Positive electrode active materials, positive electrode sheets, secondary batteries, battery modules, battery packs, and electrical devices.

Abstract

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 1+x Mn 1‑y A y P 1‑z R z O4, wherein x = -0.100 to 0.100, y = 0.001 to 0.500, z = 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be selected from one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S; the shell includes a first coating layer covering the core and a second coating layer covering the first coating layer, wherein the first coating layer includes pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al; the second coating layer contains carbon.

Description

Technical Field

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

[0002] With the rapid development of the new energy field, lithium-ion batteries, due to their excellent electrochemical performance, lack of memory effect, and low environmental pollution, are widely used in various large-scale power devices, energy storage systems, and consumer products, especially in pure electric vehicles and hybrid electric vehicles. Among these, lithium manganese phosphate (LMP) cathode active material, with its advantages of high operating voltage, wide availability of raw materials, and low environmental pollution, is considered a promising candidate to replace lithium iron phosphate (LFP) as the preferred cathode active material for power lithium-ion batteries. However, in existing technologies, the cycle performance, high-temperature storage performance, and safety performance of secondary batteries using LMP cathode active material have not been comprehensively improved, which greatly limits the wider application of LMP batteries. Therefore, it is desirable to design a LMP secondary battery that combines high specific capacity, good cycle performance, and safety performance. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems, and its purpose is to provide a lithium manganese phosphate positive electrode active material, so that the secondary battery using the positive electrode active material has high specific capacity, good cycle performance and safety performance.

[0004] To achieve the above objectives, this application provides a lithium manganese phosphate positive electrode active material and its preparation method, as well as related positive electrode sheets, secondary batteries, battery modules, battery packs, and power-consuming devices.

[0005] The first aspect of this application provides a positive electrode active material with a core-shell structure, comprising a core and a shell covering the core.

[0006] The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100 to 0.100, y = 0.001 to 0.500, z = 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be selected from one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S;

[0007] The shell includes a first covering layer covering the core and a second covering layer covering the first covering layer.

[0008] The first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al;

[0009] The second coating layer contains carbon.

[0010] Therefore, the positive electrode active material of this application can improve the specific capacity, cycle performance, and safety performance of secondary batteries. Although the mechanism is not yet clear, it is speculated that the lithium manganese phosphate positive electrode active material of this application has a core-shell structure. By doping the manganese and phosphorus sites of the lithium manganese phosphate core with elements A and R respectively, it can not only effectively reduce manganese dissolution, thereby reducing the number of manganese ions migrating to the negative electrode and reducing the electrolyte consumed due to SEI film decomposition, thus improving the cycle performance and safety performance of the secondary battery, but also promote Mn-O bond adjustment, lower the lithium ion migration barrier, promote lithium ion migration, and improve the rate performance of the secondary battery. By coating the core with a first coating layer including pyrophosphate and phosphate, the migration resistance of manganese can be further increased, reducing its dissolution, and reducing the surface lithium content and the contact between the core and the electrolyte, thereby reducing interfacial side reactions, reducing gas production, and improving the high-temperature storage performance, cycle performance, and safety performance of the secondary battery. By further coating with a carbon-containing layer as a second coating layer, the safety performance and kinetic performance of the secondary battery can be further improved.

[0011] In any embodiment, the interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°. This further improves the cycle performance and rate performance of the secondary battery.

[0012] In any embodiment, 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 cycle performance and rate performance of the secondary battery.

[0013] In any embodiment, 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 cycle performance and rate performance of the secondary battery.

[0014] In any embodiment, the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally 4-5.6% by weight, based on the weight of the core. When the coating amount of the first coating layer is within the above range, the function of the first coating layer can be effectively utilized, while the dynamic performance of the secondary battery will not be affected due to excessive coating thickness.

[0015] In any embodiment, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, optionally 1:3 to 1:1. Thus, by maintaining a suitable weight ratio of pyrophosphate to phosphate, manganese leaching can be effectively inhibited, and the surface lithium content can be effectively reduced, thereby reducing interfacial side reactions and improving the high-temperature storage performance, safety performance, and cycle performance of the secondary battery.

[0016] In any embodiment, the crystallinity of the pyrophosphate and phosphate is independently 10%-100%, optionally 50% to 100%. Pyrophosphate and phosphate with crystallinity within the above range thus facilitate the full utilization of the functions of pyrophosphate in inhibiting manganese dissolution and phosphate in reducing surface impurity lithium content and interfacial side reactions.

[0017] In any embodiment, the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the weight of the core. Thus, the presence of the second coating layer effectively reduces the contact between the active material within the coating layer and the electrolyte, reduces the corrosion of the active material by the electrolyte, and improves the conductivity of the positive electrode active material. When the coating amount of the second layer is within the above range, it can effectively increase the specific capacity of the positive electrode active material.

[0018] In any embodiment, A is selected from at least two of Fe, Ti, V, Ni, Co, and Mg. Therefore, by having A be two or more metals within the aforementioned range, doping at the manganese site enhances the doping effect, further reduces surface oxygen activity, and thus suppresses manganese leaching.

[0019] In any embodiment, the Li / Mn antisite defect concentration of the positive electrode active material is 4% or less, optionally 2% or less. Therefore, by keeping the Li / Mn antisite defect concentration within the above range, Mn... 2+ Hinder Li + This improves the transport efficiency and simultaneously enhances the specific capacity and rate performance of the positive electrode active material.

[0020] In any embodiment, the lattice change rate of the positive electrode active material is 6% or less, optionally 4% or less. Therefore, by keeping the lattice change rate within the above range, excessive interfacial stress that could affect Li can be avoided. + This improves the rate performance of secondary batteries by increasing the transmission capacity.

[0021] In any embodiment, the surface oxygen valence state of the positive electrode active material is below -1.88, optionally between -1.98 and -1.88. Therefore, having the surface oxygen valence state of the positive electrode material within this range avoids the following potential issues: an excessively high surface oxygen valence state leads to excessive electron-acquiring ability, resulting in increased interfacial side reactions with the electrolyte, thereby affecting the cycle performance and high-temperature storage performance of the secondary battery.

[0022] In any embodiment, the compaction density of the positive electrode active material at 3 tons (T) is 2.0 g / cm³. 3 The above is an option, specifically 2.2 g / cm³. 3 Therefore, if the compressive density of the positive electrode active material is within the above range, the weight of the active material per unit volume will be greater, which will be more conducive to improving the volumetric energy density of the secondary battery.

[0023] A second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0024] Steps for providing kernel material: The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100-0.100, y = 0.001-0.500, z = 0.001-0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be selected from one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S;

[0025] Coating step: MP2O7 powder and XPO4 suspension containing carbon source are provided. The core material and MP2O7 powder are added to the XPO4 suspension containing carbon source and mixed. The positive electrode active material is obtained by sintering. M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al.

[0026] The positive electrode active material has a core-shell structure, which includes a core and a shell covering the core. The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer. The first coating layer includes pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer contains carbon.

