A positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electric device

Abstract

This application provides a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device; the positive electrode sheet includes a positive current collector and a single-layer or multi-layer positive electrode film layer disposed on at least one surface thereon; when the positive electrode film layer is a single layer, at least one positive electrode film layer includes a first positive electrode active material and a material selected from LiFePO4, carbon-coated LiFePO4, LiFe b D c PO4 and carbon-coated LiFe b D c The second positive electrode active material of PO4; and / or, when the positive electrode film is multilayered, at least one layer of at least one positive electrode film contains the first and second positive electrode active materials; the first positive electrode active material includes Li-containing materials. 1+x Mn 1‑y A y P 1‑z R z The cathode electrode comprises an O4 core, a first coating layer containing pyrophosphate and phosphate, and a second coating layer containing carbon. The secondary battery fabricated using the cathode electrode of this application exhibits high energy density, high rate performance, good kinetic performance, long low-temperature cycle life, and high low-temperature cycle capacity retention.

Description

Technical Field

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

[0002] In recent years, with the increasingly wide 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. Existing lithium iron phosphate (LFP) batteries exhibit poor kinetic performance and low rate capability, failing to meet the demands of power batteries. While existing LFP batteries, using LFP as the positive electrode active material, possess excellent cycle stability and safety, the presence of one-dimensional lithium-ion channels and the presence of the LiFePO4 and FePO4 two-phase structures during charging and discharging increase the internal phase transition resistance, resulting in poor kinetic performance, low rate capability, short low-temperature cycle life, and low low-temperature capacity retention. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device to solve the problems of low energy density, poor kinetic performance, low rate performance, short low-temperature cycle life, and low low-temperature cycle capacity retention of secondary batteries made using existing positive electrode active materials.

[0004] To achieve the above objectives, a first aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the positive electrode film layer is a single-layer structure or a multi-layer structure; when the positive electrode film layer is a single-layer structure, at least one positive electrode film layer simultaneously comprises a first positive electrode active material and a second positive electrode active material having a core-shell structure; and / or, when the positive electrode film layer is a multi-layer structure, at least one layer of at least one positive electrode film layer simultaneously comprises a first positive electrode active material and a second positive electrode active material having a core-shell structure; the first positive electrode active material comprises a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, the core comprises Li 1+x Mn 1- y A y P 1-z R zO4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; wherein, A comprises 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; R comprises one or more elements selected from B, Si, N and S; x is selected from the range of -0.100 to 0.100; y is selected from the range of 0.001 to 0.500; z is selected from the range of 0.001 to 0.100; M and X independently comprise one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; the second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, LiFe b D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, and b independently is selected from the range of 0.99 to 0.999 and b+c=1.

[0005] As a result, the applicant unexpectedly discovered that by simultaneously doping specific elements at specific amounts at the Mn and P sites of the compound LiMnPO4 and then coating the compound surface with two layers to obtain a first positive electrode active material, it is possible to significantly reduce the dissolution of transition metals and reduce the oxygen activity on the particle surface, promote the migration of lithium ions, improve the conductivity and desolvation performance of the material, improve the rate performance of the battery, improve the cycle performance and high-temperature performance of the secondary battery, and at the same time reduce the corrosion of the active material by the electrolyte.

[0006] This application uses a combination of a first positive electrode active material and a second positive electrode active material, which complement each other's advantages, thereby improving the energy density of the secondary battery. At the same time, the secondary battery also has excellent kinetic performance, rate performance, low-temperature cycle life, and low-temperature cycle capacity retention.

[0007] A second aspect of this application also provides a positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; at least one positive electrode film layer has a multilayer structure, and any positive electrode film layer having a multilayer structure contains a first positive electrode active material and a second positive electrode active material having a core-shell structure in different layers; the first positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, the core contains Li 1+x Mn 1-y A y P 1-z R zO4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; wherein, A comprises 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; R comprises one or more elements selected from B, Si, N and S; x is selected from the range of -0.100 to 0.100; y is selected from the range of 0.001 to 0.500; z is selected from the range of 0.001 to 0.100; M and X independently comprise one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; the second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, LiFe b D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, and b independently is selected from the range of 0.99 to 0.999 and b+c=1; optionally, any positive electrode film layer having a multilayer structure contains a first positive electrode active material and a second positive electrode active material in adjacent layers respectively.

[0008] Therefore, the first positive electrode active material can greatly reduce the dissolution of transition metals and reduce oxygen activity on the particle surface, promote lithium ion migration, improve conductivity and desolvation performance, improve the rate performance of the battery, improve the cycle performance and high temperature performance of the secondary battery, and at the same time reduce the corrosion of the active material by the electrolyte.

[0009] This application combines a first positive electrode active material and a second positive electrode active material, with the advantages of the two materials complementing each other, thereby improving the energy density of the secondary battery. At the same time, the secondary battery also has excellent rate performance, kinetic performance, low-temperature cycle life and low-temperature cycle capacity retention.

[0010] A third aspect of this application also provides a positive electrode sheet, comprising a positive current collector and positive electrode film layers A and B respectively disposed on two surfaces of the positive current collector; positive electrode film layers A and B are each independently a single-layer structure or a multi-layer structure; at least one layer of positive electrode film layer A contains a first positive electrode active material having a core-shell structure, and at least one layer of positive electrode film layer B contains a second positive electrode active material; the first positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, the core contains Li 1+x Mn 1-y A y P 1-z Rz O4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; wherein, A comprises 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; R comprises one or more elements selected from B, Si, N and S; x is selected from the range of -0.100 to 0.100; y is selected from the range of 0.001 to 0.500; z is selected from the range of 0.001 to 0.100; M and X independently comprise one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; the second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, LiFe b D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, and b independently is selected from the range of 0.99 to 0.999 and b+c=1.

[0011] Therefore, the first positive electrode active material can greatly reduce the dissolution of transition metals and reduce oxygen activity on the particle surface, promote lithium ion migration, improve conductivity and desolvation performance, improve the rate performance of the battery, improve the cycle performance and high temperature performance of the secondary battery, and at the same time reduce the corrosion of the active material by the electrolyte.

[0012] This application combines a first positive electrode active material and a second positive electrode active material, with the advantages of the two materials complementing each other, thereby improving the energy density of the secondary battery. At the same time, the secondary battery also has excellent rate performance, kinetic performance, low-temperature cycle life and low-temperature cycle capacity retention.

[0013] Unless otherwise stated, the chemical formula Li 1+x Mn 1-y A y P 1-z R zIn O4, when A consists of two or more elements, the aforementioned limitation on the range of y values ​​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 y values ​​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 stoichiometric coefficients of R in this application has the same meaning.

[0014] Unless otherwise stated, the chemical formula LiFe b D c In PO4, when D consists of two or more elements, the aforementioned limitation on the range of c values ​​applies not only to the stoichiometric coefficient of each element as D, but also to the sum of the stoichiometric coefficients of all elements as D. For example, when D consists of two or more elements D1, D2...Dn, the stoichiometric coefficients c1, c2...cn of each of D1, D2...Dn must each fall within the range of c values ​​defined in this application, and the sum of c1, c2...cn must also fall within this range.

[0015] In any embodiment of the first to third aspects, in the second positive electrode active material, the carbon mass accounts for 0.1%-4% of the mass of carbon-coated LiFePO4; and / or, the carbon mass accounts for 0.1%-4% of the mass of carbon-coated LiFePO4. b D c The carbon content of the second positive electrode active material is 0.1%-4% by mass. Using the above-mentioned carbon content can further ensure that the secondary battery has excellent rate performance, kinetic performance and low-temperature cycling performance, as well as high energy density.

[0016] In any of the embodiments of the first to third aspects, the mass ratio of the first positive electrode active material to the second positive electrode active material is 1:7-7:1, optionally 1:4-4:1, and further optionally 1:3-3:1, for example 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 high energy density, excellent kinetic performance, excellent rate performance, long low-temperature cycle life, and high low-temperature cycle capacity retention, while reducing interfacial side reactions.

[0017] In any embodiment of the first to third aspects, in the first positive electrode active material, A includes one or more elements selected from Zn, Fe, Ti, V, Ni, Co, and Mg; optionally, A includes at least two elements selected from Fe, Ti, V, Ni, Co, and Mg. Selecting doping elements within the above 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 positive electrode active material and the electrolyte, thereby improving the battery's cycle performance and high-temperature storage performance.

[0018] In any of the embodiments of the first to third aspects, x is selected from the range of -0.100 to 0.006. By selecting a value for x within this range, the kinetic performance of the first positive electrode active material can be further improved.

[0019] In any of the embodiments of the first to third aspects, y is selected from the range of 0.1 to 0.4. By selecting a value of y within this range, the specific capacity and rate performance of the first positive electrode active material can be further improved.

[0020] In any of the embodiments of the first to third aspects, M and X independently include one or more elements selected from Li and Fe.

[0021] In any of the embodiments of the first to third aspects, the ratio of y to 1-y is selected from 1:10 to 10:1, and can be selected from 1:4 to 1:1. Here, y represents the sum of the stoichiometric coefficients of the Mn-doped elements. When the above conditions are met, the energy density and cycle performance of the secondary battery made from the positive electrode can be further improved.

[0022] In any of the embodiments of the first to third aspects, the ratio of z to 1-z is selected from 1:999 to 1:9, and can be selected from 1:499 to 1:249. Here, z represents the sum of the stoichiometric coefficients of the p-site doped elements. When the above conditions are met, the energy density and cycle performance of the secondary battery made from the positive electrode can be further improved.

[0023] In any of the embodiments of the first to third aspects, in the first positive electrode active material, the interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°.

[0024] When the interplanar spacing and the angle between the crystal orientation (111) of the phosphate and pyrophosphate in the first coating layer are within the above range, impurity phases in the coating layer can be effectively avoided, thereby improving the specific capacity of the material and enhancing the cycle performance and rate performance of the secondary battery.

[0025] In any of the embodiments of the first to third aspects, in the first positive electrode active material, the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, and can be selected as 4-5.6% by weight, based on the core weight.

[0026] When the coating amount of the first coating layer is within the above-mentioned range, it can further suppress manganese dissolution and further promote lithium-ion transport. It can also effectively avoid the following situations: if the coating amount of the first coating layer is too small, the pyrophosphate may not sufficiently inhibit manganese dissolution, and the improvement in lithium-ion transport performance may not be significant; if the coating amount of the first coating layer is too large, the coating layer may be too thick, increasing battery impedance and affecting the battery's kinetic performance.

[0027] In any of the embodiments of the first to third aspects, in the first positive electrode active material, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, and can be selected as 1:3 to 1:1.

[0028] A proper ratio of pyrophosphate and phosphate is beneficial for fully leveraging their synergistic effect and can effectively avoid the following situations: if there is too much pyrophosphate and too little phosphate, it may lead to an increase in battery impedance; if there is too much phosphate and too little pyrophosphate, the effect of inhibiting manganese dissolution will be insignificant.

[0029] In any of the embodiments of the first to third aspects, in the first positive electrode active material, the crystallinity of pyrophosphate and phosphate is independently 10% to 100%, optionally 50% to 100%.

