A novel positive electrode sheet, a battery, and an electric device

Abstract

This application provides a novel positive electrode sheet, battery, and power device; wherein the positive electrode sheet comprises a first positive electrode active material and a second positive electrode active material; the first positive electrode active material comprises a core, a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer; the core comprises the compound Li. 1+x Mn 1‑ y A y P 1‑z R z O4, the first coating layer contains crystalline pyrophosphate Li a MP2O7 and / or M b (P2O7) c The second coating layer contains crystalline phosphate X n The third coating layer contains carbon (PO4), and the second positive electrode active material contains lithium manganese oxide. The secondary battery fabricated using the positive electrode sheet of this application exhibits high energy density, high rate performance, good kinetic and low-temperature performance, good cycle performance, and high safety.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a novel positive electrode, battery, and electrical device. Background Technology

[0002] In recent years, with the increasingly widespread application of rechargeable batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant development of rechargeable batteries, higher requirements have been placed on their energy density, cycle performance, and safety performance. While using lithium manganese iron phosphate as the positive electrode active material has its advantages, it leads to a decrease in the battery's kinetic performance and rate capability, failing to meet the needs of power batteries. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems, and its purpose is to provide a novel positive electrode, battery and power device to solve the technical problems of low energy density, low rate performance, poor dynamic performance, poor low temperature performance, short cycle life and low safety of batteries made of existing positive electrode active materials.

[0004] To achieve the above objectives, the first aspect of this application provides a positive electrode sheet, comprising a first positive electrode active material and a second positive electrode active material;

[0005] The first positive electrode active material includes a core, a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer; the core contains the compound Li. 1+x Mn 1- y A y P 1-z R z O4, the first coating layer contains crystalline pyrophosphate Li a MP2O7 and / or M b (P2O7) c The second coating layer contains crystalline phosphate X n PO4, the third coating layer contains carbon;

[0006] in,

[0007] The A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge;

[0008] The R includes one or more elements selected from B, Si, N, and S;

[0009] The x is any value in the range of -0.100 to 0.100;

[0010] The value of y is any value in the range of 0.001 to 0.500;

[0011] The z can be any value in the range of 0.001 to 0.100;

[0012] The crystalline pyrophosphate Li a MP2O7 and M b (P2O7) c The M in each of these elements independently includes one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.

[0013] The value of 'a' can be any value in the range of 0 to 2.

[0014] b can be any value in the range of 1 to 4;

[0015] c can be any value in the range of 1 to 6;

[0016] X includes one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al;

[0017] The n is greater than 0 and less than or equal to 3;

[0018] The second positive electrode active material contains lithium manganese oxide.

[0019] Therefore, this application provides a novel first positive electrode active material with a core-shell structure by doping element A at the manganese site and element R at the phosphorus site of lithium manganese phosphate to obtain a doped lithium manganese phosphate core, and then sequentially coating the core surface with three layers. The first positive electrode active material can significantly reduce manganese dissolution and reduce lattice change rate. When applied to secondary batteries, it can significantly improve the high-temperature cycle performance, cycle stability, high-temperature storage performance, rate performance, safety performance, and increase the capacity of secondary batteries.

[0020] This application uses a mixture of a first positive electrode active material and a second positive electrode active material, lithium manganese oxide. The particles of the first positive electrode active material uniformly coat the surface of the second positive electrode active material, making the crystal lattice of the second positive electrode active material relatively independent and the framework stable. This makes it less prone to collapse during the charging and discharging process of the secondary battery, further improving the cycle life of the secondary battery. Furthermore, the coating layer formed by the first positive electrode active material provides elastic strain force for external impact or shear, effectively solving the safety problem of the second positive electrode active material. The complementary advantages of the two materials improve the energy density of the secondary battery, while enabling the secondary battery to have excellent rate performance, kinetic performance, cycle performance, low-temperature performance, and safety.

[0021] 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.

[0022] In this paper, "crystalline state" refers to a crystallinity of 50% or higher, i.e., 50%-100%. Crystallinity less than 50% is referred to as the glassy state. The crystalline pyrophosphate and crystalline phosphate of this application have a crystallinity of 50% to 100%. Pyrophosphate and phosphate with a certain degree of crystallinity not only fully utilize the pyrophosphate coating's ability to inhibit manganese dissolution and the phosphate coating's excellent lithium-ion conduction capabilities, reducing interfacial side reactions, but also enable better lattice matching between the pyrophosphate and phosphate coatings, thus achieving a tight bond between the coatings.

[0023] In any embodiment of the first aspect of this application, the second positive electrode active material includes LiMn2O4.

[0024] Therefore, by mixing the first positive electrode active material with the aforementioned second positive electrode active material, the energy density and rate performance of the battery are further improved, the kinetic performance, low-temperature performance and safety of the secondary battery are enhanced, and the cycle life of the secondary battery is extended.

[0025] In any embodiment of the first aspect of this application, the positive electrode sheet 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 has a single-layer structure or a multi-layer structure; at least one positive electrode film layer with a single-layer structure simultaneously includes the first positive electrode active material and the second positive electrode active material, and / or, at least one layer of at least one positive electrode film layer with a multi-layer structure simultaneously includes the first positive electrode active material and the second positive electrode active material.

[0026] In any embodiment of the first aspect of this application, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; at least one of the positive electrode film layers has a multilayer structure, and the at least one positive electrode film layer with a multilayer structure includes the first positive electrode active material and the second positive electrode active material in different layers respectively; optionally, at least one positive electrode film layer with a multilayer structure includes the first positive electrode active material and the second positive electrode active material in adjacent layers respectively.

[0027] In any embodiment of the first aspect of this application, the positive electrode sheet includes a positive current collector and a positive electrode film layer A and a positive electrode film layer B respectively disposed on two surfaces of the positive current collector; the positive electrode film layer A and the positive electrode film layer B each have a single-layer structure or a multi-layer structure independently; at least one layer of the positive electrode film layer A includes the first positive electrode active material, and at least one layer of the positive electrode film layer B includes the second positive electrode active material.

[0028] Therefore, this application utilizes a mixture of the first and second positive electrode active materials, allowing the advantages of both materials to complement each other, thereby improving the energy density of the secondary battery. Simultaneously, the secondary battery exhibits excellent rate performance, kinetic performance, cycle performance, low-temperature performance, and safety. The particles of the first positive electrode active material uniformly coat the surface of the second positive electrode active material, making the crystal lattice of the second positive electrode active material relatively independent and its framework stable, preventing collapse during the charging and discharging process of the secondary battery, thus further improving the cycle life of the secondary battery. Furthermore, the coating layer formed by the first positive electrode active material provides elastic strain force against external impacts or shearing, effectively solving the safety issues of the second positive electrode active material.

[0029] In any embodiment of the first aspect of this application, the mass ratio of the first positive electrode active material to the second positive electrode active material is 1:7 to 7:1, and optionally 1:4 to 4:1. This enables the secondary battery to possess both excellent rate performance and cycle performance, high energy density, excellent kinetic performance and low-temperature performance, reduced interfacial side reactions, and improved safety of the secondary battery.

[0030] In any embodiment of the first aspect of this application, A in the first positive electrode active material includes one or more elements selected from Fe, Ti, V, Ni, Co, and Mg. Selecting doping elements within the aforementioned range is beneficial for enhancing the doping effect. On the one hand, it further reduces the lattice change rate, thereby suppressing manganese dissolution and reducing the consumption of electrolyte and active lithium. On the other hand, it also helps to further reduce surface oxygen activity, reducing interfacial side reactions between the first positive electrode active material and the electrolyte, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0031] In any embodiment of the first aspect of this application, R in the first positive electrode active material includes one element selected from B, Si, N, and S. By selecting doping elements within the above range, the rate performance and conductivity of the secondary battery can be further improved, thereby enhancing the specific capacity, cycle performance, and high-temperature performance of the secondary battery.

[0032] In any embodiment of the first aspect of this application, the ratio of y to 1-y in the first positive electrode active material is from 1:10 to 1:1, and can be selected as from 1:4 to 1:1. This further improves the energy density, cycle performance, and rate performance of the secondary battery.

[0033] In any embodiment of the first aspect of this application, the ratio of z to 1-z in the first positive electrode active material is from 1:9 to 1:999, and can be selected as from 1:499 to 1:249. This further improves the energy density, cycle performance, and rate performance of the secondary battery.

[0034] In any embodiment of the first aspect of this application, in the first positive electrode active material, the interplanar spacing of the crystalline pyrophosphate in the first coating layer ranges from 0.293 to 0.470 nm, and the included angle of the crystal orientation (111) ranges from 18.00° to 32.00°; and / or, the interplanar spacing of the crystalline phosphate in the second coating layer ranges from 0.244 to 0.425 nm, and the included angle of the crystal orientation (111) ranges from 20.00° to 37.00°.

[0035] In this application, both the first and second coating layers of the first positive electrode active material are made of crystalline materials, and their interplanar spacing and angles are within the aforementioned range. This effectively avoids impurity phases in the coating layers, thereby improving the specific capacity of the material and enhancing the cycle performance and rate performance of the secondary battery.

[0036] In any embodiment of the first aspect of this application, in the first positive electrode active material, the carbon in the third coating layer is a mixture of SP2 carbon and SP3 carbon. Optionally, the molar ratio of SP2 carbon to SP3 carbon is any value in the range of 0.1-10, and can be any value in the range of 2.0-3.0.

[0037] This application improves the overall performance of the secondary battery by limiting the molar ratio of SP2 carbon to SP3 carbon within the above-mentioned range.

[0038] In any embodiment of the first aspect of this application, the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, more preferably greater than 0 and less than or equal to 2% by weight, based on the kernel weight; and / or,

[0039] The coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and more preferably 2-4% by weight, based on the kernel's weight; and / or,

[0040] The coating amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and even more optionally greater than 0 and less than or equal to 2% by weight, based on the kernel weight.

[0041] In the first positive electrode active material with a core-shell structure of this application, the coating amount of the three coating layers is preferably within the above-mentioned range, thereby enabling sufficient coating of the core and further improving the dynamic performance and safety performance of the secondary battery without sacrificing the specific capacity of the first positive electrode active material.

[0042] In any embodiment of the first aspect of this application, the thickness of the first coating layer in the first positive electrode active material is 1-10 nm. In this application, when the thickness of the first coating layer is in the range of 1-10 nm, it is beneficial to improve the kinetic performance of the battery and can effectively hinder the migration of transition metal ions.

[0043] In any embodiment of the first aspect of this application, the thickness of the second coating layer in the first positive electrode active material is 2-15 nm. When the thickness of the second coating layer is in the range of 2-15 nm, the surface structure of the second coating layer is stable, and the side reactions with the electrolyte are small. Therefore, it can effectively reduce interfacial side reactions, thereby improving the high-temperature performance of the secondary battery.

[0044] In any embodiment of the first aspect of this application, the thickness of the third coating layer in the first positive electrode active material is 2-25 nm. When the thickness of the third coating layer is in the range of 2-25 nm, the electrical conductivity of the material can be improved and the compaction density performance of the battery electrode sheet prepared using the first positive electrode active material can be improved.

[0045] In any embodiment of the first aspect of this application, the manganese content in the first positive electrode active material, based on the weight of the first positive electrode active material, is in the range of 10 wt% to 35 wt%, optionally in the range of 15 wt% to 30 wt%, and more preferably in the range of 17 wt% to 20 wt%.

[0046] In the first positive electrode active material with a core-shell structure of this application, the content of manganese element is within the above-mentioned range, which can effectively improve the structural stability and density of the material, thereby improving the cycle, storage and compaction density performance of the secondary battery; and can also improve the voltage platform, thereby improving the energy density of the secondary battery.

[0047] In any embodiment of the first aspect of this application, the content of phosphorus in the first positive electrode active material is in the range of 12%-25% by weight, and optionally in the range of 15%-20% by weight, based on the weight of the first positive electrode active material.

[0048] In the first positive electrode active material with a core-shell structure of this application, the phosphorus content is within the above-mentioned range, which can improve the electrical conductivity of the material and at the same time improve the stability of the pyrophosphate lattice structure in the core, the first coating layer and / or the phosphate lattice structure in the second coating layer, thereby improving the overall stability of the material.

[0049] In any embodiment of the first aspect of this application, the weight ratio of manganese to phosphorus in the first positive electrode active material is 0.90-1.25, and optionally 0.95-1.20, based on the weight of the first positive electrode active material.

[0050] In the first positive electrode active material with a core-shell structure of this application, the weight ratio of manganese to phosphorus is within the above-mentioned range, which can effectively suppress the dissolution of transition metals, improve the stability of the material and the cycle and storage performance of the secondary battery; at the same time, it can improve the discharge voltage platform of the material, thereby improving the energy density of the secondary battery.

[0051] In any embodiment of the first aspect of this application, the lattice change rate of the first positive electrode active material before and after complete lithium insertion / extraction is less than or equal to 4%, preferably less than or equal to 3.8%, and more preferably 2.0%-3.8%.

[0052] The first positive electrode active material with a core-shell structure of this application can achieve a lattice change rate of less than 4% before and after lithium insertion / extraction. Therefore, using the first positive electrode active material can improve the specific capacity and rate performance of secondary batteries.

