Positive plate and manufacturing method, secondary battery and electric device

Abstract

A positive plate and a method of manufacturing, as a secondary battery. The positive plate comprises a current collector and a positive active layer, wherein the positive active layer is installed on at least one surface of the current collector, and the positive active layer comprises a first positive active layer formed on at least the current collector and a second positive active layer formed on one side of the first positive active layer far from the current collector, wherein the first positive active layer comprises lithium iron phosphate particles and the second positive active layer comprises lithium nickel cobalt manganese oxide particles; or, the first positive active layer comprises lithium nickel cobalt manganese oxide particles and the second positive active layer comprises lithium iron phosphate particles; the primary average particle size of the lithium iron phosphate particles is 500 to 3000 nm, and the specific surface area BET of the lithium iron phosphate particles is 3 m² / g to 8 m² / g. The positive plate can reduce the degree of gas generation of the upper and lower layer coatings of lithium iron phosphate particles and lithium nickel cobalt manganese oxide particles, while also having a relatively excellent capacity per gram.

Description

Technology Field

[0001] Cross-reference regarding related applications

[0002] The present application claims priority to Chinese patent application No. 202410026235.1, filed on January 8, 2024, titled "Polygonal piece and method of manufacturing, secondary battery and electric device," and the said Chinese patent application is incorporated by reference into the present application.

[0003] This application relates to the field of secondary battery technology, and in particular to a positive electrode and a method of manufacturing, a secondary battery and an electric device. Background Technology

[0004] Recently, lithium-ion batteries are being widely applied in various fields, including energy storage power systems such as hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0005] Lithium nickel-cobalt-manganese oxide (LCD) and lithium iron phosphate (IUPAC) materials are commonly used lithium-ion cathode active materials. While a combination of these materials can be used to reduce the cost of lithium-ion batteries, this type of cathode active material generates severe gas, which significantly impacts battery safety and lifespan. Therefore, addressing the aforementioned issues in the mixed system of lithium iron phosphate and lithium nickel-cobalt-manganese oxide ternary materials is of great significance.

[0006] This application has been made in consideration of the above-described problem and aims to solve at least one of the technical problems existing in the prior art. Accordingly, this application provides a positive electrode, a method of manufacturing, a secondary battery, and an electric device. The positive electrode of this application reduces the degree of gas generation while also possessing the capacity per gram of a secondary battery.

[0007] A first aspect of the present application provides a positive plate, wherein the positive plate comprises a current collector and a positive active layer, and the positive active layer is installed on at least one surface of the current collector.

[0008] The positive active layer comprises at least a first positive active layer formed on a current collector, and a second positive active layer formed on one side of the first positive active layer far from the current collector.

[0009] The first positive active layer comprises lithium iron phosphate particles, and the second positive active layer comprises lithium nickel cobalt manganese oxide particles; or,

[0010] The first positive active layer comprises lithium nickel cobalt manganese oxide particles, and the second positive active layer comprises lithium iron phosphate particles;

[0011] The primary average particle size of lithium iron phosphate particles is 500–3000 nm, and the specific surface area BET of lithium iron phosphate particles is 3 m² 2 / g~8m 2 / g is.

[0012] Generally, the electrochemical performance of lithium iron phosphate particles is improved through nano-sizing. However, nano-sized lithium iron phosphate particles have an excessively large specific surface area, leading to severe moisture absorption. During the battery cell cycle, high moisture content in the electrode pieces easily increases interfacial side reactions, which in turn increases gas generation and poses a serious threat to the safety performance and service life of the secondary battery. Due to the aforementioned issues with lithium iron phosphate particles, the problem of gas generation in cathode active materials, which are coated with a mixture of lithium iron phosphate particles and lithium nickel cobalt manganese oxide particles in upper and lower layers, is also very pronounced. This application controls the primary average particle size of lithium iron phosphate particles to 500–3000 nm while simultaneously increasing their specific surface area to 3 m² 2 / g~8m 2It is further adjusted to / g. A relatively low specific surface area is advantageous for reducing the moisture absorption of the material as it possesses relatively low specific surface energy, thereby allowing for a reduction in moisture content during the processing and storage of the cathode active material. At the same time, a relatively low specific surface area is also advantageous for the volatilization of moisture within the material, which further reduces the moisture content of the cathode active material. However, excessively large particle size and excessively low specific surface area affect kinetic performance and lower the capacity per gram of the cathode active material. The cathode active material of the present application increases the primary average particle size of lithium iron phosphate particles and lowers their specific surface area, controlling both within a reasonable range to significantly reduce the moisture content of the cathode active material. This reduces the degree of gas generation in the secondary battery and improves the safety and circulation performance of the secondary battery, while also maintaining the capacity per gram of the cathode active material.

[0013] In any embodiment, the primary average particle size of the lithium iron phosphate particles is 650 to 2500 nm.

[0014] By controlling the primary average particle size of the lithium iron phosphate particles within an appropriate range, it is advantageous to further balance the degree of gas generation and the capacity per gram of the secondary battery.

[0015] In any embodiment, the specific surface area BET of the lithium iron phosphate particles is 4 m 2 / g~7m 2 / g is.

[0016] BET of lithium iron phosphate particles 4m 2 / g~7m 2 By controlling it within / g, it is advantageous to further balance the degree of gas generation and the capacity per gram of the secondary battery.

[0017] In any embodiment, when calculated based on the total weight of the lithium iron phosphate particles, the carbon content of the lithium iron phosphate particles is Cx weight%, and the ratio z of the specific surface area BET of the lithium iron phosphate particles to Cx satisfies 1.5≤z≤8.5, and in some embodiments, the ratio z of the specific surface area BET of the lithium iron phosphate particles to Cx satisfies 3≤z≤6.

[0018] In this application, the ratio z of the specific surface area BET and Cx of the lithium iron phosphate particles can characterize the degree of uniform density of the carbon contained in the lithium iron phosphate particles, and when the primary average particle size and carbon content of the lithium iron phosphate particles remain unchanged, the lower the ratio z, the more uniform and dense the carbon contained in the lithium iron phosphate particles becomes. Improving the degree of uniform density of the contained carbon is advantageous for improving the kinetic performance and capacity per gram of the lithium iron phosphate particles; however, if the carbon density is too high, it affects the insertion and extraction of lithium ions, thereby affecting the kinetic performance and capacity per gram of the secondary battery. The z ratio range of this application is advantageous for the carbon contained in the lithium iron phosphate particles to have an appropriate uniform density, which is advantageous for improving the conductivity performance of the particle surface and further improving the capacity per gram and kinetic performance of the secondary battery. Furthermore, the discharge voltage range of the lithium nickel cobalt manganese oxide particles is higher. In a double-layer cathode active material, improving the kinetic performance of lithium iron phosphate particles makes it more advantageous for combined discharge with lithium nickel cobalt manganese oxide particles, thereby being advantageous for further improving the overall kinetic performance of the cathode active material.

[0019] In any embodiment, the carbon content of the lithium iron phosphate particles is 0.8 wt% to 2.0 wt% when calculated based on the total weight of the lithium iron phosphate particles, and in some embodiments, the carbon content of the lithium iron phosphate particles is 1.0 wt% to 1.6 wt% when calculated based on the total weight of the lithium iron phosphate particles.

[0020] The carbon content range of the present application helps to further improve the capacity per gram of the secondary battery while simultaneously reducing the impact on the degree of moisture absorption.

[0021] In any embodiment, the lithium iron phosphate particles have the molecular formula Li m1 Fe x1 P y1 O z1 Q q1 having, where Q comprises at least one of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and 0.95≤m1≤1.15, 0.9≤x1≤1, 0.95≤y1≤1, 3.5≤z1≤4, 0 <q1≤0.1이며, 및 / 또는

[0022] Lithium nickel cobalt manganese oxide particles have the molecular formula LiR x2 Ni y2 Co z2 Mn 1-x2-y2-z2 It has O2, where R includes at least one of Cr, Ti, V, Mg, Al, and Nb, and 0≤x2<1, 0 <y2<1, 0<z2<1, 0<x2+y2+z2<1이다.

[0023] In any embodiment, Q comprises at least one of Ti, V, Mg, and Nb, and in some embodiments, Q is Ti.

[0024] Doping lithium iron phosphate particles and / or lithium nickel cobalt manganese oxide particles with the aforementioned elements helps to improve the ion transport capacity of the cathode active material. Furthermore, the discharge performance requirements for lithium nickel cobalt manganese oxide particles are relatively high. In a double-layer cathode active material, improving the kinetic performance of lithium iron phosphate particles makes it more advantageous for combined discharge with lithium nickel cobalt manganese oxide particles, thereby facilitating further improvement of the overall kinetic performance of the cathode active material.

[0025] In any embodiment, when calculated based on the total weight of the lithium iron phosphate particles, the content of Q in the lithium iron phosphate particles is 1,000 to 10,000 ppm, and in some embodiments, when calculated based on the total weight of the lithium iron phosphate particles, the content of Q in the lithium iron phosphate particles is 2,500 to 6,000 ppm.

[0026] The content of the Q element in conventional lithium iron phosphate particles is generally low or no Q element is added. The range of the Q element in this application helps to balance the primary average particle size on the basis of further improving the kinetic performance and capacity per gram of the cathode active material.

[0027] In any embodiment, the capacity ratio of the lithium iron phosphate particles is η≥88%, and η is:

[0028] A battery having lithium iron phosphate particles as the positive electrode active material is charged and discharged twice with a constant current at a rate limit of 0.1C within a voltage range of 2.0V to 3.75V, followed by a single charge and discharge with a rate limit of 1C. In a charge-discharge test with a rate limit of 1C, a capacity value at a discharge voltage of 3.2V is extracted as C1, and a capacity value discharged to 2.0V is extracted as C2, and η is defined as C1 / C2. Here, the charging process includes constant voltage charging, the constant voltage is 3.75V, and the constant voltage cutoff current is 50μA.

[0029] The capacity ratio η of the lithium iron phosphate particles can represent kinetic performance and can be controlled by adjusting the primary average particle size, carbon content, ratio of carbon source to carbon film-forming agent, and the modifier and its content. The η value of the lithium iron phosphate particles of the present application is ≥ 88%, and they have relatively excellent kinetic performance.

[0030] In any embodiment, the lithium iron phosphate particles satisfy at least one of (a) to (f):

[0031] a) Dv10≥200 nm of lithium iron phosphate particles;

[0032] b) The Dv50 of lithium iron phosphate particles is 500–5000 nm;

[0033] c) Dv90≤10000nm of lithium iron phosphate particles;

[0034] d) Dv99≤12000nm of lithium iron phosphate particles;

[0035] e) Powder compression density of lithium iron phosphate at 3T pressure ≥ 2.25 g / cm³ 3 ;

[0036] f) The powder resistivity of lithium iron phosphate is less than 60 Ω·cm.

[0037] By ensuring that the lithium iron phosphate particles satisfy at least one of (a) to (f), the lithium iron phosphate particles can be made to better realize the technical effects of the present application.

[0038] In any embodiment, when the first positive active layer comprises lithium iron phosphate particles and the second positive active layer comprises lithium nickel cobalt manganese oxide particles, the coating weight of the first positive active layer is 0.02 to 0.38 g / 1540 mm 2 and the coating weight of the second anode active layer is 0.08~0.32g / 1540mm 2 is;

[0039] When the first positive active layer comprises lithium nickel cobalt manganese oxide particles and the second positive active layer comprises lithium iron phosphate particles, the coating weight of the first active layer is 0.08 to 0.32 g / 1540 mm 2 and the coating weight of the second anode active layer is 0.02~0.38g / 1540mm 2 is;

[0040] In some embodiments,

[0041] When the first positive active layer comprises lithium iron phosphate particles and the second positive active layer comprises lithium nickel cobalt manganese oxide particles, the coating weight of the first positive active layer is 0.05 to 0.32 g / 1540 mm 2 and the coating weight of the second anode active layer is 0.1~0.28g / 1540mm 2 is;

[0042] When the first positive active layer comprises lithium nickel cobalt manganese oxide particles and the second positive active layer comprises lithium iron phosphate particles, the coating weight of the first active layer is 0.1 to 0.28 g / 1540 mm 2 and the coating weight of the second anode active layer is 0.05~0.32g / 1540mm 2 am.