[0027] In any implementation, the step of providing the core material includes the following steps:

[0028] Step (1): Mix and stir the source of manganese, the source of element A and acid in a container to obtain manganese salt particles doped with element A;

[0029] Step (2): The manganese salt particles doped with element A are mixed with lithium sources, phosphorus sources, and element R sources in a solvent to obtain a slurry. After sintering under an inert gas atmosphere, lithium manganese phosphate doped with elements A and R is obtained, wherein the lithium manganese phosphate doped with elements A and R is Li. 1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100-0.100, y = 0.001-0.500, z = 0.001-0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be selected from one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S.

[0030] In any embodiment, step (1) is performed at a temperature of 20-120°C, optionally 25-80°C; and / or,

[0031] The stirring in step (1) is carried out at 500-700 rpm for 60-420 minutes, or optionally 120-360 minutes.

[0032] Therefore, by controlling the reaction temperature, stirring rate, and mixing time during doping, the dopant 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 material.

[0033] In any embodiment, the source of element A is selected from one or more of element A's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, or hydroxide; and / or, the source of element R is selected from one or more of element R's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, or hydroxide, and inorganic acid of element R. Thus, by selecting the source of each dopant element within the above-mentioned range, the performance of the material can be effectively improved.

[0034] In any embodiment, the MP2O7 powder is prepared by adding a source of element M and a source of phosphorus to a solvent to obtain a mixture, adjusting the pH of the mixture to 4-6, stirring and reacting fully, and then drying and sintering to obtain the powder. M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al.

[0035] In any embodiment, during the preparation of MP2O7 powder, the drying step is to dry at 100-300℃, optionally 150-200℃, for 4-8 hours.

[0036] In any embodiment, during the preparation of MP2O7 powder, the sintering step is to sinter at 500-800℃, optionally 650-800℃, under an inert gas atmosphere for 4-10 hours.

[0037] In any embodiment, the sintering temperature in the coating step is 500-800℃, and the sintering time is 4-10 hours. Therefore, by controlling the sintering temperature and time during coating, the specific capacity and rate performance of the material can be further improved.

[0038] The preparation method described in this application uses widely available and inexpensive raw materials, and has a simple process, which is conducive to industrialization.

[0039] 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 described in the first aspect of this application or a positive electrode active material prepared by the method described in 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, based on the total weight of the positive electrode film layer.

[0040] In any embodiment, the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, based on the total weight of the positive electrode film layer. When the content of the positive electrode active material is within the above range, it is beneficial to fully utilize the advantages of the positive electrode active material of this application.

[0041] The fourth aspect of this application provides a secondary battery comprising the positive electrode active material described in the first aspect of this application, or the positive electrode active material prepared by the method described in the second aspect of this application, or the positive electrode sheet described in the third aspect of this application.

[0042] The fifth aspect of this application provides a battery module that includes the secondary battery described in the fourth aspect of this application.

[0043] A sixth aspect of this application provides a battery pack that includes the battery module described in the fifth aspect of this application.

[0044] The seventh aspect of this application provides an electrical device that includes at least one of the secondary battery described in the fourth aspect of this application, the battery module described in the fifth aspect of this application, or the battery pack described in the sixth aspect of this application.

[0045] The positive electrode sheet, secondary battery, battery module, battery pack and electrical device described in this application include the lithium manganese phosphate positive electrode active material described in this application, and therefore have at least the same advantages as the lithium manganese phosphate positive electrode active material. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of a core-shell structured positive electrode active material according to an embodiment of this application.

[0047] Figure 2 This is a comparison diagram of the XRD spectrum of Example 1-1 of this application before the first and second coating layers are applied, and the standard XRD spectrum of lithium manganese phosphate (00-033-0804).

[0048] Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0049] Figure 4 yes Figure 3 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0050] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application.

[0051] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0052] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown.

[0053] Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0054] Explanation of reference numerals in the attached figures:

[0055] 11 Kernel; 12 First Overlay; 13 Second Overlay;

[0056] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0057] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0058] 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 specific 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 expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​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.

[0059] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0060] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0061] 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.

[0062] 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.

[0063] The terms “above” and “below” used in this application include the number itself. For example, “above one” means one or more, and “above one of A and B” means “A”, “B” or “A and B”.

[0064] 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).

[0065] It should be noted that in this paper, the median particle size Dv 50 This refers to the particle size corresponding to a cumulative volume distribution percentage of the positive electrode active material reaching 50%. In this application, the median particle size Dv of the positive electrode active material... 50 Particle size can be determined using laser diffraction particle size analysis. For example, according to standard GB / T 19077-2016, a laser particle size analyzer (e.g., MalvernMaster Size 3000) can be used for determination.

[0066] 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. Similarly, the term "thickness of cladding layer" refers to the thickness of the layer of material covering the core in the radial direction of the core.

[0067] 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.

[0068] The inventors of this application discovered in practical operation that manganese dissolution is severe in lithium manganese phosphate cathode 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 migration of dissolved manganese into the electrolyte. After migrating to the negative electrode, the dissolved manganese is 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, affecting the safety performance of the secondary battery. Others deposit on the negative electrode surface, hindering 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 electrolyte and the active lithium inside the battery are continuously consumed, irreversibly affecting the capacity retention rate of the secondary battery.

[0069] After extensive research, the inventors discovered that the problems of severe manganese leaching 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 significantly reduces manganese leaching and lattice change rate, thereby exhibiting good cycle performance, high-temperature storage performance, and safety performance.

[0070] [Positive electrode active material]

[0071] The first aspect of this application provides a positive electrode active material with a core-shell structure, comprising a core and a shell covering the core.

[0072] The kernel includes Li 1+x Mn 1-y A y P 1-z R zO4, where x = -0.100 to 0.100, for example, x can be 0.006, 0.004, 0.003, 0.002, 0.001, 0, -0.001, -0.003, -0.004, -0.005, -0.006, -0.007, -0.008, -0.009, -0.10; y = 0.001 to 0.500, for example, y can be 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45; z = 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, 0.1; A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and can be selected from one or more of Fe, Ti, V, Ni, Co and Mg; R is selected from one or more of B, Si, N and S;

[0073] The shell includes a first covering layer covering the core and a second covering layer covering the first covering layer.

[0074] The first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al;

[0075] The second coating layer contains carbon.

[0076] Unless otherwise stated, in the above chemical formulas, when A consists of two or more elements, the limitation on the range of values ​​for y 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 y1, y2...yn of each of A1, A2...An must each fall within the range of values ​​for y defined in this application, and the sum of y1, y2...yn must also fall within this range. Similarly, for the case where R consists of two or more elements, the limitation on the range of values ​​for the stoichiometric coefficients of R in this application has the same meaning.