[0053] In any embodiment of the first aspect of this application, the Li / Mn antisite defect concentration of the first positive electrode active material is less than or equal to 4%, optionally less than or equal to 2.2%, and more preferably 1.5%-2.2%. By keeping the Li / Mn antisite defect concentration within the above range, Mn... 2+ Hinder Li + This improves the transmission capacity of the first positive electrode active material and the rate performance of the secondary battery.

[0054] In any embodiment of the first aspect of this application, the compaction density of the first positive electrode active material at 3T is greater than or equal to 2.2 g / cm³. 3 The value can be greater than or equal to 2.2 g / cm³. 3 And less than or equal to 2.8 g / cm 3 Therefore, increasing the compaction density increases the weight of the first positive electrode active material per unit volume, which is beneficial for improving the volumetric energy density of the secondary battery.

[0055] In any embodiment of the first aspect of this application, the surface oxygen valence state of the first positive electrode active material is less than or equal to -1.90, and can be selected as -1.98 to -1.90. Therefore, by limiting the surface oxygen valence state of the first positive electrode active material to the above range as described above, the interfacial side reactions between the first positive electrode material and the electrolyte can be reduced, thereby improving the battery cell's cycle life, high-temperature storage gas generation, and other performance characteristics.

[0056] In any embodiment of the first aspect of this application, the sum of the mass of the first positive electrode active material and the second positive electrode active material accounts for 88%-98.7% of the mass of the positive electrode sheet. This further ensures that the secondary battery has excellent rate performance, kinetic performance, cycle performance, and low-temperature performance, and has a high energy density.

[0057] A second aspect of this application provides a battery including the positive electrode of the first aspect of this application.

[0058] A third aspect of this application provides an electrical device, including the battery of the second aspect of this application. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the first positive electrode active material with a three-layer coating structure according to an embodiment of this application.

[0060] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0061] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0062] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0063] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0064] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0065] Figure 7This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0066] Figure 8 This is a schematic diagram of the battery structure made from the positive electrode P1 of this application.

[0067] Figure 9 This is a schematic diagram of the battery structure made from the positive electrode P2 of this application.

[0068] Figure 10 This is a schematic diagram of the battery structure made from the positive electrode P3 of this application.

[0069] Figure 11 This is a schematic diagram of the battery structure made from the positive electrode P8 of this application.

[0070] Figure 12 This is a schematic diagram of the battery structure made from the positive electrode P10 of this application.

[0071] Figure 13 This is a schematic diagram of the battery structure made from the positive electrode P11 of this application.

[0072] Figure 14 This is a schematic diagram of the battery structure made from the positive electrode P12 of this application.

[0073] Figure 15 This is a schematic diagram of the battery structure made from the positive electrode P17 of this application.

[0074] Figure 16 This is a schematic diagram of the battery structure made from the positive electrode P18 of this application.

[0075] Figure 17 This is a schematic diagram of the battery structure made from the positive electrode P23 of this application.

[0076] Figure 18 This is a schematic diagram of the battery structure made from the positive electrode P24 of this application.

[0077] Figure 19 This is a schematic diagram of the battery structure made from the positive electrode P26 of this application.

[0078] Figure 20 This is a schematic diagram of the battery structure made from the positive electrode P27 of this application.

[0079] Explanation of reference numerals in the attached figures:

[0080] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0081] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the positive electrode, 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.

[0082] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0083] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0084] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0085] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0086] 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.

[0087] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A and / or B" means "A, B, or both A and B". More specifically, the condition "A and / 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).

[0088] Unless otherwise specified, in this application, the term "at least one" means one or more, such as one, two, etc.

[0089] Unless otherwise specified, in this application, the median particle size Dv 50 This refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for the positive electrode active material. In this application, the median particle size Dv of the positive electrode active material... 50 Particle size can be determined using laser diffraction particle size analysis. For example, according to standard GB / T 19077-2016, a laser particle size analyzer (e.g., MalvernMaster Size 3000) can be used for determination.

[0090] Unless otherwise specified, in this application, the term "cladding layer" refers to a material layer covering the core, which may completely or partially cover the core. The use of "cladding layer" is for ease of description only and is not intended to limit the invention. Similarly, the term "cladding layer thickness" refers to the thickness of the material layer covering the core in the radial direction of the core.

[0091] Unless otherwise specified, in this application, the term "source" refers to a compound that is the source of a certain element. For example, the types of "sources" include, but are not limited to, carbonates, sulfates, nitrates, elements, halides, oxides, and hydroxides.

[0092] [Rechargeable Battery]

[0093] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0094] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0095] [Positive electrode plate]

[0096] This application provides a positive electrode sheet, comprising a first positive electrode active material and a second positive electrode active material;

[0097] The first positive electrode active material includes a core, a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer; the core contains the compound Li. 1+x Mn 1- y A y P 1-z R z O4, the first coating layer contains crystalline pyrophosphate Li a MP2O7 and / or M b (P2O7) c The second coating layer contains crystalline phosphate X n PO4, the third coating layer contains carbon;

[0098] in,

[0099] The A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge;

[0100] The R includes one or more elements selected from B, Si, N, and S;

[0101] The x is any value in the range of -0.100 to 0.100;

[0102] The value of y is any value in the range of 0.001 to 0.500;

[0103] The z can be any value in the range of 0.001 to 0.100;

[0104] The crystalline pyrophosphate Li a MP2O7 and M b (P2O7) c The M in each of these elements independently includes one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.

[0105] The value of 'a' can be any value in the range of 0 to 2.

[0106] b can be any value in the range of 1 to 4;

[0107] c can be any value in the range of 1 to 6;

[0108] X includes one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al;

[0109] The n is greater than 0 and less than or equal to 3;

[0110] The second positive electrode active material contains lithium manganese oxide.

[0111] The first 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 first positive electrode active material of this application has a core-shell structure, in which elements A and R are doped into the manganese and phosphorus sites of the lithium manganese phosphate core, respectively. This not only effectively reduces 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 promotes Mn-O bond adjustment, lowers the lithium ion migration barrier, promotes lithium ion migration, and improves the rate performance of the secondary battery. By coating the core with a first coating layer including crystalline pyrophosphate, it is possible to further improve the specific capacity, cycle performance, and safety performance of the secondary battery. The process involves increasing the migration resistance of manganese, reducing its dissolution, and decreasing the content of surface-mounted lithium impurities and the contact between the core and the electrolyte. This reduces interfacial side reactions and gas generation, thereby improving the high-temperature storage performance, cycle performance, and safety performance of the secondary battery. Further coating with a crystalline phosphate layer possessing excellent lithium-ion conductivity effectively reduces interfacial side reactions on the surface of the first cathode active material, further improving the high-temperature cycle and storage performance of the secondary battery. A third coating with a carbon layer further enhances the safety and kinetic performance of the secondary battery. Furthermore, the doping of element A 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, improving the structural stability of the first cathode material, significantly reducing manganese dissolution, and decreasing oxygen activity on the particle surface. The doping of element R at the phosphorus sites helps alter the ease of Mn-O bond length changes, thereby improving electronic conductivity, lowering the lithium-ion migration barrier, promoting lithium-ion migration, and improving the rate performance of the secondary battery.

[0112] This application uses a mixture of a first positive electrode active material and a second positive electrode active material, lithium manganese oxide. The particles of the first positive electrode active material uniformly coat the surface of the second positive electrode active material, making the crystal lattice of the second positive electrode active material relatively independent and the framework stable. This makes it less prone to collapse during the charging and discharging process of the secondary battery, further improving the cycle life of the secondary battery. Furthermore, the coating layer formed by the first positive electrode active material provides elastic strain force for external impact or shear, effectively solving the safety problem of the second positive electrode active material. The complementary advantages of the two materials improve the energy density of the secondary battery, while enabling the secondary battery to have excellent rate performance, kinetic performance, cycle performance, low-temperature performance, and safety.

[0113] 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.

[0114] In some embodiments, the second positive electrode active material includes LiMn2O4.

[0115] Therefore, by mixing the first positive electrode active material with the aforementioned second positive electrode active material, the energy density and rate performance of the battery are further improved, the kinetic performance, low-temperature performance and safety of the secondary battery are enhanced, and the cycle life of the secondary battery is extended.

[0116] In some embodiments, the positive electrode sheet 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 has a single-layer structure or a multi-layer structure; at least one of the positive electrode film layers with a single-layer structure simultaneously includes the first positive electrode active material and the second positive electrode active material, and / or, at least one layer of at least one of the positive electrode film layers with a multi-layer structure simultaneously includes the first positive electrode active material and the second positive electrode active material.

[0117] It should be noted that when the positive electrode includes two positive electrode film layers, "the positive electrode film layer has a single-layer structure or a multi-layer structure" means that each of the two positive electrode film layers independently has a single-layer structure or a multi-layer structure.

[0118] In some embodiments, a positive electrode film layer is disposed on each of the two surfaces of the positive electrode current collector. Each positive electrode film layer is a monolayer structure. One positive electrode film layer includes both a first positive electrode active material and a second positive electrode active material, and the other positive electrode film layer includes the first positive electrode active material and / or the second positive electrode active material.

[0119] In some embodiments, a positive electrode film layer is disposed on each of the two surfaces of the positive electrode current collector. Each positive electrode film layer has a multilayer structure, and at least one layer (e.g., one layer) in each positive electrode film layer includes both a first positive electrode active material and a second positive electrode active material. Optionally, the remaining layers in each positive electrode film layer include either the first positive electrode active material or the second positive electrode active material.

[0120] In some embodiments, a positive electrode film layer C and a positive electrode film layer D are respectively disposed on two surfaces of the positive electrode current collector. The positive electrode film layer C has a multilayer structure, and the positive electrode film layer D has a single-layer structure. At least one layer of the positive electrode film layer C simultaneously includes a first positive electrode active material and a second positive electrode active material, and / or, the positive electrode film layer D simultaneously includes a first positive electrode active material and a second positive electrode active material. Optionally, when any layer of the positive electrode film layer C and the positive electrode film layer D simultaneously include a first positive electrode active material and a second positive electrode active material, the remaining layers of the positive electrode film layer C include either a first positive electrode active material or a second positive electrode active material. Optionally, when any layer of the positive electrode film layer C simultaneously includes both a first positive electrode active material and a second positive electrode active material, the remaining layers of the positive electrode film layer C and the positive electrode film layer D each independently include either a first positive electrode active material or a second positive electrode active material. Optionally, when the positive electrode film layer D simultaneously includes both a first positive electrode active material and a second positive electrode active material, each layer of the positive electrode film layer C independently includes either a first positive electrode active material or a second positive electrode active material.

[0121] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; at least one of the positive electrode film layers has a multilayer structure, and the at least one positive electrode film layer with a multilayer structure includes the first positive electrode active material and the second positive electrode active material in different layers respectively; optionally, at least one positive electrode film layer with a multilayer structure includes the first positive electrode active material and the second positive electrode active material in adjacent layers respectively.

[0122] In some embodiments, a positive electrode film layer is disposed on each of the two surfaces of the positive electrode current collector. Each positive electrode film layer has a multilayer structure, and two adjacent layers in each positive electrode film layer include a first positive electrode active material and a second positive electrode active material, respectively.

[0123] In some embodiments of this application, a positive electrode film layer E and a positive electrode film layer F are respectively disposed on two surfaces of the positive electrode current collector. The positive electrode film layer E has a multilayer structure, and the positive electrode film layer F has a single-layer structure. Two adjacent layers in the positive electrode film layer E respectively include a first positive electrode active material and a second positive electrode active material. Optionally, the remaining layers in the positive electrode film layer E and the positive electrode film layer F each independently include a first positive electrode active material or a second positive electrode active material.

[0124] In some embodiments, the positive electrode sheet includes a positive current collector and positive electrode film layer A and positive electrode film layer B respectively disposed on two surfaces of the positive current collector; the positive electrode film layer A and the positive electrode film layer B each have a single-layer structure or a multi-layer structure independently; at least one layer of the positive electrode film layer A includes the first positive electrode active material, and at least one layer of the positive electrode film layer B includes the second positive electrode active material.

[0125] In some embodiments, the positive electrode sheet includes a positive current collector and positive electrode film layer A and positive electrode film layer B respectively disposed on two surfaces of the positive current collector; both positive electrode film layer A and positive electrode film layer B have a single-layer structure; positive electrode film layer A includes the first positive electrode active material, while positive electrode film layer B includes the second positive electrode active material.

[0126] This application utilizes a combination of a first positive electrode active material and a second positive electrode active material, leveraging the complementary advantages of both materials to improve the energy density of the secondary battery. Simultaneously, the secondary battery exhibits excellent rate performance, kinetic performance, cycle performance, low-temperature performance, and safety. The particles of the first positive electrode active material uniformly coat the surface of the second positive electrode active material, resulting in a relatively independent crystal lattice and stable framework. This prevents the second positive electrode active material from collapsing during charging and discharging, further improving the cycle life of the secondary battery. Furthermore, the coating layer formed by the first positive electrode active material provides elastic strain force against external impacts or shearing, effectively addressing the safety issues of the second positive electrode active material.