[0043] By controlling the weight of the first or second positive active layer containing lithium iron phosphate particles and the second or first positive active layer containing lithium nickel cobalt manganese oxide particles within the scope of the present application, it helps to lower the cost of the positive active material while still obtaining a relatively excellent capacity per gram.

[0044] In any embodiment, the total thickness of the positive active layer is 50 to 150 μm, and in some embodiments, the total thickness of the positive active layer is 60 to 90 μm.

[0045] The thickness of the positive electrode active material of the present application helps maintain relatively excellent kinetic performance and volumetric energy density.

[0046] In any embodiment, the first positive active layer comprises lithium iron phosphate particles, and the second positive active layer comprises lithium nickel cobalt manganese oxide particles.

[0047] By placing lithium iron phosphate particles in the first active layer, it is more advantageous for improving the electrical performance of the secondary battery.

[0048] In any embodiment, the lithium iron phosphate particles are mainly:

[0049] A raw material is provided containing at least a lithium source, an iron source, a phosphorus source, an optional carbon film-forming agent, an optional carbon source, and an optional modifier, and is obtained by a manufacturing method of sintering at least twice, wherein,

[0050] The primary sintering temperature is 500℃ to 760℃, and in some embodiments, 550℃ to 720℃;

[0051] The secondary sintering temperature is 700℃ to 800℃, and in some embodiments, 720℃ to 780℃.

[0052] Compared to traditional manufacturing methods that achieve particle growth using high temperatures, the lithium iron phosphate particles of the present application are advantageous for producing lithium iron phosphate particles having the primary average particle size and specific surface area of ​​the present application by performing two rounds of sintering and controlling the sintering temperature twice. Furthermore, in a conventional high-temperature sintering process, the carbon coating layer on the particle surface easily cracks, thereby degrading the integrity of the carbon coating. The present application is advantageous for reducing suspended carbon and improving the consistency and uniformity of the surface carbon coating by performing large particle synthesis at low temperatures.

[0053] In any embodiment, lithium iron phosphate particles are obtained by a manufacturing method comprising providing a raw material containing at least: a lithium source, an iron source, a phosphorus source, a carbon source, a carbon film-forming agent, and a modifier, and sintering at least twice, wherein,

[0054] The carbon content of the material after the first sintering is 0.01 wt% to 0.79 wt%, and in some embodiments, 0.05 wt% to 0.4 wt%;

[0055] The carbon content of the material after secondary sintering is 0.8 wt% to 2.0 wt%, and in some embodiments, 1.0 wt% to 1.6 wt%.

[0056] In the manufacturing method of the embodiment of the present application, by adding a carbon source before the first sintering, the trivalent iron in the raw material can be effectively reduced, thereby improving the purity and stability of the product. Furthermore, by controlling the first sintering temperature and the carbon content of the intermediate after the first sintering within the aforementioned range, it helps to increase the primary particle size of the lithium iron phosphate particle precursor obtained after the first sintering. Specifically, in the first sintering, a relatively low carbon content is advantageous for crystal growth of the lithium iron phosphate particle precursor at a relatively low temperature, as the carbon layer is advantageous for lowering the blocking effect on the growth process of the lithium iron phosphate particles. At the same time, it is advantageous for the solid-state diffusion reaction between the modifier that can be added and the lithium iron phosphate material, thereby being advantageous for achieving a relatively high concentration of metal ion doping. By controlling the secondary sintering temperature and the carbon content of the material after sintering within the range described above, carbon is better coated on the surface of the lithium iron phosphate particles, which helps to form a uniform and dense carbon coating layer, improves the surface conductivity performance of the lithium iron phosphate particles, and is advantageous for improving kinetic performance and capacity per gram.

[0057] In any embodiment, the method for manufacturing lithium iron phosphate particles is:

[0058] It includes the step of performing first sintering followed by first grinding, and performing second sintering followed by second grinding, wherein,

[0059] The Dv50 of the product after primary grinding is 300 nm to 1200 nm, and in some embodiments, 400 nm to 1100 nm;

[0060] The Dv50 of the product after secondary grinding is 500 nm to 5000 nm, and in some embodiments, 700 nm to 2500 nm.

[0061] By controlling the Dv50 of the product after the first grinding to within the aforementioned range, the added carbon source and the doping element that may be added are advantageous for lowering the blocking effect on the growth of the lithium iron phosphate particle precursor crystals, and help in producing micrometer-sized lithium iron phosphate particle precursors. By controlling the Dv50 value of the product after the second grinding to within the aforementioned range, it helps in obtaining lithium iron phosphate particles having the primary average particle size of the present application.

[0062] A second aspect of the present application provides a secondary battery, wherein the secondary battery comprises a positive plate according to the present application.

[0063] A third aspect of the present application provides an electric device, the electric device comprising a positive electrode according to the present application or a secondary battery according to the present application.

[0064] The foregoing description is merely an overview of the technical method of the present application, and in order to more clearly understand the technical means of the present application, and to make the description and other purposes, features, and advantages of the present application more obvious and easy to understand, specific embodiments of the present application are specifically listed below. Brief explanation of the drawing

[0065] FIG. 1 is an anode section of Example 3 of the present application, FIG. 1a is an anode section under 1,000x magnification conditions; FIG. 1b is an anode section under 3,000x magnification conditions. FIG. 2 is a schematic diagram of a secondary battery of one embodiment of the present application. FIG. 3 is an exploded view of a secondary battery of one embodiment of the present application shown in FIG. 2. FIG. 4 is a schematic diagram of a battery module of one embodiment of the present application. FIG. 5 is a schematic diagram of a battery pack of one embodiment of the present application. FIG. 6 is an exploded view of a battery pack of one embodiment of the present application illustrated in FIG. 5. FIG. 7 is a schematic diagram of an electric device using a secondary battery as a power source according to one embodiment of the present application. FIG. 8 is a scanning electron microscope image of lithium iron phosphate particles showing the primary particle size of one embodiment of the present application. Specific details for implementing the invention

[0066] Hereinafter, embodiments specifically disclosed by the positive active material and method of manufacturing the same, positive plate, secondary battery, battery module, battery pack, and electrical device of the present application will be described in detail with appropriate reference to the drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of known matters may be omitted, and repetitive descriptions of substantially identical structures may be omitted. This is intended to avoid making the following description unnecessarily long and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the contents described in the claims.

[0067] The “ranges” disclosed in this application are limited in the form of lower and upper limits, and a given range is limited by selecting one lower limit and one upper limit, and the selected lower limit and upper limit limit the boundaries of a particular range. A range limited in this way may or may not include end values ​​and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a single range. For example, if ranges 60–120 and 80–110 are listed for a specific parameter, it is expected to be understood as ranges 60–110 and 80–120. In addition, if minimum range values ​​1 and 2 are listed and maximum range values ​​3, 4, and 5 are listed, the following ranges 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5 may all be expected. In this application, unless otherwise stated, numeric ranges “a–b” represent a simplified expression of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between "0 to 5" are listed in this document, and "0 to 5" is merely an abbreviated expression for such numerical combinations. Also, specifying that any parameter is an integer greater than 2 is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0068] Unless otherwise specified, all embodiments and optional embodiments of the present application may be combined with one another to form a new technical solution.

[0069] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with one another to form a new technical solution.

[0070] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, and sequentially is preferred. For example, the statement that the method comprises steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the expression stating that the method may also comprise step (c) indicates that step (c) may be added to the method in any order, and for example, the method may comprise steps (a), (b), and (c), steps (a), (c), and (b), or steps (c), (a), and (b).

[0071] Unless otherwise specified, the terms "comprehensive" and "include" as used in this application represent open expressions, which may also be closed expressions. For example, the "comprehensive" and "include" may also encompass or include other components not listed, or may only encompass or include the listed components.

[0072] Unless otherwise specified, the term “or” in this application is inclusive. For example, the expression “A or B” indicates “A, B or both A and B”. More specifically, any one of the following conditions all satisfy the “A or B” condition: 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 A and B are both true (or exist).

[0073] Since lithium nickel cobalt manganese oxide particles have a relatively high cost, they can be mixed with lithium iron phosphate and manufactured into a mixed cathode active layer coated on the upper and lower layers, respectively. However, lithium iron phosphate particles have the problem of poor kinetic performance. To improve the electrical performance of lithium iron phosphate particles, they are typically nanoscaled; a relatively small particle size and a relatively large specific surface area are advantageous for enhancing electron transport capabilities. However, nanoscaled lithium iron phosphate particles have an excessively large specific surface area, leading to severe moisture absorption. During the battery cell cycle, if the moisture content of the electrode pieces is too high, interfacial side reactions easily increase, leading to increased gas generation. Simultaneously, the high specific surface area accelerates side reactions between the cathode active material layer and the electrolyte at high voltages, posing a serious threat to the safety performance of the secondary battery. Therefore, relatively severe gas generation occurs in the mixed cathode active layer. The present application, through the optimization of the lithium iron phosphate process and composition, increases the primary average particle size of the lithium iron phosphate particles, lowers their BET value, and controls both within a reasonable range, thereby reducing the moisture absorption of the mixed cathode active material while also possessing the capacity per gram of the mixed cathode active material.

[0074] [Polar Side]

[0075] Based on this, the present application provides a positive plate, wherein the positive plate comprises a current collector and a positive active layer, and the positive active layer is installed on at least one surface of the current collector.

[0076] The positive active layer comprises at least a first positive active layer formed on a current collector, and a second positive active layer formed on one side of the first positive active layer far from the current collector.

[0077] The first positive active layer comprises lithium iron phosphate particles, and the second positive active layer comprises lithium nickel cobalt manganese oxide particles; or,

[0078] The first positive active layer comprises lithium nickel cobalt manganese oxide particles, and the second positive active layer comprises lithium iron phosphate particles;

[0079] The primary average particle size of lithium iron phosphate particles is 500–3000 nanometers (nm), and the specific surface area BET of lithium iron phosphate particles is 3 square meters / gram (m²). 2 / g)~8m 2 / g is.

[0080] In this application, the term "primary average particle size" refers to the average value of the primary particle size of all particles, wherein the primary particle size refers to the longest distance connecting two points at the edge in a cross-sectional view. In a specific embodiment, as shown in the scanning electron microscope image of the lithium iron phosphate particles in FIG. 8, the line segment indicated by the double arrow among the particles is the primary particle size defined in this application.

[0081] In this application, the terms "specific surface area" or "BET" refer to the total area of ​​a unit mass particle, and in this application, the BET of a lithium iron phosphate particle is related to factors such as the primary average particle size of the lithium iron phosphate particle, carbon content, the degree of density of the carbon coating, and the degree of porosity of the particle.

[0082] In some embodiments, the lithium iron phosphate particles are primary particles.

[0083] In this document, "primary particle" refers to a particle that lacks distinct aggregation interfaces in scanning electron microscope images but may contain fine pores and point or line defects, and is distinguished from powder particles of the smallest unit that lack structure, such as aggregation and planar connection.

[0084] In some embodiments, the lithium iron phosphate particles are single-crystal particles and / or polycrystalline particles.

