, and VIIIB, and optionally includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge. The C element comprises one or more elements selected from Groups IIIA, IVA, VA, and VIA, and optionally includes elements selected from B (boron), S, ... One or more elements selected from Si and N, wherein D includes one or more elements selected from groups VIA and VIIA, optionally including one or more elements selected from S, F, Cl and Br, wherein m is selected from the range of 0.900 to 1.100, optionally from the range of 0.900 to 1.006, wherein x is selected from the range of 0 to 0.100, optionally from the range of 0.001 to 0.005, wherein y is selected from the range of 0.001 to 0.500, optionally from the range of 0.100 to 0.450, wherein z is selected from the range of 0.001 to 0.100, wherein n is selected from the range of 0 to 0.100, optionally from the range of 0.001 to 0.005, and wherein the core is electrically neutral.

[0123] Coating steps: Provide phosphate MPO4 and borate X respectively. a B b O c A coating solution containing a carbon source is prepared, and the core material is added to the coating solution and mixed. The mixture is then sintered to obtain a positive electrode active material. The positive electrode active material has a core-shell structure, comprising the core and a shell covering the core. The shell comprises phosphate MPO4 and borate X. a B b O cAnd carbon, and the shell comprises one or more coating layers, each coating layer independently comprising phosphate MPO4, borate X a B b O c The elements are selected from one or more of carbon, wherein M comprises one or more metallic elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA, and lanthanides, and optionally includes one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al; X comprises one or more metallic elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA, and lanthanides, and optionally includes one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al; a is selected from the range of 1 to 4; b is selected from the range of 1 to 7; c is selected from the range of 2 to 12; and the values ​​of a, b, and c satisfy the following condition: making borate X a B b O c Maintain electrical neutrality.

[0124] The preparation method of this application does not have any particular limitation on the source of the core material. Optionally, the core material in the preparation method of this application can be commercially available or prepared by the method of this application. Optionally, the core material is prepared by the method described below.

[0125] In some embodiments, optionally, the step of providing the core material includes the following steps: Step (1): mixing and stirring a source of manganese, a source of element B, and an acid in a container to obtain manganese salt particles doped with element B; Step (2): mixing the manganese salt particles doped with element B with a source of lithium, a source of phosphorus, a source of element C, a source of optional element A, and a source of optional element D in a solvent to obtain a slurry, and sintering it under an inert gas atmosphere to obtain the core material.

[0126] In some embodiments, step (1) may be performed at a temperature of 20°C to 120°C, or optionally 25°C to 80°C.

[0127] In some embodiments, the stirring in step (1) is carried out at 500 rpm to 700 rpm for 60 minutes to 420 minutes, or optionally 120 minutes to 360 minutes.

[0128] By controlling the reaction temperature, stirring rate, and mixing time during doping, the doping elements can be evenly distributed, reducing lattice defects, inhibiting manganese ion dissolution, and reducing interfacial side reactions between the positive electrode active material and the electrolyte, thereby improving the specific capacity and rate performance of the positive electrode active material.

[0129] It should be noted that, in this application, the source of a certain element may include one or more of the element's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, or hydroxide, provided that the source can achieve the purpose of the preparation method of this application.

[0130] In some embodiments, optionally, in step (1), the source of manganese is selected from one or more of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0131] In some embodiments, the source of element A may optionally be selected from one or more of element A's elemental form, carbonate, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide.

[0132] In some embodiments, the source of element B may optionally be selected from one or more of element B as a simple substance, carbonate, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide. Optionally, element B is iron, and optionally, the source of iron may be selected from one or more of ferrous carbonate, ferric hydroxide, and ferrous sulfate.

[0133] In some embodiments, optionally, in step (1), the acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, and may be oxalic acid. In some embodiments, the acid is a dilute acid with a concentration of less than 60% by weight.

[0134] In some embodiments, optionally, in step (2), the source of element C is selected from one or more of element C as a simple substance, sulfate, halide, nitrate, organic acid salt, oxide, hydroxide, and inorganic acid of element C. In some embodiments, optionally, the inorganic acid of element C is selected from one or more of phosphoric acid, nitric acid, sulfuric acid, boric acid, silicic acid, and orthosilicic acid.

[0135] In some embodiments, optionally, in step (2), the source of element D is selected from one or more of the element D in its elemental form and ammonium salt.

[0136] In some embodiments, optionally, in step (2), the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0137] In some embodiments, optionally, in step (2), the source of phosphorus is selected from one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0138] In some embodiments, the solvent used in step (2) is a solvent commonly used in the art. For example, it may be selected from at least one of ethanol and water (e.g., deionized water).

[0139] In some embodiments, optionally, in step (1), the pH of the solution is controlled to be between 4 and 6. It should be noted that the pH of the resulting mixture can be adjusted using methods commonly used in the art, for example, by adding an acid or a base.

[0140] In some embodiments, optionally, in step (2), the molar ratio of the manganese salt particles doped with element B to the lithium source and the phosphorus source is 1:(0.5-2.1):(0.5-2.1).

[0141] The amount of source added to each of elements A, B, C, and D can depend on the target doping amount.

[0142] In some embodiments, optionally, in step (2), the sintering conditions are: sintering at 600°C to 800°C for 4 to 10 hours in an inert gas atmosphere or a mixture of inert gas and hydrogen. This results in a higher crystallinity of the sintered material, thereby improving the specific capacity and rate performance of the positive electrode active material. In some embodiments, optionally, the inert gas and hydrogen mixture is nitrogen (70 vol% to 90 vol%) + hydrogen (10 vol% to 30 vol%).

[0143] In some embodiments, the carbon source may optionally be an organic carbon source, and the organic carbon source is selected from one or more of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0144] In some embodiments, the coating step may optionally include the steps of coating phosphate MPO4 and coating borate X in an optional order. a B b O c The steps include the coating process and the carbon coating process. The specific coating sequence of the above coating steps is not limited and can be adaptively adjusted according to the specific structure of the shell of the required positive electrode active material.

[0145] Optionally, the step of coating with phosphate MPO4 includes the following steps: providing a coating solution containing phosphate MPO4, adding the material to be coated to the coating solution, mixing evenly, drying, and then sintering to obtain a phosphate MPO4-coated material. The material to be coated can be a core material, a material coated with one layer of coating, or a material coated with two layers of coating, depending on the actual situation.