[0127] In some implementations, when A includes one, two, three, or four elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, A y For Q n1 D n2 E n3 K n4Where n1 + n2 + n3 + n4 = y, and n1, n2, n3, and n4 are all positive numbers and not all zero simultaneously. Q, D, E, and K are each independently selected from one of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge. Optionally, at least one of Q, D, E, and K is Fe. Optionally, one of n1, n2, n3, and n4 is zero, and the others are not zero; more alternatively, two of n1, n2, n3, and n4 are zero, and the others are not zero; still alternatively, three of n1, n2, n3, and n4 are zero, and the others are not zero. Kernel Li 1+x Mn 1-y A y P 1-z R z In O4, it is advantageous to dope one, two, three or four of the aforementioned A elements at the manganese sites, and optionally, one, two or three of the aforementioned A elements are doped. In addition, it is advantageous to dope one or two R elements at the phosphorus sites, which is beneficial to make the doped elements uniformly distributed.

[0128] In some implementations, the values ​​of x, y, and z satisfy the following condition: keeping the entire kernel electrically neutral.

[0129] Kernel Li 1+x Mn 1-y A y P 1-z R z In O4, the value of x is influenced by the valence states of A and R, as well as the values ​​of y and z, to ensure the overall system remains electrically neutral. If the value of x is too small, the lithium content of the entire core system will decrease, affecting the specific capacity of the material. The value of y limits the total amount of all dopants. If y is too small, the doping amount is too low, and the dopants will not play a role. If y exceeds 0.5, the Mn content in the system will be low, affecting the voltage plateau of the material. R is doped at the P site. Since the PO tetrahedron is relatively stable, and a large z value would affect the stability of the material, the z value is limited to 0.001-0.100.

[0130] Furthermore, maintaining the electrical neutrality of the entire core system ensures that defects and impurities in the first cathode active material are minimized. If an excess of transition metal (such as manganese) exists in the first cathode active material, due to the relatively stable structure of the material system itself, the excess transition metal is likely to precipitate as elemental or form impurities within the crystal lattice. Maintaining electrical neutrality minimizes such impurities. In addition, ensuring the electrical neutrality of the system can, in some cases, generate lithium vacancies in the material, thereby improving the material's kinetic performance.

[0131] The values ​​of a, b, c, and n satisfy the following condition: making crystalline pyrophosphate Li aMP2O7 or M b (P2O7) c , Crystalline phosphate X n PO4 remains electrically neutral.

[0132] Crystalline state refers to a crystallinity of 50% or higher, i.e., 50%-100%. Crystallinity less than 50% is called glassy state. The crystallinity of the crystalline pyrophosphate and crystalline phosphate in this application is 50% to 100%. Pyrophosphate and phosphate with a certain degree of crystallinity not only help to fully utilize the ability of the pyrophosphate coating layer to inhibit manganese dissolution and the excellent lithium-ion conduction ability of the phosphate coating layer, and reduce interfacial side reactions, but also enable the pyrophosphate coating layer and phosphate coating layer to achieve better lattice matching, thereby achieving a tighter bonding of the coating layers.

[0133] The crystallinity of the first coating layer material crystalline pyrophosphate and the second coating layer material crystalline phosphate of the first positive electrode active material can be tested by conventional techniques in the art, such as density method, infrared spectroscopy, differential scanning calorimetry and nuclear magnetic resonance absorption method, or by, for example, X-ray diffraction.

[0134] A specific X-ray diffraction method for testing the crystallinity of the first coating layer crystalline pyrophosphate and the second coating layer crystalline phosphate of the first positive electrode active material may include the following steps:

[0135] A certain amount of the first positive electrode active material powder is taken, and the total scattering intensity is measured by X-rays. It is the sum of the scattering intensities of all matter in space. It is only related to the intensity of the primary rays, the chemical structure of the first positive electrode active material powder, and the total number of electrons participating in diffraction, i.e., the mass, and is independent of the order state of the sample. Then, crystalline scattering and non-crystalline scattering are separated from the diffraction pattern. The crystallinity is the ratio of the scattering of the crystalline part to the total scattering intensity.

[0136] It should be noted that the crystallinity of pyrophosphate and phosphate in the coating layer can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature and sintering time.

[0137] Since metal ions are difficult to migrate in pyrophosphate, pyrophosphate, as the first coating layer, can effectively isolate doped metal ions from the electrolyte. Crystalline pyrophosphate has a stable structure; therefore, coating with crystalline pyrophosphate can effectively suppress the dissolution of transition metals and improve cycle performance.

[0138] The bonding between the first coating layer and the core is similar to that of a heterojunction, and the strength of this bonding is limited by the degree of lattice matching. When the lattice mismatch is below 5%, the lattice matching is good, and the two easily bond tightly. A tight bonding ensures that the coating layer will not detach during subsequent cycling, which is beneficial for ensuring the long-term stability of the material. The degree of bonding between the first coating layer and the core is mainly measured by calculating the mismatch between the lattice constants of the core and the coating. In this application, after doping the core with A and R elements, the matching degree between the core and the first coating layer is improved compared to undoped elements, and the core and the pyrophosphate coating layer can bond more tightly.

[0139] Crystalline phosphate was chosen as the second coating layer primarily because of its high lattice matching (mismatch of only 3%) with the first coating layer, crystalline pyrophosphate. Secondly, phosphate itself is more stable than pyrophosphate, and coating pyrophosphate with phosphate helps improve the material's stability. Crystalline phosphate has a very stable structure and excellent lithium-ion conductivity; therefore, using crystalline phosphate for coating can effectively reduce interfacial side reactions on the surface of the first positive electrode active material, thereby improving the high-temperature cycling and storage performance of the secondary battery. The lattice matching between the second and first coating layers is similar to the bonding between the first coating layer and the core; when the lattice mismatch is below 5%, the lattice matching is good, and the two easily bond tightly.

[0140] The main reason for using carbon as the third coating layer is its excellent electronic conductivity. Since electrochemical reactions occur in secondary batteries, requiring electrons, carbon, with its superior conductivity, is used for coating to increase electron transport between particles and between different locations on the particles. Carbon coating effectively improves the conductivity and desolvation capability of the first positive electrode active material.

[0141] Figure 1 This is a schematic diagram of the first positive electrode active material with an ideal three-layer coating structure. As shown in the figure, the innermost circle represents the core, and from the inside out are the first coating layer, the second coating layer, and the third coating layer. This diagram represents the ideal state where each layer is fully coated. In practice, each coating layer can be fully coated or partially coated.

[0142] In some embodiments, the mass ratio of the first positive electrode active material to the second positive electrode active material is 1:7 to 7:1, optionally 1:4 to 4:1, and further optionally 1:3 to 3:1, such as 1:7, 1:5, 1:3, 1:2, 3:5, 1:1, 5:3, 2:1, 3:1, 5:1, and 7:1. This ensures that the secondary battery possesses excellent rate performance, excellent cycle performance and high-temperature stability, high energy density, excellent kinetic performance and low-temperature performance, reduces interfacial side reactions, and improves the safety of the secondary battery.

[0143] In some embodiments, A in the first positive electrode active material includes one or more elements selected from Fe, Ti, V, Ni, Co, and Mg. Selecting doping elements within the aforementioned range enhances the doping effect. On one hand, it further reduces the lattice change rate, thereby suppressing manganese dissolution and reducing the consumption of electrolyte and active lithium. On the other hand, it also helps to further reduce surface oxygen activity, minimizing interfacial side reactions between the first positive electrode active material and the electrolyte, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0144] In some embodiments, R in the first positive electrode active material includes one element selected from B, Si, N, and S. By selecting doping elements within the above range, the rate performance and conductivity of the secondary battery can be further improved, thereby enhancing the specific capacity, cycle performance, and high-temperature performance of the secondary battery.

[0145] In some embodiments, the ratio of y to 1-y in the first positive electrode active material is 1:10 to 1:1, and optionally 1:4 to 1:1. Here, y represents the sum of the stoichiometric coefficients of the Mn-doped element A. Meeting the above conditions further improves the energy density, cycle performance, and rate performance of the secondary battery.

[0146] In some embodiments, the ratio of z to 1-z in the first positive electrode active material is from 1:9 to 1:999, and optionally from 1:499 to 1:249. Here, z represents the sum of the stoichiometric coefficients of the p-site doping elements R. Meeting the above conditions further improves the energy density, cycle performance, and rate performance of the secondary battery.

[0147] In some embodiments, in the first positive electrode active material, the interplanar spacing of the crystalline pyrophosphate in the first coating layer ranges from 0.293 to 0.470 nm, and the included angle of the crystal orientation (111) ranges from 18.00° to 32.00°; and / or, the interplanar spacing of the crystalline phosphate in the second coating layer ranges from 0.244 to 0.425 nm, and the included angle of the crystal orientation (111) ranges from 20.00° to 37.00°.

[0148] In this application, both the first and second coating layers of the first positive electrode active material utilize crystalline materials. Crystalline pyrophosphate and crystalline phosphate within the aforementioned interplanar spacing and angle range can more effectively suppress the lattice change rate of lithium manganese phosphate and Mn dissolution during lithium insertion / extraction, thereby improving the high-temperature cycle performance, cycle stability, and high-temperature storage performance of the secondary battery. The crystalline pyrophosphate and crystalline phosphate in the coating layers can be characterized using conventional techniques in the art, or for example, by transmission electron microscopy (TEM). Under TEM, the core and coating layers can be distinguished by measuring the interplanar spacing.

[0149] The specific testing methods for the interplanar spacing and angle of crystalline pyrophosphate and crystalline phosphate in the coating layer may include the following steps:

[0150] Take a certain amount of the coated first positive electrode active material sample powder into a test tube, and inject a solvent such as alcohol into the test tube. Then stir and disperse it thoroughly. 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 sample chamber for testing, obtain the original TEM test image, and save the original image.

[0151] Open the original image obtained from the TEM test in the diffractometer software and perform a Fourier transform 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.

[0152] The interplanar spacing range of crystalline pyrophosphates differs from that of crystalline phosphates, and can be directly determined by the value of the interplanar spacing.

[0153] In some embodiments, in the first positive electrode active material, the carbon in the third coating layer is a mixture of SP2 carbon and SP3 carbon. Optionally, the molar ratio of SP2 carbon to SP3 carbon is any value in the range of 0.1-10, and can be any value in the range of 2.0-3.0.

[0154] In some embodiments, the molar ratio of SP2 carbon to SP3 carbon may be about 0.1, about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9 or about 10, or any range of any of the above values.

[0155] In this application, "about" for a certain value represents a range, specifically a range of ±10% of that value.

[0156] By selecting the morphology of carbon in the carbon coating layer, the overall electrical performance of the secondary battery can be improved. Specifically, by using a mixture of SP2 and SP3 carbon morphologies and limiting the ratio of SP2 to SP3 carbon within a certain range, the following situations can be avoided: if the carbon in the coating layer is all amorphous SP3, the conductivity is poor; if it is all graphitized SP2, although the conductivity is good, there are few lithium-ion pathways, which is not conducive to lithium insertion / extraction. In addition, limiting the molar ratio of SP2 to SP3 carbon within the above-mentioned range can achieve both good conductivity and ensure lithium-ion pathways, thus benefiting the realization of secondary battery functions and cycle performance.

[0157] The mixing ratio of SP2 and SP3 carbon forms in the third coating layer can be controlled by sintering conditions such as sintering temperature and sintering time. For example, when using sucrose as a carbon source to prepare the third coating layer, after the sucrose is pyrolyzed at high temperature and deposited on the second coating layer under high temperature, a carbon coating layer with both SP2 and SP3 forms will be produced. The ratio of SP2 to SP3 carbon can be adjusted by selecting high-temperature pyrolysis and sintering conditions.

[0158] The structure and characteristics of the third coating carbon can be determined by Raman spectroscopy. The specific testing method is as follows: by dividing the energy spectrum of the Raman test, the Id / Ig ratio is obtained (where Id is the peak intensity of SP3 carbon and Ig is the peak intensity of SP2 carbon), thereby confirming the molar ratio between the two.

[0159] In some implementations, the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, more preferably greater than 0 and less than or equal to 2% by weight, based on the kernel's weight; and / or,

[0160] The coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and more preferably 2-4% by weight, based on the kernel's weight; and / or,

[0161] The coating amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and even more optionally greater than 0 and less than or equal to 2% by weight, based on the kernel weight.

[0162] In this application, the coverage of each layer is greater than zero.

[0163] In the first positive electrode active material with a core-shell structure of this application, the coating amount of the three coating layers is preferably within the above-mentioned range, thereby enabling sufficient coating of the core and further improving the kinetic performance and safety performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0164] For the first coating layer, by ensuring the coating amount is within the aforementioned range, the migration of transition metals can be effectively hindered, thereby improving the Li... + The migration of these molecules improves the rate performance of the material.

[0165] For the second coating layer, by keeping the coating amount within the above range, the following situations can be reduced: too much coating amount may affect the overall plateau voltage of the material; too little coating amount may not achieve sufficient coating effect.