[0085] In this document, the term "single crystal" refers to a crystal with a complete structure grown from a single crystal nucleus. The single crystal of this application is a single integrated body in the field of view of a transmission electron microscope, and there are no grain boundaries within the single crystal.

[0086] In some embodiments, the single crystal of the present application may have microscopic defects, for example, micropores, small amounts of dots and planes may be present internally, or small amounts of mutual adhesion of particles may be present on the surface of a particle.

[0087] In this document, the term "polycrystalline" refers to a crystal formed by combining small single-crystal particles in a random orientation, and grain boundaries exist within the polycrystalline structure.

[0088] In some embodiments, the number ratio of single-crystal particles is 90% or more based on the total number of lithium iron phosphate particles. By controlling the number ratio of single-crystal particles within the range described above, the proportion of single-crystal particles is relatively high compared to polycrystalline and secondary aggregates, which is advantageous for lowering BET.

[0089] The primary average particle size of lithium iron phosphate particles can be measured using methods and devices known in the art. For example, it can be tested using a scanning electron microscope and the Peret diameter statistical method. For example, the electrode piece is cut perpendicular to the large surface of the anode piece using an argon ion beam to expose a cross-section, and the cross-section is photographed using a scanning electron microscope. The first anode active layer and the second anode active layer of the cross-section have clear boundaries, and the particle size of the anode active layer containing lithium iron phosphate particles is statistically analyzed using the Peret diameter statistical method. Specifically, the total number of lithium iron phosphate particles with a primary particle size greater than 80 nm can be statistically determined from the electron microscope scanning image, and the sum of the primary particle sizes of lithium iron phosphate particles with a primary particle size greater than 80 nm can be statistically determined. The primary average particle size of the lithium iron phosphate particles = primary particle size of total lithium iron phosphate particles / total number of lithium iron phosphate particles. Here, particles with a primary particle size of 0 < primary particle size ≤ 80 nm adhere easily, so there is a relatively large error in the statistics and it is difficult to clearly identify them individually. Therefore, in the statistical process of primary particle size, particles with a primary particle size of 0 < primary particle size ≤ 80 nm are not included within the statistical range.

[0090] To improve the electrical performance of lithium iron phosphate particles, they are typically nanoscaled; a relatively small particle size and a relatively large specific surface area are advantageous for enhancing electron transport capabilities. However, nanoscaled lithium iron phosphate particles have such a large specific surface area that moisture absorption becomes severe. During the battery cell cycle, if the moisture content of the electrode pieces is too high, interfacial side reactions easily increase, leading to increased gas generation and posing a serious threat to the safety performance of the secondary battery. Due to the aforementioned problems with lithium iron phosphate particles, the issue of gas generation in the cathode active material, which is coated by mixing lithium iron phosphate particles and lithium nickel cobalt manganese oxide particles in upper and lower layers, is also very prominent. This application controls the primary average particle size of lithium iron phosphate particles to 500–3000 nm while simultaneously setting their specific surface area to 3 m² 2 / g~8m 2 It is further adjusted to / g. A relatively low specific surface area is advantageous for reducing the moisture absorption of the material as it possesses relatively low specific surface energy, thereby allowing for a reduction in moisture content during the processing and storage of the cathode active material. At the same time, a relatively low specific surface area is also advantageous for improving the volatility of moisture in the material, which further reduces the moisture content of the cathode active material. However, excessively large particle size and excessively low specific surface area affect kinetic performance and lower the capacity per gram of the cathode active material. The cathode active material of the present application increases the primary average particle size of lithium iron phosphate particles and lowers the specific surface area, controlling both within a reasonable range to significantly reduce the moisture content of the cathode active material. At the same time, by lowering the active specific surface area that reacts at high voltage, it reduces the degree of gas generation in the secondary battery and improves the safety and circulation performance of the secondary battery, while also maintaining the capacity per gram of the cathode active material.

[0091] In some embodiments, the primary average particle size of the lithium iron phosphate particles is 650 to 2500 nm.

[0092] In some embodiments, the primary average particle size of the lithium iron phosphate particles may be a numeric value within a range consisting of 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 730 nm, 750 nm, 780 nm, 800 nm, 830 nm, 850 nm, 870 nm, 900 nm, 950 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 2000 nm, 2100 nm, 2200 nm, 2300 nm, 2400 nm, 2500 nm, 2600 nm, 2700 nm, 2800 nm, 2900 nm, 3000 nm, or any two of the primary average particle sizes described above.

[0093] By controlling the primary average particle size of the above lithium iron phosphate particles to within an appropriate range, it is advantageous to further balance the degree of gas generation and the capacity per gram of the secondary battery.

[0094] In some embodiments, the specific surface area BET of the lithium iron phosphate particles is 4 m 2 / g~7m 2 / g is.

[0095] In some embodiments, the specific surface area BET of the lithium iron phosphate particles is 3 m 2 / g, 3.5m 2 / g, 4m 2 / g, 4.5m 2 / g, 5m 2 / g, 5.5m 2 / g, 6m 2 / g, 6.5m 2 / g, 7m 2 / g, 7.5m 2 / g, 8m 2 / g, or a value within the range consisting of any two specific surface area BETs described above.

[0096] The specific surface area BET of a particle can be measured using methods and devices known in the art. For example, it can be tested by referring to GB / T 19587-2017. For example, lithium iron phosphate particles are taken as a sample and placed in a sample tube, the sample tube is immersed in liquid nitrogen at -196 degrees Celsius (°C), and the amount of nitrogen gas adsorbed on the solid surface is measured at different pressures with relative pressures of 0.05 to 0.30. The specific surface area of ​​the sample is obtained by calculating the amount of monolayer adsorption of the sample based on the BET multilayer adsorption theory and its formula.

[0097] If the BET of lithium iron phosphate particles is too high, moisture absorption increases, leading to severe gas generation in the secondary battery. If the BET of lithium iron phosphate particles is too low, the capacity per gram decreases. The BET of lithium iron phosphate particles is 4m 2 / g~7m 2 By controlling it within / g, it is advantageous to further balance the degree of gas generation and the capacity per gram of the secondary battery.

[0098] In some embodiments, when calculated based on the total weight of the lithium iron phosphate particles, the carbon content of the lithium iron phosphate particles is Cx weight%, and the ratio z of the specific surface area BET of the lithium iron phosphate particles to Cx satisfies 1.5≤z≤8.5.

[0099] In some embodiments, the ratio z of the specific surface area BET and Cx of the lithium iron phosphate particles satisfies 3≤z≤6.

[0100] In some embodiments, the z may be a numeric value within a range consisting of 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.3, 4.5, 4.8, 5, 5.3, 5.5, 5.8, 6, 6.3, 6.5, 6.8, 7, 7.3, 7.5, 7.8, 8, 8.3, 8.5, or any two of the above-mentioned z values.

[0101] In this application, the ratio z of the specific surface area BET and Cx of the lithium iron phosphate particles can characterize the degree of uniform density of carbon contained in the lithium iron phosphate particles. When the primary average particle size and carbon content of the lithium iron phosphate particles remain unchanged, the lower the ratio z, the higher the coverage utilization rate of carbon in the particles, the less suspended carbon there is, and the more uniform and dense the carbon contained in the lithium iron phosphate particles becomes. Improving the degree of uniform density of the contained carbon is advantageous for improving the kinetic performance and capacity per gram of the lithium iron phosphate particles. However, if the carbon density is too high, it affects the insertion and extraction of lithium ions, which may have some effect on the kinetic performance and capacity per gram of the secondary battery. The z ratio range of this application is advantageous for improving the conductivity performance of the particle surface and further improving the capacity per gram and kinetic performance of the secondary battery by ensuring that the carbon contained in the lithium iron phosphate particles has an appropriate uniform density. Furthermore, the discharge performance requirements for lithium nickel cobalt manganese oxide particles are relatively high. In a double-layer cathode active material, improving the kinetic performance of lithium iron phosphate particles makes it more advantageous for combined discharge with lithium nickel cobalt manganese oxide particles, thereby facilitating further improvement of the overall kinetic performance of the cathode active material.

[0102] In some embodiments, when calculated based on the total weight of the lithium iron phosphate particles, the carbon content of the lithium iron phosphate particles is 0.8 wt% to 2.0 wt%.

[0103] In some embodiments, when calculated based on the total weight of the lithium iron phosphate particles, the carbon content of the lithium iron phosphate particles is 1.0 wt% to 1.6 wt%.

[0104] In some embodiments, when calculated based on the total weight of the lithium iron phosphate particles, the carbon content of the lithium iron phosphate particles is a value within the range consisting of 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, or any two of the carbon contents described above.

[0105] The carbon content of iron phosphate particles can be measured using methods and devices known in the art. For example, it can be tested by referring to GB / T 20123-2006 / ISO 15350:2000.

[0106] In some embodiments, the carbon contained in the lithium iron phosphate particles is coated on the surface of the particles. In some embodiments, the carbon contained in the lithium iron phosphate particles is embedded within the particles. In some embodiments, some of the carbon contained in the lithium iron phosphate particles is coated on the surface of the particles, and some is embedded within the particles.

[0107] Increasing the carbon content of lithium iron phosphate particles helps improve the capacity per gram of the secondary battery, but if the carbon content is too high, the degree of moisture absorption may increase. The carbon content range of the present application helps to further improve the capacity per gram of the secondary battery while reducing the impact on the degree of moisture absorption.

[0108] In some embodiments, lithium iron phosphate particles have the molecular formula Li m1 Fe x1 P y1 O z1 Q q1 having, where Q comprises at least one of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and 0.95≤m1≤1.15, 0.9≤x1≤1, 0.95≤y1≤1, 3.5≤z1≤4, 0 <q1≤0.1이며, 및 / 또는

[0109] Lithium nickel cobalt manganese oxide particles have the molecular formula LiR x2 Ni y2 Co z2 Mn 1-x2-y2-z2 It has O2, where R includes at least one of Cr, Ti, V, Mg, Al, and Nb, and 0≤x2<1, 0 <y2<1, 0<z2<1, 0<x2+y2+z2<1이다.

[0110] In some embodiments, lithium iron phosphate particles have the molecular formula Li m1 Fe x1 P y1 O z1 Q q1 It has, and m1 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, x1 can be 0.9, 1.0, y1 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, z1 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, and q1 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0111] In some embodiments, Q comprises at least one of Ti, V, Mg, and Nb. In some embodiments, Q is Ti.

[0112] In some embodiments, lithium nickel cobalt manganese oxide particles have the molecular formula LiR x2 Ni y2 Co z2 Mn 1-x2-y2-z2It has O2, and x2 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, y2 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, and z2 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, and 0 <x2+y2+z2<1이다. 일부 실시양태에서, 리튬니켈코발트망간산화물 입자 중의 리튬 원소 및 산소 원소의 함량 비율은 배터리 화성 및 순환 과정에서 변동이 발생하게 된다.

[0113] Doping lithium iron phosphate particles and / or lithium nickel cobalt manganese oxide particles with the aforementioned elements helps to improve the ion transport capacity of the cathode active material. The aforementioned elements create vacancies in the crystal lattice of the particles or change the length of interatomic bonds, thereby allowing lithium ions to move easily within the crystal lattice. This effectively improves the conductivity performance of the particles themselves and can improve the kinetic performance and capacity per gram of the cathode active material. Furthermore, the discharge performance requirements of lithium nickel cobalt manganese oxide particles are relatively high. In a double-layer cathode active material, improving the kinetic performance of the lithium iron phosphate particles makes it more advantageous for combined discharge with lithium nickel cobalt manganese oxide particles, which is beneficial for further improving the overall kinetic performance of the cathode active material.