[0077] like Figure 1 As shown, the lithium manganese phosphate cathode active material of this application has a core-shell structure with two coating layers, wherein the core includes Li 1+x Mn 1-y A y P 1-z R zO4. The element A doping at the manganese sites of lithium manganese phosphate in the core helps reduce the lattice change rate of lithium manganese phosphate during lithium insertion / extraction, improves the structural stability of the lithium manganese phosphate cathode material, greatly reduces manganese dissolution, and lowers the oxygen activity on the particle surface. The element R doping at the phosphorus sites 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.

[0078] The first coating layer of the positive electrode active material in this application comprises pyrophosphate and phosphate. Since the migration barrier of transition metals in pyrophosphate is high (>1 eV), the dissolution of transition metals can be effectively suppressed. Phosphate, on the other hand, has excellent lithium-ion conduction capabilities and can reduce surface lithium impurities. Furthermore, since the second coating layer is a carbon-containing layer, it can effectively improve the conductivity and desolvation capability of LiMnPO4. In addition, the "barrier" effect of the second coating layer can further hinder the migration of manganese ions into the electrolyte and reduce the corrosion of the active material by the electrolyte.

[0079] Therefore, by performing specific element doping and surface coating on lithium manganese phosphate, this application can effectively suppress the dissolution of Mn during the lithium insertion / extraction process, while promoting the migration of lithium ions, thereby improving the rate performance of the cell and enhancing the cycle performance and high-temperature performance of the secondary battery.

[0080] It should be pointed out that, as Figure 2 As shown in the figure, by comparing the XRD spectra before and after LiMnPO4 doping in this application, it can be seen that the positions of the main characteristic peaks of the positive electrode active material in this application are basically the same as those of the material before LiMnPO4 doping. This indicates that the doped lithium manganese phosphate positive electrode active material does not have impurity phases, and the improvement in the performance of the secondary battery mainly comes from element doping, rather than impurity phases.

[0081] In some embodiments, optionally, the interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°.

[0082] When the interplanar spacing and the angle between the crystal orientation (111) of the phosphate and pyrophosphate in the first coating layer are within the above range, impurity phases in the coating layer can be effectively avoided, thereby improving the specific capacity, cycle performance and rate performance of the material.

[0083] 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 cathode active material can be further improved.

[0084] In some embodiments, optionally, the ratio of z to 1-z in the core 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 cathode active material can be further improved.

[0085] In some implementations, optionally, the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally 4-5.6% by weight, based on the weight of the core.

[0086] When the coating amount of the first coating layer is within the above-mentioned range, it can further suppress manganese dissolution and further promote lithium-ion transport. It can also effectively avoid the following situations: if the coating amount of the first coating layer is too small, the pyrophosphate may not sufficiently inhibit manganese dissolution, and the improvement on lithium-ion transport performance may not be significant; if the coating amount of the first coating layer is too large, the coating layer may be too thick, increasing battery impedance and affecting the battery's kinetic performance.

[0087] In some embodiments, optionally, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, and optionally 1:3 to 1:1.

[0088] A proper ratio of pyrophosphate and phosphate is beneficial for fully leveraging their synergistic effect and can effectively avoid the following situations: if there is too much pyrophosphate and too little phosphate, it may lead to an increase in battery impedance; if there is too much phosphate and too little pyrophosphate, the effect of inhibiting manganese dissolution will be insignificant.

[0089] In some embodiments, optionally, the crystallinity of the pyrophosphate and the phosphate is each independently 10% to 100%, optionally 50% to 100%.

[0090] In the first coating layer of the lithium manganese phosphate cathode active material of this application, the presence of pyrophosphate and phosphate with a certain degree of crystallinity helps maintain the structural stability of the first coating layer and reduces lattice defects. This is beneficial in two ways: firstly, it allows the pyrophosphate to fully inhibit manganese dissolution; secondly, it helps the phosphate reduce the surface lithium content and lower the valence state of surface oxygen, thereby reducing interfacial side reactions between the cathode material and the electrolyte, reducing electrolyte consumption, and improving the cycle performance and safety performance of the battery.

[0091] It should be noted that, in this application, the crystallinity of pyrophosphate and phosphate can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature and sintering time. The crystallinity of pyrophosphate and phosphate 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.

[0092] In some implementations, the second coating layer may optionally have a coating amount greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the weight of the core.

[0093] The carbon-containing layer, serving as the second coating layer, acts as a barrier, preventing direct contact between the positive electrode active material and the electrolyte, thereby reducing electrolyte corrosion and improving battery safety at high temperatures. Furthermore, its strong conductivity reduces internal resistance, enhancing battery kinetic performance. However, due to the low specific capacity of carbon materials, excessive use of the second coating layer may decrease the overall specific capacity of the positive electrode active material. Therefore, when the coating amount is within the aforementioned range, it can further improve battery kinetic and safety performance without sacrificing the specific capacity of the positive electrode active material.

[0094] In some embodiments, the A may optionally be selected from at least two of Fe, Ti, V, Ni, Co, and Mg.

[0095] Simultaneous doping of two or more of the aforementioned elements at the manganese sites in lithium manganese phosphate cathode active materials is beneficial to enhancing the doping effect. On the one hand, it further reduces the lattice change rate, thereby inhibiting the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it is also beneficial to further reduce surface oxygen activity, reduce interfacial side reactions between cathode active materials and electrolyte, thereby improving the cycle performance and high-temperature storage performance of the battery.

[0096] In some embodiments, the Li / Mn antisite defect concentration of the positive electrode active material is optionally below 4%, and optionally below 2%.

[0097] In the positive electrode active material of this application, the Li / Mn antisite defect refers to the Li / Mn antisite defect in the LiMnPO4 lattice. + and Mn 2+ The positions of Li have been interchanged. + The transmission channel is a one-dimensional channel, Mn 2+ In Li + It is difficult to migrate in the transmission channel, therefore, the Mn of the inversion defect is difficult to migrate. 2+ It will hinder Li +The transport of Li / Mn antisite defects can be improved by controlling the concentration of Li / Mn antisite defects at a low level. In this application, the antisite defect concentration can be determined, for example, according to JIS K 0131-1996.

[0098] In some embodiments, the lattice change rate of the positive electrode active material is optionally less than 6%, and optionally less than 4%.

[0099] The lithium insertion / extraction process in LiMnPO4 is a two-phase reaction. The interfacial stress between the two phases is determined by the rate of lattice change; the smaller the rate of lattice change, 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.

[0100] In some embodiments, optionally, the average discharge voltage of the positive electrode active material is 3.5V or higher, and the discharge specific capacity is 140mAh / g or higher; optionally, the average discharge voltage is 3.6V or higher, and the discharge specific capacity is 145mAh / g or higher.

[0101] Although the average discharge voltage of undoped LiMnPO4 is above 4.0V, its discharge specific capacity is low, usually less than 120mAh / g, and therefore its energy density is low. By adjusting the lattice change rate through doping, its discharge specific capacity can be greatly improved, and the overall energy density can be significantly increased with a slight decrease in average discharge voltage.