[0166] For the third coating layer, the carbon coating mainly plays the role of enhancing electron transport between particles. However, since the structure also contains a large amount of amorphous carbon, the carbon density is low. Therefore, if the coating amount is too large, it will affect the compaction density of the electrode.

[0167] In some embodiments, the thickness of the first coating layer in the first positive electrode active material is 1-10 nm.

[0168] In some embodiments, the thickness of the first coating layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm, or any range of any of the above values.

[0169] In this application, when the thickness of the first coating layer is in the range of 1-10 nm, it is beneficial to improve the dynamic performance of the battery and can effectively hinder the migration of transition metal ions.

[0170] In some embodiments, the thickness of the second coating layer in the first positive electrode active material is 2-15 nm.

[0171] In some embodiments, the thickness of the second coating layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, or any range of the above values.

[0172] In this application, when the thickness of the second coating layer is in the range of 2-15nm, the surface structure of the second coating layer is stable and the side reactions with the electrolyte are small. Therefore, it can effectively reduce the interface side reactions and thus improve the high-temperature performance of the secondary battery.

[0173] In some embodiments, the thickness of the third coating layer in the first positive electrode active material is 2-25 nm.

[0174] In some embodiments, the thickness of the third coating layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm, about 17 nm, about 18 nm, about 19 nm, about 20 nm, about 21 nm, about 22 nm, about 23 nm, about 24 nm, or about 25 nm, or any range of any of the above values.

[0175] In this application, when the thickness of the third coating layer is in the range of 2-25 nm, it can improve the electrical conductivity of the material and improve the compaction density performance of the battery electrode prepared using the first positive electrode active material.

[0176] The thickness of the coating layer is mainly tested by FIB. The specific method may include the following steps: randomly select a single particle from the powder of the first positive electrode active material to be tested, cut a thin slice with a thickness of about 100 nm from the middle position or near the middle position of the selected particle, and then perform TEM test on the thin slice to measure the thickness of the coating layer. Measure 3-5 positions and take the average value.

[0177] In some embodiments, the manganese content in the first positive electrode active material is in the range of 10%-35% by weight, preferably in the range of 15%-30% by weight, and more preferably in the range of 17%-20% by weight, based on the weight of the first positive electrode active material.

[0178] In this application, when only the core of the first positive electrode active material contains manganese, the manganese content can correspond to the content of the core.

[0179] In the first positive electrode active material with a core-shell structure of this application, the content of manganese element is within the above-mentioned range, which can effectively improve the structural stability and density of the material, thereby improving the cycle, storage and compaction density performance of the secondary battery; and can also improve the voltage platform, thereby improving the energy density of the secondary battery.

[0180] In some embodiments, the phosphorus content in the first positive electrode active material is in the range of 12% to 25% by weight, and optionally in the range of 15% to 20% by weight, based on the weight of the first positive electrode active material.

[0181] In the first positive electrode active material with a core-shell structure of this application, the phosphorus content is within the above-mentioned range, which can improve the electrical conductivity of the material and at the same time improve the stability of the pyrophosphate lattice structure in the core, the first coating layer and / or the phosphate lattice structure in the second coating layer, thereby improving the overall stability of the material.

[0182] In some embodiments, the weight ratio of manganese to phosphorus in the first positive electrode active material ranges from 0.90 to 1.25, and can be selected as 0.95 to 1.20, based on the weight of the first positive electrode active material.

[0183] In the first positive electrode active material with a core-shell structure of this application, the weight ratio of manganese to phosphorus is within the above-mentioned range, which can effectively suppress the dissolution of transition metals, improve the stability of the material and the cycle and storage performance of the secondary battery; at the same time, it can improve the discharge voltage platform of the material, thereby improving the energy density of the secondary battery.

[0184] The measurement of manganese and phosphorus can be performed using conventional techniques in the field. In particular, the content of manganese and phosphorus is determined by the following method: the material is dissolved in dilute hydrochloric acid (concentration 10-30%), the content of each element in the solution is tested by ICP, and then the content of manganese is measured and converted to obtain its weight percentage.

[0185] In some embodiments, the lattice change rate of the first positive electrode active material before and after complete lithium insertion / extraction is less than or equal to 4%, optionally less than or equal to 3.8%, and more preferably 2.0%-3.8%.

[0186] The lithium insertion / extraction process of lithium manganese phosphate (LiMnPO4) is a two-phase reaction. The interfacial stress between the two phases is determined by the rate of lattice change before and after lithium insertion / extraction; 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. + The first positive electrode active material of this application, with a core-shell structure, achieves a lattice change rate of less than 4% before and after lithium insertion / extraction, thus improving the rate performance of the secondary battery. The lattice change rate can be measured using methods known in the art, such as X-ray diffraction (XRD).

[0187] In some embodiments, the Li / Mn antisite defect concentration of the first positive electrode active material is less than or equal to 4%, optionally less than or equal to 2.2%, and more preferably 1.5%-2.2%.

[0188] The Li / Mn inversion defect in this application refers to the Li / Mn inversion defect in the LiMnPO4 lattice. + With Mn 2+The positions of the Li and Mn antisite defects have been interchanged. Accordingly, the Li / Mn antisite defect concentration refers to the concentration relative to Mn. 2+ Interchangeable Li + Zhan Li + Percentage of the total amount. In this application, the concentration of Li / Mn antisite defects can be tested, for example, according to JIS K 0131-1996.

[0189] The first positive electrode active material with a core-shell structure of this application can achieve the aforementioned low Li / Mn antisite defect concentration. Although the mechanism is not yet fully understood, the inventors of this application speculate that due to the presence of Li in the LiMnPO4 lattice... + With Mn 2+ The positions will be swapped, and Li + The transmission channel is a one-dimensional channel, therefore Mn 2+ In Li + Migration will be difficult within the channel, thus hindering Li + The transport of Mn. Therefore, the first positive electrode active material with a core-shell structure of this application, due to its low Li / Mn antisite defect concentration within the aforementioned range, can reduce Mn transport. 2+ Hinder Li + This improves the transport efficiency and enhances the specific capacity and rate performance of the first positive electrode active material.

[0190] In some embodiments, the compaction density of the first positive electrode active material at 3T is greater than or equal to 2.2 g / cm³. 3 The value can be greater than or equal to 2.2 g / cm³. 3 And less than or equal to 2.8 g / cm 3 The higher the compaction density, the greater the weight of active material per unit volume. Therefore, increasing the compaction density is beneficial for improving the volumetric energy density of the battery cell. Compaction density can be measured according to GB / T24533-2009.

[0191] In some embodiments, the surface oxygen valence state of the first positive electrode active material is less than or equal to -1.90, and can be selected as -1.98 to -1.90.

[0192] Oxygen's stable valence state is -2. The closer the valence state is to -2, the stronger its ability to gain electrons, i.e., the stronger its oxidizing power. Under normal circumstances, its surface valence state is below -1.7. This application, by limiting the surface oxygen valence state of the first positive electrode active material within the above-mentioned range, can reduce the interfacial side reactions between the first positive electrode material and the electrolyte, thereby improving the cell's cycle life, high-temperature storage gas generation, and other performance characteristics.

[0193] The surface oxygen valence state can be measured by methods known in the art, such as by electron energy loss spectroscopy (EELS).

[0194] In some embodiments, the combined mass of the first and second positive electrode active materials accounts for 88%-98.7% of the mass of the positive electrode sheet. This further ensures that the secondary battery has excellent rate performance, kinetic performance, cycle performance, and low-temperature performance, and has a high energy density.

[0195] In some embodiments, the average particle size of the primary particles of the first positive electrode active material ranges from 50 to 500 nm, and the volume median particle size (Dv50) is in the range of 200 to 300 nm. Since particle agglomeration can occur, the actual measured size of the agglomerated secondary particles may be 500 to 40,000 nm. The size of the primary positive electrode active material particles affects the material processing and the compaction density performance of the electrode sheet. By selecting an average particle size within the above range, the following issues can be reduced: a small average particle size of the primary particles of the first positive electrode active material may cause particle agglomeration, making dispersion difficult and requiring more binder, resulting in poor electrode sheet brittleness; a large average particle size of the primary particles of the first positive electrode active material may result in larger interparticle voids and reduced compaction density.

[0196] The above scheme can effectively suppress the lattice change rate of lithium manganese phosphate and the dissolution of Mn during the lithium insertion / extraction process, thereby improving the high-temperature cycle stability and high-temperature storage performance of secondary batteries.

[0197] In this application, the median particle size Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for the material. In this application, the median particle size Dv50 of the material can be determined using laser diffraction particle size analysis. For example, it can be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000) in accordance with standard GB / T19077-2016.

[0198] By controlling the process (e.g., thoroughly mixing and grinding materials from various sources), it is possible to ensure that each element is uniformly distributed in the crystal lattice and that no aggregation occurs. The main characteristic peak positions in the XRD pattern of lithium manganese phosphate doped with A and R elements are consistent with those of undoped LiMnPO4, indicating that no impurity phase was introduced during the doping process. Therefore, the improvement in core performance mainly comes from elemental doping, rather than impurity phases. After preparing the first positive electrode active material, the inventors of this application used focused ion beam (FIB) to cut the middle region of the prepared first positive electrode active material particles. Tests conducted using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) revealed that the elements were uniformly distributed and no aggregation occurred.

[0199] 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.).

[0200] In some embodiments, the positive electrode film may also include other positive electrode active materials known in the art for use in batteries. As an example, the positive electrode active material may include at least one of the following: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, at least one of lithium nickel oxides (such as LiNiO2), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and their modified compounds. Examples of lithium-containing phosphates with an olivine structure include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0201] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0202] 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.

[0203] The preparation method of the first positive electrode active material includes the following steps:

[0204] The steps for providing the core material: The core chemical formula is Li 1+x Mn 1-y A y P 1-z R zO4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be one or more elements selected from Fe, Ti, V, Ni, Co and Mg, and R is one or more elements selected from B, Si, N and S, and optionally, R is one element selected from B, Si, N and S;

[0205] Coating steps: Provide Li separately a MP2O7 and / or M b (P2O7) c and X n A PO4 suspension is prepared by adding the core material to the suspension and mixing, followed by sintering to obtain the first positive electrode active material. Here, 'a' is selected from any value in the range of 0 to 2, 'b' is selected from any value in the range of 1 to 4, and 'c' is selected from any value in the range of 1 to 6. The values ​​of 'a', 'b', and 'c' satisfy the following condition: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] a MP2O7 or M b (P2O7) c Maintaining electrical neutrality; M is each independently selected from one or more elements chosen from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al; n is greater than 0 and less than or equal to 3; X is selected from one or more elements chosen from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al;

[0206] The first positive electrode active material has a core-shell structure, comprising a core, a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer. The first coating layer comprises crystalline pyrophosphate Li. a MP2O7 and / or M b (P2O7) c The second coating layer includes crystalline phosphate X. n PO4, with carbon as the third coating layer.

[0207] In some implementations, the step of providing the core material includes the following steps:

[0208] Step (1): Mix and stir the manganese source, dopant of element A and acid in a container to obtain manganese salt particles doped with element A;

[0209] Step (2): Manganese salt particles doped with element A are mixed with lithium source, phosphorus source and dopant element R in a solvent to obtain a slurry. After sintering under an inert gas atmosphere, a core doped with elements A and R is obtained, wherein the core doped with elements A and R is Li. 1+x Mn 1-y A y P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from 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 elements selected from Fe, Ti, V, Ni, Co and Mg, R includes one or more elements selected from B, Si, N and S, and optionally, R includes one element selected from B, Si, N and S.

[0210] The preparation method of this application does not have any particular restrictions on the source of materials. The source of a certain element may include one or more of the element's elemental form, sulfate, halide, nitrate, organic acid salt, oxide or hydroxide. The precursor is from this source to achieve the purpose of the preparation method of this application.

[0211] In some embodiments, in the step of providing the core material, the dopant of element A includes one or more of the following elements: elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide.

[0212] In some embodiments, during the step of providing the core material, the dopant of element R includes one or more of the following: inorganic acid, flavonoid, organic acid, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide of each of the elements B, Si, N, and S.

[0213] In some embodiments, during the step of providing the core material, the manganese source may be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the manganese source may be one or more selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0214] In some embodiments, during the step of providing the core material, the acid may be one or more organic acids selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, silicic acid, silicate acid, siliceous acid, and organic acids such as oxalic acid. In some embodiments, the acid is a dilute organic acid with a concentration of less than 60% by weight.

[0215] In some embodiments, during the step of providing the core material, the lithium source may be a lithium-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the lithium source may be one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0216] In some embodiments, during the step of providing the core material, the phosphorus source may be a phosphorus-containing substance known in the art for use in the preparation of lithium manganese phosphate. As an example, the phosphorus source may be one or more selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0217] In some embodiments, in the step of providing the core material, after reacting a manganese source, a dopant of element A, and an acid in a solvent to obtain a suspension of manganese salt doped with element A, the suspension is filtered, dried, and milled to obtain manganese salt particles doped with element A with a particle size of 50-200 nm.