[0114] In some embodiments, when calculated based on the total weight of the lithium iron phosphate particles, the content of Q in the lithium iron phosphate particles is 1000 to 10000 parts per million (1000 to 10000 ppm).

[0115] In some embodiments, when calculated based on the total weight of the lithium iron phosphate particles, the content of Q in the lithium iron phosphate particles is 2500 to 6000 ppm.

[0116] In some embodiments, when calculated based on the total weight of the lithium iron phosphate particles, the content of Q in the lithium iron phosphate particles is a value within a range consisting of 1000 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm, 6500 ppm, 7000 ppm, 7500 ppm, 8000 ppm, 8500 ppm, 9000 ppm, 9500 ppm, 10000 ppm, or any two of the above-mentioned Q contents.

[0117] The content of Q, for example, the content of Ti, in lithium iron phosphate particles can be measured using methods and devices known in the art. For example, it can be tested by referring to GB / T 33822-2017.

[0118] The content of the element Q in conventional lithium iron phosphate particles is generally low or no element Q is added. Increasing the content of the element Q in lithium iron phosphate particles helps to further improve the bulk ion transport capacity of the lithium iron phosphate particles. However, as the content of the element Q increases further, the bulk ion transport capacity may not increase continuously and may affect the primary average particle size of the lithium iron phosphate particles. The range of the element Q in this application helps to balance the primary average particle size on the basis of further improving the kinetic performance and capacity per gram of the cathode active material.

[0119] In some embodiments, the capacity ratio of lithium iron phosphate particles is η≥88%, and η is:

[0120] A battery having the above-mentioned lithium iron phosphate particles as a positive electrode active material is charged and discharged twice with a constant current at a rate limit of 0.1 Cullon (C) within a voltage range of 2.0 volts (V) to 3.75 V, followed by a single charge and discharge with a constant current at a rate limit of 1 C. In the charge and discharge test with a rate limit of 1 C, a capacity value at a discharge voltage of 3.2 V is extracted as C1, and a capacity value discharged to 2.0 V is extracted as C2, and η is defined as C1 / C2. Here, the charging process includes constant voltage charging, the constant voltage is 3.75 V, and the constant voltage cutoff current is 50 microamperes (μA).

[0121] In some embodiments, the capacity ratio η of the lithium iron phosphate particles may be a numeric value within a range consisting of 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or any two of the above-mentioned η values.

[0122] The η value of the lithium iron phosphate particles can be measured using methods and devices known in the art. For example, a button battery is first manufactured using lithium iron phosphate particles as the positive electrode active material, and the specific button battery manufacturing process is as follows: 2.0000 grams (g) of lithium iron phosphate particles are mixed with 0.1111 g of conductive carbon black and 0.1111 g of polyvinylidene fluoride, then added to 2.5 g of the organic solvent N-methylpyrrolidone and mixed sufficiently uniformly to form a slurry. The slurry is coated onto an aluminum foil with a coating thickness of 140 micrometers (μm), vacuum dried at 120°C for 2 hours (h), and punched into a circular sheet with a diameter of 13 millimeters (mm) using a punching machine. Pressed at 10 megapascals (Mpa) using a press machine and vacuum held at 120°C for 12 hours to obtain a positive electrode. The weight of the positive electrode is weighed, wherein the loading amount of lithium iron phosphate particles is 11 to 12 milligrams (mg). A button battery is assembled in a glove box protected by an argon atmosphere, a metallic lithium sheet is used as the negative electrode, a mixed solvent of EC (ethylene carbonate) and DMC (1,2-dimethyl carbonate) with a volume ratio of 1:1 is used as the electrolyte, LiPF6 is used as the electrolyte, and a Celgard 2400 microporous polyethylene membrane is used as the separator.

[0123] The electrical performance of the manufactured button battery is tested using a LAND meter. Specifically, the button battery is charged and discharged twice with a constant current at a rate of 0.1C within a voltage range of 2.0V to 3.75V, followed by a single charge and discharge with a rate of 1C. In the charge-discharge test with a rate of 1C, the capacity value at a discharge voltage of 3.2V is extracted as C1, and the capacity value discharged to 2.0V is extracted as C2, where η = C1 / C2. Here, the charging process includes constant voltage charging, the constant voltage is 3.75V, and the constant voltage cutoff current is 50μA.

[0124] The capacity ratio η of the lithium iron phosphate particles can represent kinetic performance and platform maintenance performance, and can be controlled by adjusting the primary average particle size of the lithium iron phosphate particles, carbon content, the ratio of carbon source to carbon film agent, and the modifier and its content. The η value of the lithium iron phosphate particles of the present application is ≥ 88%, and they possess relatively excellent kinetic performance. At the same time, when the η value is relatively high, the secondary battery can still maintain relatively excellent output performance even when discharged to a low SOC (State of Charge); that is, when a battery with a high η value is discharged at a large current from a low electric charge, the voltage drop value is relatively small.

[0125] In some embodiments, the lithium iron phosphate particles satisfy at least one of (a) to (f):

[0126] a) Dv10≥200 nm of lithium iron phosphate particles;

[0127] b) The Dv50 of lithium iron phosphate particles is 500–5000 nm;

[0128] c) Dv90≤10000nm of lithium iron phosphate particles;

[0129] d) Dv99≤12000nm of lithium iron phosphate particles;

[0130] e) Powder compression density of lithium iron phosphate at 3T pressure ≥ 2.25 grams / square millimeter (g / cm³) 3 );

[0131] f) The powder resistivity of lithium iron phosphate is less than 60 ohm·centimeters (Ω·cm).

[0132] In this document, the term "Dv10" refers to the particle size corresponding when the percentage of the volumetric cumulative particle size distribution among the particles reaches 10%.

[0133] In this document, the term "Dv90" refers to the particle size corresponding when the percentage of volume-cumulative particle size distribution among particles reaches 90%.

[0134] In this document, the term "Dv99" refers to the particle size corresponding to when the percentage of volumetric cumulative particle size distribution among particles reaches 99%.

[0135] In this document, the term "powder compression density" refers to the density of a compact having a constant density and strength, formed during an external compression process in which, due to the movement and deformation of the powder, a relatively large gap is filled, the contact area between particles increases, attractive forces are generated between atoms, and the mechanical interlocking action between particles is strengthened; the unit is g / cm³ 3 am.

[0136] In some embodiments, Dv10 of lithium iron phosphate particles <Dv50이다.

[0137] In some embodiments, the Dv90 > Dv50 of the lithium iron phosphate particles.

[0138] In some embodiments, the Dv50 of the lithium iron phosphate particles may be a numerical value within a range consisting of 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1700 nm, 1900 nm, 2000 nm, 2300 nm, 2500 nm, 2700 nm, 2900 nm, 3000 nm, 3200 nm, 3400 nm, 3600 nm, 3800 nm, 4000 nm, 4200 nm, 4400 nm, 4600 nm, 4800 nm, 5000 nm, or the Dv50 of any two products after secondary grinding described above.

[0139] The Dv10, Dv50, Dv90, and Dv99 of lithium iron phosphate particles can be measured using methods and devices known in the art. For example, with reference to GB / T19077.1-2016, they can be measured using a laser particle size analyzer (Malvern Master Size 3000).

[0140] The powder compression density of lithium iron phosphate particles at different pressures can be measured using methods and devices known in the art. For example, with reference to GB / T 24533-2009, it can be measured using a compression density measuring instrument. Specifically, a certain amount of lithium iron phosphate particles is placed on a compression mold (the diameter of the mold is already known), and a metal circular sheet is provided at the top and bottom of the middle hollow of the mold. When the lithium iron phosphate particles are placed between the metal circular sheets, a metal circular column is placed at the top, the mold is placed on a compression density measuring instrument, and different pressures (e.g., 3T) are applied, the device can read the thickness of the lithium iron phosphate particles at different pressures, and the powder compression density of the lithium iron phosphate particles is given by ρ=m / v, where v=(SХH), m is the mass of the lithium iron phosphate particles, S is the bottom area of ​​the mold, and H is the thickness of the lithium iron phosphate particles after compression.

[0141] The powder resistivity of lithium iron phosphate particles can be measured using methods and devices known in the art. For example, with reference to GB / T 33822-2017, it can be measured using a powder resistivity meter (Suzhou Jingge, ST2722 type). Specifically, a certain amount of lithium iron phosphate particles (e.g., 1 g) is weighed and placed into the material chamber of the powder resistivity meter, and then a pressure of 8 MPa is applied to test the forward resistivity and reverse resistivity of the lithium iron phosphate particles, respectively, and the average value of both is taken as the powder resistivity of the lithium iron phosphate particles.

[0142] By ensuring that the lithium iron phosphate particles satisfy at least one of (a) to (f), the lithium iron phosphate particles can be made to better realize the technical effects of the present application.

[0143] In some embodiments, when the first positive active layer comprises lithium iron phosphate particles and the second positive active layer comprises lithium nickel cobalt manganese oxide particles, the coating weight of the first positive active layer is 0.02 to 0.38 g / 1540 mm 2 and the coating weight of the second anode active layer is 0.08~0.32g / 1540mm 2 is;

[0144] When the first positive active layer comprises lithium nickel cobalt manganese oxide particles and the second positive active layer comprises lithium iron phosphate particles, the coating weight of the first active layer is 0.08 to 0.32 g / 1540 mm 2 and the coating weight of the second anode active layer is 0.02~0.38g / 1540mm 2 am.

[0145] In some embodiments, when the first positive active layer comprises lithium iron phosphate particles and the second positive active layer comprises lithium nickel cobalt manganese oxide particles, the coating weight of the first positive active layer is 0.05 to 0.32 g / 1540 mm 2 and the coating weight of the second anode active layer is 0.1~0.28g / 1540mm 2 is;

[0146] When the first positive active layer comprises lithium nickel cobalt manganese oxide particles and the second positive active layer comprises lithium iron phosphate particles, the coating weight of the first active layer is 0.1 to 0.28 g / 1540 mm 2 and the coating weight of the second anode active layer is 0.05~0.32g / 1540mm 2 am.

[0147] In some embodiments, the coating weight of the anode active material of the first or second layer containing lithium iron phosphate particles is 0.02 g / 1540 mm 2 , 0.04g / 1540mm 2 , 0.06g / 1540mm 2 , 0.08g / 1540mm 2 , 0.10g / 1540mm 2 , 0.12g / 1540mm 2, 0.14g / 1540mm 2 , 0.15g / 1540mm 2 , 0.16g / 1540mm 2 , 0.18g / 1540mm 2 , 0.20g / 1540mm 2 , 0.22g / 1540mm 2 , 0.24g / 1540mm 2 , 0.26g / 1540mm 2 , 0.28g / 1540mm 2 , 0.30g / 1540mm 2 , 0.32g / 1540mm 2 , 0.34g / 1540mm 2 , 0.36g / 1540mm 2 , 0.38g / 1540mm 2 , or may be a value within the range consisting of any two coating weights described above; and the coating weight of the second / or first cathode active material comprising lithium nickel cobalt manganese oxide particles is 0.08 g / 1540 mm 2 , 0.10g / 1540mm 2 , 0.12g / 1540mm 2 , 0.14g / 1540mm 2 , 0.16g / 1540mm 2 , 0.18g / 1540mm 2 , 0.20g / 1540mm 2 , 0.22g / 1540mm 2 , 0.24g / 1540mm 2 , 0.25g / 1540mm 2 , 0.26g / 1540mm 2 , 0.28g / 1540mm 2 , 0.30g / 1540mm 2 , 0.32g / 1540mm 2 , or it may be a value within the range consisting of any two coating weights described above.