[0030] In the first coating layer of the lithium manganese phosphate cathode active material of this application, the presence of pyrophosphate and phosphate with a certain degree of crystallinity helps maintain the structural stability of the first coating layer and reduces lattice defects. This is beneficial in two ways: firstly, it allows the pyrophosphate to fully inhibit manganese dissolution; secondly, it helps the phosphate to reduce the content of surface impurities and lower the valence state of surface oxygen, thereby reducing interfacial side reactions between the cathode material and the electrolyte, reducing electrolyte consumption, and improving the cycle performance and safety performance of the secondary battery.

[0031] In any of the embodiments of the first to third aspects, in the first positive electrode active material, the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, and can be selected as 3-5% by weight, based on the weight of the core.

[0032] The carbon-containing layer, as the second coating layer, functions as a "barrier," preventing direct contact between the first positive electrode active material and the electrolyte, thereby reducing electrolyte corrosion of the active material and improving battery safety at high temperatures. On the other hand, its strong conductivity reduces internal resistance, thus improving the kinetic performance of the secondary battery. However, due to the low specific capacity of carbon materials, excessive use of the second coating layer may reduce the overall specific capacity of the positive electrode active material. Therefore, when the coating amount of the second coating layer is within the aforementioned range, it can further improve the kinetic and safety performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0033] In any embodiment of the first to third aspects, the Li / Mn antisite defect concentration of the first positive electrode active material is 4% or less, and optionally 2% or less. In the first positive electrode active material of this application, the Li / Mn antisite defect refers to the Li / Mn antisite defect in the LiMnPO4 lattice. + and Mn 2+ The positions of Li have been interchanged. + The transmission channel is a one-dimensional channel, Mn 2+ In Li + It is difficult to migrate in the transmission channel, therefore, the Mn of the inversion defect is difficult to migrate. 2+ It will hinder Li + Transport efficiency. By controlling the concentration of Li / Mn antisite defects at low levels, the specific capacity and rate performance of LiMnPO4 can be improved.

[0034] In any embodiment of the first to third aspects, the lattice change rate of the first positive electrode active material is 6% or less, optionally 4% or less. The lithium insertion / extraction process of LiMnPO4 is a two-phase reaction. The interfacial stress between the two phases is determined by the magnitude of the lattice change rate; the smaller the lattice change rate, the smaller the interfacial stress. + The easier the transmission, the better. Therefore, reducing the lattice change rate of the core will be beneficial for enhancing Li. + This improves the transmission capacity, thereby enhancing the rate performance of secondary batteries.

[0035] In any of the embodiments of the first to third aspects, the surface oxygen valence state of the first positive electrode active material is below -1.88, optionally between -1.98 and -1.88. This is because the higher the valence state of oxygen in a compound, the stronger its electron-accepting ability, i.e., the stronger its oxidizing power. In the first positive electrode active material of this application, by controlling the surface valence state of oxygen at a low level, the reactivity of the positive electrode material surface can be reduced, the interfacial side reactions between the positive electrode material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0036] In any of the embodiments of the first to third aspects, the compaction density of the first positive electrode active material at 3 tons (T) is 2.0 g / cm³. 3 The above is optional, 2.2 g / cm³. 3 The higher the compaction density of the first positive electrode active material, that is, the greater the weight of active material per unit volume, the more beneficial it is to improving the volumetric energy density of the secondary battery.

[0037] In any of the embodiments of the first to third aspects, 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, and low-temperature cycling performance, and also has a high energy density.

[0038] A fourth aspect of this application provides a secondary battery, including a positive electrode sheet of any one of the first to third aspects of this application.

[0039] The fifth aspect of this application provides a battery module, including the secondary battery of the fourth aspect of this application.

[0040] A sixth aspect of this application provides a battery pack that includes the battery module of the fifth aspect of this application.

[0041] A seventh aspect of this application provides an electrical device comprising at least one selected from the fourth aspect of this application, the fifth aspect of this application, and the sixth aspect of this application. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of a first positive electrode active material having a core-shell structure according to an embodiment of this application.

[0043] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0044] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0045] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0046] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0047] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0048] 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.

[0049] Figure 8 This is a schematic diagram of the battery structure made from the positive electrode P1 of this application.

[0050] Figure 9 This is a schematic diagram of the battery structure made from the positive electrode P2 of this application.

[0051] Figure 10 This is a schematic diagram of the battery structure made from the positive electrode P3 of this application.

[0052] Figure 11 This is a schematic diagram of the battery structure made from the positive electrode P8 of this application.

[0053] Figure 12 This is a schematic diagram of the battery structure made from the positive electrode P10 of this application.

[0054] Figure 13 This is a schematic diagram of the battery structure made from the positive electrode P11 of this application.

[0055] Figure 14 This is a schematic diagram of the battery structure made from the positive electrode P12 of this application.

[0056] Figure 15 This is a schematic diagram of the battery structure made from the positive electrode P17 of this application.

[0057] Figure 16 This is a schematic diagram of the battery structure made from the positive electrode P18 of this application.

[0058] Figure 17 This is a schematic diagram of the battery structure made from the positive electrode P23 of this application.

[0059] Figure 18 This is a schematic diagram of the battery structure made from the positive electrode P24 of this application.

[0060] Figure 19 This is a schematic diagram of the battery structure made from the positive electrode P26 of this application.

[0061] Figure 20 This is a schematic diagram of the battery structure made from the positive electrode P27 of this application.

[0062] Explanation of reference numerals in the attached figures:

[0063] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 11 Core; 12 First covering layer; 13 Second covering layer. Detailed Implementation

[0064] 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.

[0065] 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.

[0066] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0067] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0068] 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.

[0069] 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.

[0070] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0071] 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.

[0072] 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.

[0073] 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.

[0074] [Rechargeable Battery]

[0075] 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.

[0076] 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.

[0077] [Positive electrode plate]

[0078] An embodiment of the first aspect of this application provides a positive electrode sheet, including 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 is a single-layer structure or a multi-layer structure; when the positive electrode film layer is a single-layer structure, at least one positive electrode film layer simultaneously includes a first positive electrode active material and a second positive electrode active material having a core-shell structure; and / or, when the positive electrode film layer is a multi-layer structure, at least one layer of at least one positive electrode film layer simultaneously includes a first positive electrode active material and a second positive electrode active material having a core-shell structure; the first positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, the core contains Li 1+x Mn 1-y A y P 1-z R z O4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; wherein, A comprises 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; R comprises one or more elements selected from B, Si, N and S; x is selected from the range of -0.100 to 0.100; y is selected from the range of 0.001 to 0.500; z is selected from the range of 0.001 to 0.100; M and X independently comprise one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; the second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, LiFe b D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, and b independently is selected from the range of 0.99 to 0.999 and b+c=1.

[0079] It should be noted that when the positive electrode includes two positive electrode film layers, "the positive electrode film layer is a single-layer structure or a multi-layer structure" means that each of the two positive electrode film layers is an independent single-layer structure or a multi-layer structure; "when the positive electrode film layer is a single-layer structure" means that one or both positive electrode film layers are single-layer structures; "when the positive electrode film layer is a multi-layer structure" means that one or both positive electrode film layers are multi-layer structures.

[0080] The first positive electrode active material of this application is a core-shell structure with two coating layers, wherein the core includes Li1+ x Mn 1-y A y P 1-z R z O4. The doping of element A at the manganese sites of lithium manganese phosphate helps reduce the lattice change rate of lithium manganese phosphate during lithium insertion / extraction, improves the structural stability of the lithium manganese phosphate cathode material, significantly reduces manganese dissolution, and lowers the oxygen activity on the particle surface. The doping of element R at the phosphorus sites helps change the ease of Mn-O bond length changes, thereby lowering the lithium-ion migration barrier, promoting lithium-ion migration, and improving the rate performance of the secondary battery. The first coating layer of the first cathode active material of this application includes pyrophosphate and phosphate. Since the migration barrier of transition metals in pyrophosphate is high (>1 eV), the dissolution of transition metals can be effectively suppressed. Phosphate has excellent lithium-ion conduction ability and can reduce the surface impurity lithium content. In addition, since the second coating layer is a carbon-containing layer, it can effectively improve the conductivity and desolvation ability of LiMnPO4. Furthermore, the "barrier" effect of the second coating layer can further hinder the migration of manganese ions into the electrolyte and reduce the corrosion of the active material by the electrolyte. Therefore, the first positive electrode active material of this application, through specific elemental doping and surface coating of lithium manganese phosphate, can effectively suppress Mn dissolution during the lithium insertion / extraction process while promoting lithium ion migration, thereby improving the rate performance of the cell and enhancing the cycle performance and high-temperature performance of the secondary battery. It should be noted that the positions of the main characteristic peaks of the first positive electrode active material of this application are basically consistent with those of the undoped LiMnPO4, indicating that the doped lithium manganese phosphate positive electrode active material has no impurity phase, and the improvement in secondary battery performance mainly comes from elemental doping, rather than impurity phase.

[0081] This application utilizes a mixture 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. The stable internal lattice structure of both materials allows the doping elements in the first positive electrode active material to effectively reduce the lithium-ion migration barrier during charge and discharge, facilitating rapid lithium-ion insertion and extraction. Furthermore, the unique second coating layer of the first positive electrode active material significantly enhances electronic conductivity. The uniform dispersion of the first positive electrode active material around the second positive electrode active material further improves the overall electronic conductivity of the mixed material, thus enhancing the rate performance and kinetic performance of the secondary battery. Moreover, the lower lattice variation of the first positive electrode active material reduces material polarization at low temperatures, effectively improving the low-temperature cycle life and low-temperature cycle capacity retention of the secondary battery.

[0082] In some embodiments of the first aspect, 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 contains a first positive electrode active material and a second positive electrode active material. Optionally, the positive electrode film layer D contains one or both of the first positive electrode active material and the second positive electrode active material. Optionally, the remaining layers of the positive electrode film layer C contain either the first positive electrode active material or the second positive electrode active material.

[0083] In some embodiments of the first aspect, 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. The positive electrode film layer D simultaneously contains a first positive electrode active material and a second positive electrode active material. Optionally, any layer of the positive electrode film layer C contains either the first positive electrode active material or the second positive electrode active material.

[0084] In some embodiments of the first aspect, a positive electrode film layer is respectively disposed on two surfaces of the positive electrode current collector, each positive electrode film layer having a multilayer structure, and at least one layer of each positive electrode film layer simultaneously comprising a first positive electrode active material and a second positive electrode active material; optionally, the remaining layers of the positive electrode film layer comprise either the first positive electrode active material or the second positive electrode active material.

[0085] A second aspect of this application provides a positive electrode sheet, including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; at least one positive electrode film layer has a multilayer structure, and any positive electrode film layer with a multilayer structure includes a first positive electrode active material and a second positive electrode active material having a core-shell structure in different layers; the first positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, the core contains Li 1+x Mn 1-y A y P 1-z R z O4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; wherein, A comprises 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; R comprises one or more elements selected from B, Si, N and S; x is selected from the range of -0.100 to 0.100; y is selected from the range of 0.001 to 0.500; z is selected from the range of 0.001 to 0.100; M and X independently comprise one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; the second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, LiFeb D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, and b independently is selected from the range of 0.99 to 0.999 and b+c=1; optionally, any positive electrode film layer having a multilayer structure contains a first positive electrode active material and a second positive electrode active material in adjacent layers respectively.