[0146] Optionally, the coated borate X a B b O cThe steps include the following: providing borate X a B b O c The coating solution is prepared, and then the material to be coated is added to the coating solution, mixed evenly, dried, and then sintered to obtain borate X. a B b O c The coating material. The material to be coated may be a core material, a material with one coating layer, or a material with two coating layers, depending on the actual situation.

[0147] Optionally, the carbon coating step includes the following steps: providing a coating solution containing a carbon source, then adding the material to be coated into the coating solution, mixing evenly, drying, and then sintering to obtain a carbon-coated material. The material to be coated can be a core material, a material coated with one layer, or a material coated with two layers, depending on the actual situation.

[0148] In some embodiments, the first coating step is to coat borate X. a B b O c The process involves three steps: a second coating step is coating with phosphate MPO4, and a third coating step is coating with carbon. The resulting positive electrode active material has a core-shell structure, comprising the core and a shell covering the core. The shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer. The first coating layer comprises borate X. a B b O c The second coating layer comprises phosphate MPO4, and the third coating layer comprises carbon.

[0149] In some embodiments, the first coating step is the coating step of phosphate MPO4, and the second coating step is the coating step of borate X. a B b O c The third coating step is a carbon coating step, thereby obtaining a positive electrode active material with a core-shell structure, which includes the core and a shell covering the core. The shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer. The first coating layer includes phosphate MPO4, and the second coating layer includes borate X. a B b O c The third coating layer contains carbon.

[0150] In some embodiments, the solvents used in the above coating steps are solvents commonly used in the art. For example, the solvents may each be independently selected from at least one of ethanol and water (e.g., deionized water).

[0151] In some embodiments, optionally, in each of the above-described coating steps, the drying can be carried out at a drying temperature of 100°C to 200°C, optionally 110°C to 190°C, more preferably 120°C to 180°C, even more preferably 120°C to 170°C, and most preferably 120°C to 160°C, for a drying time of 3 hours to 9 hours, optionally 4 hours to 8 hours, more preferably 5 hours to 7 hours, and most preferably about 6 hours.

[0152] In some embodiments, the coating solution containing phosphate MPO4 is commercially available, or optionally prepared by adding a source of element M and a source of phosphorus to a solvent, stirring until homogeneous, obtaining a mixture, and then heating the mixture to 60°C to 120°C and maintaining the temperature for 2 to 8 hours to obtain the coating solution. Optionally, the pH of the mixture is 4 to 6. It should be noted that the pH of the mixture can be adjusted using methods commonly used in the art, for example, by adding an acid or base. Optionally, the source of element M is selected from one or more of element M as a single substance, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide. Optionally, the source of phosphorus is selected from one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0153] In some embodiments, the borate X a B b O c The coating solution is commercially available, or optionally prepared by adding a source of element X and a source of boron to a solvent and stirring until homogeneous to obtain the coating solution. Optionally, the source of element X is selected from one or more of the following: elemental form of element X, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide. Optionally, the source of boron is selected from one or more of boric acid, borate, and boron oxide.

[0154] In some embodiments, the sintering in the step of coating phosphate MPO4 is performed at 500°C to 800°C for 4 to 10 hours. Optionally, the sintering can be performed at about 500°C, about 600°C, about 700°C, or about 800°C for about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; optionally, the sintering temperature and sintering time can be within any range of the above values.

[0155] In the step of coating MPO4 with phosphate, by controlling the sintering temperature and time within the above range, the following situations can be avoided: when the sintering temperature is too low and the sintering time is too short in the step of coating MPO4 with phosphate, the crystallinity of phosphate MPO4 will be low, with more amorphous state, and its coating effect will be poor, the inhibition of manganese ion dissolution will be insufficient, and the improvement of lithium ion transport performance will not be significant; while when the sintering temperature is too high and the sintering time is too long, the thickness of the formed coating layer will increase, increasing the battery impedance and affecting the kinetic performance and energy density of the secondary battery.

[0156] In some embodiments, the coated borate X a B b O c The sintering process described in the steps involves sintering at 300°C to 500°C for 2 to 10 hours. Optionally, the sintering can be carried out at approximately 300°C, approximately 350°C, approximately 400°C, approximately 450°C, or approximately 500°C for approximately 2 hours, approximately 3 hours, approximately 4 hours, approximately 5 hours, approximately 6 hours, approximately 7 hours, approximately 8 hours, approximately 9 hours, or approximately 10 hours; alternatively, the sintering temperature and sintering time can be within any range of the above values.

[0157] The coated borate X a B b O c In the process, by controlling the sintering temperature and time within the above range, the following situation can be avoided: when the coated borate X a B b O c If the sintering temperature is too low or the sintering time is too short during the process, it will cause borate X a B b O c The crystallinity is low, with more amorphous states. At the same time, its coating effect is poor, and its inhibition of manganese ion dissolution is insufficient. It also does not significantly improve the performance of lithium ion and electron transport. When the sintering temperature is too high or the sintering time is too long, the thickness of the coating layer will increase, which will increase the battery impedance and affect the kinetic performance and energy density of the secondary battery.

[0158] In some embodiments, the sintering in the carbon coating step is performed at 500°C to 800°C for 4 to 10 hours. Optionally, the sintering can be performed at about 500°C, about 600°C, about 700°C, or about 800°C for about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; optionally, the sintering temperature and sintering time can be within any range of the above values.

[0159] In the carbon coating step, by controlling the sintering temperature and time within the above range, the following situations can be avoided: when the sintering temperature in the carbon coating step is too low, the graphitization degree of the carbon material will decrease, affecting its conductivity and thus affecting the specific capacity of the positive electrode active material; when the sintering temperature is too high, the graphitization degree of the carbon material will be too high, affecting the Li + The transmission of the cathode material can affect its specific capacity, etc.; if the sintering time is too short, the coating layer will be too thin, affecting its conductivity and thus the specific capacity of the cathode material; if the sintering time is too long, the coating layer will be too thick, affecting the compaction density of the cathode material, etc.

[0160] In some embodiments, optionally, the median particle size Dv50 of the primary particles of the core-shell structured lithium manganese phosphate cathode active material of this application is 50 nm to 2000 nm.