[0148] The coating weight of the first positive active layer and the second positive active layer can be measured using methods and devices known in the art. For example, 1540 mm at the positive plate2 The circular sheet is punched out, the current collector, the first positive active layer, and the second positive active layer are separated, and the weight of the second positive active layer and the second positive active layer is weighed.

[0149] By controlling the weight of the first or second positive active layer containing lithium iron phosphate particles and the second or first positive active layer containing lithium nickel cobalt manganese oxide particles within the scope of the present application, it helps to lower the cost of the positive active material while still obtaining a relatively excellent capacity per gram.

[0150] In some embodiments, the total thickness of the positive active layer is 50 to 150 μm.

[0151] In some embodiments, the total thickness of the positive active layer is 60 to 90 μm.

[0152] In some embodiments, the total thickness of the positive active layer may be a numeric value within a range consisting of 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, or the total thickness of any two positive active layers described above.

[0153] The thickness of the positive active layer can be measured using a micrometer.

[0154] The thickness of the positive electrode active material of the present application helps maintain relatively excellent kinetic performance and volumetric energy density.

[0155] In some embodiments, the first positive active layer comprises lithium iron phosphate particles, and the second positive active layer comprises lithium nickel cobalt manganese oxide particles.

[0156] The compression density of lithium iron phosphate particles is lower than that of lithium nickel cobalt manganese oxide particles, and when located in a second positive active layer far from the current collector, the gap is reduced during the cold compression process of the electrode piece, thereby affecting the infiltration of the electrolyte, increasing positive polarization, and affecting the performance of the battery cell to some extent. At the same time, since lithium iron phosphate particles can be used as a conductive transition layer for the current collector and lithium nickel cobalt manganese oxide particles, it is advantageous for improving the conductivity of the electrode. Therefore, placing lithium iron phosphate particles in the first active layer is more advantageous for improving the electrical performance of the secondary battery.

[0157] In some embodiments, the lithium iron phosphate particles are mainly:

[0158] A raw material is provided containing at least a lithium source, an iron source, a phosphorus source, an optional carbon film-forming agent, an optional carbon source, and an optional modifier, and is obtained by a manufacturing method of sintering at least twice, wherein,

[0159] The primary sintering temperature is 500℃ to 760℃, and in some embodiments, 550℃ to 720℃;

[0160] The secondary sintering temperature is 700℃ to 800℃, and in some embodiments, 720℃ to 780℃.

[0161] In some embodiments, the primary sintering temperature may be a numeric value within a range consisting of 500°C, 530°C, 550°C, 580°C, 600°C, 630°C, 650°C, 680°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, or any two primary sintering temperatures described above; and the secondary sintering temperature may be a numeric value within a range consisting of 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, or any two secondary sintering temperatures described above.

[0162] In some embodiments, the temperature rise rate of the first sintering and the second sintering is independently 2 degrees Celsius / min (°C / min) to 20°C / min.

[0163] In some embodiments, the temperature rise rate during the first sintering and the second sintering is independently 2°C / min, 5°C / min, 7°C / min, 10°C / min, 13°C / min, 15°C / min, 17°C / min, or 20°C / min.

[0164] In some embodiments, the isothermal sintering time for the first sintering is 1 to 6 hours. In some embodiments, the isothermal sintering time for the first sintering may be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours.

[0165] In some embodiments, the isothermal sintering time for the second sintering is 2 to 12 hours. In some embodiments, the isothermal sintering time for the second sintering may be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours.

[0166] Compared to traditional manufacturing methods that utilize high temperatures to achieve particle growth, the lithium iron phosphate particles of the embodiments of the present application are advantageous for producing lithium iron phosphate particles having the primary average particle size and specific surface area of ​​the present application by performing two sintering cycles and controlling the sintering temperatures twice. Furthermore, by controlling the temperature rise rate of the first and / or second sintering cycles, the sintering temperature, and the isothermal sintering time, it helps to reduce side reactions, thereby producing the lithium iron phosphate particles of the present application more effectively. Moreover, in conventional high-temperature sintering processes, the carbon coating layer on the particle surface easily cracks, degrading the integrity of the carbon coating. The present application is advantageous for improving the consistency and uniformity of the surface carbon coating by performing large particle synthesis at low temperatures.

[0167] In some embodiments, lithium iron phosphate particles are obtained by a manufacturing method comprising: providing a raw material containing at least a lithium source, an iron source, a phosphorus source, a carbon source, a carbon film-forming agent, and a modifier, and sintering at least twice, wherein,

[0168] The carbon content of the material after the first sintering is 0.01 wt% to 0.79 wt%, and in some embodiments, 0.05 wt% to 0.4 wt%;

[0169] The carbon content of the material after secondary sintering is 0.8 wt% to 2.0 wt%, and in some embodiments, 1.0 wt% to 1.6 wt%.

[0170] In some embodiments, the carbon content of the material after the first sintering may be a value within a range consisting of 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.20 wt%, 0.25 wt%, 0.30 wt%, 0.35 wt%, 0.40 wt%, 0.45 wt%, 0.50 wt%, 0.55 wt%, 0.60 wt%, 0.65 wt%, 0.70 wt%, 0.75 wt%, 0.79 wt%, or any two of the above-mentioned carbon contents; The carbon content of the material after the second sintering may be a value within the range consisting of 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, or any two of the above-mentioned carbon contents.

[0171] In the manufacturing method of the embodiment of the present application, by adding a carbon source before the first sintering, the trivalent iron in the raw material can be effectively reduced, thereby improving the purity and stability of the product. Furthermore, by controlling the first sintering temperature and the carbon content of the intermediate after the first sintering within the aforementioned range, it helps to increase the primary particle size of the lithium iron phosphate particle precursor obtained after the first sintering. Specifically, during the first sintering process, a relatively low carbon content is advantageous for the carbon layer to lower the blocking effect on the growth process of the lithium iron phosphate particles and is advantageous for crystal growth of the lithium iron phosphate particle precursor at a relatively low temperature. At the same time, it is advantageous for the solid-state diffusion reaction between the modifier that can be added and the lithium iron phosphate material, thereby being advantageous for realizing a relatively high concentration of metal ion doping. By controlling the secondary sintering temperature and the carbon content of the material after sintering within the range described above, carbon is better coated on the surface of the lithium iron phosphate particles, which helps to form a uniform and dense carbon coating layer, improves the surface conductivity performance of the lithium iron phosphate particles, and is advantageous for improving kinetic performance and capacity per gram.

[0172] In some embodiments, at least a raw material containing a lithium source, an iron source, a phosphorus source, a carbon source, a modifier, and a carbon film-forming agent is provided and sintered at least twice.

[0173] In some embodiments, when calculated based on the atomic moles of each element, the mixing ratio of the lithium source, iron source, and phosphorus source satisfies Fe:P=(0.96~0.985):1 and Li:Fe=(1.0~0.95):1.1.

[0174] In some embodiments, when calculated based on the atomic moles of each element, the mixing ratio of iron source to phosphorus source satisfies Fe:P=0.96:1, Fe:P=0.965:1, Fe:P=0.97:1, Fe:P=0.975:1, Fe:P=0.98:1, or Fe:P=0.985:1.

[0175] In some embodiments, when calculated based on the atomic moles of each element, the mixing ratio of the lithium source and the iron source satisfies Li:Fe=1.0:1.1, Li:Fe=0.99:1.1, Li:Fe=0.98:1.1, Li:Fe=0.97:1.1, Li:Fe=0.96:1.1, or Li:Fe=0.95:1.1.

[0176] In some embodiments, the weight ratio of the carbon source to the carbon film agent is (9 to 0.25):1. In some embodiments, the weight ratio of the carbon source to the carbon film agent may be 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, 0.8:1, 0.5:1, or 0.25:1.

[0177] In some embodiments, the lithium source is a compound containing lithium. In some embodiments, the lithium source comprises at least one of lithium dihydrogen phosphate, lithium oxalate, lithium carbonate, lithium oxide, lithium hydroxide, and lithium acetate. In some embodiments, the lithium source comprises lithium carbonate.

[0178] In some embodiments, the iron source is a compound containing iron. In some embodiments, the iron source comprises at least one of iron hydroxide, ferrous chloride, ferric trioxide, ferrous phosphate, ferrous pyrophosphate, ferrous oxalate, iron powder, ferrous nitrate, ferric tetroxide, and ferric oxyhydroxide. In some embodiments, the iron source comprises ferric trioxide.

[0179] In some embodiments, the phosphorus source is a phosphoric acid compound. In some embodiments, the phosphorus source comprises at least one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. In some embodiments, the phosphorus source comprises phosphoric acid.

[0180] In some embodiments, the carbon source comprises at least one of citric acid, glucose, sucrose, starch, fructose, and lactose. In some embodiments, the carbon source comprises glucose.

[0181] In some embodiments, the carbon film-forming agent comprises at least one of polyethylene glycol, polyaniline, polyacrylonitrile, polyvinylpyrrolidone, and polyvinyl alcohol. In some embodiments, the carbon film-forming agent comprises polyaniline.

[0182] In some embodiments, the modifier comprises at least one of titanium dioxide, vanadium pentoxide, n-butyl titanate, ammonium metavanadate, niobium ethanolate, niobium oxalate, niobium pentoxide, magnesium hydroxide, and magnesium nitrate. In some embodiments, the modifier comprises titanium dioxide.

[0183] Using raw materials in the aforementioned ratio is advantageous for forming the lithium iron phosphate particles of the present application.

[0184] In some embodiments, the method for manufacturing the lithium iron phosphate particles is:

[0185] It includes the step of performing first sintering followed by first grinding, and performing second sintering followed by second grinding, wherein,

[0186] The Dv50 of the product after primary grinding is 300 nm to 1200 nm, and in some embodiments, 400 nm to 1100 nm;

[0187] The Dv50 of the product after secondary grinding is 500 nm to 5000 nm, and in some embodiments, 700 nm to 2500 nm.

[0188] In this application, the term "Dv50" refers to the particle size corresponding when the percentage of volume-cumulative particle size distribution among the particles reaches 50%.

[0189] In some embodiments, the Dv50 of the product after primary grinding may be a numerical value within a range consisting of 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, or any two of the Dv50s of the products after primary grinding described above.

[0190] In some embodiments, the Dv50 of the product after secondary grinding may be a numerical value within a range consisting of 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1700nm, 1900nm, 2000nm, 2300nm, 2500nm, 2700nm, 2900nm, 3000nm, 3200nm, 3400nm, 3600nm, 3800nm, 4000nm, 4200nm, 4400nm, 4600nm, 4800nm, 5000nm, or any two of the Dv50s of the products after secondary grinding described above.

[0191] In some embodiments, the grinding includes one or more of mechanical crushing, grinding, sanding, and airflow crushing.

[0192] The Dv50 of the particles can be measured using methods and devices commonly used in the industry. For example, referring to GB / T19077.1-2016, it can be measured using a laser particle size analyzer (Malvern Master Size 3000).

[0193] By controlling the Dv50 of the product after the first grinding to within the aforementioned range, the added carbon source and the doping element that may be added are advantageous for lowering the blocking effect on the growth of the lithium iron phosphate particle precursor crystals, and help in producing micrometer-sized lithium iron phosphate particle precursors. By controlling the Dv50 value of the product after the second grinding to within the aforementioned range, it helps in obtaining lithium iron phosphate particles having the primary average particle size of the present application.

[0194] In some embodiments, the positive plate comprises a positive current collector and a positive film layer installed on at least one surface of the positive current collector, the positive film layer comprises a positive active material, an adhesive and a conductor, and the positive active material is a positive active material according to an embodiment of the present application or a positive active material manufactured by a method of manufacturing an embodiment of the present application.