[0086] The first positive electrode active material of this application can greatly reduce the dissolution of transition metals and reduce the oxygen activity on the particle surface, promote the migration of lithium ions, improve conductivity and desolvation performance, improve the rate performance of the battery, improve the cycle performance and high temperature performance of the secondary battery, and at the same time reduce the corrosion of the active material by the electrolyte.

[0087] This application utilizes a mixture 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. The stable internal lattice structure of both materials allows the doping elements in the first positive electrode active material to effectively reduce the lithium-ion migration barrier during charge and discharge, facilitating rapid lithium-ion insertion and extraction. Furthermore, the unique second coating layer of the first positive electrode active material significantly enhances electronic conductivity. The uniform dispersion of the first positive electrode active material around the second positive electrode active material further improves the overall electronic conductivity of the mixed material, thus enhancing the rate performance and kinetic performance of the secondary battery. Moreover, the lower lattice variation of the first positive electrode active material reduces material polarization at low temperatures, effectively improving the low-temperature cycle life and low-temperature cycle capacity retention of the secondary battery.

[0088] In some embodiments of the second aspect, a positive electrode film layer is disposed on each of the two surfaces of the positive electrode current collector, each positive electrode film layer having a multilayer structure, and each adjacent layer in each positive electrode film layer containing a first positive electrode active material and a second positive electrode active material, respectively.

[0089] In some embodiments of the second aspect, 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 contain 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 contain a first positive electrode active material or a second positive electrode active material.

[0090] A third aspect of this application provides a positive electrode sheet, including a positive current collector and positive electrode film layers A and B respectively disposed on two surfaces of the positive current collector; positive electrode film layers A and B are each independently a single-layer structure or a multi-layer structure; at least one layer of positive electrode film layer A contains a first positive electrode active material having a core-shell structure, and at least one layer of positive electrode film layer B contains a second positive electrode active material; the first positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, the core contains Li 1+x Mn 1-y A y P 1-z R z O4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; wherein, A comprises 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; R comprises one or more elements selected from B, Si, N and S; x is selected from the range of -0.100 to 0.100; y is selected from the range of 0.001 to 0.500; z is selected from the range of 0.001 to 0.100; M and X independently comprise one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; the second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, LiFe b D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, and b independently is selected from the range of 0.99 to 0.999 and b+c=1.

[0091] The first positive electrode active material of this application can greatly reduce the dissolution of transition metals and reduce the oxygen activity on the particle surface, promote the migration of lithium ions, improve conductivity and desolvation performance, improve the rate performance of the battery, improve the cycle performance and high temperature performance of the secondary battery, and at the same time reduce the corrosion of the active material by the electrolyte.

[0092] This application utilizes a mixture 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. The stable internal lattice structure of both materials allows the doping elements in the first positive electrode active material to effectively reduce the lithium-ion migration barrier during charge and discharge, facilitating rapid lithium-ion insertion and extraction. Furthermore, the unique second coating layer of the first positive electrode active material significantly enhances electronic conductivity. The uniform dispersion of the first positive electrode active material around the second positive electrode active material further improves the overall electronic conductivity of the mixed material, thus enhancing the rate performance and kinetic performance of the secondary battery. Moreover, the lower lattice variation of the first positive electrode active material reduces material polarization at low temperatures, effectively improving the low-temperature cycle life and low-temperature cycle capacity retention of the secondary battery.

[0093] Unless otherwise stated, the chemical formula Li 1+x Mn 1-y A y P 1-z R z In O4, when A consists of two or more elements, the aforementioned limitation on the range of y values ​​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 y values ​​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 limitations on the range of stoichiometric coefficients of R, M, and X in this application also have the above meaning.

[0094] Unless otherwise stated, the chemical formula LiFe b D c In PO4, when D consists of two or more elements, the aforementioned limitation on the range of c values ​​applies not only to the stoichiometric coefficient of each element as D, but also to the sum of the stoichiometric coefficients of all elements as D. For example, when D consists of two or more elements D1, D2...Dn, the stoichiometric coefficients c1, c2...cn of each of D1, D2...Dn must each fall within the range of c values ​​defined in this application, and the sum of c1, c2...cn must also fall within this range.

[0095] like Figure 1 As shown, the first positive electrode active material with a core-shell structure of this application includes a core 11, a first coating layer 12 covering the core 11, and a second coating layer 13 covering the first coating layer 12, wherein the core 11 includes Li 1+x Mn 1- y Ay P 1-z R z O4. The element A doping at the manganese sites of lithium manganese phosphate (LiMP) in core 11 helps reduce the lattice change rate of LiMP during lithium insertion / extraction, improves the structural stability of the LiMP cathode material, significantly reduces manganese dissolution, and lowers the oxygen activity on the particle surface. The element R doping at the phosphorus sites helps alter the ease of Mn-O bond length changes, thereby lowering the lithium-ion migration barrier, promoting lithium-ion migration, and improving the rate performance of the secondary battery.

[0096] In some embodiments of the first to third aspects, Li 1+x Mn 1-y A y P 1-z R z O4 remains electrically neutral.

[0097] In some embodiments of the first to third aspects, LiFe b D c PO4 remains electrically neutral.

[0098] In some embodiments of the first to third aspects, in the second positive electrode active material, the carbon mass accounts for 0.1%-4% of the mass of carbon-coated LiFePO4; and / or, the carbon mass accounts for 0.1%-4% of the mass of carbon-coated LiFePO4. b D c The carbon content of the second positive electrode active material is 0.1%-4% by mass. Using the above-mentioned carbon content can further ensure that the secondary battery has excellent rate performance, kinetic performance and low-temperature cycling performance, as well as high energy density.

[0099] In some embodiments of the first to third aspects, the mass ratio of the first positive electrode active material to the second positive electrode active material is 1:7-7:1, optionally 1:4-4:1, and further optionally 1:3-3:1, for example 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 high energy density, excellent kinetic performance, excellent rate performance, long low-temperature cycle life, and high low-temperature cycle capacity retention, while reducing interfacial side reactions.

[0100] In some embodiments of the first to third aspects, in the first positive electrode active material, A includes one or more elements selected from Zn, Fe, Ti, V, Ni, Co, and Mg; optionally, A includes at least two elements selected from Fe, Ti, V, Ni, Co, and Mg. Selecting doping elements within the above 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 positive electrode active material and the electrolyte, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0101] In some embodiments of the first to third aspects, x is selected from the range of -0.100 to 0.006. By selecting a value for x within this range, the kinetic performance of the first positive electrode active material can be further improved.

[0102] In some embodiments of the first to third aspects, y is selected from the range of 0.1 to 0.4. By selecting a value for y within this range, the specific capacity of the first positive electrode active material and the rate performance of the secondary battery can be further improved.

[0103] In some embodiments of the first to third aspects, M and X independently include one or more elements selected from Li and Fe.

[0104] In some embodiments of the first to third aspects, the ratio of y to 1-y is selected from 1:10 to 10:1, and can be selected from 1:4 to 1:1. Here, y represents the sum of the stoichiometric coefficients of the Mn-doped elements. When the above conditions are met, the energy density and cycle performance of the secondary battery made from the positive electrode are further improved.

[0105] In some embodiments of the first to third aspects, the ratio of z to 1-z is selected from 1:999 to 1:9, and optionally from 1:499 to 1:249. Here, z represents the sum of the stoichiometric coefficients of the p-site doping elements. When the above conditions are met, the energy density and cycle performance of the secondary battery made from the positive electrode can be further improved.

[0106] In some embodiments of the first to third aspects, in the first positive electrode active material, the interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°.

[0107] When the interplanar spacing and the angle between the crystal orientation (111) of the phosphate and pyrophosphate in the first coating layer are within the above range, impurity phases in the coating layer can be effectively avoided, thereby improving the specific capacity of the material and enhancing the cycle performance and rate performance of the secondary battery.

[0108] In some embodiments of the first to third aspects, in the first positive electrode active material, the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally 4-5.6% by weight, based on the core weight.

[0109] When the coating amount of the first coating layer is within the above-mentioned range, it can further suppress manganese dissolution and further promote lithium-ion transport. It can also effectively avoid the following situations: if the coating amount of the first coating layer is too small, the pyrophosphate may not sufficiently inhibit manganese dissolution, and the improvement on lithium-ion transport performance may not be significant; if the coating amount of the first coating layer is too large, the coating layer may be too thick, increasing battery impedance and affecting the kinetic performance of the secondary battery.

[0110] In some embodiments of the first to third aspects, in the first positive electrode active material, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, and optionally 1:3 to 1:1.

[0111] A proper ratio of pyrophosphate and phosphate is beneficial for fully leveraging their synergistic effect and can effectively avoid the following situations: if there is too much pyrophosphate and too little phosphate, it may lead to an increase in battery impedance; if there is too much phosphate and too little pyrophosphate, the effect of inhibiting manganese dissolution will be insignificant.

[0112] In some embodiments of the first to third aspects, the crystallinity of pyrophosphate and phosphate in the first positive electrode active material is independently 10% to 100%, optionally 50% to 100%. In the first coating layer of the lithium manganese phosphate positive electrode active material of this application, the pyrophosphate and phosphate with a certain degree of crystallinity are beneficial for maintaining the structural stability of the first coating layer and reducing lattice defects. This is beneficial for fully utilizing the role of pyrophosphate in inhibiting manganese dissolution, and also for phosphate to reduce the surface lithium content and lower the valence state of surface oxygen, thereby reducing interfacial side reactions between the positive electrode material and the electrolyte, reducing electrolyte consumption, and improving the cycle performance and safety performance of the secondary battery.

[0113] In some embodiments of the first to third aspects, in the first positive electrode active material, the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the weight of the core.

[0114] The carbon-containing layer, as the second coating layer, functions as a "barrier," preventing direct contact between the first positive electrode active material and the electrolyte, thereby reducing electrolyte corrosion and improving the safety performance of the secondary battery at high temperatures. Furthermore, its strong conductivity reduces the internal resistance of the secondary battery, thus improving its kinetic performance. However, due to the low specific capacity of carbon materials, excessive amounts of the second coating layer may reduce the overall specific capacity of the positive electrode active material. Therefore, when the coating amount of the second coating layer is within the aforementioned range, it can further improve the kinetic and safety performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0115] In some embodiments of the first to third aspects, the Li / Mn antisite defect concentration of the first positive electrode active material is 4% or less, optionally 2% or less. In the first positive electrode active material of this application, the Li / Mn antisite defect refers to the Li / Mn antisite defect in the LiMnPO4 lattice. + and Mn 2+ The positions of Li have been interchanged. + The transmission channel is a one-dimensional channel, Mn 2+ In Li + It is difficult to migrate in the transmission channel, therefore, the Mn of the inversion defect is difficult to migrate. 2+ It will hinder Li + The transport of Li / Mn antisite defects can be improved by controlling the specific capacity of LiMnPO4 and the rate performance of the secondary battery. In this application, the antisite defect concentration can be determined, for example, according to JIS K 0131-1996.

[0116] In some embodiments of the first to third aspects, the lattice change rate of the first positive electrode active material is 6% or less, optionally 4% or less. The lithium insertion / extraction process of LiMnPO4 is a two-phase reaction. The interfacial stress between the two phases is determined by the magnitude of the lattice change rate; the smaller the lattice change rate, the smaller the interfacial stress. + The easier the transmission, the better. Therefore, reducing the lattice change rate of the core will be beneficial for enhancing Li. + This improves the transmission capacity, thereby enhancing the rate performance of secondary batteries.