[0218] In some embodiments, in the step of providing the core material, the slurry in step (2) is dried to obtain powder, and then the powder is sintered to obtain a core doped with element A and element R.

[0219] In some embodiments, step (1) is performed at a temperature of 20-120°C, optionally 40-120°C; and / or

[0220] In step (1), stirring is carried out at 400-700 rpm for 1-9 hours, or optionally 3-7 hours.

[0221] Optionally, the reaction temperature in step (1) can be about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C or about 120°C; the stirring in step (1) can be carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours or about 9 hours; optionally, the reaction temperature and stirring time in step (1) can be within any range of the above values.

[0222] In some embodiments, step (2) is carried out at a temperature of 20-120°C, optionally 40-120°C, for 1-12 hours. Optionally, the reaction temperature in step (2) can be carried out at about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C, or about 120°C; the mixing in step (2) can be carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, about 11 hours, or about 12 hours; optionally, the reaction temperature and mixing time in step (2) can be within any range of the above values.

[0223] When the temperature and time during the core particle preparation process are within the above range, the obtained core and the positive electrode active material made from it have fewer lattice defects, which is beneficial to suppress manganese dissolution, reduce interfacial side reactions between the positive electrode active material and the electrolyte, and thus improve the cycle performance and safety performance of the secondary battery.

[0224] In some embodiments, during the step of providing the core material, in the process of preparing dilute manganese acid particles doped with elements A and R, the pH of the solution is controlled to be 3.5-6, optionally, the pH of the solution is controlled to be 4-6, and more preferably, the pH of the solution is controlled to be 4-5. It should be noted that in this application, the pH of the resulting mixture can be adjusted by methods commonly used in the art, for example, by adding an acid or a base.

[0225] In some embodiments, in step (2), the molar ratio of manganese salt particles to lithium source and phosphorus source is 1:0.5-2.1:0.5-2.1. Optionally, the molar ratio of manganese salt particles doped with element A to lithium source and phosphorus source is about 1:1:1.

[0226] In some embodiments, during the step of providing the core material, the sintering conditions in the preparation of A- and R-doped lithium manganese phosphate are as follows: sintering at 600-950°C for 4-10 hours in an inert gas or a mixture of inert gas and hydrogen; optionally, sintering can be performed at approximately 650°C, approximately 700°C, approximately 750°C, approximately 800°C, approximately 850°C, or approximately 900°C for approximately 2 hours, approximately 3 hours, approximately 4 hours, approximately 5 hours, approximately 6 hours, approximately 7 hours, approximately 8 hours, approximately 9 hours, or approximately 10 hours; optionally, the sintering temperature and sintering time can be within any range of the above values. In the preparation of lithium manganese phosphate doped with elements A and R, if the sintering temperature is too low or the sintering time is too short, the crystallinity of the material core will be low, which will affect the overall performance. If the sintering temperature is too high, impurity phases are likely to appear in the material core, which will also affect the overall performance. If the sintering time is too long, the material core particles will be too large, which will affect the specific capacity, compaction density and rate performance.

[0227] In some embodiments, during the step of providing the core material, the protective atmosphere is a mixture of 70-90 vol% nitrogen and 10-30 vol% hydrogen.

[0228] In some implementations, the coating step includes:

[0229] First coating step: Dissolve the source of element M, phosphorus source, acid, and optionally lithium source in a solvent to obtain a first coating layer suspension; thoroughly mix the core obtained in the core step with the first coating layer suspension obtained in the first coating step, dry, and then sinter to obtain the material coated by the first coating layer.

[0230] Second coating step: Dissolve the source of element X, phosphorus source and acid in solvent to obtain a second coating layer suspension; mix the material coated by the first coating layer obtained in the first coating step with the second coating layer suspension obtained in the second coating step, dry, and then sinter to obtain a material coated by two coating layers.

[0231] The third coating step: Dissolve the carbon source in a solvent to obtain a third coating layer solution; then add the material coated by the two coating layers obtained in the second coating step to the third coating layer solution, mix evenly, dry, and then sinter to obtain a material coated by the three coating layers, i.e., the positive electrode active material.

[0232] In some embodiments, during the coating step, the source of element M includes one or more of the following: elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide, selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al.

[0233] In some embodiments, during the coating step, the source of element X includes one or more of the following: elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al.

[0234] The amount of each source added for elements A, R, M, and X depends on the target doping amount, and the ratio of the amount of lithium source, manganese source, and phosphorus source used conforms to the stoichiometric ratio.

[0235] As an example, carbon sources include one or more of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0236] In some embodiments, in the first coating step, the pH of the solution containing the source of element M, the phosphorus source, and the acid, and optionally the lithium source, is controlled to be 3.5-6.5, then stirred and reacted for 1-5 hours, then the solution is heated to 50-120°C and held at that temperature for 2-10 hours, and / or sintering is carried out at 650-800°C for 2-6 hours.

[0237] In some embodiments, the reaction proceeds fully in the first coating step. Optionally, the reaction proceeds for approximately 1.5 hours, approximately 2 hours, approximately 3 hours, approximately 4 hours, approximately 4.5 hours, or approximately 5 hours in the first coating step. Optionally, the reaction time in the first coating step can be within any range of the above-mentioned values.

[0238] In some embodiments, the solution pH is controlled to be 4-6 during the first coating step. Optionally, during the first coating step, the solution is heated to approximately 55°C, approximately 60°C, approximately 70°C, approximately 80°C, approximately 90°C, approximately 100°C, approximately 110°C, or approximately 120°C, and held at this temperature for approximately 2 hours, approximately 3 hours, approximately 4 hours, approximately 5 hours, approximately 6 hours, approximately 7 hours, approximately 8 hours, approximately 9 hours, or approximately 10 hours; optionally, the temperature and holding time during the first coating step can be within any range of the above values.

[0239] In some embodiments, during the first coating step, sintering may be performed at about 650°C, about 700°C, about 750°C, or about 800°C for about 2 hours, about 3 hours, about 4 hours, about 5 hours, or about 6 hours; alternatively, the sintering temperature and sintering time may be within any range of the above values.

[0240] In the first coating step, by controlling the sintering temperature and time within the above ranges, the following situations can be avoided: If the sintering temperature is too low and the sintering time is too short in the first coating step, the crystallinity of the first coating layer will be low, with a large amount of amorphous material. This will reduce the effect of inhibiting metal dissolution, thus affecting the cycle performance and high-temperature storage performance of the secondary battery. Conversely, if the sintering temperature is too high, impurities will appear in the first coating layer, also affecting its effect of inhibiting metal dissolution, thus affecting the cycle performance and high-temperature storage performance of the secondary battery. If the sintering time is too long, the thickness of the first coating layer will increase, affecting the Li... + The migration of these molecules affects the material's specific capacity and rate performance.

[0241] In some embodiments, in the second coating step, the source of element X, the phosphorus source and the acid are dissolved in a solvent, stirred and reacted for 1-10 hours, then the solution is heated to 60-150°C and held at that temperature for 2-10 hours, and / or sintering is carried out at 500-700°C for 6-10 hours.

[0242] Optionally, in the second coating step, the reaction proceeds fully. Optionally, in the second coating step, the reaction proceeds for approximately 1.5 hours, approximately 2 hours, approximately 3 hours, approximately 4 hours, approximately 4.5 hours, approximately 5 hours, approximately 6 hours, approximately 7 hours, approximately 8 hours, approximately 9 hours, or approximately 10 hours. Optionally, in the second coating step, the reaction time can be within any range of the above values.

[0243] Optionally, in the second coating step, the solution is heated to approximately 65°C, approximately 70°C, approximately 80°C, approximately 90°C, approximately 100°C, approximately 110°C, approximately 120°C, approximately 130°C, approximately 140°C, or approximately 150°C, and held at that temperature for approximately 2 hours, approximately 3 hours, approximately 4 hours, approximately 5 hours, approximately 6 hours, approximately 7 hours, approximately 8 hours, approximately 9 hours, or approximately 10 hours; optionally, in the second coating step, the heating temperature and holding time can be within any range of the above values.

[0244] In the steps of providing the core material and the first coating step and the second coating step, before sintering, that is, in the preparation of the core material in which the chemical reaction occurs (steps (1)-(2)) and in the preparation of the first coating layer suspension and the second coating layer suspension, by selecting appropriate reaction temperature and reaction time as described above, the following situations can be avoided: when the reaction temperature is too low, the reaction cannot occur or the reaction rate is slow; when the temperature is too high, the product decomposes or forms an impurity phase; when the reaction time is too long, the product particle size is large, which may increase the time and difficulty of subsequent processes; when the reaction time is too short, the reaction is incomplete and less product is obtained.

[0245] Optionally, in the second coating step, sintering can be performed at about 550°C, about 600°C, or about 700°C for about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; alternatively, the sintering temperature and sintering time can be within any range of the above values.

[0246] In the second coating step, by controlling the sintering temperature and time within the above range, the following situations can be avoided: When the sintering temperature in the second coating step is too low and the sintering time is too short, the crystallinity of the second coating layer will be low, with more amorphous phases, reducing the performance of the material surface reactivity and thus affecting the cycle and high-temperature storage performance of the secondary battery; when the sintering temperature is too high, impurity phases will appear in the second coating layer, which will also affect its effect of reducing the material surface reactivity and thus affect the cycle and high-temperature storage performance of the secondary battery; when the sintering time is too long, the thickness of the second coating layer will increase, affecting the voltage plateau of the material and thus reducing the energy density of the material.

[0247] In some embodiments, the sintering in the third coating step is carried out at 700-800°C for 6-10 hours. Optionally, in the third coating step, the sintering can be carried out at about 700°C, about 750°C, or about 800°C for about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; alternatively, the sintering temperature and sintering time can be within any range of the above values.

[0248] In the third coating step, by controlling the sintering temperature and time within the above range, the following situations can be avoided: If the sintering temperature in the third coating step is too low, the graphitization degree of the third coating layer will decrease, affecting its conductivity and thus the specific capacity of the material; if the sintering temperature is too high, the graphitization degree of the third coating layer will be too high, affecting the Li... + The transmission of electrical conductivity can affect the specific capacity of the material. If the sintering time is too short, the coating layer will be too thin, affecting its conductivity and thus the specific capacity of the material. If the sintering time is too long, the coating layer will be too thick, affecting the compaction density of the material.

[0249] In the first, second, and third coating steps described above, the drying is carried out at a temperature of 100°C to 200°C, optionally 110°C to 190°C, more preferably 120°C to 180°C, even more preferably 120°C to 170°C, and most preferably 120°C to 160°C. The drying time is 3-9 hours, optionally 4-8 hours, more preferably 5-7 hours, and most preferably about 6 hours.

[0250] The first positive electrode active material prepared by the method described in this application results in a reduced dissolution of Mn and Mn-site dopant elements in the secondary battery after cycling, and improved high-temperature stability, high-temperature cycling performance, and rate performance. Furthermore, the raw materials are widely available, inexpensive, and the process is simple, facilitating industrialization.

[0251] [Negative electrode plate]

[0252] 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.

[0253] 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.

[0254] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0255] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0256] In some embodiments, the negative electrode film layer may optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0257] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0258] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0259] 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.

[0260] [Electrolytes]

[0261] 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.

[0262] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0263] 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.

[0264] 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.

[0265] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0266] [Isolation membrane]

[0267] 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.

[0268] 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.

[0269] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0270] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0271] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0272] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0273] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0274] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0275] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0276] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0277] 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.

[0278] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0279] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0280] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0281] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0282] [Preparation Example]

[0283] The following describes preparation examples of this application. The preparation examples 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 preparation examples, they should be performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0284] The raw materials used in the preparation examples of this application are sourced from the following sources:

[0285]

[0286]

[0287] Preparation of positive electrode active materials and their slurries

[0288] Preparation Example 1

[0289] Step S1: Preparation of Fe, Co, V and S co-doped manganese oxalate

[0290] 689.6 g of manganese carbonate, 455.27 g of ferrous carbonate, 4.65 g of cobalt sulfate, and 4.87 g of vanadium dichloride were added to a mixer and mixed thoroughly for 6 hours. The resulting mixture was then transferred to a reaction vessel, and 5 L of deionized water and 1260.6 g of oxalic acid dihydrate were added. The mixture was heated to 80°C and stirred thoroughly at 500 rpm for 6 hours until homogeneous mixing and the reaction was terminated without bubble formation, yielding a Fe, Co, and V co-doped manganese oxalate suspension. The suspension was then filtered, dried at 120°C, and milled to obtain manganese oxalate particles with a particle size of 100 nm.

[0291] Step S2: Preparation of core Li 0.997 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.997 S 0.003 O4

[0292] Take 1793.1g of manganese oxalate, 368.3g of lithium carbonate, 1146.6g of ammonium dihydrogen phosphate, and 4.9g of dilute sulfuric acid prepared in (1), add them to 20L of deionized water, stir thoroughly, and react uniformly at 80℃ for 10h to obtain a slurry. Transfer the slurry to a spray drying equipment for spray drying and granulation, and dry at 250℃ to obtain a powder. In a protective atmosphere (90% nitrogen and 10% hydrogen), sinter the powder in a roller kiln at 700℃ for 4h to obtain the core material. The elemental content of the core material is detected by inductively coupled plasma atomic emission spectrometry (ICP), and the core chemical formula is as shown above.