[0102] In some embodiments, the surface oxygen valence state of the positive electrode active material is optionally below -1.88, and optionally between -1.98 and -1.88.

[0103] This is because the higher the valence state of oxygen in a compound, the stronger its ability to gain electrons, i.e., the stronger its oxidizing power. In the lithium manganese phosphate cathode active material of this application, by controlling the surface valence state of oxygen at a low level, the reactivity of the cathode material surface can be reduced, the interfacial side reactions between the cathode material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0104] 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 is an option, specifically 2.2 g / cm³. 3 above.

[0105] A higher compaction density of the positive electrode active material, i.e., a greater weight of active material per unit volume, is more conducive to improving the volumetric energy density of the battery. In this application, the compaction density can be measured, for example, according to GB / T 24533-2009.

[0106] 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:

[0107] Steps for providing kernel material: The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100-0.100, y = 0.001-0.500, z = 0.001-0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be selected from one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S;

[0108] Coating step: MP2O7 powder and XPO4 suspension containing carbon source are provided. The core material and MP2O7 powder are added to the XPO4 suspension containing carbon source and mixed. The positive electrode active material is obtained by sintering. M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al.

[0109] The positive electrode active material has a core-shell structure, which includes a core and a shell covering the core. The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer. The first coating layer includes pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer contains carbon.

[0110] The preparation method of this application does not have any particular restrictions on the source of materials. 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.

[0111] In some implementations, the step of providing the core material may optionally include the following steps:

[0112] Step (1): Mix and stir the source of manganese, the source of element A and acid in a container to obtain manganese salt particles doped with element A;

[0113] Step (2): The manganese salt particles doped with element A are mixed with lithium sources, phosphorus sources, and element R sources in a solvent to obtain a slurry. After sintering under an inert gas atmosphere, lithium manganese phosphate doped with elements A and R is obtained, wherein the lithium manganese phosphate doped with elements A and R is Li.1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100-0.100, y = 0.001-0.500, z = 0.001-0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be selected from one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S.

[0114] In some embodiments, step (1) may optionally be performed at a temperature of 20-120°C, optionally 25-80°C; and / or,

[0115] The stirring in step (1) is carried out at 500-700 rpm for 60-420 minutes, or optionally 120-360 minutes.

[0116] By controlling the reaction temperature, stirring rate, and mixing time during doping, the doping elements can be evenly distributed, reducing lattice defects, suppressing manganese 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 material.

[0117] 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, and the precursor is the source that enables the preparation method of this application to achieve its purpose. As an example, the source of element A is selected from one or more of element A's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, or hydroxide; and / or, the source of element R is selected from one or more of element R's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, or hydroxide, and element R's inorganic acid.

[0118] In some embodiments, optionally, the source of manganese in this application is one or more selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0119] In some embodiments, element A may optionally be iron, and the source of iron may optionally be one or more selected from ferrous carbonate, ferric hydroxide, and ferrous sulfate.

[0120] 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.

[0121] In some embodiments, the inorganic acid of element R is optionally selected from one or more of phosphoric acid, nitric acid, boric acid, silicic acid, and orthosilicic acid.

[0122] In some embodiments, optionally, the lithium source in this application is one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0123] In some embodiments, optionally, the source of phosphorus in this application is one or more selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0124] In some embodiments, the carbon source in this application 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.

[0125] In some embodiments, optionally, the solvent used in the preparation method described in this application is a solvent commonly used in the art. For example, the solvent in the preparation method of this application may be independently selected from at least one of ethanol and water (e.g., deionized water).

[0126] In some embodiments, optionally, the pH of the solution is controlled to be 4-6 during the preparation of A-doped manganese salt particles. 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.

[0127] In some embodiments, optionally, in step (2), the molar ratio of the manganese salt particles to the lithium source and the phosphorus source is 1:0.5-2.1:0.5-2.1.

[0128] In some embodiments, optionally, in step (2), the sintering conditions are: sintering at 600-800°C for 4-10 hours in an inert gas or a mixture of inert gas and hydrogen.

[0129] In some embodiments, the inert gas and hydrogen mixture may optionally be nitrogen (70-90% by volume) + hydrogen (10-30% by volume).

[0130] In some embodiments, the MP2O7 powder is optionally a commercially available product, or optionally, the MP2O7 powder is prepared by adding a source of element M and a source of phosphorus to a solvent to obtain a mixture, adjusting the pH of the mixture to 4-6, stirring and reacting fully, and then drying and sintering to obtain the powder, wherein M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al.

[0131] In some embodiments, optionally, during the preparation of MP2O7 powder, the drying step is to dry at 100-300°C, optionally 150-200°C, for 4-8 hours.

[0132] In some embodiments, optionally, during the preparation of MP2O7 powder, the sintering step is to sinter at 500-800°C, optionally 650-800°C, in an inert gas atmosphere for 4-10 hours.

[0133] In some embodiments, optionally, the XPO4 suspension containing the carbon source is commercially available, or optionally, it is prepared by mixing a lithium source, an X source, a phosphorus source, and a carbon source uniformly in a solvent, and then heating the reaction mixture to 60-120°C and maintaining the temperature for 2-8 hours to obtain the XPO4 suspension containing the carbon source. Optionally, during the preparation of the XPO4 suspension containing the carbon source, the pH of the mixture is adjusted to 4-6.

[0134] In some embodiments, optionally, in step (3), the mass ratio of the A and R-doped lithium manganese phosphate, MP2O7 powder, and the carbon-containing XPO4 suspension is 1:(0.001-0.05):(0.001-0.05).

[0135] In some embodiments, optionally, the sintering temperature in the coating step is 500-800℃ and the sintering time is 4-10h.

[0136] In some embodiments, optionally, the median particle size Dv50 of the primary particles of the double-coated lithium manganese phosphate cathode active material of this application is 50-2000 nm.

[0137] [Positive electrode plate]

[0138] 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 comprising the lithium manganese phosphate positive electrode active material of the first aspect of this application or the lithium manganese phosphate positive electrode active material prepared according to 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, based on the total weight of the positive electrode film layer.

[0139] In some embodiments, optionally, the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, based on the total weight of the positive electrode film layer.

[0140] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0141] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0142] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0143] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0144] In some embodiments, the positive electrode film layer of this application comprises 90-99.5% of the lithium manganese phosphate positive electrode active material of the first aspect of this application, 0.4-5.5% of binder, 0.1-2.5% of conductive carbon and 0.001-1% of other additives, based on the total weight of the positive electrode film layer.

[0145] In some embodiments, the positive electrode film layer of this application may optionally include other additives such as dispersants, wetting agents, rheology modifiers, and other additives commonly used in the art.

[0146] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0147] In some embodiments, the coating weight of the positive electrode film in this application is 0.28-0.45 g / 1540.25 mm. 2 The compacted density reaches 2.2-2.8 g / cm³. 3 .