[0195] For example, the positive current collector has two surfaces facing each other in its thickness direction, and the positive film layer is installed on any one or both of the two surfaces facing each other of the positive current collector.

[0196] In some embodiments, the positive current collector may use a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer 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 (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0197] In some embodiments, the anode film layer may also optionally include an adhesive. For example, the adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene ternary copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene ethylene ternary copolymer, tetrafluoroethylene-hexafluoropropyl copolymer, and fluorine-containing acrylate resin.

[0198] In some embodiments, the anode film layer also optionally comprises a conductor. For example, the conductor may comprise at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0199] In some embodiments, an anode piece may be manufactured in the following manner: a positive slurry is formed by dispersing the components used in the above-described manufacturing of the anode piece, e.g., a positive active material, a conductor, an adhesive, and any other components, in a solvent (e.g., N-methylpyrrolidone); and the positive slurry is applied to a positive current collector and the anode piece is obtained through processes such as drying and cold pressing.

[0200] [Cathode]

[0201] The cathode piece comprises a cathode current collector and a cathode film layer installed on at least one surface of the cathode current collector, and the cathode film layer comprises a cathode active material.

[0202] For example, a cathode current collector has two surfaces facing each other in its thickness direction, and a cathode film layer is installed on any one or both of the two surfaces facing each other of the cathode current collector.

[0203] In some embodiments, the negative current collector may use 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, silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0204] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art. For example, the negative electrode active material may include at least one of materials such as synthetic graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of single-element silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of single-element tin, tin oxide, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials may also be used. Such negative electrode active materials may be used alone or in combination of two or more.

[0205] In some embodiments, the cathode film layer also optionally comprises an adhesive. The adhesive 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).

[0206] In some embodiments, the cathode film layer also optionally comprises a conductor. The conductor may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0207] In some embodiments, the cathode film layer also optionally includes other auxiliary agents such as a thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0208] In some embodiments, a cathode plate may be manufactured in the following manner: a cathode slurry is formed by dispersing the components used in the above-described cathode plate manufacturing, e.g., a cathode active material, a conductor, an adhesive, and any other components, in a solvent (e.g., deionized water); and the cathode plate may be obtained by applying the cathode slurry to a cathode current collector and undergoing processes such as drying and cold pressing.

[0209] [Electrolyte]

[0210] The electrolyte serves to conduct ions between the anode and the cathode. The present application has no specific limitations on the type of electrolyte and can be selected according to demand. For example, the electrolyte may be in a liquid state, a gel state, or a completely solid state.

[0211] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent.

[0212] 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 difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro(bis-oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0213] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene 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.

[0214] In some embodiments, the electrolyte also optionally includes additives. For example, the additives may include a cathode film-forming additive and an anode film-forming additive, and may also include additives that can improve specific performance of the battery, such as an additive that improves the overcharge performance of the battery, or an additive that improves the high or low temperature performance of the battery.

[0215] [Separator]

[0216] In some embodiments, the secondary battery also includes a separator. The present application makes no particular limitation on the type of separator, and any known porous separator having good chemical and mechanical stability may be selected and used.

[0217] In some embodiments, the material of the separator may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and there are no particular limitations thereon. If the separator is a multilayer composite film, the material of each layer may be the same or different, and there are no particular limitations thereon.

[0218] In some embodiments, the anode, cathode, and separator can be manufactured into an electrode assembly through a winding process or a lamination process.

[0219] In some embodiments, the secondary battery may include an external packaging material. The external packaging material may be used to package the electrode assembly and electrolyte described above.

[0220] In some embodiments, the external packaging material of the secondary battery may be a rigid shell, such as a rigid plastic shell, an aluminum shell, a steel shell, etc. The external packaging material of the secondary battery may also be a soft pack, such as a pouch-type soft pack. The material of the soft pack may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0221] [Secondary Battery]

[0222] The present application provides a secondary battery, said secondary battery includes a positive plate of an embodiment of the present application.

[0223] In this application, there are no special restrictions on the shape of the secondary battery, and it may be cylindrical, square, or any other shape. For example, FIG. 2 is a secondary battery (5) with a square structure as an example.

[0224] In some embodiments, referring to FIG. 3, the outer packaging material may include a housing (51) and a cover plate (53). Here, the housing (51) may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving chamber. The housing (51) has an opening communicating with the receiving chamber, and the cover plate (53) is designed to cover the opening and install it to close the receiving chamber. The positive electrode, the negative electrode, and the separator may form an electrode assembly (52) through a winding process or a lamination process. The electrode assembly (52) is packaged within the receiving chamber. An electrolyte is infiltrated into the electrode assembly (52). The number of electrode assemblies (52) included in the secondary battery (5) may be one or more, and a person skilled in the art may select according to specific actual needs.

[0225] In some embodiments, the secondary battery may be assembled into a battery module, and the specific number of secondary batteries included in the battery module may be one or more, and the specific number may be selected by a person skilled in the art according to the application and capacity of the battery module.

[0226] FIG. 4 is a battery module (4) as an example. Referring to FIG. 4, a plurality of secondary batteries (5) may be installed in the battery module (4) so ​​as to be arranged sequentially along the length direction of the battery module (4). Of course, they may also be arranged in any other arbitrary way. Additionally, the plurality of secondary batteries (5) may be secured with fasteners.

[0227] In some embodiments, the battery module (4) may also include a housing having a receiving space, and a plurality of secondary batteries (5) are received in the receiving space.

[0228] In some embodiments, the battery module described above may be assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, and the specific number may be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0229] FIGS. 5 and 6 illustrate a battery pack (1) as an example. Referring to FIGS. 5 and 6, the battery pack (1) may include a battery case and a plurality of battery modules (4) installed in the battery case. The battery case includes an upper case (2) and a lower case (3), wherein the upper case (2) is installed over the lower case (3) and may form a closed space for accommodating the battery modules (4). The plurality of battery modules (4) may be arranged in the battery case in any manner.

[0230] [Electrical device]

[0231] Additionally, the present application also provides an electric device, the electric device comprising a positive plate according to an embodiment of the present application or a secondary battery according to an embodiment of the present application.

[0232] In some embodiments, the electric device according to the embodiments of the present application may also include at least one of a battery module or a battery pack. The secondary battery, battery module, or battery pack may be used as a power source for the electric device and may also be used as an energy storage unit for the electric device. The electric device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0233] As for the electrical device, a secondary battery, battery module, or battery pack can be selected depending on the usage demand.

[0234] FIG. 7 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the requirements for high power output and high energy density for the secondary battery of the electric device, a battery pack or battery module may be used.

[0235] Other examples of devices may include mobile phones, tablet computers, laptops, etc. These devices should generally be thin and light, and can use a secondary battery as a power source.

[0236] Examples

[0237] The following describes embodiments of the present application. The embodiments described below are illustrative and are intended only to interpret the present application and should not be construed as a limitation thereof. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature of the art or product descriptions. Where the manufacturer of the reagents or equipment used is not specified, they are all ordinary products available on the market.

[0238] Example 1

[0239] a. Manufacturing method

[0240] 1) Preparation of the first anode active layer slurry

[0241] Preparation of lithium iron phosphate particles:

[0242] Lithium carbonate, diiron trioxide, phosphoric acid, glucose, titanium dioxide (based on the total weight of the lithium iron phosphate particles, the amount of titanium dioxide added satisfies the requirement that the titanium content in the manufactured lithium iron phosphate particles is 5000 ppm), and polyaniline were each weighed, wherein the weight ratio of the Li, Fe, and P elements satisfies Fe:P=0.968:1 and Li:Fe=1:0.98, and the weight ratio of glucose and polyaniline satisfies Glucose:Polyaniline=1:2. The amount of glucose and polyaniline added satisfies the requirement that the carbon content accounts for 0.15% of the weight of the lithium iron phosphate precursor after the completion of the first sintering. Water was added to the above-described materials to obtain a mixture slurry.

[0243] The mixture slurry was uniformly mixed using a ball mill and ground using a bead mill to obtain a slurry with a solid content of 38% and a Dv50 of 400 nm, after which it was spray-dried (the negative pressure of the high-speed spray dryer was -650 to -200 Pascals (Pa), the inlet temperature was 300°C to 360°C, and the outlet temperature was 100°C to 140°C). The dried reaction product was charged into a sintering furnace for primary sintering, with the temperature rise rate controlled at 5°C / min, the holding temperature controlled at 650°C, and the holding time set to 4 hours. After cooling the material, it was ground using a mechanical mill to obtain a powder.

[0244] The obtained powder, glucose, polyaniline, and water were mixed (based on the total weight of the lithium iron phosphate particles, the amount of glucose and polyaniline added satisfies a carbon content of 1.2% in the product after secondary sintering, and the weight ratio of glucose and polyaniline satisfies glucose:polyaniline = 1:2), and the solid content of the mixture is 40%. After uniform mixing, a slurry was obtained by processing using a ball mill and a bead mill, and the Dv50 of the insoluble matter in the slurry is 550 nm. The slurry was spray-dried (the negative pressure of the high-speed spray dryer is -650 to -200 Pa, the inlet temperature is 300 to 360°C, and the outlet temperature is 100 to 140°C). The dried reactant was charged into a sintering furnace and subjected to secondary low-temperature sintering (controlled temperature rise rate to 5℃ / min, sintering temperature to 750℃, and sintering time to 4 hours). After the material cooled, it was subjected to secondary grinding until the primary average particle size reached 870 nm. After demagnetization, lithium iron phosphate particles were obtained with a carbon content of 1.2% and a Ti element content of 5000 ppm.

[0245] Lithium iron phosphate particles, a conductive carbon black, an adhesive polyvinylidene fluoride, and a dispersant polyvinylpyrrolidone were mixed in a mass ratio of 93.0:4.0:2.5:0.5, and a material containing the aforementioned positive electrode active material was mixed and then added to N-methylpyrrolidone, mixed and stirred, and uniformly dispersed to prepare a first positive electrode slurry.

[0246] 2) Preparation of the slurry of the second anode active layer

[0247] Lithium nickel cobalt manganese oxide particles (CPE-16, purchased from Guangdong Brunp Recycling Technology Co., Ltd.), a conductive carbon black, and an adhesive polyvinylidene fluoride were mixed in a mass ratio of 96.14:2.7:1.16, and after mixing the material containing the aforementioned cathode active material, it was added to N-methylpyrrolidone and mixed and stirred to uniformly disperse the mixture to prepare a second cathode slurry.

[0248] 3) Preparation of the anode section

[0249] 0.15g / 1540mm of the first anode active layer slurry 2 A single-sided weight is uniformly applied to the surface of the aluminum foil of the current collector with a coating thickness of 39.75 μm, and a second positive active material slurry is applied at a thickness of 0.25 g / 1540 mm 2 After uniformly applying a coating thickness of 47.2 μm to the surface of the first anode active slurry with a single-sided weight, it was transferred to a vacuum drying oven and completely dried. The dried electrode piece was rolled and punched to obtain an anode piece.

[0250] 4) Manufacturing of the cathode

[0251] Synthetic graphite as a cathode active material, carbon black as a conductor, sodium carboxymethylcellulose as a thickener, and styrene-butadiene rubber as an adhesive were added to deionized water in a mass ratio of 97.35:0.7:1:0.95 and uniformly stirred to obtain a cathode slurry;

[0252] Then 216mg / 1540mm2 A cathode slurry was coated onto a copper foil according to the weight of both sides, and the cathode piece was obtained by drying, cold pressing, and slitting.

[0253] 5) Preparation of separator membrane

[0254] A polypropylene membrane was used as a separator.