[0293] Step S3: Preparation of the first coating layer suspension

[0294] Preparation of Li2FeP2O7 solution: 7.4g lithium carbonate, 11.6g ferrous carbonate, 23.0g ammonium dihydrogen phosphate and 12.6g oxalic acid dihydrate were dissolved in 500mL deionized water, and the pH was controlled at 5. The mixture was then stirred and reacted at room temperature for 2h to obtain a solution. The solution was then heated to 80℃ and maintained at this temperature for 4h to obtain the first coating layer suspension.

[0295] Step S4: Coating with the first coating layer

[0296] The 1571.9g of doped lithium manganese phosphate core material obtained in step S2 was added to the first coating layer suspension (coating material content of 15.7g) obtained in step S3. The mixture was stirred and mixed thoroughly for 6 hours. After being mixed evenly, the mixture was dried in an oven at 120℃ for 6 hours and then sintered at 650℃ for 6 hours to obtain the pyrophosphate coated material.

[0297] Step S5: Preparation of the second coating layer suspension

[0298] 3.7 g lithium carbonate, 11.6 g ferrous carbonate, 11.5 g ammonium dihydrogen phosphate and 12.6 g oxalic acid dihydrate were dissolved in 1500 mL deionized water, stirred and reacted for 6 h to obtain a solution. The solution was then heated to 120 °C and maintained at this temperature for 6 h to obtain a second coating layer suspension.

[0299] Step S6: Coating with the second coating layer

[0300] The 1586.8g of pyrophosphate-coated material obtained in step S4 was added to the second coating suspension (coating material content of 47.1g) obtained in step S5. The mixture was stirred and mixed thoroughly for 6 hours. After mixing evenly, the mixture was dried in an oven at 120℃ for 6 hours and then sintered at 700℃ for 8 hours to obtain the two-layer coated material.

[0301] Step S7: Preparation of the third coating layer aqueous solution

[0302] Dissolve 37.3g of sucrose in 500g of deionized water, then stir and dissolve completely to obtain a sucrose aqueous solution.

[0303] Step S8: Coating with the third coating layer

[0304] 1633.9g of the two-layer coated material obtained in step S6 was added to the sucrose solution obtained in step S7 and stirred together for 6 hours. After mixing evenly, the mixture was placed in an oven at 150°C and dried for 6 hours. Then, it was sintered at 700°C for 10 hours to obtain the three-layer coated material.

[0305] Preparation Examples 2 to 42 and Comparative Examples 1 to 17

[0306] The positive electrode active materials of Preparation Examples 2 to 42 and Comparative Examples 1 to 17 were prepared by a method similar to that of Preparation Example 1. The differences in the preparation of the positive electrode active materials are shown in Tables 1-6.

[0307] Among them, Comparative Examples 1-2, 4-10 and 12 do not cover the first layer, so there are no steps S3-S4; Comparative Examples 1-11 do not cover the second layer, so there are no steps S5-S6.

[0308]

[0309]

[0310]

[0311]

[0312]

[0313]

[0314]

[0315]

[0316]

[0317]

[0318]

[0319]

[0320]

[0321]

[0322]

[0323] Preparation Example 43

[0324] Lithium manganese oxide (LiMn2O4) is used as the positive electrode active material.

[0325] Preparation Example 44

[0326] The positive electrode active materials of Preparation Example 1 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0327] Preparation Example 45

[0328] The positive electrode active materials of Preparation Example 2 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0329] Preparation Example 46

[0330] The positive electrode active materials of Preparation Example 3 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0331] Preparation Example 47

[0332] The positive electrode active materials of Preparation Example 4 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0333] Preparation Example 48

[0334] The positive electrode active materials of Preparation Example 5 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0335] Preparation Example 49

[0336] The positive electrode active materials of Preparation Example 6 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0337] Preparation Example 50

[0338] The positive electrode active materials of Preparation Example 7 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0339] Preparation Example 51

[0340] The positive electrode active materials of Preparation Example 8 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0341] Preparation Example 52

[0342] The positive electrode active materials of Preparation Example 9 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0343] Preparation Example 53

[0344] The positive electrode active materials of Preparation Example 10 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0345] Preparation Example 54

[0346] The positive electrode active materials of Preparation Example 11 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0347] Preparation Example 55

[0348] The positive electrode active materials of Preparation Example 12 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0349] Preparation Example 56

[0350] The positive electrode active materials of Preparation Example 13 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0351] Preparation Example 57

[0352] The positive electrode active materials of Preparation Example 14 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0353] Preparation Example 58

[0354] The positive electrode active materials of Preparation Example 15 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0355] Preparation Example 59

[0356] The positive electrode active materials of Preparation Example 16 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0357] Preparation Example 60

[0358] The positive electrode active materials of Preparation Example 17 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0359] Preparation Example 61

[0360] The positive electrode active materials of Preparation Example 18 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0361] Preparation Example 62

[0362] The positive electrode active materials of Preparation Example 19 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0363] Preparation Example 63

[0364] The positive electrode active materials of Preparation Example 20 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0365] Preparation Example 64

[0366] The positive electrode active materials of Preparation Example 21 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0367] Preparation Example 65

[0368] The positive electrode active materials of Preparation Example 22 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0369] Preparation Example 66

[0370] The positive electrode active materials of Preparation Example 23 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0371] Preparation Example 67

[0372] The positive electrode active materials of Preparation Example 24 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0373] Preparation Example 68

[0374] The positive electrode active materials of Preparation Example 25 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0375] Preparation Example 69

[0376] The positive electrode active materials of Preparation Example 26 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0377] Preparation Example 70

[0378] The positive electrode active materials of Preparation Example 27 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0379] Preparation Example 71

[0380] The positive electrode active materials of Preparation Example 28 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0381] Preparation Example 72

[0382] The positive electrode active materials of Preparation Example 29 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0383] Preparation Examples 73 to 85

[0384] The positive electrode active materials of Preparation Examples 73 to 85 were prepared using a method similar to that of Preparation Example 1. The differences in the preparation of the positive electrode active materials are shown in Tables 7-8.

[0385] Table 7: Investigation of the first coating layer material (Preparation Examples 73-79)

[0386]

[0387] Table 8: Investigation of the second coating layer material (Preparation Examples 80-85)

[0388]

[0389]

[0390] Comparative Example 18

[0391] The positive electrode active materials of Comparative Example 1 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0392] Comparative Example 19

[0393] The positive electrode active materials of Comparative Example 2 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0394] Comparative Example 20

[0395] The positive electrode active materials of Comparative Example 3 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0396] Comparative Example 21

[0397] The positive electrode active materials of Comparative Example 4 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0398] Comparative Example 22

[0399] The positive electrode active materials of Comparative Example 5 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0400] Comparative Example 23

[0401] The positive electrode active materials of Comparative Example 6 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0402] Comparative Example 24

[0403] The positive electrode active materials of Comparative Example 7 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0404] Comparative Example 25

[0405] The positive electrode active materials of Comparative Example 8 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0406] Comparative Example 26

[0407] The positive electrode active materials of Comparative Example 9 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0408] Comparative Example 27

[0409] The positive electrode active materials of Comparative Example 10 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0410] Comparative Example 28

[0411] The positive electrode active materials of Comparative Example 12 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0412] Comparative Example 29

[0413] The positive electrode active materials of Comparative Example 13 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0414] Comparative Example 30

[0415] The positive electrode active materials of Comparative Example 14 and Preparation Example 43 were mixed at a mass ratio of 1:1.

[0416] The above-prepared positive electrode active material, conductive agent superconducting carbon black (Super-P), and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) in a weight ratio of 92:2.5:5.5 and stirred until uniformly mixed to obtain a slurry of positive electrode active material with a solid content of 60% w / w.

[0417] Preparation of positive electrode sheet

[0418] Example 1

[0419] The slurry for preparing the positive electrode active material in Example 1 was prepared at a concentration of 0.019 g / cm³. 2 The coating is evenly applied to both sides of the current collector aluminum foil, vacuum dried at a high temperature of 100-120℃ for 14 hours, and then compacted by a roller press to obtain the positive electrode P1.

[0420] Example 2

[0421] The slurry for preparing the positive electrode active material in Example 43 was prepared at a concentration of 0.019 g / cm³. 2 The coating is evenly applied to both sides of the current collector aluminum foil, and then vacuum dried at a high temperature of 100-120℃ for 14 hours. The foil is then compacted by a roller press to obtain the positive electrode P2.

[0422] Example 3

[0423] The slurry for preparing the positive electrode active material in Example 1 was prepared at a concentration of 0.019 g / cm³. 2The coating amount is uniformly coated on one side of the aluminum foil. The slurry for preparing the positive electrode active material in Example 43 is applied at a rate of 0.2 g / cm³. 2 The coating is evenly applied to the other side of the aluminum foil, and then vacuum dried at a high temperature of 100-120℃ for 14 hours. The foil is then compacted by a roller press to obtain the positive electrode P3.

[0424] Example 4

[0425] The slurry for preparing the positive electrode active material in Example 44 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount is evenly applied to both sides of the current collector aluminum foil, and the rest is the same as in Example 3, to obtain the positive electrode P4.

[0426] Example 5

[0427] The slurry for preparing the positive electrode active material in Example 1 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount was uniformly coated on one side of the aluminum foil, and the slurry for preparing the positive electrode active material in Example 44 was applied at a rate of 0.019 g / cm³. 2 The coating amount is evenly coated on the other side of the aluminum foil, and the rest is the same as in Example 3, to obtain the positive electrode P5.

[0428] Example 6

[0429] The slurry for preparing the positive electrode active material in Example 43 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount was uniformly coated on one side of the aluminum foil, and the slurry for preparing the positive electrode active material in Example 44 was applied at a rate of 0.019 g / cm³. 2 The coating amount is evenly coated on the other side of the aluminum foil, and the rest is the same as in Example 3, to obtain the positive electrode P6.

[0430] Example 7

[0431] The slurry for preparing the positive electrode active material of Example 1 and the slurry for preparing the positive electrode active material of Example 43 were sequentially coated on both sides of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 Then, it is dried in a high temperature vacuum at 100-120℃ for 14 hours, and then compacted by a roller press to obtain the positive electrode P7.

[0432] Example 8

[0433] The slurry for preparing the positive electrode active material of Example 43 and the slurry for preparing the positive electrode active material of Example 1 were sequentially coated on both sides of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 The rest is the same as in Example 7, and the positive electrode P8 is obtained.

[0434] Example 9

[0435] The slurry for preparing the positive electrode active material of Example 1 and the slurry for preparing the positive electrode active material of Example 44 were sequentially coated on both sides of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 The rest is the same as in Example 7, and the positive electrode P9 is obtained.

[0436] Example 10

[0437] The slurry for preparing the positive electrode active material of Example 44 and the slurry for preparing the positive electrode active material of Example 1 were sequentially coated on both sides of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 The rest is the same as in Example 7, and the positive electrode P10 is obtained.

[0438] Example 11

[0439] The slurry for preparing the positive electrode active material of Example 43 and the slurry for preparing the positive electrode active material of Example 44 were sequentially coated on both sides of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The rest is the same as in Example 7, and the positive electrode P11 is obtained.

[0440] Example 12

[0441] The slurry for preparing the positive electrode active material of Example 44 and the slurry for preparing the positive electrode active material of Example 43 were sequentially coated on both sides of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The rest is the same as in Example 7, and the positive electrode P12 is obtained.

[0442] Example 13

[0443] The slurry for preparing the positive electrode active material of Example 1 and the slurry for preparing the positive electrode active material of Example 43 were sequentially coated on side A of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 A slurry for preparing the positive electrode active material of Example 1 was uniformly coated on side B of an aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 Then, it is dried in a high temperature vacuum at 100-120℃ for 14 hours, and then compacted by a roller press to obtain the positive electrode P13.

[0444] Example 14

[0445] The slurry for preparing the positive electrode active material of Example 1 and the slurry for preparing the positive electrode active material of Example 43 were sequentially coated on side A of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 The slurry for preparing the positive electrode active material of Example 43 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P14 is obtained.

[0446] Example 15

[0447] The slurry for preparing the positive electrode active material of Example 1 and the slurry for preparing the positive electrode active material of Example 43 were sequentially coated on side A of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 The slurry for preparing the positive electrode active material of Example 44 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P15 is obtained.

[0448] Example 16

[0449] The slurry for preparing the positive electrode active material of Example 43 and the slurry for preparing the positive electrode active material of Example 1 were sequentially coated on side A of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 A slurry for preparing the positive electrode active material of Example 1 was uniformly coated on side B of an aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P16 is obtained.

[0450] Example 17

[0451] The slurry for preparing the positive electrode active material of Example 43 and the slurry for preparing the positive electrode active material of Example 1 were sequentially coated on side A of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 The slurry for preparing the positive electrode active material of Example 43 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P17 is obtained.