[0117] In some embodiments of the first to third aspects, the surface oxygen valence state of the first positive electrode active material is below -1.88, optionally between -1.98 and -1.88. This is because the higher the valence state of oxygen in a compound, the stronger its electron-accepting ability, i.e., the stronger its oxidizing power. In the first positive electrode active material of this application, by controlling the surface oxygen valence state at a low level, the reactivity of the positive electrode material surface can be reduced, the interfacial side reactions between the positive electrode material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0118] In some embodiments of the first to third aspects, the compaction density of the first positive electrode active material at 3 tons (T) is 2.0 g / cm³. 3 The above is optional, 2.2 g / cm³. 3 The higher the compaction density of the first positive electrode active material, that is, the greater the weight of active material per unit volume, the more beneficial it is to improving the volumetric energy density of the secondary battery. In this application, the compaction density can be measured, for example, according to GB / T 24533-2009.

[0119] In some embodiments of the first to third aspects, the combined 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, and low-temperature cycling performance, as well as high energy density.

[0120] In some embodiments of the first to third aspects, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0121] In some embodiments of the first to third aspects, 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material 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 polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] In some embodiments of the first to third aspects, the positive electrode film may further comprise 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 manganese oxides (such as LiMnO2, LiMn2O4), 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 manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0123] In some embodiments of the first to third aspects, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0124] In some embodiments of the first to third aspects, the positive electrode film layer 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.

[0125] In some embodiments of the first to third aspects, the method for preparing the first positive electrode active material includes the following steps:

[0126] Steps for providing kernel materials: Kernel materials contain 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, and R includes one or more elements selected from B, Si, N and S;

[0127] Coating step: A powder containing pyrophosphate MP2O7 and a suspension containing a carbon source and phosphate XPO4 are provided. The core material, the powder containing pyrophosphate MP2O7, and the suspension containing a carbon source and phosphate XPO4 are mixed and sintered to obtain a positive electrode active material, wherein M and X independently include one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.

[0128] The positive electrode active material has a core-shell structure, comprising a core and a shell covering the core, wherein the core contains Li. 1+ x Mn 1-y A y P 1-z R z O4, the shell includes a first coating layer covering the core and a second coating layer covering the first coating layer. The first coating layer contains pyrophosphate M. a P2O7 and phosphate XPO4, with the second coating layer containing carbon.

[0129] In some embodiments of the first to third aspects, the step of providing the kernel material includes the following steps:

[0130] Step (1): Mix the manganese source, the source of element A, and the acid to obtain a mixture;

[0131] Step (2): The mixture is mixed with a lithium source, a phosphorus source, a source of element R, and a solvent of choice, and sintered under an inert gas atmosphere to obtain a mixture containing Li. 1+x Mn 1-y A y P 1-z R z The core material of O4. The definitions of A and R are as above.

[0132] In some embodiments, step (1) is performed at 20°C-120°C, optionally at 40°C-120°C (e.g., about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C or about 120°C); and / or, in step (1), mixing is performed by stirring at 400-700 rpm for 1-9 h (more preferably 3-7 h, e.g., about 2 h, about 3 h, about 4 h, about 5 h, about 6 h, about 7 h, about 8 h or about 9 h).

[0133] In some embodiments, in step (2), the mixture is mixed for 1-10 hours (e.g., about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 70 hours, about 80 hours, about 90 hours, about 100 hours, about 110 hours, or about 120 hours) at a temperature of 20-120°C, optionally 40-120°C (e.g., about 30°C, about 50°C, about 80°C, about 90°C, about 100°C, about 110°C, or about 120°C).

[0134] In some embodiments, in step (2), mixing is performed at a pH of 3.5-6, optionally at a pH of 4-6, and more preferably at a pH of 4-5. It should be noted that the pH can be adjusted in this application using methods commonly used in the art, for example, by adding an acid or a base.

[0135] In some embodiments, optionally, in step (2), the molar ratio of the mixture or manganese salt particles doped with element A to the lithium source and phosphorus source is 1:0.5-2.1:0.5-2.1, optionally about 1:1:1.

[0136] In some embodiments, in step (2), sintering is carried out at 600-950°C for 4-10 hours in an inert gas or a mixture of inert gas and hydrogen; optionally, the protective atmosphere is a mixture of 70-90% nitrogen and 10-30% hydrogen by volume; optionally, sintering can be carried out at about 650°C, about 700°C, about 750°C, about 800°C, about 850°C or about 900°C for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; optionally, the sintering temperature and sintering time can be within any range of the above values, which can improve the crystallinity of the core, reduce the generation of impurity phases, maintain a certain particle size of the core, thereby improving the specific capacity and compaction density of the positive electrode active material, and improving the overall performance of the secondary battery, including the rate performance.

[0137] In some alternative embodiments, the mixture obtained in step (1) is filtered, dried, and ground to obtain element A-doped manganese salt particles with a particle size Dv50 of 50-200 nm. The element A-doped manganese salt particles are used in step (2) to mix with lithium source, phosphorus source, element R source and optional solvent.

[0138] In some alternative embodiments, the mixed materials from step (2) are dried to obtain a powder, and then the powder is sintered to obtain a product containing Li. 1+x Mn 1-y A y P 1-z R z O4 core material.

[0139] In some embodiments, the powder containing pyrophosphate MP2O7 is prepared by the following steps:

[0140] The source of element M, the phosphorus source, and an optional solvent are mixed to obtain a mixture. The pH of the mixture is adjusted to 4-6, and mixing is continued. After drying and sintering, the mixture is ready.

[0141] In some embodiments, in the step of preparing the powder containing pyrophosphate MP2O7, drying is performed at 100°C-300°C for 4-8 hours, optionally at 150°C-200°C; and / or sintering is performed at 500°C-800°C under inert gas protection for 4-10 hours, optionally at 650°C-800°C.

[0142] In some embodiments, the sintering temperature in the coating step is 500-800℃, and the sintering time is 4-10h.

[0143] 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 and hydroxide, provided that the source can achieve the purpose of the preparation method of this application.

[0144] In some embodiments, the source of element A is selected from one or more of element A's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide; and / or, the source of element R is selected from one or more of element R's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, hydroxide, and inorganic acid of element R.

[0145] In some embodiments, the source of element M is one or more selected from elemental form, carbonate, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide.

[0146] The amount of each source added for elements A, R, and M depends on the target doping amount, and the ratio of the amount of lithium source, manganese source, and phosphorus source used conforms to the stoichiometric ratio.

[0147] In this application, the manganese source can be any manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the manganese source can be one or more selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0148] In this application, the acid may be one or more organic acids selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, silicic acid, siliceous acid, and organic acids such as oxalic acid. In some embodiments, the acid is a dilute organic acid with a concentration of 60% by weight or less.

[0149] In this application, the lithium source may be any lithium-containing material known in the art that can be used to prepare lithium manganese phosphate. As an example, the lithium source may be one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0150] In this application, the phosphorus source may be any phosphorus-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the phosphorus source may be one or more selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0151] In this application, as an example, the carbon source is one or more selected from starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0152] [Negative electrode plate]

[0153] 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.

[0154] 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.

[0155] 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.).

[0156] 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.

[0157] 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).

[0158] 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.

[0159] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0160] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as 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 a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0161] [Electrolytes]

[0162] 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.

[0163] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] [Isolation membrane]

[0168] 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.

[0169] 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.

[0170] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0171] 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.

[0172] 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.

[0173] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

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

[0179] Figure 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.

[0180] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as 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 (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

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

[0182] 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.

[0183] [Example]

[0184] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially. Unless otherwise specified, the content of each component in the embodiments of this invention is based on the mass of the component excluding crystallization water.

[0185] The sources of raw materials involved in the preparation examples and embodiments of this application are as follows:

[0186]

[0187] Example 1-1

[0188] (1) Preparation of co-doped lithium manganese phosphate core

[0189] Preparation of Fe, Co, and V co-doped manganese oxalate: 689.5 g of manganese carbonate (calculated as MnCO3), 455.2 g of ferrous carbonate (calculated as FeCO3), 4.6 g of cobalt sulfate (calculated as CoSO4), and 4.9 g of vanadium dichloride (calculated as VCl2) were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (calculated as C2H2O4·2H2O) were added. The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no bubbles were generated), yielding a suspension of Fe, Co, V, and S co-doped manganese oxalate. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain Fe, Co, and V co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0190] Preparation of Fe, Co, V, and S co-doped lithium manganese phosphate: 1793.4 g of manganese oxalate dihydrate particles obtained in the previous step, 369.0 g of lithium carbonate (calculated as Li₂CO₃), 1.6 g of 60% dilute sulfuric acid (calculated as 60% H₂SO₄), and 1148.9 g of ammonium dihydrogen phosphate (calculated as NH₄H₂PO₄) were added to 20 L of deionized water. The mixture was stirred for 10 hours to ensure homogeneity, resulting in a slurry. The slurry was transferred to a spray dryer for spray drying and granulation. The drying temperature was set at 250 °C, and the drying time was 4 hours to obtain powder. Under a protective atmosphere of nitrogen (90 vol%) and hydrogen (10 vol%), the powder was sintered at 700 °C for 4 hours to obtain 1572.1 g of Fe, Co, V, and S co-doped lithium manganese phosphate.

[0191] (2) Preparation of lithium iron pyrophosphate and lithium iron phosphate

[0192] Preparation of lithium iron pyrophosphate powder: 4.77 g lithium carbonate, 7.47 g ferrous carbonate, 14.84 g ammonium dihydrogen phosphate, and 1.3 g oxalic acid dihydrate were dissolved in 50 ml deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80 °C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain powder. The powder was sintered at 650 °C under a nitrogen atmosphere for 8 hours, and then naturally cooled to room temperature before grinding to obtain Li₂FeP₂O₇ powder.

[0193] Preparation of lithium iron phosphate suspension: 11.1 g lithium carbonate, 34.8 g ferrous carbonate, 34.5 g ammonium dihydrogen phosphate, 1.3 g oxalic acid dihydrate, and 74.6 g sucrose (in C2) were added. 12 H 22 O 11 The solution (hereinafter referred to as "the solution") was dissolved in 150 ml of deionized water to obtain a mixture, which was then stirred for 6 hours to allow the mixture to react fully. The reacted solution was then heated to 120°C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4.

[0194] (3) Covering

[0195] 1572.1g of the Fe, Co, V, and S co-doped lithium manganese phosphate and 15.72g of the lithium iron pyrophosphate (Li2FeP2O7) powder were added to the lithium iron phosphate (LiFePO4) suspension prepared in the previous step. After stirring and mixing evenly, the mixture was transferred to a vacuum oven and dried at 150°C for 6 hours. The resulting product was then dispersed by sand milling. After dispersion, the product was sintered at 700°C for 6 hours under a nitrogen atmosphere to obtain the target product, double-layer coated lithium manganese phosphate.

[0196] Examples 1-2 to 1-6

[0197] In the preparation of the co-doped lithium manganese phosphate core, the preparation conditions of the lithium manganese phosphate core in Examples 1-2 to 1-6 are the same as those in Example 1-1, except that vanadium dichloride and cobalt sulfate are not used, and 463.4g of ferrous carbonate, 1.6g of 60% dilute sulfuric acid, 1148.9g of ammonium dihydrogen phosphate and 369.0g of lithium carbonate are used.