[0148] [Negative electrode plate]

[0149] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0150] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0151] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0152] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0153] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0154] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0155] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0156] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0157] [Electrolytes]

[0158] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0159] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0160] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0161] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0162] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0163] [Isolation membrane]

[0164] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0165] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0166] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0167] [Rechargeable Battery]

[0168] The fourth aspect of this application provides a secondary battery comprising the positive electrode active material described in the first aspect of this application, or the positive electrode active material prepared by the method described in the second aspect of this application, or the positive electrode sheet described in the third aspect of this application.

[0169] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0170] In some embodiments, the lithium-ion secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0171] In some implementations, the outer packaging of a lithium-ion secondary battery can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of a lithium-ion secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0172] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0173] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0174] In some implementations, refer to Figure 4The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0175] In some implementations, lithium-ion secondary batteries can be assembled into battery modules, and the number of lithium-ion batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0176] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple lithium-ion batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple lithium-ion batteries 5 can be fixed in place using fasteners.

[0177] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple lithium-ion batteries 5 are housed.

[0178] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0179] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0180] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0181] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0182] Figure 8 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0183] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0184] Example

[0185] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially. Unless otherwise specified, the content of each component in the embodiments of this invention is based on the mass of the component excluding crystallization water.

[0186] The sources of raw materials involved in the embodiments of this application are as follows:

[0187] name Chemical formula factory Specification 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

[0188] 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[H25O4]]> 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

[0189] Example 1-1

[0190] Preparation of a double-layer coated lithium manganese phosphate cathode active material

[0191] (1) Preparation of co-doped lithium manganese phosphate core

[0192] Preparation of Fe, Co, and V 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), yielding a suspension of Fe, Co, V, and S co-doped manganese oxalate. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain Fe, Co, and V co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0193] Preparation of Fe, Co, V, and S co-doped lithium manganese phosphate: 1793.4 g of manganese oxalate dihydrate particles obtained in the previous step, 369.0 g of lithium carbonate (calculated as Li₂CO₃), 1.6 g of 60% dilute sulfuric acid (calculated as 60% H₂SO₄), and 1148.9 g of ammonium dihydrogen phosphate (calculated as NH₄H₂PO₄) were added to 20 L of deionized water. The mixture was stirred for 10 hours to ensure homogeneity, resulting in a slurry. The slurry was then 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 nitrogen (90 vol%) + hydrogen (10 vol%) protective atmosphere, the powder was sintered at 700 °C for 4 hours to obtain 1572.1 g of Fe, Co, V, and S co-doped lithium manganese phosphate.

[0194] (2) Preparation of lithium iron pyrophosphate and lithium iron phosphate

[0195] Preparation of lithium iron pyrophosphate powder: 4.77 g lithium carbonate, 7.47 g ferrous carbonate, 14.84 g ammonium dihydrogen phosphate, and 1.3 g oxalic acid dihydrate were dissolved in 50 ml deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80 °C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain powder. The powder was sintered at 650 °C under a nitrogen atmosphere for 8 hours, and after naturally cooling to room temperature, it was ground to obtain Li₂FeP₂O₇ powder.

[0196] Preparation of lithium iron phosphate suspension: 11.1 g lithium carbonate, 34.8 g ferrous carbonate, 34.5 g ammonium dihydrogen phosphate, 1.3 g oxalic acid dihydrate, and 74.6 g sucrose (in C2) were added. 12 H 22 O11 The solution (hereinafter referred to as "the solution") was dissolved in 150 ml of deionized water to obtain a mixture, which was then stirred for 6 hours to allow the mixture to react fully. The resulting solution was then heated to 120°C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4.

[0197] (3) Covering

[0198] 1572.1g of the Fe, Co, V, and S co-doped lithium manganese phosphate and 15.72g of the lithium iron pyrophosphate (Li2FeP2O7) powder were added to the lithium iron phosphate (LiFePO4) suspension prepared in the previous step. After stirring and mixing evenly, the mixture was transferred to a vacuum oven and dried at 150°C for 6 hours. The product was then dispersed by sand milling. After dispersion, the product was sintered at 700°C for 6 hours under a nitrogen atmosphere to obtain the target product, double-layer coated lithium manganese phosphate.

[0199] Preparation of the positive electrode sheet

[0200] The double-layer coated lithium manganese phosphate positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) prepared above were added to N-methylpyrrolidone (NMP) in a weight ratio of 92:2.5:5.5 and stirred until homogeneous to obtain the positive electrode slurry. Then, the positive electrode slurry was prepared at a ratio of 0.280 g / 1540.25 mm. 2 The material is evenly coated onto aluminum foil, then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0201] Preparation of the negative electrode sheet

[0202] 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-Na) (thickener) in deionized water at a weight ratio of 90:5:2:2:1 and stirring until homogeneous. The negative electrode slurry was then prepared at a concentration of 0.117 g / 1540.25 mm. 2 The negative electrode sheet is obtained by uniformly coating the copper foil of the negative electrode current collector, drying, cold pressing, and slitting.

[0203] Preparation of Electrolyte

[0204] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) / 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 and stirred until homogeneous to obtain the electrolyte.

[0205]

Isolation Film

[0206] 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).

[0207] [Preparation of a full cell]

[0208] The obtained positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to obtain a bare cell. The bare cell is placed in an outer packaging, injected with the electrolyte, and sealed to obtain a full battery (hereinafter also referred to as "full battery").

[0209] [Preparation of button cells]

[0210] The double-layer coated lithium manganese phosphate positive electrode active material, PVDF, and acetylene black prepared above were added to NMP at a weight ratio of 90:5:5, and stirred in a drying chamber to form a slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet. The coating amount was 0.2 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 .

[0211] 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").

[0212] Examples 1-2 to 1-6

[0213] 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.

[0214] In addition, during the preparation of lithium iron pyrophosphate and lithium iron phosphate, and during the coating of the first and second 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 Li2FeP2O7 / LiFePO4 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, the other conditions were the same as in Example 1-1.

[0215] Examples 1-7 to 1-10

[0216] 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 second 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.

[0217] Examples 1-11 to 1-14

[0218] Except for adjusting the amounts of various raw materials according to the coating amounts shown in Table 1 during the preparation of lithium iron pyrophosphate and lithium iron phosphate so that the amounts of Li2FeP2O7 / LiFePO4 are 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.

[0219] Examples 1-15

[0220] Except for the use of 492.80 g ZnCO3 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.

[0221] Examples 1-16 to 1-18

[0222] Except that in Examples 1-16, 466.4 g of NiCO3, 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 1-17 to 1-19 were the same as those of Examples 1-7.

[0223] Examples 1-19 to 1-20

[0224] 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.

[0225] Examples 1-21 to 1-22

[0226] 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.

[0227] Examples 1-23 to 1-24

[0228] 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.

[0229] Examples 1-25

[0230] 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.

[0231] Examples 1-26

[0232] 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.