[0161] Positive electrode sheet

[0162] A third aspect of this application provides a positive electrode sheet comprising 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 comprises the positive electrode active material of the first aspect of this application or a positive electrode active material prepared by the method of the second aspect of this application, and the content of the positive electrode active material in the positive electrode film layer is 10% by weight or more, optionally from 90% by weight to 99.5% by weight, based on the total weight of the positive electrode film layer. The positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0163] The positive electrode film layer does not exclude other positive electrode active materials besides the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the method of the second aspect of this application. For example, the positive electrode film layer may also include other positive electrode active materials besides the positive electrode active materials mentioned above in this application. Optionally, the other positive electrode active materials may include at least one of lithium transition metal oxides and their modified compounds. As an example, the other positive electrode active materials may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0164] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode 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 resins.

[0166] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. As an example, the metal material may be selected from at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0167] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0168] Secondary batteries

[0169] A fourth aspect of this application provides a secondary battery that includes the positive electrode of the third aspect of this application.

[0170] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. Typically, a secondary battery consists of an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is positioned between the positive and negative electrodes, primarily preventing short circuits while allowing active ions to pass through. The electrolyte, located between the positive and negative electrodes, conducts the active ions.

[0171] The secondary battery mentioned in the embodiments or implementations of this application refers to a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the secondary battery mentioned in this application may include battery cells, battery modules, or battery packs. A battery cell is the smallest unit constituting a secondary battery, capable of charging and discharging independently. This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. Figure 1 The example shown is a square-structured battery cell 5.

[0172] In some embodiments, the battery cell includes an electrode assembly, and the battery cell may also include an outer packaging. The electrode assembly is made from positive electrode sheets, negative electrode sheets, and a separator through a winding process and / or a stacking process, and the outer packaging is used to encapsulate the electrode assembly. The outer packaging can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging can also be a flexible package, such as a pouch. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0173] In some implementations, such as Figure 2 As shown, 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 enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted as needed.

[0174] In some embodiments of this application, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 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 battery cells 5 can be fixed in place using fasteners.

[0175] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0176] 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 adjusted according to the application and capacity of the battery pack. Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, 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. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0177] [Positive electrode plate]

[0178] The positive electrode used in the secondary battery of this application is the positive electrode described in any embodiment of the third aspect of this application.

[0179] [Negative electrode plate]

[0180] In some embodiments, 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 and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0181] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0182] In some embodiments, the negative electrode film may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0183] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0184] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0185] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material may be selected from at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0186] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0187] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0188] [Electrolytes]

[0189] This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0190] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0191] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0192] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0193] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0194] [Isolation membrane]

[0195] Secondary batteries using electrolytes, as well as some secondary batteries using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. 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.

[0196] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0197] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer package, dried, and injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0198] Electrical appliances

[0199] The fifth aspect of this application provides an electrical device comprising a secondary battery as described in this application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, tablets, 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.

[0200] The electrical device can select the specific type of secondary battery according to its usage requirements, such as a battery cell, battery module, or battery pack.

[0201] Figure 6 This is a schematic diagram illustrating an example of an electrical device. This device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used as the power source.

[0202] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0203] Example

[0204] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0205] The sources of raw materials involved in the embodiments of this application are as follows:

[0206] manganese carbonate <![CDATA[MnCO3]]> Shandong Xiya Chemical Industry Co., Ltd. 1Kg lithium carbonate <![CDATA[Li2CO3]]> Shandong Xiya Chemical Industry Co., Ltd. 1Kg Magnesium carbonate <![CDATA[MgCO3]]> Shandong Xiya Chemical Industry Co., Ltd. 1Kg Zinc carbonate <![CDATA[ZnCO3]]> Wuhan Xinru Chemical Co., Ltd. 25Kg Ferrous carbonate <![CDATA[FeCO3]]> Xi'an Lanzhiguang Fine Materials Co., Ltd. 1Kg Nickel sulfate <![CDATA[NiCO3]]> Shandong Xiya Chemical Industry Co., Ltd. 1Kg Titanium sulfate <![CDATA[Ti(SO4)2]]> Shandong Xiya Chemical Industry Co., Ltd. 1Kg Cobalt sulfate <![CDATA[CoSO4]]> Xiamen Zhixin Chemical Co., Ltd. 500g Vanadium dichloride <![CDATA[VCl2]]> Shanghai Jinjinle Industrial Co., Ltd. 1Kg Oxalic acid dihydrate <![CDATA[C2H2O4·2H2O]]> Shanghai Jinjinle Industrial Co., Ltd. 1Kg Ammonium dihydrogen phosphate <![CDATA[NH4H2PO4]]> Shanghai Chengshao Biotechnology Co., Ltd. 500g sucrose <![CDATA[C 12 H 22 O 11 ]]> Shanghai Yuanye Biotechnology Co., Ltd. 100g sulfuric acid <![CDATA[H2SO4]]> Shenzhen Haisi'an Biotechnology Co., Ltd. Quality score 60% Nitric acid <![CDATA[HNO3]]> Anhui Lingtian Fine Chemical Co., Ltd. Quality score 60% Silicate <![CDATA[H2SiO3]]> Shanghai Yuanye Biotechnology Co., Ltd. 100g Boric acid <![CDATA[H3BO3]]> Changzhou Qidi Chemical Co., Ltd. 1Kg

[0207] Example 1-1

[0208] Preparation of positive electrode active materials

[0209] (1) Preparation of co-doped lithium manganese phosphate core

[0210] Preparation of co-doped manganese oxalate: 689.5 g of manganese carbonate (calculated as MnCO3), 455.2 g of ferrous carbonate (calculated as FeCO3), 4.6 g of cobalt sulfate (calculated as CoSO4), and 4.9 g of vanadium dichloride (calculated as VCl2) were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (calculated as C2H2O4·2H2O) were added. The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no bubbles were generated), resulting in a co-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0211] Preparation of co-doped lithium manganese phosphate: 1793.4 g of manganese oxalate dihydrate particles (calculated as Li₂CO₃), 369.0 g of lithium carbonate (calculated as 60% H₂SO₄), 1.6 g of 60% dilute sulfuric acid (calculated as 60% H₂SO₄), and 1148.9 g of ammonium dihydrogen phosphate (calculated as NH₄H₂PO₄) obtained in the previous step were added to 20 liters of deionized water. The mixture was stirred for 10 hours to ensure homogeneity, resulting in a slurry. The slurry was transferred to a spray dryer for spray drying and granulation. The drying temperature was set at 250°C, and the drying time was 4 hours to obtain powder. Under a protective atmosphere of nitrogen (90% by volume) + hydrogen (10% by volume), the powder was sintered at 700°C for 4 hours to obtain 1572.1 g of co-doped lithium manganese phosphate, i.e., the core.