[0198] In addition, during the preparation of lithium iron pyrophosphate and lithium iron phosphate, and during the coating of the first and second coating layers, the raw materials used were adjusted according to the ratio of the coating amount shown in Table 1 to the coating amount corresponding to Example 1-1, so that the amounts of Li2FeP2O7 / LiFePO4 in Examples 1-2 to 1-6 were 12.6g / 37.7g, 15.7g / 47.1g, 18.8g / 56.5g, 22.0g / 66.0g and 25.1g / 75.4g, respectively, and the amount of sucrose in Examples 1-2 to 1-6 was 37.3g, the other conditions were the same as in Example 1-1.

[0199] Examples 1-7 to 1-10

[0200] Except that the amounts of sucrose used were 74.6g, 149.1g, 186.4g and 223.7g respectively, so that the corresponding coating amounts of the carbon layer as the second coating layer were 31.4g, 62.9g, 78.6g and 94.3g respectively, the conditions of Examples 1-7 to 1-10 were the same as those of Examples 1-3.

[0201] Examples 1-11 to 1-14

[0202] Except for adjusting the amounts of various raw materials according to the coating amounts shown in Table 1 during the preparation of lithium iron pyrophosphate and lithium iron phosphate so that the amounts of Li2FeP2O7 / LiFePO4 are 23.6g / 39.3g, 31.4g / 31.4g, 39.3g / 23.6g and 47.2g / 15.7g respectively, the conditions of Examples 1-11 to 1-14 are the same as those of Examples 1-7.

[0203] Examples 1-15

[0204] Except for the use of 492.80 g ZnCO3 instead of ferrous carbonate in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-15 were the same as those of Examples 1-14.

[0205] Examples 1-16 to 1-18

[0206] Except that in Examples 1-16, 466.4 g of NiCO3, 5.0 g of zinc carbonate, and 7.2 g of titanium sulfate were used instead of ferrous carbonate in the preparation of the co-doped lithium manganese phosphate core; in Examples 1-17, 455.2 g of ferrous carbonate and 8.5 g of vanadium dichloride were used in the preparation of the co-doped lithium manganese phosphate core; and in Examples 1-18, 455.2 g of ferrous carbonate, 4.9 g of vanadium dichloride, and 2.5 g of magnesium carbonate were used in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-17 to 1-19 were the same as those of Examples 1-7.

[0207] Examples 1-19 to 1-20

[0208] Except that in Examples 1-19, 369.4 g of lithium carbonate and 1.05 g of 60% dilute nitric acid were used instead of dilute sulfuric acid in the preparation of the co-doped lithium manganese phosphate core, and in Examples 1-20, 369.7 g of lithium carbonate and 0.78 g of silicic acid were used instead of dilute sulfuric acid in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-19 to 1-20 were the same as those of Examples 1-18.

[0209] Examples 1-21 to 1-22

[0210] Except that in Examples 1-21, 632.0 g of manganese carbonate, 463.30 g of ferrous carbonate, 30.5 g of vanadium dichloride, 21.0 g of magnesium carbonate, and 0.78 g of silicic acid were used in the preparation of the co-doped lithium manganese phosphate core; and in Examples 1-22, 746.9 g of manganese carbonate, 289.6 g of ferrous carbonate, 60.9 g of vanadium dichloride, 42.1 g of magnesium carbonate, and 0.78 g of silicic acid were used in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-21 to 1-22 were the same as those of Examples 1-20.

[0211] Examples 1-23 to 1-24

[0212] Except for Examples 1-23, which used 804.6 g manganese carbonate, 231.7 g ferrous carbonate, 1156.2 g ammonium dihydrogen phosphate, 1.2 g boric acid (99.5% by mass), and 370.8 g lithium carbonate in the preparation of the co-doped lithium manganese phosphate core, and Examples 1-24, which used 862.1 g manganese carbonate, 173.8 g ferrous carbonate, 1155.1 g ammonium dihydrogen phosphate, 1.86 g boric acid (99.5% by mass), and 371.6 g lithium carbonate in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-23 to 1-24 were the same as those of Examples 1-22.

[0213] Examples 1-25

[0214] Except for the use of 370.1g of lithium carbonate, 1.56g of silicic acid and 1147.7g of ammonium dihydrogen phosphate in the preparation of the co-doped lithium manganese phosphate core in Examples 1-25, the conditions in Examples 1-25 were the same as those in Examples 1-20.

[0215] Examples 1-26

[0216] Except for the use of 368.3g lithium carbonate, 4.9g dilute sulfuric acid with a mass fraction of 60%, 919.6g manganese carbonate, 224.8g ferrous carbonate, 3.7g vanadium dichloride, 2.5g magnesium carbonate, and 1146.8g ammonium dihydrogen phosphate in the preparation of the co-doped lithium manganese phosphate core in Examples 1-26, the conditions in Examples 1-26 are the same as those in Examples 1-20.

[0217] Examples 1-27

[0218] Except for the use of 367.9g of lithium carbonate, 6.5g of 60% dilute sulfuric acid, and 1145.4g of ammonium dihydrogen phosphate in the preparation of the co-doped lithium manganese phosphate core in Examples 1-27, the conditions in Examples 1-27 were the same as those in Examples 1-20.

[0219] Examples 1-28 to 1-33

[0220] Except for Examples 1-28 to 1-33, which used 1034.5g of manganese carbonate, 108.9g of ferrous carbonate, 3.7g of vanadium dichloride, and 2.5g of magnesium carbonate in the preparation of the co-doped lithium manganese phosphate core, the amounts of lithium carbonate used were 367.6g, 367.2g, 366.8g, 366.4g, 366.0g, and 332.4g, respectively; the amounts of ammonium dihydrogen phosphate used were 1144.5g, 1143.4g, 1142.2g, 1141.1g, 1139.9g, and 1138.8g, respectively; and the amounts of 60% dilute sulfuric acid used were 8.2g, 9.8g, 11.4g, 13.1g, 14.7g, and 16.3g, respectively. The conditions in Examples 1-28 to 1-33 were the same as in Examples 1-20.

[0221] Examples 1-34 to Examples 1-53

[0222] The positive electrode active materials of Examples 1-34 to Examples 1-53 are shown in Table 1.

[0223] Table 1. Positive electrode active materials of Examples 1-34 to 1-53

[0224]

[0225] Example 2-1

[0226] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 550℃ and the sintering time was 1h to control the crystallinity of Li2FeP2O7 to 30%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 650℃ and the sintering time was 2h to control the crystallinity of LiFePO4 to 30%, the other conditions were the same as in Examples 1-1.

[0227] Example 2-2

[0228] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 550℃ and the sintering time was 2h to control the crystallinity of Li2FeP2O7 to 50%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 650℃ and the sintering time was 3h to control the crystallinity of LiFePO4 to 50%, the other conditions were the same as in Examples 1-1.

[0229] Example 2-3

[0230] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step is 600℃ and the sintering time is 3h to control the crystallinity of Li2FeP2O7 to 70%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step is 650℃ and the sintering time is 4h to control the crystallinity of LiFePO4 to 70%, the other conditions are the same as in Examples 1-1.

[0231] Examples 2-4

[0232] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 650℃ and the sintering time was 4h to control the crystallinity of Li2FeP2O7 to 100%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 700℃ and the sintering time was 6h to control the crystallinity of LiFePO4 to 100%, the other conditions were the same as in Examples 1-1.

[0233] Examples 3-1 to 3-12

[0234] Except for the preparation of Fe, Co, and V co-doped manganese oxalate particles, the heating temperature / stirring time in the reactor in Example 3-1 was 60℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-2 was 70℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-3 was 80℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-4 was 90℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-5 was 100℃ / 120 minutes; and the heating temperature / stirring time in the reactor in Example 3-6 was 110℃ / 120 minutes. Example 3 -7 The heating temperature / stirring time in the reactor in Examples 3-7 was 120℃ / 120 minutes; the heating temperature / stirring time in the reactor in Examples 3-8 was 130℃ / 120 minutes; the heating temperature / stirring time in the reactor in Examples 3-9 was 100℃ / 60 minutes; the heating temperature / stirring time in the reactor in Examples 3-10 was 100℃ / 90 minutes; the heating temperature / stirring time in the reactor in Examples 3-11 was 100℃ / 150 minutes; the heating temperature / stirring time in the reactor in Examples 3-12 was 100℃ / 180 minutes. Except for these conditions, the other conditions in Examples 3-1 to 3-12 were the same as in Examples 1-1.

[0235] Examples 4-1 to 4-4:

[0236] Except that the drying temperature / drying time in the drying step of the preparation of lithium iron pyrophosphate (Li2FeP2O7) was 100℃ / 4h, 150℃ / 6h, 200℃ / 6h and 200℃ / 6h respectively, and the sintering temperature and sintering time in the sintering step of the preparation of lithium iron pyrophosphate (Li2FeP2O7) were 700℃ / 6h, 700℃ / 6h and 600℃ / 6h respectively, the other conditions were the same as in Examples 1-7.

[0237] Examples 4-5 to 4-7:

[0238] Except that the drying temperature / drying time in the drying step during the coating process is 150℃ / 6h, 150℃ / 6h and 150℃ / 6h respectively, and the sintering temperature and sintering time in the sintering step during the coating process are 600℃ / 4h, 600℃ / 6h and 800℃ / 8h respectively, the other conditions are the same as in Examples 1-12.

[0239] Comparative Example 1

[0240] Preparation of manganese oxalate: 1149.3 g of manganese carbonate was added to the reaction vessel, along with 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (as C2H2O4). (Calculated as 2H2O, the same below). The reactor was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no bubbles were generated), resulting in a manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0241] Preparation of carbon-coated lithium manganese phosphate: Take 1789.6g of the above-obtained manganese oxalate dihydrate particles, 369.4g of lithium carbonate (calculated as Li2CO3, the same below), 1150.1g of ammonium dihydrogen phosphate (calculated as NH4H2PO4, the same below) and 31g of sucrose (calculated as C). 12 H 22 O 11 Add (the same amount, hereinafter the same) to 20 liters of deionized water, stir the mixture for 10 hours to make it uniform, and obtain a slurry. Transfer the slurry to a spray drying equipment for spray drying granulation, set the drying temperature to 250℃, and dry for 4 hours to obtain powder. Under the protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), sinter the above powder at 700℃ for 4 hours to obtain carbon-coated lithium manganese phosphate.

[0242] Comparative Example 2

[0243] Except for the use of 689.5g of manganese carbonate and the addition of 463.3g of ferrous carbonate, the other conditions of Comparative Example 2 were the same as those of Comparative Example 1.

[0244] Comparative Example 3

[0245] Except for the use of 1148.9g of ammonium dihydrogen phosphate and 369.0g of lithium carbonate, and the addition of 1.6g of 60% dilute sulfuric acid, the other conditions of Comparative Example 3 were the same as those of Comparative Example 1.

[0246] Comparative Example 4

[0247] Except for the use of 689.5g of manganese carbonate, 1148.9g of ammonium dihydrogen phosphate and 369.0g of lithium carbonate, and the addition of 463.3g of ferrous carbonate and 1.6g of 60% dilute sulfuric acid, the other conditions of Comparative Example 4 were the same as those of Comparative Example 1.