[0255] 6) Battery manufacturing

[0256] The above-described positive electrode, separator, and negative electrode were sequentially stacked, and the separator was positioned between the positive electrode and the negative electrode to perform a separating function. Then, the assembly was wound to obtain a bare cell. Electrode tabs were welded to the bare cell, the bare cell was mounted in an aluminum shell, dried in a vacuum oven at 100°C for 8 hours, and then an electrolyte was injected and sealed to obtain an uncharged battery. Then, the uncharged battery was sequentially subjected to processes such as standing, cold pressing, formation, molding, and capacity testing to obtain the lithium-ion battery of Example 1.

[0257] The batteries of Examples 2 to 6 are manufactured using a method similar to that of Example 1, but the primary average particle size and / or specific surface area of ​​the lithium iron phosphate particles were adjusted, and the specific material parameters are as shown in Table 1. The differences from Example 1 in the process of manufacturing the lithium iron phosphate particles are as follows:

[0258] Example 2: The Dv50 of the mixed slurry after the first polishing was reduced to 450 nm;

[0259] Example 3: The Dv50 of the mixed slurry after the first polishing was increased to 900 nm. FIGS. 1a and FIGS. 1b are anode section diagrams according to Example 3 under 1,000x and 3,000x magnification conditions, respectively;

[0260] Example 4: The Dv50 of the mixed slurry after the first polishing was increased to 1100 nm;

[0261] Example 5: The Dv50 of the mixed slurry after the first polishing was reduced to 350 nm;

[0262] Example 6: The Dv50 of the mixed slurry after the first polishing was increased to 1200 nm.

[0263] The batteries of Examples 7 to 9 are manufactured using a method similar to that of Example 1, but the specific surface area and carbon content of the lithium iron phosphate particles were adjusted, and the specific material parameters are as shown in Table 1. The differences from Example 1 in the process of manufacturing the lithium iron phosphate particles are as follows:

[0264] Example 7: The carbon content of the product after secondary sintering was adjusted to 0.8%;

[0265] Example 8: The carbon content of the product after secondary sintering was adjusted to 1.4%;

[0266] Example 9: The carbon content of the product after secondary sintering was adjusted to 1.5%.

[0267] The batteries of Examples 10 and 11 are manufactured using a method similar to that of Example 1, but the specific surface area of ​​the lithium iron phosphate particles was adjusted, and the specific material parameters are as shown in Table 1. The differences from Example 1 in the process of manufacturing the lithium iron phosphate particles are as follows:

[0268] Example 10: In the first sintering process, the weight ratio of glucose to polyaniline was set to 1:4;

[0269] Example 11: In the first sintering process, the weight ratio of glucose to polyaniline was set to 1:0.5.

[0270] The batteries of Examples 12–14 are manufactured using a method similar to that of Example 1, but the content of the Q element has been adjusted, and the specific material parameters are as shown in Table 1. The differences from Example 1 in the process of manufacturing the lithium iron phosphate particles are as follows:

[0271] Example 12: The first sintering temperature was controlled to 590°C, the second sintering temperature to 720°C, and the Ti content to 0 ppm;

[0272] Example 13: The first sintering temperature was controlled to 620°C, the second sintering temperature to 740°C, and the Ti content to 2500 ppm;

[0273] Example 14: The first sintering temperature was controlled to 655°C, the second sintering temperature to 755°C, and the Ti content to 6000 ppm.

[0274] The batteries of Examples 15 to 17 are manufactured using a method similar to that of Example 1, but the coating weight of the first positive active layer has been adjusted, as specifically shown in Table 1.

[0275] Example 18 is similar to the manufacturing method of Example 1, but lithium nickel cobalt manganese oxide particles are used as the first positive active layer and lithium iron phosphate particles are used as the second positive active layer.

[0276] The battery of Comparative Example 1 is similar to the manufacturing method of Example 1, but the lithium iron phosphate particles used are different from those of Example 1, and refer to Table 1 for the specific parameters of the lithium iron phosphate particles used in Comparative Example 1. The manufacturing method of the lithium iron phosphate particles of Comparative Example 1 is as follows:

[0277] Lithium carbonate, diiron trioxide, phosphoric acid, glucose, titanium dioxide (based on the total weight of the lithium iron phosphate particles, the amount of titanium dioxide added satisfies the requirement that the titanium content in the manufactured lithium iron phosphate particles is 5000 ppm), and polyaniline were each weighed, wherein the weight ratio of the Li, Fe, and P elements satisfies Fe:P=0.968:1; Li:Fe=1:0.98, the weight ratio of glucose and polyaniline satisfies glucose:polyaniline=1:2, and the amount of glucose added satisfies the requirement that the carbon content accounts for 1.2% of the weight of the lithium iron phosphate particles after the completion of one sintering step. Water was added to the above-described materials to obtain a mixture slurry.

[0278] The slurry was uniformly mixed using a ball mill and ground using a bead mill to obtain a slurry with a solid content of 38% and a Dv50 of 400 nm, after which it was spray-dried (the negative pressure of the high-speed spray dryer was -650 to -200 Pa, the inlet temperature was 300°C to 360°C, and the outlet temperature was 100°C to 140°C). The dried reaction product was charged into a sintering furnace and sintered once, with the temperature rise rate controlled at 5°C / min, the holding temperature controlled at 810°C, and the holding time set to 4 hours. After the material was cooled, the material was processed using an air-flow grinding or mechanical grinding method to obtain lithium iron phosphate particles, the Dv50 of which was 300 nm.

[0279] The battery of Comparative Example 2 is manufactured using a method similar to that of Example 1, but the primary average particle size of the lithium iron phosphate particles is larger than that of Example 1, specifically as shown in Table 1. The differences from Example 1 in the process of manufacturing the lithium iron phosphate particles are as follows:

[0280] Comparative Example 2: The Dv50 of the product after one grinding was 1300 nm, and the secondary sintering temperature was 780°C.

[0281] The batteries of Comparative Examples 3 and 4 are manufactured using a method similar to that of Example 1, but the specific surface area and carbon content of the lithium iron phosphate particles have been adjusted, as specifically shown in Table 1. The differences from Example 1 in the process of manufacturing the lithium iron phosphate particles are as follows:

[0282] Comparative Example 3: The carbon content of the product after secondary sintering was controlled to 0.7%;

[0283] Comparative Example 4: The secondary sintering temperature was 770℃, and the carbon content of the product after secondary sintering was controlled to 2.1%.

[0284] B. Battery Performance Test

[0285] 1. Performance test of cathode active material

[0286] 1) Primary average particle size test method for lithium iron phosphate particles

[0287] Using an argon ion beam, the electrode piece is cut perpendicular to the large surface of the anode piece to expose the cross-section, and the cross-section is photographed using a scanning electron microscope. The first anode active layer and the second anode active layer of the cross-section have clear boundaries, and the particle size of the anode active layer containing lithium iron phosphate particles is statistically analyzed using the Peret diameter statistical method. Specifically, in the electron microscope scanning image, the total number of lithium iron phosphate particles with a primary particle size larger than 80 nm can be statistically calculated, and the sum of the primary particle sizes of lithium iron phosphate particles with a primary particle size larger than 80 nm can be statistically calculated. The primary average particle size of the lithium iron phosphate particles = primary particle size of the total lithium iron phosphate particles / total number of lithium iron phosphate particles.

[0288] Here, particles with a primary particle size of 0 < primary particle size ≤ 80 nm easily adhere, so there is a relatively large error in the statistics and it is difficult to clearly identify them individually. Therefore, in the statistical process of primary particle size, particles with a primary particle size of 0 < primary particle size ≤ 80 nm are not included within the statistical range.

[0289] 2) Test method for the specific surface area of ​​lithium iron phosphate particles

[0290] In accordance with the GB / T19587-2017 test standard method, the specific surface area of ​​lithium iron phosphate particles and lithium nickel cobalt manganese oxide particles was tested using the gas adsorption method. Specifically, lithium iron phosphate particles were taken as a sample and placed in a sample tube, and the sample tube was immersed in liquid nitrogen at -196°C. The amount of nitrogen gas adsorbed on the solid surface was measured at different pressures with relative pressures of 0.05 to 0.30, and the specific surface area of ​​the sample was obtained by calculating the monolayer adsorption amount of the sample based on the BET multilayer adsorption theory and its formula.

[0291] 3) Test method for carbon content of lithium iron phosphate particles

[0292] After burning lithium iron phosphate particles using a high-frequency induction furnace, the carbon content was measured using the infrared absorption method, and the specific test procedure follows the standard GB / T 20123-2006 / ISO 15350:2000.

[0293] 4) Test method for Q element (e.g., Ti element) content of lithium iron phosphate particles

[0294] The test method for the Q element content of lithium iron phosphate particles was performed by referring to GB / T 33822-2017.

[0295] 5) Measurement of the η value of lithium iron phosphate particles

[0296] First, a button battery was manufactured using lithium iron phosphate particles as the positive electrode active material, and the specific button battery manufacturing process is as follows: 2.0000g of lithium iron phosphate particles were mixed with 0.1111g of conductive carbon black and 0.1111g of polyvinylidene fluoride, then added to 2.5g of the organic solvent N-methylpyrrolidone and mixed sufficiently and uniformly to form a slurry. The slurry was coated onto an aluminum foil with a coating thickness of 140μm, vacuum dried at 120°C for 2 hours, and punched into a circular sheet with a diameter of 13mm using a punching machine. Pressed at 10MPa using a press machine and vacuum held at 120°C for 12 hours to obtain a positive electrode piece. The weight of the positive electrode piece was weighed, wherein the loaded amount of lithium iron phosphate particles was 11–12mg. A button battery was assembled inside a glove box protected by an argon atmosphere, a metallic lithium sheet was used as the negative electrode, a mixed solvent of EC (ethylene carbonate) and DMC (1,2-dimethyl carbonate) with a volume ratio of 1:1 was used as the electrolyte, LiPF6 was used as the electrolyte, and a Celgard 2400 microporous polyethylene membrane was used as the separator.

[0297] The electrical performance of the manufactured button battery was tested using a LAND meter. Specifically, the button battery was charged and discharged twice with a constant current at a rate of 0.1C within a voltage range of 2.0V to 3.75V, followed by a single charge and discharge with a rate of 1C. In the charge-discharge test with a rate of 1C, the capacity value at a discharge voltage of 3.2V was extracted as C1, and the capacity value discharged to 2.0V was extracted as C2, where η = C1 / C2. Here, the charging process included constant voltage charging, the constant voltage was 3.75V, and the constant voltage cutoff current was 50μA.

[0298] 2. Battery performance testing

[0299] 1) Battery Capacity Test Method per Gram

[0300] Place the battery in an oven environment at 25°C and leave it standing for 2 hours, ensuring the battery temperature is maintained at 25°C; discharge the battery to 2.0V with a constant current of 1 / 3C; pause for 5 minutes; charge the battery to 4.35V with a constant current of 1 / 3C, then charge it at a constant voltage of 4.35V until the cutoff current is 0.05C; pause for 5 minutes;

[0301] The battery was discharged to 2.0V with a constant current of 1 / 3C. This step is intended to test the capacity of the actual battery cell, and in combination with the mass of the positive active material, the capacity per gram of the battery can be calculated, where capacity per gram = capacity / mass of the positive active material.

[0302] 2) Test method for gas generation conditions

[0303] A suitable amount of diethyl carbonate (DEC) was taken to wipe the liquid inlet of the battery cell, and one end of a clean, oil-free hollow long joint was welded to the liquid inlet of the battery cell. The other end of the long joint was connected to a Teflon hose filled with silicone oil through a clamp. The other end of the hose was connected to a TDK plug-in and plug-out barometer filled with silicone oil through a joint sufficiently coated with AB adhesive. Epoxy resin adhesive was sufficiently applied to the long joint, clamp, and connection points, and left to stand for 24 hours to serve as a fixing and gas leak prevention measure.