[0212] (2) Covering of the first covering layer

[0213] 3.7 g of lithium carbonate, 11.6 g of ferrous carbonate, 11.5 g of ammonium dihydrogen phosphate, and 0.43 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water to obtain a mixture. The mixture was then stirred for 6 hours to allow it to react completely. The resulting solution was then heated to 120 °C and maintained at that temperature for 6 hours to obtain a first coating layer containing LiFePO4.

[0214] 1572.1g of the co-doped lithium manganese phosphate (core) was added to the coating liquid of the first coating layer, stirred and mixed evenly, and then transferred to a vacuum oven to dry at 150°C for 6 hours. The product was then dispersed by sand milling and sintered at 700°C for 6 hours to obtain the material coated by the first coating layer.

[0215] (3) Covering of the second covering layer

[0216] 42.4 g of lithium hydroxide and 20.6 g of boron oxide were added to 500 mL of deionized water to obtain the second coating layer solution.

[0217] The material coated by the first coating layer is added to the coating liquid of the second coating layer, stirred and mixed evenly, and then transferred to a vacuum oven to dry at 150°C for 6 hours. The product is then dispersed by sand milling, and the product is sintered at 400°C for 10 hours to obtain a material coated by two coating layers.

[0218] (4) Covering of the third covering layer

[0219] Dissolve 74.6g of sucrose in 500ml of deionized water, then stir and dissolve completely to obtain the third coating layer solution.

[0220] The materials coated by the two coating layers are added to the coating liquid of the third coating layer, stirred and mixed evenly, and then transferred to a vacuum oven to dry at 150°C for 6 hours. Then, the mixture is sintered at 700°C for 6 hours under a nitrogen atmosphere to obtain the material coated by the three coating layers, i.e., the positive electrode active material.

[0221] Preparation of positive electrode sheet

[0222] The prepared positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) at a weight ratio of 92:2.5:5.5 and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then coated with a surface density of 0.018 g / cm³. 2 The material is evenly coated onto aluminum foil, then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0223] Preparation of negative electrode sheet

[0224] A negative electrode slurry was prepared by dissolving artificial graphite (anode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) in deionized water at a weight ratio of 90:5:2:2:1 and stirring until homogeneous. The negative electrode slurry was then coated with a solution to achieve a surface density of 0.0075 g / cm³. 2 The negative electrode sheet is obtained by uniformly coating the copper foil of the negative electrode current collector, drying, cold pressing, and slitting.

[0225] Preparation of electrolyte

[0226] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 3:7 as an organic solvent. 12.5% ​​by weight (based on the weight of the organic solvent) of LiPF6 was added and dissolved in the organic solvent. The mixture was stirred until homogeneous to obtain the electrolyte.

[0227] Preparation of the separating membrane

[0228] The material used was a commercially available PP-PE copolymer microporous film with a thickness of 20 μm and an average pore size of 80 nm (from Zogo Electronics Technology Co., Ltd., model 20).

[0229] Preparation of full cells

[0230] 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 electrode assembly is then wound up. The electrode assembly is placed in an outer package, injected with the electrolyte, and sealed to obtain a full cell (hereinafter also referred to as "full cell").

[0231] Preparation of button cells

[0232] The prepared positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (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 surface density was 0.015 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 .

[0233] 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. The solution is assembled with the positive electrode prepared above in a button cell to form a button cell (hereinafter also referred to as "button cell").

[0234] Examples 1-2 to 1-35

[0235] Except for the preparation of the positive electrode active material, all other processes are the same as those in Example 1-1.

[0236] Examples 1-2 to 1-6

[0237] In the preparation of the co-doped lithium manganese phosphate core, the preparation conditions of the lithium manganese phosphate core in Examples 1-2 to 1-6 are the same as those in Example 1-1, except that vanadium dichloride and cobalt sulfate are not used, and 463.4 g of ferrous carbonate, 1.6 g of 60% dilute sulfuric acid, 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate are used.

[0238] During the coating process of the first, second, and third coating layers, the raw materials used were adjusted according to the ratio of the coating amount shown in Table 1 to the coating amount corresponding to Example 1-1, so that the amounts of LiFePO4 / Li3BO3 in Examples 1-2 to 1-6 were 12.6g / 37.7g, 15.7g / 47.1g, 18.8g / 56.5g, 22.0g / 66.0g, and 25.1g / 75.4g, respectively, and the amount of sucrose in Examples 1-2 to 1-6 was 37.3g. Other conditions were the same as in Example 1-1.

[0239] Examples 1-7 to 1-10

[0240] Except that the amounts of sucrose used were 74.6g, 149.1g, 186.4g and 223.7g respectively, so that the corresponding coating amounts of the carbon layer as the third coating layer were 31.4g, 62.9g, 78.6g and 94.3g respectively, the conditions of Examples 1-7 to 1-10 were the same as those of Examples 1-3.

[0241] Examples 1-11 to 1-14

[0242] In the process of coating the first coating layer, the second coating layer and the third coating layer, except that the amount of each raw material used is adjusted according to the coating amount shown in Table 1 so that the amount of LiFePO4 / Li3BO3 is 23.6g / 39.3g, 31.4g / 31.4g, 39.3g / 23.6g and 47.2g / 15.7g respectively, the conditions of Examples 1-11 to 1-14 are the same as those of Examples 1-7.

[0243] Examples 1-15

[0244] Except for the use of 492.80 g of zinc carbonate instead of ferrous carbonate in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-15 were the same as those of Examples 1-14.

[0245] Examples 1-16 to 1-18

[0246] Except that in Examples 1-16, 466.4 g of nickel carbonate, 5.0 g of zinc carbonate, and 7.2 g of titanium sulfate were used instead of ferrous carbonate in the preparation of the co-doped lithium manganese phosphate core; in Examples 1-17, 455.2 g of ferrous carbonate and 8.5 g of vanadium dichloride were used in the preparation of the co-doped lithium manganese phosphate core; and in Examples 1-18, 455.2 g of ferrous carbonate, 4.9 g of vanadium dichloride, and 2.5 g of magnesium carbonate were used in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-16 to 1-18 were the same as those of Examples 1-7.