[0233] Examples 1-27

[0234] 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.

[0235] Examples 1-28 to 1-33

[0236] 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.

[0237] Examples 2-1 to 2-4

[0238] Example 2-1

[0239] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 550°C and the sintering time was 1h to control the crystallinity of Li2FeP2O7 to 30%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 650°C and the sintering time was 2h to control the crystallinity of LiFePO4 to 30%, all other conditions were the same as in Examples 1-1.

[0240] Example 2-2

[0241] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 550°C and the sintering time was 2h to control the crystallinity of Li2FeP2O7 to 50%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 650°C and the sintering time was 3h to control the crystallinity of LiFePO4 to 50%, the other conditions were the same as in Examples 1-1.

[0242] Example 2-3

[0243] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 600℃ and the sintering time was 3h to control the crystallinity of Li2FeP2O7 to 70%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 650℃ and the sintering time was 4h to control the crystallinity of LiFePO4 to 70%, the other conditions were the same as in Examples 1-1.

[0244] Examples 2-4

[0245] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 650℃ and the sintering time was 4h to control the crystallinity of Li2FeP2O7 to 100%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 700℃ and the sintering time was 6h to control the crystallinity of LiFePO4 to 100%, the other conditions were the same as in Examples 1-1.

[0246] Examples 3-1 to 3-12

[0247] Except for the preparation of Fe, Co, and V co-doped manganese oxalate particles, the heating temperature / stirring time in the reactor in Example 3-1 was 60℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-2 was 70℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-3 was 80℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-4 was 90℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-5 was 100℃ / 120 minutes; and the heating temperature / stirring time in the reactor in Example 3-6 was 110℃ / 120 minutes. Example 3 -7 The heating temperature / stirring time in the reactor in Examples 3-7 was 120℃ / 120 minutes; the heating temperature / stirring time in the reactor in Examples 3-8 was 130℃ / 120 minutes; the heating temperature / stirring time in the reactor in Examples 3-9 was 100℃ / 60 minutes; the heating temperature / stirring time in the reactor in Examples 3-10 was 100℃ / 90 minutes; the heating temperature / stirring time in the reactor in Examples 3-11 was 100℃ / 150 minutes; the heating temperature / stirring time in the reactor in Examples 3-12 was 100℃ / 180 minutes. Except for these conditions, the other conditions in Examples 3-1 to 3-12 were the same as in Examples 1-1.

[0248] Examples 4-1 to 4-7

[0249] Examples 4-1 to 4-4: Except that the drying temperature / drying time in the drying step of the preparation of lithium iron pyrophosphate (Li2FeP2O7) was 100℃ / 4h, 150℃ / 6h, 200℃ / 6h and 200℃ / 6h respectively; and the sintering temperature and sintering time in the sintering step of the preparation of lithium iron pyrophosphate (Li2FeP2O7) were 700℃ / 6h, 700℃ / 6h, 700℃ / 6h and 600℃ / 6h respectively, the other conditions were the same as in Examples 1-7.

[0250] Examples 4-5 to 4-7: Except that the drying temperature / drying time in the drying step during the coating process is 150℃ / 6h, 150℃ / 6h and 150℃ / 6h respectively; and the sintering temperature and sintering time in the sintering step during the coating process are 600℃ / 4h, 600℃ / 6h and 800℃ / 8h respectively, the other conditions are the same as in Examples 1-12.

[0251] Comparative Example 1

[0252] 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.

[0253] 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.

[0254] Comparative Example 2

[0255] Except for the use of 689.5g of manganese carbonate and the addition of 463.3g of ferrous carbonate, the other conditions of Comparative Example 2 were the same as those of Comparative Example 1.

[0256] Comparative Example 3

[0257] 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.

[0258] Comparative Example 4

[0259] 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.

[0260] Comparative Example 5

[0261] Except for the additional step of preparing lithium iron pyrophosphate powder: 9.52 g of lithium carbonate, 29.9 g of ferrous carbonate, 29.6 g of ammonium dihydrogen phosphate, and 32.5 g of oxalic acid dihydrate were dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80°C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120°C for 4 hours to obtain powder. The powder was sintered at 500°C under a nitrogen atmosphere for 4 hours, and then naturally cooled to room temperature before grinding. The crystallinity of Li₂FeP₂O₇ was controlled to be 5%. Except for the amount of Li₂FeP₂O₇ used when preparing the carbon-coated material, which was 62.8 g, the other conditions of Comparative Example 5 were the same as those of Comparative Example 4.

[0262] Comparative Example 6

[0263] Except for the additional step of preparing a lithium iron phosphate suspension: 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, and then stirred for 6 hours to allow the mixture to react fully. The resulting solution was then heated to 120 °C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4. In the preparation of lithium iron phosphate (LiFePO4), except for the sintering temperature of 600 °C and the sintering time of 4 h in the coating sintering step to control the crystallinity of LiFePO4 to 8%, and the amount of LiFePO4 used in preparing the carbon-coated material being 62.8 g, the other conditions of Comparative Example 6 were the same as those of Comparative Example 4.

[0264] Comparative Example 7

[0265] Preparation of lithium iron pyrophosphate powder: 2.38 g lithium carbonate, 7.5 g ferrous carbonate, 7.4 g ammonium dihydrogen phosphate, and 8.1 g oxalic acid dihydrate were dissolved in 50 ml deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80 °C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain powder. The powder was sintered at 500 °C under a nitrogen atmosphere for 4 hours, and after naturally cooling to room temperature, it was ground to control the crystallinity of Li₂FeP₂O₇ to 5%.

[0266] Preparation of lithium iron phosphate suspension: 11.1 g lithium carbonate, 34.7 g ferrous carbonate, 34.4 g ammonium dihydrogen phosphate, 37.7 g oxalic acid dihydrate, and 37.3 g sucrose (in C2) were added. 12 H 22 O 11 The solution (hereinafter the same) was dissolved in 1500 ml of deionized water and then stirred for 6 hours to allow the mixture to react fully. The resulting solution was then heated to 120°C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4.

[0267] 15.7 g of the obtained lithium iron pyrophosphate powder was added to the above-mentioned lithium iron phosphate (LiFePO4) and sucrose suspension. In the preparation process, the sintering temperature in the coating sintering step was 600℃ and the sintering time was 4 h to control the crystallinity of LiFePO4 to 8%. The other conditions of Comparative Example 7 were the same as those of Comparative Example 4, and amorphous lithium iron pyrophosphate, amorphous lithium iron phosphate, and carbon-coated positive electrode active materials were obtained.

[0268] Comparative Examples 8-11

[0269] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the drying temperature / drying time in the drying step was 80℃ / 3h, 80℃ / 3h, and 80℃ / 3h in Comparative Examples 8-10, respectively; the sintering temperature and sintering time in the sintering step were 400℃ / 3h, 400℃ / 3h, and 350℃ / 2h in Comparative Examples 8-10, respectively; and the drying temperature / drying time in the drying step of lithium iron phosphate (LiFePO4) preparation in Comparative Example 11 was 80℃ / 3h; and the Li2FeP2O7 / LiFePO4 dosage was 47.2g / 15.7g, 15.7g / 47.2g, 62.8g / 0g, and 0g / 62.8g in Comparative Examples 8-11, respectively, all other conditions were the same as in Examples 1-7.