[0248] Comparative Example 5

[0249] Except for the additional steps: when preparing lithium iron pyrophosphate powder, 9.52 g of lithium carbonate, 29.9 g of ferrous carbonate, 29.6 g of ammonium dihydrogen phosphate, and 32.5 g of oxalic acid dihydrate were dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80 °C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain powder. The powder was sintered at 500 °C under a nitrogen atmosphere for 4 hours, and then naturally cooled to room temperature before grinding. The crystallinity of Li₂FeP₂O₇ was controlled to be 5%. Except for the amount of Li₂FeP₂O₇ used when preparing the carbon-coated material, which was 62.8 g, the other conditions of Comparative Example 5 were the same as those of Comparative Example 4.

[0250] Comparative Example 6

[0251] Except for the additional step of preparing the lithium iron phosphate suspension, 14.7 g of lithium carbonate, 46.1 g of ferrous carbonate, 45.8 g of ammonium dihydrogen phosphate, and 50.2 g of oxalic acid dihydrate were dissolved in 500 ml of deionized water and stirred for 6 hours to allow the mixture to react fully. The resulting solution was then heated to 120 °C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4. In the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 600 °C, and the sintering time was 4 h to control the crystallinity of LiFePO4 to 8%. In preparing the carbon-coated material, the amount of LiFePO4 used was 62.8 g. All other conditions in Comparative Example 6 were the same as in Comparative Example 4.

[0252] Comparative Example 7

[0253] Preparation of lithium iron pyrophosphate powder: 2.38 g lithium carbonate, 7.5 g ferrous carbonate, 7.4 g ammonium dihydrogen phosphate, and 8.1 g oxalic acid dihydrate were dissolved in 50 ml deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80 °C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain powder. The powder was sintered at 500 °C under a nitrogen atmosphere for 4 hours, and then naturally cooled to room temperature before grinding to control the crystallinity of Li₂FeP₂O₇ to 5%.

[0254] Preparation of lithium iron phosphate suspension: 11.1 g lithium carbonate, 34.7 g ferrous carbonate, 34.4 g ammonium dihydrogen phosphate, 37.7 g oxalic acid dihydrate, and 37.3 g sucrose (in C2) were added. 12 H 22 O 11The solution (hereinafter the same) was dissolved in 1500 ml of deionized water and then stirred for 6 hours to allow the mixture to react fully. The resulting solution was then heated to 120°C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4.

[0255] 15.7 g of the obtained lithium iron pyrophosphate powder was added to the above-mentioned lithium iron phosphate (LiFePO4) and sucrose suspension. In the preparation process, the sintering temperature in the coating sintering step was 600℃ and the sintering time was 4 h to control the crystallinity of LiFePO4 to 8%. The other conditions of Comparative Example 7 were the same as those of Comparative Example 4, and amorphous lithium iron pyrophosphate, amorphous lithium iron phosphate, and carbon-coated positive electrode active materials were obtained.

[0256] Comparative Examples 8-11

[0257] Except that the drying temperature / drying time in the drying step of the preparation of lithium iron pyrophosphate (Li2FeP2O7) was 80℃ / 3h, 80℃ / 3h, and 80℃ / 3h in Comparative Examples 8-10, respectively; the sintering temperature and sintering time in the sintering step of the preparation of lithium iron pyrophosphate (Li2FeP2O7) were 400℃ / 3h, 400℃ / 3h, and 350℃ / 2h in Comparative Examples 8-10, respectively; the drying temperature / drying time in the drying step of the preparation of lithium iron phosphate (LiFePO4) in Comparative Example 11 was 80℃ / 3h; and the amounts of Li2FeP2O7 / LiFePO4 used in Comparative Examples 8-11 were 47.2g / 15.7g, 15.7g / 47.2g, 62.8g / 0g, and 0g / 62.8g, respectively, all other conditions were the same as in Examples 1-7.

[0258] 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.

[0259] Preparation of positive electrode sheet

[0260] Example 5-1

[0261] The slurry of the positive electrode active material in Example 1-1 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.

[0262] Example 5-2

[0263] The slurry of the positive electrode active material in Examples 1-34 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.

[0264] Example 5-3

[0265] The slurry of the positive electrode active material in Example 1-1 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount is uniformly coated on one side of the aluminum foil, and the slurry of the positive electrode active material from Examples 1-34 is applied at a rate of 0.019 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.

[0266] Example 5-4

[0267] The slurry of the positive electrode active material in Examples 1-35 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 Examples 5-3, to obtain the positive electrode P4.

[0268] Example 5-5

[0269] The slurry of the positive electrode active material in Example 1-1 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount is uniformly coated on one side of the aluminum foil, and the slurry of the positive electrode active material from Examples 1-35 is 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 Examples 5-3, to obtain the positive electrode P5.

[0270] Examples 5-6

[0271] The slurry of the positive electrode active material in Examples 1-34 was prepared at a concentration of 0.019 g / cm³. 2 The coating amount is uniformly coated on one side of the aluminum foil, and the slurry of the positive electrode active material from Examples 1-35 is 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 Examples 5-3, to obtain the positive electrode P6.

[0272] Examples 5-7

[0273] The slurry of the positive electrode active material from Example 1-1 and the slurry of the positive electrode active material from Example 1-34 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 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.

[0274] Examples 5-8

[0275] The slurry of the positive electrode active material from Examples 1-34 and the slurry of the positive electrode active material from Example 1-1 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 Examples 5-7, and the positive electrode P8 is obtained.

[0276] Examples 5-9

[0277] The slurry of the positive electrode active material from Example 1-1 and the slurry of the positive electrode active material from Example 1-35 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 Examples 5-7, and the positive electrode P9 is obtained.

[0278] Examples 5-10

[0279] The slurry of the positive electrode active material from Examples 1-35 and the slurry of the positive electrode active material from Example 1-1 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 Examples 5-7, and the positive electrode P10 is obtained.

[0280] Examples 5-11

[0281] The slurries of the positive electrode active materials from Examples 1-34 and 1-35 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 Examples 5-7, and the positive electrode P11 is obtained.

[0282] Examples 5-12

[0283] The slurries of the positive electrode active materials from Examples 1-35 and Examples 1-34 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 Examples 5-7, and the positive electrode P12 is obtained.

[0284] Examples 5-13

[0285] The slurry of the positive electrode active material from Example 1-1 and the slurry of the positive electrode active material from Example 1-34 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Example 1-1 was uniformly coated onto side B of the aluminum foil, with a coating amount of 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.

[0286] Examples 5-14

[0287] The slurry of the positive electrode active material from Example 1-1 and the slurry of the positive electrode active material from Example 1-34 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-34 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P14 is obtained.

[0288] Examples 5-15

[0289] The slurry of the positive electrode active material from Example 1-1 and the slurry of the positive electrode active material from Example 1-34 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-35 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P15 is obtained.

[0290] Examples 5-16

[0291] The slurry of the positive electrode active material from Examples 1-34 and the slurry of the positive electrode active material from Example 1-1 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Example 1-1 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P16 is obtained.

[0292] Examples 5-17

[0293] The slurry of the positive electrode active material from Examples 1-34 and the slurry of the positive electrode active material from Example 1-1 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-34 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P17 is obtained.

[0294] Example 5-18

[0295] The slurry of the positive electrode active material from Examples 1-34 and the slurry of the positive electrode active material from Example 1-1 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2The slurry of the positive electrode active material from Examples 1-35 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P18 is obtained.

[0296] Example 5-19

[0297] The slurry of the positive electrode active material from Example 1-1 and the slurry of the positive electrode active material from Example 1-35 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Example 1-1 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P19 is obtained.

[0298] Example 5-20

[0299] The slurry of the positive electrode active material from Example 1-1 and the slurry of the positive electrode active material from Example 1-35 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-34 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P20 is obtained.

[0300] Example 5-21

[0301] The slurry of the positive electrode active material from Example 1-1 and the slurry of the positive electrode active material from Example 1-35 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-35 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P21 is obtained.

[0302] Example 5-22

[0303] The slurry of the positive electrode active material from Examples 1-35 and the slurry of the positive electrode active material from Example 1-1 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Example 1-1 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P22 is obtained.

[0304] Example 5-23

[0305] The slurry of the positive electrode active material from Examples 1-35 and the slurry of the positive electrode active material from Example 1-1 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-34 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P23 is obtained.

[0306] Example 5-24

[0307] The slurry of the positive electrode active material from Examples 1-35 and the slurry of the positive electrode active material from Example 1-1 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-35 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P24 is obtained.

[0308] Example 5-25

[0309] The slurries of the positive electrode active materials from Examples 1-34 and 1-35 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Example 1-1 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P25 is obtained.

[0310] Example 5-26

[0311] The slurries of the positive electrode active materials from Examples 1-34 and 1-35 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-34 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P26 is obtained.

[0312] Example 5-27

[0313] The slurries of the positive electrode active materials from Examples 1-34 and 1-35 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-35 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2The rest is the same as in Examples 5-13, and the positive electrode P27 is obtained.

[0314] Example 5-28

[0315] The slurries of the positive electrode active materials from Examples 1-35 and Examples 1-34 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Example 1-1 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P28 is obtained.

[0316] Example 5-29

[0317] The slurries of the positive electrode active materials from Examples 1-35 and Examples 1-34 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-34 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P29 is obtained.

[0318] Examples 5-30

[0319] The slurries of the positive electrode active materials from Examples 1-35 and Examples 1-34 were sequentially coated onto side A of the aluminum foil, with each layer of slurry having a coating weight of 0.010 g / cm³. 2 The slurry of the positive electrode active material from Examples 1-35 was uniformly coated onto side B of the aluminum foil, with a coating amount of 0.020 g / cm³. 2 The rest is the same as in Examples 5-13, and the positive electrode P30 is obtained.

[0320] Example 5-31

[0321] The slurry of the positive electrode active material in Examples 1-36 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 P31.

[0322] Example 5-32

[0323] The slurry of the positive electrode active material in Examples 1-37 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.

[0324] Example 5-33

[0325] The slurry of the positive electrode active material in Examples 1-38 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.

[0326] Examples 5-34

[0327] The slurry of the positive electrode active material in Examples 1-39 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.

[0328] Examples 5-35

[0329] The slurry of the positive electrode active material in Examples 1-40 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 P35.

[0330] Examples 5-36

[0331] The slurry of the positive electrode active material in Examples 1-41 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 P36.

[0332] Example 5-37

[0333] The slurry of the positive electrode active material in Examples 1-42 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 P37.

[0334] Example 5-38

[0335] The slurry of the positive electrode active material in Examples 1-43 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, vacuum dried at a high temperature of 100-120℃ for 14 hours, and then compacted by a roller press to obtain the positive electrode P38.

[0336] Example 5-39

[0337] The slurry of the positive electrode active material in Examples 1-44 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 P39.

[0338] Examples 5-40

[0339] The slurry of the positive electrode active material in Examples 1-45 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 P40.

[0340] Example 5-41

[0341] The slurry of the positive electrode active material in Examples 1-46 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 P41.

[0342] Example 5-42

[0343] The slurry of the positive electrode active material in Examples 1-47 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 P42.

[0344] Examples 5-43

[0345] The slurry of the positive electrode active material in Examples 1-48 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 P43.