[0247] Examples 1-19 to 1-20

[0248] Except that in Examples 1-19, 369.4 g of lithium carbonate and 1.05 g of 60% dilute nitric acid were used instead of dilute sulfuric acid in the preparation of the co-doped lithium manganese phosphate core, and in Examples 1-20, 369.7 g of lithium carbonate and 0.78 g of silicic acid were used instead of dilute sulfuric acid in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-19 to 1-20 were the same as those of Examples 1-18.

[0249] Examples 1-21 to 1-22

[0250] Except that in Examples 1-21, 632.0 g of manganese carbonate, 463.30 g of ferrous carbonate, 30.5 g of vanadium dichloride, 21.0 g of magnesium carbonate, and 0.78 g of silicic acid were used in the preparation of the co-doped lithium manganese phosphate core; and in Examples 1-22, 746.9 g of manganese carbonate, 289.6 g of ferrous carbonate, 60.9 g of vanadium dichloride, 42.1 g of magnesium carbonate, and 0.78 g of silicic acid were used in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-21 to 1-22 were the same as those of Examples 1-20.

[0251] Examples 1-23 to 1-24

[0252] Except for Examples 1-23, which used 804.6 g manganese carbonate, 231.7 g ferrous carbonate, 1156.2 g ammonium dihydrogen phosphate, 1.2 g boric acid (99.5% by mass), and 370.8 g lithium carbonate in the preparation of the co-doped lithium manganese phosphate core, and Examples 1-24, which used 862.1 g manganese carbonate, 173.8 g ferrous carbonate, 1155.1 g ammonium dihydrogen phosphate, 1.86 g boric acid (99.5% by mass), and 371.6 g lithium carbonate in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-23 to 1-24 were the same as those of Examples 1-22.

[0253] Examples 1-25

[0254] Except for the use of 370.1g of lithium carbonate, 1.56g of silicic acid and 1147.7g of ammonium dihydrogen phosphate in the preparation of the co-doped lithium manganese phosphate core in Examples 1-25, the conditions in Examples 1-25 were the same as those in Examples 1-20.

[0255] Examples 1-26

[0256] Except for the use of 368.3g lithium carbonate, 4.9g dilute sulfuric acid with a mass fraction of 60%, 919.6g manganese carbonate, 224.8g ferrous carbonate, 3.7g vanadium dichloride, 2.5g magnesium carbonate, and 1146.8g ammonium dihydrogen phosphate in the preparation of the co-doped lithium manganese phosphate core in Examples 1-26, the conditions in Examples 1-26 are the same as those in Examples 1-20.

[0257] Examples 1-27

[0258] Except for the use of 367.9g of lithium carbonate, 6.5g of 60% dilute sulfuric acid, and 1145.4g of ammonium dihydrogen phosphate in the preparation of the co-doped lithium manganese phosphate core in Examples 1-27, the conditions in Examples 1-27 were the same as those in Examples 1-20.

[0259] Examples 1-28 to 1-33

[0260] Except for Examples 1-28 to 1-33, which used 1034.5g of manganese carbonate, 108.9g of ferrous carbonate, 3.7g of vanadium dichloride, and 2.5g of magnesium carbonate in the preparation of the co-doped lithium manganese phosphate core, the amounts of lithium carbonate used were 367.6g, 367.2g, 366.8g, 366.4g, 366.0g, and 332.4g, respectively; the amounts of ammonium dihydrogen phosphate used were 1144.5g, 1143.4g, 1142.2g, 1141.1g, 1139.9g, and 1138.8g, respectively; and the amounts of 60% dilute sulfuric acid used were 8.2g, 9.8g, 11.4g, 13.1g, 14.7g, and 16.3g, respectively. The conditions in Examples 1-28 to 1-33 were the same as in Examples 1-20.

[0261] Examples 1-34

[0262] Except that the second coating layer in Example 1-1 is first applied in the preparation of the positive electrode active material, and then the first coating layer in Example 1-1 is applied, the conditions of Example 1-34 are the same as those of Example 1-1.

[0263] Examples 1-35

[0264] Except for the addition of 3.84 g of molybdenum sulfate (calculated as Mo(SO4)3) and 0.57 g of ammonium bifluoride (calculated as NH4HF2) in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-35 were the same as those of Examples 1-1.

[0265] Examples 2-1 to 2-3

[0266] Except for the preparation of the positive electrode active material, all other processes are the same as those in Example 1-1.

[0267] Example 2-1

[0268] During the coating process, except that the sintering temperature in the coating sintering step is 650°C and the sintering time is 2 hours to control the crystallinity of LiFePO4 to 30%, the other conditions are the same as in Example 1-1.

[0269] During the process of coating the second coating layer, the conditions were the same as in Examples 1-1, except that the sintering temperature in the coating sintering step was 300°C and the sintering time was 2 hours to control the crystallinity of Li3BO3 to 30%.

[0270] Example 2-2

[0271] During the coating process, except that the sintering temperature in the coating sintering step is 650°C and the sintering time is 3 hours to control the crystallinity of LiFePO4 to 50%, the other conditions are the same as in Example 1-1.

[0272] During the process of coating the second coating layer, the conditions were the same as in Examples 1-1, except that the sintering temperature in the coating sintering step was 350°C and the sintering time was 2 hours to control the crystallinity of Li3BO3 to 50%.

[0273] Example 2-3

[0274] During the coating process, except that the sintering temperature in the coating sintering step is 650°C and the sintering time is 4 hours to control the crystallinity of LiFePO4 to 70%, the other conditions are the same as in Example 1-1.

[0275] During the process of coating the second coating layer, the conditions were the same as in Examples 1-1, except that the sintering temperature in the coating sintering step was 400°C and the sintering time was 2 hours to control the crystallinity of Li3BO3 to 70%.

[0276] Comparative Examples 1 to 7

[0277] Except for the preparation of the positive electrode active material according to the following method, all other processes are the same as those in Example 1-1.

[0278] Comparative Example 1

[0279] Preparation of manganese oxalate: 1149.3 g of manganese carbonate was added to a reaction vessel, along with 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (calculated as C2H2O4·2H2O, the same below). The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no more bubbles were generated), resulting in a manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0280] Preparation of carbon-coated lithium manganese phosphate: Take 1789.6g of the above-obtained manganese oxalate dihydrate particles, 369.4g of lithium carbonate (calculated as Li2CO3, the same below), 1150.1g of ammonium dihydrogen phosphate (calculated as NH4H2PO4, the same below) and 31g of sucrose (calculated as C). 12 H 22 O 11 The mixture (hereinafter the same) is added to 20 liters of deionized water, and stirred for 10 hours to ensure uniform mixing, resulting in a slurry. The slurry is then transferred to a spray dryer for spray drying and granulation. The drying temperature is set at 250°C, and the mixture is dried for 4 hours to obtain a powder. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the powder is sintered at 700°C for 4 hours to obtain carbon-coated lithium manganese phosphate.