[0452] Example 18

[0453] The slurry for preparing the positive electrode active material of Example 43 and the slurry for preparing the positive electrode active material of Example 1 were sequentially coated on side A of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 The slurry for preparing the positive electrode active material of Example 44 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P18 is obtained.

[0454] Example 19

[0455] The slurry for preparing the positive electrode active material of Example 1 and the slurry for preparing the positive electrode active material of Example 44 were sequentially coated on side A of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 A slurry for preparing the positive electrode active material of Example 1 was uniformly coated on side B of an aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P19 is obtained.

[0456] Example 20

[0457] The slurry for preparing the positive electrode active material of Example 1 and the slurry for preparing the positive electrode active material of Example 44 were sequentially coated on side A of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 The slurry for preparing the positive electrode active material of Example 43 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P20 is obtained.

[0458] Example 21

[0459] The slurry for preparing the positive electrode active material of Example 1 and the slurry for preparing the positive electrode active material of Example 44 were sequentially coated on side A of the aluminum foil. The coating amount of each slurry layer was 0.010 g / cm³. 2 The slurry for preparing the positive electrode active material of Example 44 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P21 is obtained.

[0460] Example 22

[0461] The slurry for preparing the positive electrode active material of Example 44 and the slurry for preparing the positive electrode active material of Example 1 were sequentially coated on side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 A slurry for preparing the positive electrode active material of Example 1 was uniformly coated on side B of an aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P22 is obtained.

[0462] Example 23

[0463] The slurry for preparing the positive electrode active material of Example 44 and the slurry for preparing the positive electrode active material of Example 1 were sequentially coated on side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry for preparing the positive electrode active material of Example 43 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P23 is obtained.

[0464] Example 24

[0465] The slurry for preparing the positive electrode active material of Example 44 and the slurry for preparing the positive electrode active material of Example 1 were sequentially coated on side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry for preparing the positive electrode active material of Example 44 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2The rest is the same as in Example 13, and the positive electrode P24 is obtained.

[0466] Example 25

[0467] The slurry for preparing the positive electrode active material of Example 43 and the slurry for preparing the positive electrode active material of Example 44 were sequentially coated on side A of the aluminum foil, with a coating weight of 0.010 g / cm³ for each layer of slurry. 2 A slurry for preparing the positive electrode active material of Example 1 was uniformly coated on side B of an aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P25 is obtained.

[0468] Example 26

[0469] The slurry for preparing the positive electrode active material of Example 43 and the slurry for preparing the positive electrode active material of Example 44 were sequentially coated on side A of the aluminum foil, with a coating weight of 0.010 g / cm³ for each layer of slurry. 2 The slurry for preparing the positive electrode active material of Example 43 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P26 is obtained.

[0470] Example 27

[0471] The slurry for preparing the positive electrode active material of Example 43 and the slurry for preparing the positive electrode active material of Example 44 were sequentially coated on side A of the aluminum foil, with a coating weight of 0.010 g / cm³ for each layer of slurry. 2 The slurry for preparing the positive electrode active material of Example 44 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P27 is obtained.

[0472] Example 28

[0473] The slurry for preparing the positive electrode active material of Example 44 and the slurry for preparing the positive electrode active material of Example 43 were sequentially coated on side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 A slurry for preparing the positive electrode active material of Example 1 was uniformly coated on side B of an aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P28 is obtained.

[0474] Example 29

[0475] The slurry for preparing the positive electrode active material of Example 44 and the slurry for preparing the positive electrode active material of Example 43 were sequentially coated on side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2The slurry for preparing the positive electrode active material of Example 43 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P29 is obtained.

[0476] Example 30

[0477] The slurry for preparing the positive electrode active material of Example 44 and the slurry for preparing the positive electrode active material of Example 43 were sequentially coated on side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry for preparing the positive electrode active material of Example 44 was uniformly coated on side B of the aluminum foil. The coating amount of the slurry was 0.020 g / cm³. 2 The rest is the same as in Example 13, and the positive electrode P30 is obtained.

[0478] Example 31

[0479] The slurry of the positive electrode active material in Example 45 was prepared at 0.019 g / cm³. 2 The coating is evenly applied to both sides of the current collector aluminum foil, vacuum dried at a high temperature of 100-120℃ for 14 hours, and then compacted by a roller press to obtain the positive electrode P31.

[0480] Example 32

[0481] The slurry for preparing the positive electrode active material in Example 46 was prepared at a concentration of 0.019 g / cm³. 2 The coating is evenly applied to both sides of the current collector aluminum foil, vacuum dried at a high temperature of 100-120℃ for 14 hours, and then compacted by a roller press to obtain the positive electrode P32.

[0482] Example 33

[0483] The slurry for preparing the positive electrode active material in Example 47 was prepared at a concentration of 0.019 g / cm³. 2 The coating is evenly applied to both sides of the current collector aluminum foil, vacuum dried at a high temperature of 100-120℃ for 14 hours, and then compacted by a roller press to obtain the positive electrode P33.

[0484] Example 34

[0485] The slurry for preparing the positive electrode active material in Example 48 was prepared at a concentration of 0.019 g / cm³. 2 The coating is evenly applied to both sides of the current collector aluminum foil, vacuum dried at a high temperature of 100-120℃ for 14 hours, and then compacted by a roller press to obtain the positive electrode P34.

[0486] Example 35

[0487] The slurry for preparing the positive electrode active material in Example 49 was prepared at a concentration of 0.019 g / cm³. 2The coating is evenly applied to both sides of the current collector aluminum foil, vacuum dried at a high temperature of 100-120℃ for 14 hours, and then compacted by a roller press to obtain the positive electrode P35.

[0488] Example 36

[0489] The slurry of the positive electrode active material in Example 50 was prepared at 0.019 g / cm³. 2 The coating is evenly applied to both sides of the current collector aluminum foil, vacuum dried at a high temperature of 100-120℃ for 14 hours, and then compacted by a roller press to obtain the positive electrode P36.

[0490] Example 37

[0491] The slurry for preparing the positive electrode active material in Example 51 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount is evenly applied to both sides of the current collector aluminum foil, and the rest is the same as in Example 3, to obtain the positive electrode P37.

[0492] Example 38

[0493] The slurry for preparing the positive electrode active material in Example 52 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount is evenly applied to both sides of the current collector aluminum foil, and the rest is the same as in Example 3, to obtain the positive electrode P38.

[0494] Example 39

[0495] The slurry for preparing the positive electrode active material in Example 53 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount is evenly applied to both sides of the current collector aluminum foil, and the rest is the same as in Example 3, to obtain the positive electrode P39.

[0496] Example 40

[0497] The slurry for preparing the positive electrode active material in Example 54 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount is evenly applied to both sides of the current collector aluminum foil, and the rest is the same as in Example 3, to obtain the positive electrode P40.

[0498] Example 41

[0499] The slurry of the positive electrode active material in Example 55 was prepared at 0.019 g / cm³. 2 The coating amount is evenly applied to both sides of the current collector aluminum foil, and the rest is the same as in Example 3, to obtain the positive electrode P41.

[0500] Example 42

[0501] The slurry for preparing the positive electrode active material in Example 56 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount is evenly applied to both sides of the current collector aluminum foil, and the rest is the same as in Example 3, to obtain the positive electrode P42.

[0502] Positive electrode plates P43 to P99 were fabricated according to the method of Example 42, with different parameters shown in Table 9.

[0503] Table 9 Positive electrode parameters

[0504]

[0505]

[0506]

[0507]

[0508]

[0509]

[0510]

[0511] "*": The first layer refers to the layer in contact with the surface of the aluminum foil, and the second layer refers to the layer set on the first layer.

[0512] "#": The first positive electrode active material refers to the positive electrode active material prepared in Preparation Examples 1 to 29, Comparative Examples 1 to 10 and Comparative Examples 12-14.

[0513] Preparation of negative electrode sheet

[0514] Artificial graphite (anode active material), superconducting carbon black (Super-P) (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) were dissolved in deionized water at a mass ratio of 95%:1.5%:1.8%:1.7%. After thorough mixing, a negative electrode slurry with a viscosity of 3000 mPa·s and a solid content of 52% was obtained. The negative electrode slurry was coated onto a 6 μm copper foil for the negative electrode current collector, and then baked at 100℃ for 4 hours to dry it. After rolling, a negative electrode sheet with a compacted density of 1.75 g / cm3 was obtained.

[0515] Separating membrane

[0516] Polypropylene film is used.

[0517] Preparation of electrolyte

[0518] Ethylene carbonate, dimethyl carbonate, and 1,2-propanediol carbonate were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the mixture to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0519] Preparation of full cells

[0520] Using the aforementioned positive electrode sheet, a bare cell is formed by winding the negative electrode sheet, separator, and positive electrode sheet in that order. Aluminum and copper tabs are punched out to obtain the bare cell. Two bare cells are then welded together—one copper tab to the copper tab and the other aluminum tab to the aluminum tab—to the battery top cover using an adapter plate. After insulating the bare cell, it is placed inside an aluminum casing. The top cover is then welded to the aluminum casing to form a dry cell. The dry cell is baked to remove water, then electrolyte is injected. The battery undergoes formation and aging to obtain a complete cell. The battery structure made from positive electrode sheets P1, P2, P3, P8, P10, P11, P12, P17, P18, P23, P24, P26, and P27 is as follows: Figure 8-20 As shown.

[0521] Preparation of button cells

[0522] The positive electrode, negative electrode, and electrolyte are assembled together in a button cell to form a button cell (hereinafter also referred to as "button cell").

[0523] I. Performance Testing of Positive Electrode Active Materials

[0524] 1. Method for testing lattice change rate:

[0525] Under a constant temperature environment of 25℃, the positive electrode active material sample was placed in an XRD (model Bruker D8 Discover) and tested at 1° / min. The test data were then organized and analyzed. Referring to the standard PDF card, the lattice constants a0, b0, c0 and v0 were calculated (a0, b0 and c0 represent the length of 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).

[0526] 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 for testing fresh samples. (v0-v1) / v0×100% was taken as the lattice change rate (cell volume change rate) before and after complete lithium insertion / extraction.

[0527] 2. Determination of Li / Mn antisite defect concentration:

[0528] 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.

[0529] 3. Determination of compacted density:

[0530] Take 5g of the prepared positive electrode active material powder and place it in a compaction mold (CARVER mold, model 13mm). 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) on the instrument. Calculate the compaction density using ρ = m / v. The area value used is the standard small image area of ​​1540.25mm². 2 .

[0531] 4. Determination of the constant current ratio during 3C charging:

[0532] Under a constant temperature of 25℃, the fresh full cells prepared in the above preparation examples and comparative examples were allowed to stand for 5 minutes, then discharged at 1 / 3C to 2.5V. After standing for 5 minutes, they were charged at 1 / 3C 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 standing for 5 minutes, the charging capacity at this point was recorded as C0. After discharging at 1 / 3C to 2.5V, standing for 5 minutes, and then charging at 3C to 4.3V, and standing for 5 minutes, the charging capacity at this point was recorded as C1. The constant current ratio for 3C charging is C1 / C0 × 100%.

[0533] The higher the constant current ratio during 3C charging, the better the rate performance of the secondary battery.

[0534] 5. Dissolution test of transition metal Mn (and Fe doped at Mn sites):

[0535] Full cells made from the positive electrode active materials of the above-mentioned preparation examples and comparative examples, after being cycled at 45°C until their capacity decayed to 80%, were discharged at a rate of 0.1C to a cutoff voltage of 2.0V. The cells were then disassembled, and the negative electrode was removed. Thirty unit areas (1540.25 mm²) were randomly selected from the negative electrode. 2The 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.

[0536] 6. Determination of surface oxygen valence state:

[0537] Take 5g of the positive electrode active material sample prepared above and prepare a button cell according to the above preparation method. Charge the button cell at a low rate of 0.05C until the current decreases to 0.01C. Then, remove the positive electrode sheet from the button cell and soak it in DMC for 8 hours. Then, dry it, scrape off the powder, and screen out particles with a particle size of less than 500nm. Measure the obtained particles 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, calculate the number of occupied electrons by integrating the valence band density of states data, and thus deduce the valence state of the surface oxygen after charging.

[0538] 7. Measurement of manganese and phosphorus elements in positive electrode active materials:

[0539] Dissolve 5g of the prepared positive electrode active material in 100ml of aqua regia (concentrated hydrochloric acid: concentrated nitric acid = 1:3) (concentrated hydrochloric acid concentration ~37%, concentrated nitric acid concentration ~65%). Use ICP to test the content of each element in the solution, and then measure and convert the content of manganese or phosphorus (amount of manganese or phosphorus / amount of positive electrode active material * 100%) to obtain its weight percentage.

[0540] 8. Method for measuring the initial specific capacity of button cells:

[0541] At 2.5-4.3V, the coin cells prepared in the above preparation examples and comparative examples were charged to 4.3V at 0.1C, and then charged at 4.3V at a constant voltage until the current was less than or equal to 0.05mA. After standing for 5 minutes, they were discharged to 2.0V at 0.1C. The discharge capacity at this time is the initial specific capacity, denoted as D0.