[0346] Examples 5-44

[0347] The slurry of the positive electrode active material in Examples 1-49 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 P44.

[0348] Examples 5-45

[0349] The slurry of the positive electrode active material in Examples 1-50 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 P45.

[0350] Examples 5-46

[0351] The slurry of the positive electrode active material in Examples 1-51 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 P46.

[0352] Examples 5-47

[0353] The slurry of the positive electrode active material in Examples 1-52 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 P47.

[0354] Examples 5-48

[0355] The slurry of the positive electrode active material in Examples 1-53 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 P48.

[0356] The parameters of each positive electrode are shown in Table 2.

[0357] Table 2 Parameters of the positive electrode plate

[0358]

[0359]

[0360]

[0361]

[0362]

[0363] “ ": 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."

[0364] "#": The first positive electrode active material is the positive electrode active material prepared in Example 1-1, and the second positive electrode active material is the positive electrode active material of Examples 1-34, 1-36, 1-38 to 1-45.

[0365] Preparation of negative electrode sheet

[0366] Artificial graphite (anode active material), superconducting carbon black (Super-P) (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) were dissolved in deionized water at a mass ratio of 95%:1.5%:1.8%:1.7%. After thorough mixing, a negative electrode slurry with a viscosity of 3000 mPa·s and a solid content of 52% was obtained. The negative electrode slurry was coated onto a 6 μm thick copper foil for the negative electrode current collector, then baked at 100°C for 4 hours to dry it. After rolling, a compacted density of 1.75 g / cm³ was obtained. 3 The negative electrode sheet.

[0367] Separating membrane

[0368] Polypropylene film is used.

[0369] Preparation of electrolyte

[0370] 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.

[0371] Preparation of full cells

[0372] 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.

[0373] Preparation of button cells

[0374] The prepared positive electrode active material, PVDF, and acetylene black were added to NMP at a weight ratio of 90:5:5, and stirred in a drying chamber to form a slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet. The coating amount was 0.2 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 .

[0375] A lithium sheet is used as the negative electrode, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC) in a volume ratio of 1:1:1 is used as the electrolyte. The lithium sheet and the positive electrode prepared above are assembled into a coin cell in a coin cell box to form a coin cell (hereinafter also referred to as "coin cell").

[0376] Property testing of positive electrode active materials

[0377] 1. Determination of the core chemical formula and the composition of different coating layers:

[0378] High spatial resolution characterization of the internal microstructure and surface structure of the positive electrode active material was performed using spherical aberration electron microscopy (ACSTEM). Combined with three-dimensional reconstruction technology, the core chemical formula and the composition of the first and second coating layers of the positive electrode active material were obtained.

[0379] 2. Initial capacity test of button cells:

[0380] At 2.5~4.3V, the button cell prepared above is charged to 4.3V at 0.1C, and then charged at 4.3V at constant voltage until the current is less than or equal to 0.05mA. After standing for 5 minutes, it is discharged to 2.0V at 0.1C. The discharge capacity at this time is the initial specific capacity, denoted as D0.

[0381] 3. Average discharge voltage (V) test of coin cells:

[0382] The coin cells prepared above were placed in a constant temperature environment of 25°C for 5 minutes, discharged at 0.1C to 2.5V, placed in a constant temperature environment for 5 minutes, charged at 0.1C to 4.3V, and then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. After being placed in a constant temperature environment for 5 minutes, they were discharged at 0.1C to 2.5V. The discharge capacity at this time is the initial specific capacity, denoted as D0, and the discharge energy is the initial energy, denoted as E0. The average discharge voltage V of the coin cells is E0 / D0.

[0383] 4. Full battery 60℃ gas expansion test:

[0384] The prepared full cell was stored at 60°C at 100% state of charge (SOC). The open-circuit voltage (OCV) and internal resistance (IMP) of the cell were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. The full cell was removed after every 48 hours of storage, allowed to stand for 1 hour, and then the OCV and IMP were measured. After cooling to room temperature, the cell volume was measured using the water displacement method. The water displacement method involves first measuring the cell's weight F1 separately using a balance with automatic unit conversion, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the experiment, the weight F2 of the battery cell and the buoyancy F of the battery cell are measured at this moment.浮 That is, F1-F2, and then according to Archimedes' principle, F 浮 The cell volume V is calculated to be V = (F1 - F2) / .

[0385] 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.

[0386] 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.

[0387] In addition, measure the residual capacity of the battery cell. Charge the full battery at 1C to 4.3V within the 2.5~4.3V range, then charge it at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, and record the charging capacity at this point as the residual capacity of the battery cell.

[0388] 5. Cyclic performance test of the entire battery at 45°C:

[0389] Under constant temperature conditions of 45℃, the prepared full battery was charged at 1C to 4.3V within a range of 2.5~4.3V, and then charged at a constant voltage of 4.3V until the current was less than or equal to 0.05mA. After resting for 5 minutes, it was discharged at 1C to 2.5V, and the discharge capacity at this point was recorded as D0. The aforementioned charge-discharge cycle was repeated until the discharge capacity decreased to 80% of D0. The number of cycles completed at this point was recorded.

[0390] 6. Lattice change rate test:

[0391] Under a constant temperature of 25℃, the positive electrode active material sample prepared above was placed in an XRD (model Bruker D8 Discover) and tested at 1° / min. The test data was then organized and analyzed. Referring to the standard PDF card, the lattice constants a0, b0, c0 and v0 were calculated (a0, b0 and c0 represent the length of each aspect of the unit cell, and v0 represents the volume of the unit cell, which can be directly obtained from the XRD refinement results).

[0392] Using the above-described method for preparing coin cells, the positive electrode active material sample was prepared into a coin cell, and the coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. The positive electrode sheet was then removed from the coin cell and immersed in dimethyl carbonate (DMC) for 8 hours. After drying, the powder was scraped off, and particles with a diameter less than 500 nm were screened out. Samples were taken, and their cell volume v1 was calculated in the same manner as the fresh samples tested above. The lattice change rate (cell volume change rate) before and after complete lithium insertion / extraction is shown in the table.

[0393] 7. Li / Mn inverse defect concentration test:

[0394] 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.

[0395] 8. Transition metal dissolution test:

[0396] The full battery, after being cycled at 45°C until its capacity decayed to 80%, was discharged at a 0.1C rate until the cutoff voltage of 2.0V. Then, the battery was disassembled, the negative electrode was removed, and 30 unit areas (1540.25 mm²) were randomly selected from the negative electrode. 2 The discs were tested using an Agilent ICP-OES730 inductively coupled plasma emission spectrometry (ICP). The amounts of Fe (if the Mn site of the positive electrode active material is doped with Fe) and Mn were calculated based on the ICP results, thus determining the amount of Mn (and Mn-doped Fe) dissolved after cycling. The testing standard was based on EPA-6010D-2014.

[0397] 9. Surface oxygen valence state test:

[0398] 5g of the positive electrode active material sample prepared above was used to prepare a coin cell according to the above method. The coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. Then, the positive electrode sheet of the coin cell was removed and immersed in dimethyl carbonate (DMC) for 8 hours. After drying, the powder was scraped off, and particles with a diameter of less than 500nm were screened out. The obtained particles were measured using electron energy loss spectroscopy (EELS, using a Talos F200S instrument) to obtain the energy loss near-edge structure (ELNES), which reflects the density of states and energy level distribution of the element. Based on the density of states and energy level distribution, the number of occupied electrons was calculated by integrating the valence band density of states data, thereby deducing the valence state of the surface oxygen after charging.

[0399] 10. Compacted density measurement:

[0400] Take 5g of the prepared positive electrode active material powder and place it in a compaction mold (CARVER mold, model 13mm, USA). Then place the mold on a compaction density instrument. Apply a pressure of 3T and read the thickness of the powder under pressure (thickness after depressurization; the area of ​​the container used for testing is 1540.25mm²) on the instrument. 2 The compaction density is calculated using ρ=m / v.

[0401] 11. X-ray diffraction method for determining the crystallinity of pyrophosphate and phosphate.

[0402] Take 5g of the positive electrode active material powder prepared above, and measure the total scattering intensity by X-rays. It is the sum of the scattering intensity of all matter in space. It is only related to the intensity of the primary rays, the chemical structure, and the total number of electrons participating in the diffraction, i.e., the mass, and is not related to the order state of the sample. Then, separate the crystalline scattering and non-crystalline scattering from the diffraction pattern. The crystallinity is the ratio of the scattering of the crystalline part to the total scattering intensity.

[0403] 12. Interplanar spacing and angles

[0404] 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 sample chamber of a TEM (Talos F200s G2) for testing. Obtain the original TEM test image and save it in the original image format (xx.dm3).

[0405] 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.

[0406] The results are shown in Table 3-6.

[0407] Table 3 Performance test results of Examples 1-1 to 1-33 and Comparative Examples 1-7

[0408]

[0409]

[0410]

[0411]

[0412]

[0413] Notes: 1) The crystallinity of Li2FeP2O7 and LiFePO4 in Examples 1-1 to 1-33 is 100%; 2) In Comparative Examples 5-7, the crystallinity of Li2FeP2O7 is 5% and the crystallinity of LiFePO4 is 8%.

[0414] As can be seen from Examples 1-1 to 1-33 and Comparative Examples 1-4, the presence of the first coating layer is beneficial for reducing the Li / Mn antisite defect concentration and the amount of Fe and Mn dissolved after cycling in the obtained material, thereby increasing the coin capacity of the battery and improving its safety and cycle performance. When other elements are doped at the Mn and phosphorus sites respectively, the lattice change rate, antisite defect concentration, and the amount of Fe and Mn dissolved in the obtained material can be significantly reduced, thereby increasing the specific capacity of the battery and improving its safety and cycle performance.

[0415] As can be seen from Examples 1-1 to 1-6, as the amount of the first coating layer increases from 3.2% to 6.4%, the concentration of Li / Mn antisite defects in the resulting material gradually decreases, and the dissolution of Fe and Mn after cycling gradually decreases. This leads to improved battery safety and cycling performance at 45°C, but a slight decrease in coin cell capacity. Optionally, the battery exhibits optimal overall performance when the total amount of the first coating layer is 4-5.6% by weight.

[0416] Based on Examples 1-3 and Examples 1-7 to 1-10, it can be seen that as the amount of the second coating layer increases from 1% to 6%, the concentration of Li / Mn antisite defects in the resulting material gradually decreases, and the dissolution of Fe and Mn after cycling gradually decreases. This leads to improved battery safety and cycling performance at 45°C, but a slight decrease in coin cell capacity. Optionally, the battery exhibits optimal overall performance when the total amount of the second coating layer is 3-5% by weight.

[0417] Based on Examples 1-11 to 1-15 and Comparative Examples 5-6, it can be seen that when Li2FeP2O7 and LiFePO4 are present in the first coating layer, especially when the weight ratio of Li2FeP2O7 and LiFePO4 is 1:3 to 3:1, and especially when it is 1:3 to 1:1, the improvement in battery performance is more significant.

[0418] Table 4 Performance test results of Examples 2-1 to 2-4

[0419]

[0420] As shown in Table 4, as the crystallinity of pyrophosphate and phosphate in the first coating layer gradually increases, the lattice change rate, Li / Mn antisite defect concentration, and Fe and Mn dissolution of the corresponding materials gradually decrease, the coin capacity of the battery gradually increases, and the safety performance and cycle performance gradually improve.