[0281] Comparative Example 2

[0282] Except for the use of 689.5g of manganese carbonate and the addition of 463.3g of ferrous carbonate, the conditions for Comparative Example 2 were the same as those for Comparative Example 1.

[0283] Comparative Example 3

[0284] Except for the use of 1148.9g of ammonium dihydrogen phosphate and 369.0g of lithium carbonate, and the addition of 1.6g of 60% dilute sulfuric acid, the other conditions of Comparative Example 3 were the same as those of Comparative Example 1.

[0285] Comparative Example 4

[0286] Except for the use of 689.5g of manganese carbonate, 1148.9g of ammonium dihydrogen phosphate and 369.0g of lithium carbonate, and the addition of 463.3g of ferrous carbonate and 1.6g of 60% dilute sulfuric acid, the other conditions of Comparative Example 4 were the same as those of Comparative Example 1.

[0287] Comparative Example 5

[0288] Except for the additional coating steps, the other conditions were the same as those in Comparative Example 4, and the amorphous lithium iron phosphate (62.8g) and carbon-coated positive electrode active material were finally obtained.

[0289] 14.7 g of lithium carbonate, 46.1 g of ferrous carbonate, 45.8 g of ammonium dihydrogen phosphate, and 50.2 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water. The mixture was then stirred for 6 hours to allow for complete reaction. The resulting solution was then heated to 120 °C and maintained at that temperature for 6 hours to obtain the coating solution. The sintering temperature in the coating sintering step was 600 °C, and the sintering time was 4 hours to control the crystallinity of LiFePO4 to 8%.

[0290] Comparative Example 6

[0291] Except for the additional coating steps, the other conditions were the same as those in Comparative Example 4, and the amorphous lithium borate (62.8 g) and carbon-coated positive electrode active material were finally obtained.

[0292] 56.5 g of lithium hydroxide and 27.5 g of boron oxide were added to 500 mL of deionized water to obtain the coating solution. In the coating sintering step, only drying was performed; high-temperature sintering was not conducted, resulting in a Li3BO3 crystallinity of 5%.

[0293] Comparative Example 7

[0294] Except for the additional coating steps, the other conditions were the same as those in Comparative Example 4, and the following positive electrode active materials were finally obtained: amorphous lithium iron phosphate (15.7g), amorphous lithium borate (47.1g), and carbon-coated materials.

[0295] The first coating layer was prepared by dissolving 3.7 g of lithium carbonate, 11.6 g of ferrous carbonate, 11.5 g of ammonium dihydrogen phosphate, and 12.6 g of oxalic acid dihydrate in 500 mL of deionized water. The mixture was then stirred for 6 hours to allow for complete reaction. The resulting solution was then heated to 120 °C and maintained at this temperature for 6 hours to obtain the first coating layer suspension. The sintering temperature in the coating sintering step was 600 °C, and the sintering time was 4 hours to control the crystallinity of LiFePO4 to 8%.

[0296] The second coating layer was prepared by adding 42.4 g of lithium hydroxide and 20.6 g of boron oxide to 500 mL of deionized water to obtain the second coating layer solution. In the coating sintering step, only drying was performed; high-temperature sintering was not conducted, resulting in a Li3BO3 crystallinity of 5%.

[0297] Relevant parameter testing

[0298] 1. Determination of the core chemical formula and composition of different coating layers:

[0299] 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.

[0300] 2. Initial capacity test of button cells:

[0301] The button cell obtained above is charged to 4.3V at 0.1C, and then charged at a constant voltage of 4.3V 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.

[0302] 3. Average discharge voltage (V) test of coin cells:

[0303] The coin cells prepared above are 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 are 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.

[0304] 4. Full battery gas expansion test at 60°C:

[0305] The prepared full cell was stored at 60°C at 100% state of charge (SOC). The open-circuit voltage (OCV) and internal resistance (IMP) were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. After every 48 hours of storage, the full cell was removed, allowed to stand for 1 hour, and then the open-circuit voltage (OCV) and internal resistance (IMP) were measured. After cooling to room temperature, the cell volume was measured using the water displacement method. The water 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 at this moment is measured, and the buoyant force F on the battery is measured. 浮 That is, F1-F2, and then according to Archimedes' principle, F 浮 =ρ×g×V 排 The battery volume V is calculated to be V = (F1 - F2) / (ρ × g).

[0306] Based on the OCV and IMP test results, the batteries in all embodiments maintained a SOC of over 99% throughout the entire testing process until the end of storage.

[0307] After 30 days of storage, the battery volume was measured, and the percentage increase in battery volume after storage was calculated relative to the battery volume before storage.

[0308] 5. Cyclic performance test of the entire battery at 45°C:

[0309] Under a constant temperature environment of 45℃, 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.

[0310] 6. Transition metal dissolution test:

[0311] 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.

[0312] 7. Methods for measuring lattice change rate:

[0313] Under a constant temperature of 25℃, the positive electrode active material sample prepared above was placed in an XRD (model Bruker D8 Discover) and tested at 1° / minute. The test data were 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 the unit cell in each direction, and v0 represents the volume of the unit cell, which can be directly obtained from the XRD refinement results).

[0314] 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 was then removed from the coin cell 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.

[0315] 8. Li / Mn inverse defect concentration test:

[0316] 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.

[0317] 9. Surface oxygen valence state test:

[0318] 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.

[0319] 10. Compacted density measurement:

[0320] 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 (tons) 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.

[0321] 11. X-ray diffraction method for testing the crystallinity of phosphates and borates:

[0322] 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.

[0323] 12. Interplanar spacing and included angles:

[0324] 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 and obtain the original TEM test image.

[0325] 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.

[0326] Table 1 shows the composition of the positive electrode active materials in Examples 1-1 to 1-35 and Comparative Examples 1 to 7.

[0327] Table 2 shows the performance data of the positive electrode active materials, positive electrode sheets, coin cells or all-electric cells of Examples 1-1 to 1-35 and Comparative Examples 1 to 7, measured according to the above performance test methods.

[0328] Table 3 shows the performance data of the positive electrode active material, positive electrode sheet, button cell or all-electric cell of Examples 2-1 to 2-3, measured according to the above performance test methods.