[0270] The preparation of the positive electrode, negative electrode, electrolyte, separator, and battery in the above embodiments and comparative examples are all the same as the processes in Examples 1-1.

[0271] [Relevant Parameter Tests]

[0272] 1. Initial capacity test of button cells:

[0273] At a voltage of 2.5–4.3V, the button cell prepared above is charged to 4.3V at 0.1C, and then charged at 4.3V at a constant voltage until the current is less than or equal to 0.05mA. After standing for 5 minutes, it is discharged to 2.0V at 0.1C. The discharge capacity at this time is the initial specific capacity, denoted as D0.

[0274] 2. Average discharge voltage (V) test of coin cell:

[0275] The coin cells prepared above were placed in a constant temperature environment of 25°C for 5 minutes, discharged at 0.1C to 2.5V, placed in a constant temperature environment for 5 minutes, charged at 0.1C to 4.3V, and then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. After being placed in a constant temperature environment for 5 minutes, they were discharged at 0.1C to 2.5V. The discharge capacity at this time is the initial specific capacity, denoted as D0, and the discharge energy is the initial energy, denoted as E0. The average discharge voltage V of the coin cells is E0 / D0.

[0276] 3. Full battery gas expansion test at 60°C:

[0277] The prepared full cell was stored at 60°C at 100% state of charge (SOC). The open-circuit voltage (OCV) and internal resistance (IMP) of the cell were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. The full cell was removed after every 48 hours of storage, allowed to stand for 1 hour, and then the OCV and IMP were measured. After cooling to room temperature, the cell volume was measured using the displacement method. The displacement method involves first measuring the cell's weight F1 separately using a balance with automatic unit conversion, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the process, measure the weight F2 of the battery cell at this moment, and the buoyancy F of the battery cell. 浮 That is, F1-F2, and then according to Archimedes' principle, F 浮 =ρ×g×V 排 The cell volume V is calculated to be V = (F1 - F2) / (ρ × g).

[0278] Based on the OCV and IMP test results, the batteries in all embodiments maintained a SOC of over 99% throughout the entire experiment until the end of storage.

[0279] After 30 days of storage, the cell volume was measured, and the percentage increase in cell volume after storage was calculated relative to the cell volume before storage.

[0280] In addition, measure the residual capacity of the battery cell. Charge the full battery at 1C to 4.3V within the range of 2.5V to 4.3V, then charge it at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, and record the charging capacity at this point as the residual capacity of the battery cell.

[0281] 4. Cyclic performance test of the entire battery at 45°C:

[0282] Under constant temperature conditions of 45℃ and at a voltage range of 2.5–4.3V, the prepared full battery was charged at 1C to 4.3V, and then charged at a constant voltage of 4.3V until the current was less than or equal to 0.05mA. After resting for 5 minutes, it was discharged at 1C to 2.5V, and the discharge capacity at this point was recorded as D0. The aforementioned charge-discharge cycle was repeated until the discharge capacity decreased to 80% of D0. The number of cycles completed at this point was recorded.

[0283] 5. Lattice change rate test:

[0284] Under a constant temperature environment of 25℃, the positive electrode active material sample prepared above was placed in an XRD (model Bruker D8 Discover) and tested at 1° / min. The test data was then organized and analyzed. Referring to the standard PDF card, the lattice constants a0, b0, c0 and v0 were calculated (a0, b0 and c0 represent the length of each aspect of the unit cell, and v0 represents the volume of the unit cell, which can be directly obtained from the XRD refinement results).

[0285] 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.

[0286] 6. Li / Mn inverse defect concentration test:

[0287] 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.

[0288] 7. Transition metal dissolution test:

[0289] 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.

[0290] 8. Surface oxygen valence state test:

[0291] 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.

[0292] 9. Compacted density measurement:

[0293] Take 5g of the prepared positive electrode active material powder and place it in a compaction mold (CARVER mold, model 13mm, USA). Then place the mold on a compaction density instrument. Apply a pressure of 3T and read the thickness of the powder under pressure (thickness after depressurization; the area of ​​the container used for testing is 1540.25mm²) on the instrument. 2 The compaction density is calculated using ρ = m / v.

[0294] 10. X-ray diffraction method for testing the crystallinity of pyrophosphate and phosphate.

[0295] 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.

[0296] 11. Interplanar spacing and angles

[0297] Take 1g of each of the above-prepared positive electrode active material powders into a 50mL test tube, and inject 10mL of 75% alcohol into the test tube. Then, stir and disperse the mixture thoroughly for 30 minutes. Then, use a clean disposable plastic pipette to take an appropriate amount of the above solution and drop it onto a 300-mesh copper grid. At this time, some powder will remain on the copper grid. Transfer the copper grid along with the sample to the TEM (Talos F200s G2) sample chamber for testing, obtain the original TEM test image, and save the original image format (xx.dm3).

[0298] 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.

[0299]

[0300]

[0301]

[0302]

[0303]

[0304] As can be seen from Examples 1-1 to 1-33 and Comparative Examples 1-4, the presence of the first coating layer 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 coin capacity of the battery and improving its safety and cycle performance. When other elements are doped at the Mn and phosphorus 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.

[0305] As can be seen from Examples 1-1 to 1-6, as the amount of the first coating layer 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, but a slight decrease in coin cell capacity. Optionally, the battery exhibits optimal overall performance when the total amount of the first coating layer is 4-5.6% by weight.

[0306] Based on Examples 1-3 and Examples 1-7 to 1-10, it can be seen that as the amount of the second coating layer increases from 1% to 6%, 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, but a slight decrease in coin cell capacity. Optionally, the battery exhibits optimal overall performance when the total amount of the second coating layer is 3-5% by weight.

[0307] Based on Examples 1-11 to 1-15 and Comparative Examples 5-6, it can be seen that when Li2FeP2O7 and LiFePO4 are present in the first coating layer, especially when the weight ratio of Li2FeP2O7 and LiFePO4 is 1:3 to 3:1, and especially when it is 1:3 to 1:1, the improvement in battery performance is more significant.

[0308]

[0309]

[0310]

[0311]

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 1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100~0.100, y = 0.001~0.500, z = 0.001~0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R is selected from one or more of B, Si, N and S; The shell includes a first covering layer covering the core and a second covering layer covering the first covering layer. in, The first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al, and the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:

1. The second coating layer contains carbon.

2. The positive electrode active material according to claim 1, wherein, The A is selected from one or more of Fe, Ti, V, Ni, Co and Mg.

3. The positive electrode active material according to claim 1, wherein, The interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°.