[0304] Prior to the test, the pressure gauge was connected to the power supply and zeroed; a jig was mounted on the battery cell and placed inside the furnace to prepare for the test. The specific test steps are as follows:

[0305] (1) left standing at 45℃ for 2 hours; (2) discharged the battery to 2.0V with a constant current of 1C; (3) left standing for 5 minutes; (4) charged to 0.5Cn Ah with a constant current of 1.2C; (5) charged to 0.3Cn Ah with a constant current of 0.87C; (6) charged to 4.35V with a constant current of 1 / 3C, then charged to a constant voltage of 4.2V with a cutoff current of 0.05C; (7) left standing for 5 minutes; (8) discharged to 2.0V with a constant current of 1C; (9) left standing for 5 minutes; (10) cycled steps (4) to (9) 1000 times. The test was stopped when the gas generation value reached 0.35Mpa.

[0306] The specific test steps for Cn are as follows: the battery cell is left at 25°C for 30 minutes; discharged to 2.0V with a constant current of 1C; left for 5 minutes; charged to 4.35V with a constant current of 1 / 3C, then charged to a constant voltage of 4.2V with a cutoff current of 0.05C; left for 5 minutes; discharged to 2.0V with a constant current of 1C (capacity Cn is extracted at this stage); left for 5 minutes.

[0307] C. Analysis of test results for each example and comparative example

[0308] Batteries of each example and comparative example were manufactured according to the method described above, and each performance parameter was measured. Refer to Table 1 for the parameter table of the positive electrode active material and refer to Table 2 for the performance test result table.

[0309]

[0310]

[0311]

[0312] According to the results in the table above, as can be seen from Examples 1 to 18 and Comparative Example 1, increasing the primary average particle size of the lithium iron phosphate particles and lowering the specific surface area can reduce the degree of gas generation in the cathode section of the double-layer cathode active material coated with lithium iron phosphate particles and lithium nickel cobalt manganese oxide particles, respectively. As can be seen from Examples 1 to 18 and Comparative Example 2, when the primary average particle size of the lithium iron phosphate particles is too large, the capacity per gram and kinetic performance of the secondary battery decrease. As can be seen from Examples 1 to 18 and Comparative Examples 3 and 4, when the BET of the lithium iron phosphate particles is too small, the capacity per gram of the secondary battery decreases, and when the BET of the lithium iron phosphate particles is too large, the degree of gas generation in the secondary battery increases. In summary, the primary average particle size of the lithium iron phosphate particles is 500 to 3000 nm, and the specific surface area BET is 3 m² 2 / g~8m 2 When / g, it is possible to reduce the amount of gas generated by the secondary battery while simultaneously maintaining the capacity per gram of the secondary battery.

[0313] As can be seen from Examples 1 to 6, when the primary average particle size of the lithium iron phosphate particles is controlled to 500 to 3000 nm, the degree of gas generation in the secondary battery can be reduced, while the capacity per gram of the secondary battery can be achieved.

[0314] As can be seen from Example 1 and Examples 7–9, the BET value of the lithium iron phosphate particles is 3m 2 / g~8m 2 When controlled at / g, it is possible to reduce the degree of gas generation in the secondary battery while simultaneously maintaining the capacity per gram of the secondary battery.

[0315] As can be seen from Example 1 and Examples 10-11, increasing the proportion of the carbon source film-forming agent is advantageous for achieving a dense coating of the carbon layer, and the degree of carbon coating density of the present application is advantageous for further improving the kinetic performance and capacity per gram of the secondary battery.

[0316] As can be seen from Example 1 and Examples 12 to 14, the kinetic performance of the cathode active material can be improved by adding a metal element, such as titanium, to the lithium iron phosphate particles. Furthermore, increasing the content of the metal element within, for example, a range of 1,000 to 10,000 ppm is advantageous for further improving kinetic performance and minimizing the influence on the primary average particle size of the lithium iron phosphate particles.

[0317] As can be seen from Example 1 and Examples 15–17, lowering the content of the positive electrode active layer containing lithium iron phosphate particles in the double-layer positive electrode active layer can improve the capacity per gram of the secondary battery, but it increases the cost of the secondary battery. The weight of the positive electrode active layer containing lithium iron phosphate particles is 20–150 g / m² 2 By controlling it within the range, it is advantageous to further improve the capacity per gram of the secondary battery while controlling the cost of the secondary battery.

[0318] As can be seen from Examples 1 and 18, placing lithium iron phosphate particles in the first positive active layer close to the current collector is advantageous for further improving the capacity per gram of the secondary battery.

[0319] It should be noted that the present application is not limited to the embodiments described above. The embodiments described above are merely examples, and any embodiments having substantially the same configuration as the technical concept and exhibiting the same functional effects within the scope of the technical solution of the present application are included within the technical scope of the present application. Furthermore, other methods constructed by applying various modifications to the embodiments conceived by a person skilled in the art without departing from the spirit of the present application, and by combining parts of the components of the embodiments, are also included within the scope of the present application. Explanation of the symbols

[0320] 1: Battery pack; 2: Top case; 3: Bottom case; 4: Battery module; 5: Secondary battery, 51: Housing; 52: Electrode assembly; 53: Top cover assembly.

Claims

Claim 1 As a positive plate, the positive plate comprises a current collector and a positive active layer, wherein the positive active layer is installed on at least one surface of the current collector, and the positive active layer comprises a first positive active layer formed on at least the current collector and a second positive active layer formed on one side of the first positive active layer far from the current collector; wherein the first positive active layer comprises lithium iron phosphate particles and the second positive active layer comprises lithium nickel cobalt manganese oxide particles; or, wherein the first positive active layer comprises lithium nickel cobalt manganese oxide particles and the second positive active layer comprises lithium iron phosphate particles; wherein the primary average particle size of the lithium iron phosphate particles is 500 to 3000 nm and the specific surface area BET of the lithium iron phosphate particles is 3 m 2 / g~8m 2 A positive plate characterized by being / g. Claim 2 A positive plate according to claim 1, characterized in that the primary average particle size of the lithium iron phosphate particles is 650 to 2500 nm. Claim 3 In claim 1 or 2, the specific surface area BET of the lithium iron phosphate particles is 4m 2 / g~7m 2 A positive plate characterized by being / g. Claim 4 A positive plate according to any one of claims 1 to 3, characterized in that, when calculated based on the total weight of the lithium iron phosphate particles, the carbon content of the lithium iron phosphate particles is 0.8 wt% to 2.0 wt%. Claim 5 A positive electrode according to claim 4, characterized in that, when calculated based on the total weight of the lithium iron phosphate particles, the carbon content of the lithium iron phosphate particles is 1.0 wt% to 1.6 wt%. Claim 6 In any one of claims 1 to 5, the lithium iron phosphate particles are of the molecular formula Li m1 Fe x1 P y1 O z1 Q q1 having, where Q comprises at least one of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and 0.95≤m1≤1.15, 0.9≤x1≤1, 0.95≤y1≤1, 3.5≤z1≤4, 0 <q1≤0.1이며, 및 / 또는상기 리튬니켈코발트망간산화물 입자는 분자식 LiR x2 Ni y2 Co z2 Mn 1-x2-y2-z2 It has O2, wherein R comprises at least one of Cr, Ti, V, Mg, Al, and Nb, and 0≤x2<1, 0 <y2<1, 0<z2<1, 0<x2+y2+z2<1인 것을 특징으로 하는, 양극편. Claim 7 An anode piece according to claim 6, wherein the above-mentioned Q comprises at least one of Ti, V, Mg, and Nb. Claim 8 A positive plate according to claim 6 or 7, characterized in that, when calculated based on the total weight of the lithium iron phosphate particles, the content of Q among the lithium iron phosphate particles is 1,000 to 10,000 ppm. Claim 9 A positive electrode according to any one of claims 1 to 8, wherein the capacity ratio of the lithium iron phosphate particles is η≥88%, and η is defined as follows: a battery having the lithium iron phosphate particles as a positive electrode active material is charged and discharged twice at a constant current with a rate limit of 0.1C within a voltage range of 2.0V to 3.75V, followed by charged and discharged once at a constant current with a rate limit of 1C; in a charge-discharge test with a rate limit of 1C, a capacity value at a discharge voltage of 3.2V is extracted as C1, a capacity value discharged to 2.0V is extracted as C2, and η=C1 / C2; wherein the charging process includes constant voltage charging, the constant voltage is 3.75V, and the constant voltage cutoff current is 50uA. Claim 10 In any one of claims 1 to 9, the lithium iron phosphate particles comprise: a) Dv10 ≥ 200 nm of the lithium iron phosphate particles; b) Dv50 ≥ 500 ≥ 5000 nm of the lithium iron phosphate particles; c) Dv90 ≤ 10000 nm of the lithium iron phosphate particles; d) Dv99 ≤ 12000 nm of the lithium iron phosphate particles; e) powder compression density ≥ 2.25 g / cm³ of the lithium iron phosphate at a pressure of 3T. 3 ;f) A positive plate characterized by satisfying at least one of (a) to (f) the powder resistivity of the lithium iron phosphate being less than 60 Ω·cm. Claim 11 In any one of claims 1 to 10, when the first positive active layer comprises lithium iron phosphate particles and the second positive active layer comprises lithium nickel cobalt manganese oxide particles, the coating weight of the first positive active layer is 0.02 to 0.38 g / 1540 mm 2 And, the coating weight of the second anode active layer is 0.08~0.32g / 1540mm 2 And; when the first positive active layer comprises lithium nickel cobalt manganese oxide particles and the second positive active layer comprises lithium iron phosphate particles, the coating weight of the first positive active layer is 0.08~0.32g / 1540mm 2 And, the coating weight of the second anode active layer is 0.02~0.38g / 1540mm 2 A positive plate characterized by being. Claim 12 An anode piece characterized in that, in any one of claims 1 to 11, the total thickness of the anode active layer is 50 to 150 μm. Claim 13 A positive electrode according to any one of claims 1 to 12, wherein the first positive electrode active layer comprises lithium iron phosphate particles and the second positive electrode active layer comprises lithium nickel cobalt manganese oxide particles. Claim 14 An anode piece according to any one of claims 1 to 13, wherein the lithium iron phosphate particles are obtained by a manufacturing method comprising providing a raw material containing mainly: at least a lithium source, an iron source, and a phosphorus source, and sintering at least twice, wherein the first sintering temperature is 500℃ to 760℃; and the second sintering temperature is 700℃ to 800℃. Claim 15 The anode piece according to claim 14, wherein the lithium iron phosphate particles are obtained by a manufacturing method comprising providing a raw material containing at least: a lithium source, an iron source, a phosphorus source, a carbon source, a carbon film-forming agent, and a modifier, and sintering at least twice, wherein the carbon content of the material after the first sintering is 0.01 wt% to 0.79 wt%; and the carbon content of the material after the second sintering is 0.8 wt% to 2.0 wt%. Claim 16 A positive plate according to claim 14 or 15, wherein the method for manufacturing the lithium iron phosphate particles comprises the step of performing a first grinding after performing the first sintering, and performing a second grinding after performing the second sintering, wherein the Dv50 of the product after the first grinding is 300 nm to 1200 nm; and the Dv50 of the product after the second grinding is 500 nm to 5000 nm. Claim 17 A secondary battery characterized by including a positive plate according to any one of claims 1 to 16. Claim 18 An electric device characterized by including a positive plate according to any one of claims 1 to 16 or a secondary battery according to claim 17.

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