[0329] Table 1

[0330]

[0331] Table 2

[0332]

[0333] Table 3

[0334]

[0335] Based on Examples 1-1 to 1-35 and Comparative Examples 1 to 7, the presence of the first and second coating layers is beneficial for reducing the Li / Mn antisite defect concentration and the amount of Fe and Mn dissolved after cycling in the obtained material, thereby increasing the specific capacity of the battery and improving its safety and cycle performance. When other elements are doped at the Mn and P sites respectively, the lattice change rate, antisite defect concentration, and the amount of Fe and Mn dissolved in the obtained material can be significantly reduced, thereby increasing the specific capacity of the battery and improving its safety and cycle performance. In addition, the interplanar spacing of the phosphate in the coating layer is 0.348 nm, and the included angle of the crystal orientation (111) is 25.562°.

[0336] As can be seen from Examples 1-2 to 1-6, as the total amount of the first and second coating layers increases from 3.2% to 6.4%, the concentration of Li / Mn antisite defects in the resulting material gradually decreases, and the dissolution of Fe and Mn after cycling gradually decreases. This leads to improved battery safety and cycling performance at 45°C, although the specific capacity decreases slightly. Optionally, the battery exhibits optimal overall performance when the total amount of the first and second coating layers is between 4% and 5.6% by weight.

[0337] Based on Examples 1-3 and Examples 1-7 to 1-10, it can be seen that as the amount of the third coating layer increases from 1% to 6%, the leaching of Fe and Mn after cycling gradually decreases, resulting in improved battery safety and cycle performance at 45°C, although the specific capacity decreases slightly. Optionally, the battery exhibits optimal overall performance when the total amount of the third coating layer is between 2% and 5% by weight.

[0338] Based on Examples 1-11 to 1-15 and Comparative Examples 5 to 6, it can be seen that when LiFePO4 is present in the first coating layer and Li3BO3 is present in the second coating layer, and the weight ratio of LiFePO4 to Li3BO3 is 1:3 to 3:1, especially when it is 1:3 to 1:1, the improvement in battery performance is more significant.

[0339] Figure 7 This is a comparison diagram of the XRD pattern of the positive electrode active material core prepared in Example 1-1 and the standard XRD pattern (00-033-0804) of lithium manganese phosphate. Figure 7 As shown, the core of the positive electrode active material in this application is basically consistent with the position of the main characteristic peaks before lithium manganese phosphate doping, indicating that the core of the positive electrode active material in this application has no impurity phase, and the improvement of the secondary battery performance mainly comes from element doping, rather than impurity phase.

[0340] As shown in Table 3, as the crystallinity of phosphates and borates gradually increases, the lattice change rate, Li / Mn antisite defect concentration, and Fe and Mn dissolution of the corresponding positive electrode active materials gradually decrease, the specific capacity of the battery gradually increases, and the safety performance and cycle performance gradually improve.

[0341] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material with a core-shell structure, comprising a core and a shell covering the core, The kernel includes Li m A x Mn 1-y B y P 1-z C z O 4-n D n The A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; the B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; the C comprises one or more elements selected from boron, S, Si, and N; the D comprises one or more elements selected from S, F, Cl, and Br; the m is selected from the range of 0.900 to 1.100; the x is selected from the range of 0 to 0.100; the y is selected from the range of 0.001 to 0.500; the z is selected from the range of 0.001 to 0.100; the n is selected from the range of 0 to 0.100; and the core is electrically neutral. in, The shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer. The third coating layer comprises carbon, and the first coating layer comprises phosphate MPO4, and the second coating layer comprises borate X. a B b O c Or the first coating layer includes borate X a B b O c The second coating layer comprises phosphate MPO4. M comprises one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al; X comprises one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al; a is selected from the range of 1 to 4; b is selected from the range of 1 to 7; c is selected from the range of 2 to 12; and the values ​​of a, b, and c satisfy the following condition: making borate X a B b O c Maintain electrical neutrality The crystallinity of the phosphate MPO4 is 10% to 100%, and the borate X a B b O c The crystallinity ranges from 10% to 100%.

2. The positive electrode active material according to claim 1, wherein, The m is selected from the range of 0.900 to 1.006, the x is selected from the range of 0.001 to 0.005, the y is selected from the range of 0.100 to 0.450, and the n is selected from the range of 0.001 to 0.

005.

3. The positive electrode active material according to claim 2, wherein, The coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, based on the weight of the core; and / or, The coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, based on the weight of the core; And / or, The coating amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, based on the weight of the core.

4. The positive electrode active material according to claim 3, wherein, The first coating layer has a coating amount of 1% to 5% by weight, based on the weight of the core; and / or, The second coating layer has a coating amount of 1% to 5% by weight, based on the weight of the core; and / or, The third coating layer has a coating weight of 2% to 5% by weight, based on the weight of the core.

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

6. The positive electrode active material according to claim 5, wherein, The total amount of coating by the first coating layer and the second coating layer is 4% to 5.6% by weight, based on the weight of the core.

7. The positive electrode active material according to any one of claims 1-6, wherein, The phosphate MPO4 and the borate X a B b O c The weight ratio is 1:3 to 3:

1.

8. The positive electrode active material according to claim 7, wherein, The phosphate MPO4 and the borate X a B b O c The weight ratio is 1:3 to 1:

1.

9. The positive electrode active material according to claim 1, wherein, The interplanar spacing of the phosphate MPO4 is 0.345 nm to 0.358 nm, and the included angle of the crystal orientation (111) is 24.25° to 26.45°.

10. The positive electrode active material according to claim 1, wherein, The crystallinity of the phosphate MPO4 is 50% to 100%; and / or, The borate X a B b O c The crystallinity is 50% to 100%.

11. The positive electrode active material according to claim 1, wherein, In the kernel, the ratio of y to 1-y is 1:10 to 10:1; and / or, In the kernel, the ratio of z to 1-z is 1:9 to 1:999; and / or, In the core, B includes one or more elements selected from Fe, Ti, V, Ni, Co, and Mg.

12. The positive electrode active material according to claim 11, wherein, In the kernel, the ratio of y to 1-y is 1:4 to 1:1; and / or, In the kernel, the ratio of z to 1-z is 1:499 to 1:249; and / or, In the core, B comprises at least two elements selected from Fe, Ti, V, Ni, Co, and Mg.