4. The positive electrode active material according to claim 1, wherein, In the kernel, the ratio of y to 1-y is between 1:10 and 10:

1.

5. The positive electrode active material according to any one of claims 1 to 4, wherein, In the kernel, the ratio of y to 1-y is 1:4 to 1:

1.

6. The positive electrode active material according to any one of claims 1 to 4, wherein, In the kernel, the ratio of z to 1-z is between 1:9 and 1:

999.

7. The positive electrode active material according to any one of claims 1 to 4, wherein, In the kernel, the ratio of z to 1-z is between 1:499 and 1:

249.

8. The positive electrode active material according to any one of claims 1 to 4, wherein, The coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, based on the weight of the core.

9. The positive electrode active material according to any one of claims 1 to 4, wherein, The first coating layer has a coating weight of 4-5.6% by weight, based on the weight of the core.

10. The positive electrode active material according to any one of claims 1 to 4, wherein, The weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 1:

1.

11. The positive electrode active material according to any one of claims 1-4, wherein, The crystallinity of the pyrophosphate and the phosphate is independently between 10% and 100%.

12. The positive electrode active material according to any one of claims 1-4, wherein, The crystallinity of the pyrophosphate and phosphate is independently between 50% and 100%.

13. The positive electrode active material according to any one of claims 1-4, wherein, The second coating layer has a coating amount greater than 0% by weight and less than or equal to 6% by weight, based on the weight of the core.

14. The positive electrode active material according to any one of claims 1-4, wherein, The second coating layer has a coating amount of 3-5% by weight, based on the weight of the core.

15. The positive electrode active material according to any one of claims 1-4, wherein, The A is selected from at least two of Fe, Ti, V, Ni, Co and Mg.

16. The positive electrode active material according to any one of claims 1-4, wherein, The concentration of Li / Mn antisite defects in the positive electrode active material is below 4%.

17. The positive electrode active material according to any one of claims 1-4, wherein, The concentration of Li / Mn antisite defects in the positive electrode active material is below 2%.

18. The positive electrode active material according to any one of claims 1-4, wherein, The lattice variation rate of the positive electrode active material is less than 6%.

19. The positive electrode active material according to any one of claims 1-4, wherein, The lattice change rate of the positive electrode active material is less than 4%.

20. The positive electrode active material according to any one of claims 1-4, wherein, The surface oxygen valence state of the positive electrode active material is below -1.

88.

21. The positive electrode active material according to any one of claims 1-4, wherein, The surface oxygen valence state of the positive electrode active material is -1.98 to -1.

88.

22. The positive electrode active material according to any one of claims 1-4, wherein, The compaction density of the positive electrode active material at 3 tons is 2.0 g / cm³. 3 above.

23. The positive electrode active material according to any one of claims 1-4, wherein, The compaction density of the positive electrode active material at 3 tons is 2.2 g / cm³. 3 above.

24. A method for preparing a positive electrode active material, comprising the following steps: Steps for providing kernel material: The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100-0.100, y = 0.001-0.500, z = 0.001-0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R is selected from one or more of B, Si, N and S; Coating step: MP2O7 powder and XPO4 suspension containing carbon source are provided. The core material and MP2O7 powder are added to the XPO4 suspension containing carbon source and mixed. The positive electrode active material is obtained by sintering. M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al. The positive electrode active material has a core-shell structure, which includes a core and a shell covering the core. The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer. The first coating layer includes pyrophosphate MP2O7 and phosphate XPO4. The second coating layer contains carbon. The weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:

1.

25. The method for preparing the positive electrode active material according to claim 24, wherein A is selected from one or more of Fe, Ti, V, Ni, Co and Mg.

26. The method for preparing the positive electrode active material according to claim 24, wherein the step of providing the core material includes the following steps: Step (1): Mix and stir the manganese source, the source of element A and the acid in a container to obtain manganese salt particles doped with element A; Step (2): The manganese salt particles doped with element A are mixed with lithium sources, phosphorus sources, and element R sources in a solvent to obtain a slurry. After sintering under an inert gas atmosphere, lithium manganese phosphate doped with elements A and R is obtained, wherein the lithium manganese phosphate doped with elements A and R is Li. 1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100-0.100, y = 0.001-0.500, z = 0.001-0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R is selected from one or more of B, Si, N and S.

27. The method according to claim 26, wherein, Step (1) is performed at a temperature of 20-120°C; and / or, The stirring in step (1) is carried out at 500-700 rpm for 60-420 minutes.

28. The method according to claim 26, wherein, Step (1) is performed at a temperature of 25-80°C; and / or, The stirring in step (1) is carried out at 500-700 rpm for 120-360 minutes.

29. The method according to any one of claims 26 to 28, wherein, The source of element A is selected from one or more of element A's elemental form, sulfate, halide, nitrate, organic acid salt, oxide or hydroxide; and / or, the source of element R is selected from one or more of element R's elemental form, sulfate, halide, nitrate, organic acid salt, oxide or hydroxide, and inorganic acid of element R.

30. The method according to any one of claims 24 to 28, wherein, The MP2O7 powder was prepared by the following method: The source of element M and the source of phosphorus are added to the solvent to obtain a mixture. The pH of the mixture is adjusted to 4-6, stirred and reacted fully, and then dried and sintered to obtain the final product. M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al.

31. The method according to claim 30, wherein, The drying process involves drying at 100-300℃ for 4-8 hours.

32. The method according to claim 30, wherein, The drying process involves drying at 150-200℃ for 4-8 hours.

33. The method according to claim 30, wherein, In the step of adding the source of element M and the source of phosphorus to the solvent to obtain a mixture, adjusting the pH of the mixture to 4-6, stirring and reacting fully, and then drying and sintering, the sintering is carried out at 500-800℃ in an inert gas atmosphere for 4-10 hours.

34. The method according to claim 30, wherein, In the step of adding the source of element M and the source of phosphorus to the solvent to obtain a mixture, adjusting the pH of the mixture to 4-6, stirring and reacting fully, and then drying and sintering, the sintering is carried out at 650-800℃ in an inert gas atmosphere for 4-10 hours.

35. The method according to claim 30, wherein, The sintering temperature for obtaining the positive electrode active material by sintering is 500-800℃, and the sintering time is 4-10h.

36. 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 1-23 or a positive electrode active material prepared by any one of claims 24-35, 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.

37. The positive electrode sheet according to claim 36, wherein the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, based on the total weight of the positive electrode film layer.

38. A secondary battery comprising a positive electrode active material according to any one of claims 1-23, or a positive electrode active material prepared by any one of claims 24-35, or a positive electrode sheet according to claim 36 or 37.

39. A battery module, characterized in that, Includes the secondary battery as described in claim 38.

40. A battery pack, characterized in that, Includes the battery module as described in claim 39.

41. An electrical appliance, characterized in that, It includes at least one selected from the secondary battery of claim 38, the battery module of claim 39, or the battery pack of claim 40.

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