[0421] Table 5 Performance test results of Examples 3-1 to 3-12

[0422]

[0423]

[0424] As shown in Table 5, adjusting the reaction temperature and time within the reactor during the preparation of manganese oxalate particles can further improve the various properties of the cathode material presented in this application. For example, as the reaction temperature gradually increases from 60℃ to 130℃, the lattice change rate and the Li / Mn antisite defect concentration first decrease and then increase, with similar trends observed in the post-cycle metal dissolution and safety performance. Meanwhile, the coin capacity and cycle performance first increase and then decrease with increasing temperature. Maintaining a constant reaction temperature while adjusting the reaction time also yields similar results.

[0425] Table 6 Performance test results of Examples 4-1 to 4-7 and Comparative Examples 8-11

[0426]

[0427] As shown in Table 6, when preparing lithium iron pyrophosphate using the method of this application, the performance of the obtained material can be improved by adjusting the drying temperature / time and sintering temperature / time during the preparation process, thereby improving battery performance. As shown in Comparative Examples 8-11, when the drying temperature during the lithium iron pyrophosphate preparation process is below 100°C or the sintering temperature is below 400°C, the desired Li2FeP2O7 cannot be obtained, thus failing to improve material performance and the performance of batteries containing the obtained material.

[0428] Battery test

[0429] The secondary battery prepared using positive electrode plates P2-P48 was tested as follows:

[0430] (1) The energy density of the secondary battery was determined according to the method in GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles";

[0431] (2) The low-temperature discharge capacity retention rate of the secondary battery at -20℃ (two charge-discharge cycles) was determined according to the national standard GBT31486-2015 "Electrical performance requirements and test methods for power batteries for electric vehicles" to obtain the battery's kinetic data.

[0432] (3) Test the room temperature cycle life of the secondary battery at 80% SOH according to the standard cycle test method in GBT31484-2015 "Requirements and test methods for cycle life of power batteries for electric vehicles";

[0433] (4) Referring to the standard cycle test method in GB / T 31484-2015 "Requirements and test methods for cycle life of power batteries for electric vehicles", the test process temperature was adjusted to -10℃, the charging and discharging current was adjusted to 0.33C, and the other conditions remained unchanged. The low temperature cycle life of the secondary battery at 80% SOH was tested.

[0434] (5) Refer to the national standard GB / T 31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles" to determine the specific power data of the secondary battery at 20% SOC. The detailed steps are as follows:

[0435] a) Charge according to method 6.3.4 in national standard GB / T31486-2015;

[0436] b) At room temperature, the secondary battery is discharged at a 1C current for 48 minutes, then discharged at the specified maximum discharge current for 10 seconds, then left to stand for 30 minutes, and then charged at the specified maximum charging current for 10 seconds.

[0437] c) The specific power (W / kg) of the battery cell is calculated by dividing the discharge energy of a 10-second charge-discharge cycle by the 10-second charge-discharge time.

[0438] The results are shown in Table 7.

[0439] Table 7 Results of battery tests

[0440]

[0441]

[0442] Based on the above results, we can conclude that:

[0443] Compared with secondary batteries using positive electrode P2, secondary batteries using positive electrode P3-P30 have higher energy density, higher low-temperature discharge capacity retention, higher specific power, and longer low-temperature cycle life. Secondary batteries using positive electrode P3-P5, P7, P9-P12, P14-15, P17-18, P20-P22, P24, and P26-P30 have longer room temperature cycle life.

[0444] Compared with secondary batteries using positive electrode P31, secondary batteries using positive electrode P32 have higher energy density, higher low-temperature discharge capacity retention, higher specific power, and longer low-temperature cycle life.

[0445] Positive electrode sheets P41-P48 contain a first positive electrode active material and a second positive electrode active material, while positive electrode sheets P33-P40 contain only an equal amount of the corresponding second positive electrode active material. Compared with positive electrode sheets containing only the second positive electrode active material, secondary batteries made from positive electrode sheets containing both the first and second positive electrode active materials have higher energy density, higher low-temperature discharge capacity retention, higher specific power, and longer low-temperature cycle life.

[0446] The above demonstrates that the secondary battery made from the positive electrode sheet of this application has higher energy density, better dynamic performance, higher cell rate performance, longer low-temperature cycle life, higher low-temperature cycle capacity retention, and higher safety.

[0447] 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 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; at least one layer of the at least one positive electrode film layer having a multilayer structure simultaneously contains a first positive electrode active material and a second positive electrode active material having a core-shell structure; The first positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, The kernel contains Li 1+x Mn 1-y A y P 1-z R z O4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; the crystallinity of the pyrophosphate and the phosphate is independently from 10% to 100%; 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 selected from the range of -0.100 to 0.100; The value of y is selected from the range of 0.001 to 0.500; The z is selected from the range of 0.001 to 0.100; The M and X independently include one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; The second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, and LiFe b D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein the D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, wherein the b is independently selected from the range of 0.99 to 0.999 and b+c=1.

2. A positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the positive electrode film layer is a single-layer structure; at least one of the positive electrode film layers simultaneously comprises a first positive electrode active material and a second positive electrode active material having a core-shell structure; the mass ratio of the first positive electrode active material to the second positive electrode active material is 1:7-7:1; The first positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, The kernel contains Li 1+x Mn 1-y A y P 1-z R z O4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; the crystallinity of the pyrophosphate and the phosphate is independently from 10% to 100%; 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 selected from the range of -0.100 to 0.100; The value of y is selected from the range of 0.001 to 0.500; The z is selected from the range of 0.001 to 0.100; The M and X independently include one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; The second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, and LiFe b D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein the D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, wherein the b is independently selected from the range of 0.99 to 0.999 and b+c=1.

3. A positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; at least one of the positive electrode film layers is a multilayer structure, and any positive electrode film layer having a multilayer structure contains a first positive electrode active material and a second positive electrode active material having a core-shell structure in different layers; The first positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, The kernel contains Li 1+x Mn 1-y A y P 1-z R z O4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; the crystallinity of the pyrophosphate and the phosphate is independently from 10% to 100%; 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 selected from the range of -0.100 to 0.100; The value of y is selected from the range of 0.001 to 0.500; The z is selected from the range of 0.001 to 0.100; The M and X independently include one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; The second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, and LiFe b D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein the D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, wherein the b is independently selected from the range of 0.99 to 0.999 and b+c=1.

4. The positive electrode sheet according to claim 3, wherein, Any of the positive electrode film layers having a multilayer structure contains the first positive electrode active material and the second positive electrode active material in adjacent layers, respectively.

5. A positive electrode sheet, 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; at least one of the positive electrode film layer A and the positive electrode film layer B is a multilayer structure; at least one layer of the positive electrode film layer A contains a first positive electrode active material having a core-shell structure, and at least one layer of the positive electrode film layer B contains a second positive electrode active material; The first positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, The kernel contains Li 1+x Mn 1-y A y P 1-z R z O4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; the crystallinity of the pyrophosphate and the phosphate is independently from 10% to 100%; 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 selected from the range of -0.100 to 0.100; The value of y is selected from the range of 0.001 to 0.500; The z is selected from the range of 0.001 to 0.100; The M and X independently include one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; The second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, and LiFe b D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein the D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, wherein the b is independently selected from the range of 0.99 to 0.999 and b+c=1.

6. A positive electrode sheet, 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 are monolayer structures; the positive electrode film layer A contains a first positive electrode active material having a core-shell structure, and the positive electrode film layer B contains a second positive electrode active material; the mass ratio of the first positive electrode active material to the second positive electrode active material is 1:7-7:1; The first positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer; wherein, The kernel contains Li 1+x Mn 1-y A y P 1-z R z O4, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer comprises carbon; the crystallinity of the pyrophosphate and the phosphate is independently from 10% to 100%; 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 selected from the range of -0.100 to 0.100; The value of y is selected from the range of 0.001 to 0.500; The z is selected from the range of 0.001 to 0.100; The M and X independently include one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; The second positive electrode active material is selected from LiFePO4, carbon-coated LiFePO4, and LiFe b D c PO4 and carbon-coated LiFe b D c One or more of PO4, wherein the D independently includes one or more elements selected from Ti, Zn, Co, Mn, La, V, Mg, Al, Nb, W, Zr, Nb, Sm, Cr, Cu and B, wherein the b is independently selected from the range of 0.99 to 0.999 and b+c=1.

7. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the second positive electrode active material, The carbon content accounts for 0.1%-4% of the mass of the carbon-coated LiFePO4; and / or, The carbon mass percentage of the carbon-coated LiFe b D c 0.1%-4% of the mass of PO4.

8. The positive electrode sheet according to claim 1, 3, 4 or 5, wherein, The mass ratio of the first positive electrode active material to the second positive electrode active material is 1:7-7:

1.

9. 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 1:4-4:

1.

10. 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 Zn, Fe, Ti, V, Ni, Co, and Mg; and / or, The x is selected from the range of -0.100 to 0.006; and / or, The value of y is selected from the range of 0.1 to 0.4; and / or, The M and X independently include one or more elements selected from Li and Fe; and / or, The ratio of y to 1-y is selected from 1:10 to 10:1; and / or, The ratio of z to 1-z is selected from 1:999 to 1:

9.

11. The positive electrode according to any one of claims 1 to 6, wherein, The A element comprises at least two elements selected from Fe, Ti, V, Ni, Co, and Mg.

12. The positive electrode according to any one of claims 1 to 6, wherein, The ratio of y to 1-y is selected from 1:4 to 1:

1.

13. The positive electrode according to any one of claims 1 to 6, wherein, The ratio of z to 1-z is selected from 1:499 to 1:

249.

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

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% by weight and less than or equal to 7% 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 4%-5.6% 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 weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:

1.

18. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 1:

1.

19. The positive electrode sheet according to any one of claims 1 to 6, wherein, In the first positive electrode active material, the crystallinity of the pyrophosphate and the phosphate is independently 50% to 100%.

20. 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 second coating layer is greater than 0% by weight and less than or equal to 6% by weight, based on the weight of the core.

21. 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 second coating layer is 3%-5% by weight, based on the weight of the core.

22. The positive electrode sheet according to any one of claims 1 to 6, wherein, The concentration of Li / Mn antisite defects in the first positive electrode active material is below 4%.

23. The positive electrode sheet according to any one of claims 1 to 6, wherein, The concentration of Li / Mn antisite defects in the first positive electrode active material is below 2%.

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 is less than 6%.

25. 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 is less than 4%.

26. 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 below -1.

88.

27. 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.

88.

28. The positive electrode sheet according to any one of claims 1 to 6, wherein, The first positive electrode active material has a compaction density of 2.0 g / cm³ under 3 tons of pressure. 3 above.

29. The positive electrode sheet according to any one of claims 1 to 6, wherein, The first positive electrode active material has a compaction density of 2.2 g / cm³ under 3 tons of pressure. 3 above.

30. 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.

31. A secondary battery comprising a positive electrode sheet according to any one of claims 1 to 30.

32. A battery module comprising the secondary battery of claim 31.

33. A battery pack comprising the battery module of claim 32.

34. An electrical device comprising at least one selected from the secondary battery of claim 31, the battery module of claim 32, and the battery pack of claim 33.

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