[0542] 9. Cell expansion test after 30 days of storage at 60℃:

[0543] Full cells prepared in the above-mentioned preparation examples and comparative examples were stored at 60°C at 100% state of charge (SOC). The open-circuit voltage (OCV) and internal resistance (IMP) of the cells were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. The full cells were removed after every 48 hours of storage, allowed to stand for 1 hour, and then the open-circuit voltage (OCV) and internal resistance (IMP) were measured. After cooling to room temperature, the cell volume was measured using the water displacement method. The water displacement method involved first measuring the cell's weight F1 separately using a balance with automatic unit conversion of dial data, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the experiment, the weight F2 of the battery cell and the buoyancy F of the battery cell are measured at this time. 浮 That is, F1-F2, and then according to Archimedes' principle, F 浮 =ρ×g×V 排 The cell volume V is calculated to be V = (F1 - F2) / (ρ × g).

[0544] 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.

[0545] 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.

[0546] 10. Cyclic performance test of the entire battery at 45°C:

[0547] Under constant temperature conditions of 45℃, the capacitor is charged at 1C to 4.3V within a range of 2.5-4.3V, then charged at a constant voltage of 4.3V until the current is ≤0.05mA. After resting for 5 minutes, it is discharged at 1C to 2.5V. The capacitance is denoted as D. n (n = 0, 1, 2, ...). Repeat the above process until the capacity decays to 80%, and record the number of repetitions at this point. This number of cycles corresponds to 80% capacity retention at 45°C.

[0548] 11. Interplanar spacing and angle test:

[0549] 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).

[0550] 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.

[0551] By comparing the obtained interplanar spacing and corresponding angle data with their standard values, the substances and crystal states of different coating layers can be identified.

[0552] 12. Coating thickness test:

[0553] The thickness of the coating layer was tested by cutting a thin slice of about 100 nm thickness from the middle of a single particle of the positive electrode active material prepared above using FIB. Then, the slice was subjected to TEM testing to obtain the original TEM test image, which was saved in the original image format (xx.dm3).

[0554] Open the original images obtained from the TEM test in DigitalMicrograph software, identify the cladding layer using the lattice spacing and angle information, and measure the thickness of the cladding layer.

[0555] Measure the thickness of the selected particle at three locations and take the average value.

[0556] 13. Determination of the molar ratio of SP2 and SP3 forms in the third coating layer of carbon:

[0557] This test was performed using Raman spectroscopy. By splitting the energy spectrum from the Raman test, the Id / Ig ratio was obtained, where Id is the peak intensity of SP3 carbon and Ig is the peak intensity of SP2 carbon, thus confirming the molar ratio between the two.

[0558] 14. Determination of the core chemical formula and composition of different coating layers:

[0559] High spatial resolution characterization of the internal microstructure and surface structure of the positive electrode active material was performed using spherical aberration electron microscopy (ACSTEM). Combined with three-dimensional reconstruction technology, the core chemical formula and the composition of different coating layers of the positive electrode active material were obtained.

[0560] The performance test results of the positive electrode active materials prepared in the examples and comparative examples are shown in the table below.

[0561]

[0562]

[0563]

[0564]

[0565]

[0566]

[0567]

[0568]

[0569]

[0570]

[0571]

[0572]

[0573]

[0574]

[0575] IV. Battery Testing

[0576] The secondary batteries prepared using positive electrode plates P1-P99 were tested as follows:

[0577] (1) The energy density and furnace temperature of the secondary battery were determined according to the method in GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles";

[0578] (2) Needle penetration test: The secondary battery is fully charged to 100% SOC, and the cell is pierced with a Φ8mm steel needle at a speed of 25mm / 2. Observe for 1 hour. If no fire occurs, the test is passed.

[0579] (3) The room temperature 1C rate charging capacity retention rate (Vs 0.33C) and the low temperature (-20℃) discharge capacity retention rate of the secondary battery were determined according to the national standard GBT31486-2015 "Electrical performance requirements and test methods for power batteries for electric vehicles" to obtain cell dynamic performance data.

[0580] (4) The cycle life data of the secondary battery were determined in accordance with the national standard GBT31484-2015 "Cycle life requirements and test methods for power batteries for electric vehicles".

[0581] The results are shown in Table 16.

[0582] Table 16 Results of Battery Tests

[0583]

[0584]

[0585]

[0586] Based on the above results, we can conclude that:

[0587] Compared with secondary batteries using positive electrode P1, secondary batteries using positive electrode P3-P30 have higher energy density, higher capacity retention rate at room temperature rate charging, and higher capacity retention rate at low temperature discharge. Furthermore, secondary batteries using positive electrode P3-P30 successfully passed furnace temperature tests and nail penetration tests. Secondary batteries using positive electrode P3-P30 have a longer cycle life than secondary batteries using positive electrode P2.

[0588] Compared with batteries using positive electrode plates P59-P86 that contain only the first positive electrode material, batteries using positive electrode plates P31-P58 that contain both the first and second positive electrode active materials have higher room temperature rate charging capacity retention and low temperature discharge capacity retention; batteries using positive electrode plates P31-P58 have a longer cycle life than batteries using positive electrode plates P2.

[0589] The above demonstrates that the secondary battery made from the positive electrode sheet of this application has higher energy density, higher rate performance, better kinetic performance and low-temperature performance, longer cycle life and higher safety.

[0590] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode sheet, comprising a first positive electrode active material and a second positive electrode active material; The first positive electrode active material includes a core, a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer; the core contains the compound Li. 1+x Mn 1-y A y P 1- z R z O4, the first coating layer contains crystalline pyrophosphate Li a MP2O7 and / or M b (P2O7) c The second coating layer contains crystalline phosphate X n PO4, the third coating layer contains carbon; in, The A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; The R includes one or more elements selected from B, Si, N, and S; The x is any value in the range of -0.100 to 0.100; The value of y is any value in the range of 0.001 to 0.500; The z can be any value in the range of 0.001 to 0.100; The crystalline pyrophosphate Li a MP2O7 and M b (P2O7) c The M in each element independently includes one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al. The value of 'a' can be any value in the range of 0 to 2. b can be any value in the range of 1 to 4; c can be any value in the range of 1 to 6; X includes one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al; The n is greater than 0 and less than or equal to 3; The second positive electrode active material contains lithium manganese oxide.

2. The positive electrode sheet according to claim 1, wherein, The second positive electrode active material includes LiMn2O4.

3. The positive electrode sheet according to claim 1, 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 having a single-layer structure or a multi-layer structure; at least one of the positive electrode film layers having a single-layer structure simultaneously comprising the first positive electrode active material and the second positive electrode active material, and / or, at least one layer of at least one of the positive electrode film layers having a multi-layer structure simultaneously comprising the first positive electrode active material and the second positive electrode active material.

4. The positive electrode sheet according to claim 1, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; at least one of the positive electrode film layers has a multilayer structure, and at least one positive electrode film layer having a multilayer structure comprises the first positive electrode active material and the second positive electrode active material in different layers respectively.

5. The positive electrode sheet according to claim 4, wherein, At least one of the positive electrode film layers having a multilayer structure includes the first positive electrode active material and the second positive electrode active material in adjacent layers, respectively.

6. The positive electrode sheet according to claim 1, comprising a positive current collector and a positive electrode film layer A and a positive electrode film layer B respectively disposed on two surfaces of the positive current collector; the positive electrode film layer A and the positive electrode film layer B each independently have a single-layer structure or a multi-layer structure; at least one layer of the positive electrode film layer A comprises the first positive electrode active material, and at least one layer of the positive electrode film layer B comprises the second positive electrode active material.

7. The positive electrode sheet according to any one of claims 1 to 6, wherein, The mass ratio of the first positive electrode active material to the second positive electrode active material is 1:7 to 7:

1.

8. The positive electrode sheet according to any one of claims 1 to 6, wherein, The mass ratio of the first positive electrode active material to the second positive electrode active material is 1:4 to 4:

1.

9. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, The A includes one or more elements selected from Fe, Ti, V, Ni, Co, and Mg, and / or, The R includes one element selected from B, Si, N, and S, and / or, The ratio of y to 1-y is 1:10 to 1:1, and / or, The ratio of z to 1-z is 1:9 to 1:

999.

10. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, The ratio of y to 1-y is 1:4 to 1:1; and / or, The ratio of z to 1-z is 1:499 to 1:

249.

11. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, the interplanar spacing of the crystalline pyrophosphate in the first coating layer ranges from 0.293 to 0.470 nm, and the included angle of the crystal orientation (111) ranges from 18.00° to 32.00°; and / or, the interplanar spacing of the crystalline phosphate in the second coating layer ranges from 0.244 to 0.425 nm, and the included angle of the crystal orientation (111) ranges from 20.00° to 37.00°.

12. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, the carbon in the third coating layer is a mixture of SP2 carbon and SP3 carbon.

13. The positive electrode sheet according to claim 12, wherein, In the first positive electrode active material, the molar ratio of SP2 carbon to SP3 carbon is any value within the range of 0.1-10.

14. The positive electrode sheet according to claim 12, wherein, In the first positive electrode active material, the molar ratio of SP2 carbon to SP3 carbon is any value within the range of 2.0-3.

0.

15. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, The coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, based on the weight of the core; and / or, The coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, based on the weight of the core; And / or, The coating amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, based on the weight of the core.

16. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, The coating amount of the first coating layer is greater than 0 and less than or equal to 5.5% by weight, based on the weight of the core; and / or, The second coating layer has a coating amount greater than 0 and less than or equal to 5.5% by weight, based on the weight of the core; and / or, The coating amount of the third coating layer is greater than 0 and less than or equal to 5.5% by weight, based on the weight of the core.

17. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, The coating amount of the first coating layer is greater than 0 and less than or equal to 2% by weight, based on the weight of the core; and / or, The second coating layer has a coating amount of 2-4% by weight, based on the weight of the core; And / or, The coating amount of the third coating layer is greater than 0 and less than or equal to 2% by weight, based on the weight of the core.

18. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, The thickness of the first coating layer is 1-10 nm; and / or, The thickness of the second coating layer is 2-15 nm; and / or, The thickness of the third coating layer is 2-25 nm.

19. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, based on the weight of the first positive electrode active material, The manganese content is in the range of 10% to 35% by weight; and / or, The phosphorus content is in the range of 12% to 25% by weight; and / or, The weight ratio of manganese to phosphorus is 0.90-1.

25.

20. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, based on the weight of the first positive electrode active material, The manganese content is in the range of 15%-30% by weight; and / or, The phosphorus content is in the range of 15%-20% by weight; and / or, The weight ratio of manganese to phosphorus is 0.95-1.

20.

21. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, the manganese content is in the range of 17%-20% by weight, based on the weight of the first positive electrode active material.

22. The positive electrode sheet according to any one of claims 1 to 6, wherein, The lattice change rate of the first positive electrode active material before and after complete lithium insertion / extraction is less than or equal to 4%.

23. The positive electrode sheet according to any one of claims 1 to 6, wherein, The lattice change rate of the first positive electrode active material before and after complete lithium insertion / extraction is less than or equal to 3.8%.

24. The positive electrode sheet according to any one of claims 1 to 6, wherein, The lattice change rate of the first positive electrode active material before and after complete lithium insertion / extraction is 2.0%-3.8%.

25. The positive electrode sheet according to any one of claims 1 to 6, wherein, The Li / Mn antisite defect concentration of the first positive electrode active material is less than or equal to 4%; wherein, the Li / Mn antisite defect concentration is related to the Mn... 2+ Interchangeable Li + Zhan Li + Percentage of the total.

26. The positive electrode sheet according to any one of claims 1 to 6, wherein, The Li / Mn antisite defect concentration of the first positive electrode active material is less than or equal to 2.2%; wherein, the Li / Mn antisite defect concentration is related to the Mn... 2+ Interchangeable Li + Zhan Li + Percentage of the total.

27. The positive electrode sheet according to any one of claims 1 to 6, wherein, The Li / Mn antisite defect concentration of the first positive electrode active material is 1.5%-2.2%; wherein, the Li / Mn antisite defect concentration is related to the Mn... 2+ Interchangeable Li + Zhan Li + Percentage of the total.

28. The positive electrode sheet according to any one of claims 1 to 6, wherein, The compaction density of the first positive electrode active material at 3T is greater than or equal to 2.2 g / cm³. 3 .

29. The positive electrode sheet according to any one of claims 1 to 6, wherein, The compaction density of the first positive electrode active material at 3T is greater than or equal to 2.2 g / cm³. 3 And less than or equal to 2.8 g / cm 3 .

30. The positive electrode sheet according to any one of claims 1 to 6, wherein, The surface oxygen valence state of the first positive electrode active material is less than or equal to -1.

90.

31. The positive electrode sheet according to any one of claims 1 to 6, wherein, The surface oxygen valence state of the first positive electrode active material is -1.98 to -1.

90.

32. The positive electrode sheet according to any one of claims 1 to 6, wherein, The sum of the masses of the first positive electrode active material and the second positive electrode active material accounts for 88%-98.7% of the mass of the positive electrode sheet.

33. A battery comprising a positive electrode sheet according to any one of claims 1 to 32.

34. An electrical device comprising the battery of claim 33.

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