13. The positive electrode active material according to any one of claims 8-12, wherein, The ratio of b to c is 1:

3.

14. The positive electrode active material according to any one of claims 8-12, wherein, The positive electrode active material satisfies at least one of the following conditions (1) to (4): (1) The concentration of Li / Mn antisite defects in the positive electrode active material is below 4%; (2) The lattice change rate of the positive electrode active material is less than 8%; (3) The surface oxygen valence state of the positive electrode active material is below -1.88; (4) The compaction density of the positive electrode active material at 3 tons is 2.0 g / cm³. 3 above.

15. The positive electrode active material according to claim 14, wherein, The positive electrode active material satisfies at least one of the following conditions (1) to (4): (1) The concentration of Li / Mn antisite defects in the positive electrode active material is below 2%; (2) The lattice change rate of the positive electrode active material is less than 4%; (3) The surface oxygen valence state of the positive electrode active material is -1.98 to -1.88; (4) The compaction density of the positive electrode active material at 3 tons is 2.2 g / cm³. 3 above.

16. A method for preparing a positive electrode active material, comprising the following steps: Steps for providing kernel material: The kernel includes Li m A x Mn 1-y B y P 1-z C z O 4-n D n The A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; the B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; the C comprises one or more elements selected from boron, S, Si, and N; the D comprises one or more elements selected from S, F, Cl, and Br; the m is selected from the range of 0.900 to 1.100; the x is selected from the range of 0 to 0.100; the y is selected from the range of 0.001 to 0.500; the z is selected from the range of 0.001 to 0.100; the n is selected from the range of 0 to 0.100; and the core is electrically neutral. The coating process includes a first coating step, a second coating step, and a third coating step, wherein the first coating step is the coating of phosphate MPO4, the second coating step is the coating of borate X, and so on. a B b O c The third coating step is a carbon coating step, or the first coating step is a borate X coating step. a B b O c The first step is to coat the first layer of phosphate, the second coating step is to coat the second layer of phosphate (MPO4), and the third coating step is to coat the third layer of carbon. The step of coating with phosphate MPO4 includes the following steps: providing a coating solution containing phosphate MPO4, adding the material to be coated into the coating solution, mixing evenly, drying, and then sintering to obtain a material coated with phosphate MPO4; The coated borate X a B b O c The steps include the following: providing borate X a B b O c The coating solution is prepared, and then the material to be coated is added to the coating solution, mixed evenly, dried, and then sintered to obtain borate X. a B b O c Covering material; The carbon coating process includes the following steps: providing a coating solution containing a carbon source, then adding the material to be coated into the coating solution, mixing evenly, drying, and then sintering to obtain a carbon-coated material. Wherein, M comprises one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al; X comprises one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb, and Al; the crystallinity of the phosphate MPO4 is 10% to 100%; and the borate X... a B b O c The crystallinity is 10% to 100%, where a is selected from the range of 1 to 4, b is selected from the range of 1 to 7, and c is selected from the range of 2 to 12, and the values ​​of a, b, and c satisfy the following condition: making borate X a B b O c Maintain electrical neutrality.

17. The method according to claim 16, wherein, The m is selected from the range of 0.900 to 1.006, the x is selected from the range of 0.001 to 0.005, the y is selected from the range of 0.100 to 0.450, and the n is selected from the range of 0.001 to 0.

005.

18. The method according to claim 16 or 17, wherein, The steps for providing the core material include the following steps: Step (1): Mix and stir the source of manganese, the source of element B and acid in a container to obtain manganese salt particles doped with element B; Step (2): Mix the manganese salt particles doped with element B with the source of lithium, the source of phosphorus and the source of element C in a solvent to obtain a slurry, or mix the manganese salt particles doped with element B with the source of lithium, the source of phosphorus, the source of element C, the source of element A and the source of element D in a solvent to obtain a slurry, and sinter it under an inert gas atmosphere to obtain the core material.

19. The method according to claim 18, wherein, Step (1) is performed at 20°C to 120°C; and / or, The stirring in step (1) is carried out at 500 rpm to 700 rpm for 60 minutes to 420 minutes; and / or, The sintering in step (2) is sintering at 600°C to 800°C for 4 to 10 hours in an inert gas or a mixture of inert gas and hydrogen atmosphere.

20. The method according to claim 19, wherein, Step (1) is performed at a temperature between 25°C and 80°C; and / or, The stirring in step (1) is carried out at 500 rpm to 700 rpm for 120 minutes to 360 minutes.

21. The method according to claim 18, wherein, The source of element A is selected from one or more of the following: elemental form, carbonate, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide; and / or, The source of element B is selected from one or more of the following: elemental form, carbonate, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide; and / or, The source of element C is selected from one or more of element C as a simple substance, sulfate, halide, nitrate, organic acid salt, oxide, hydroxide, and inorganic acid of element C; and / or, The source of element D is selected from one or more of the element D in its elemental form and its ammonium salt.

22. The method according to claim 16, wherein, The coating solution containing phosphate MPO4 is prepared by the following method: adding the source of element M and the source of phosphorus to a solvent, stirring until homogeneous, obtaining a mixture, and then heating the mixture to 60°C to 120°C and maintaining it for 2 hours to 8 hours to obtain the coating solution; and / or, The containing borate X a B b O c The coating solution was prepared by the following method: the source of element X and the source of boron were added to the solvent and stirred evenly to obtain the coating solution.

23. The method according to claim 16, wherein, The sintering in the step of coating phosphate MPO4 is performed at 500°C to 800°C for 4 to 10 hours; and / or, The coated borate X a B b O c The sintering in the step is sintering at 300°C to 500°C for 2 to 10 hours; and / or, The sintering in the carbon coating step is performed at 500°C to 800°C for 4 to 10 hours.

24. A positive electrode sheet, comprising 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 comprising a positive electrode active material according to any one of claims 1-15 or a positive electrode active material prepared by any one of claims 16-23, and the positive electrode active material having a content of 10% by weight or more in the positive electrode film layer based on the total weight of the positive electrode film layer.

25. The positive electrode sheet according to claim 24, wherein, The content of the positive electrode active material in the positive electrode film is 90% to 99.5% by weight, based on the total weight of the positive electrode film.

26. A secondary battery comprising the positive electrode active material according to any one of claims 1-15 or the positive electrode active material prepared by any one of claims 16-23 or the positive electrode sheet according to claim 24 or 25.

27. An electrical device comprising the secondary battery of claim 26.

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