Positive electrode active material, positive electrode sheet, electrode assembly, battery cell, battery, and power tool

Abstract

The application discloses a positive electrode active material, a positive electrode sheet, an electrode assembly, a battery monomer, a battery and an electric device, wherein the positive electrode active material comprises a nickel-cobalt-manganese ternary material and a lithium iron phosphate material; the lithium iron phosphate material comprises a lithium iron phosphate core and a conductive shell coated on the surface of the lithium iron phosphate core; the mass ratio of the conductive shell in the lithium iron phosphate material is greater than 0.2%; and the resistivity R1 of the nickel-cobalt-manganese ternary material and the resistivity R2 of the lithium iron phosphate material satisfy R1 / R2 <= 60. In the positive electrode active material, the ratio of the resistivity R1 of the nickel-cobalt-manganese ternary material and the resistivity R2 of the lithium iron phosphate material is controlled within a certain standard, so that the electric conductance of the lithium iron phosphate material and the nickel-cobalt-manganese ternary material is more matched, and in the case of mixing the lithium iron phosphate material and the nickel-cobalt-manganese ternary material, the problem that the capacity attenuation is rapid in the early stage of the normal-temperature cycle process can be improved.

Description

[0001] This application is a divisional application of the application filed on September 9, 2022, with application number 202211106932.5, entitled "Positive electrode active material, positive electrode sheet, electrode assembly, battery cell, battery and electrical device". Technical Field

[0002] This application relates to the field of batteries, and more specifically, to a positive electrode active material, a positive electrode sheet, an electrode assembly, a battery cell, a battery, and an electrical device. Background Technology

[0003] The proposed cathode active material, a mixture of lithium iron phosphate (LFP) and nickel-cobalt-manganese (NCM) materials, exhibits rapid capacity decay in the early stages of room temperature cycling, leading to capacity loss in the later stages of battery cell cycling. Summary of the Invention

[0004] In view of the above problems, this application provides a positive electrode active material, a positive electrode sheet, an electrode assembly, a battery cell, a battery, and an electrical device. When the positive electrode active material is a mixture of lithium iron phosphate material and nickel-cobalt-manganese ternary material, it can improve the problem of rapid capacity decay in the early stage during room temperature cycling.

[0005] The embodiments of this application are implemented as follows:

[0006] In a first aspect, embodiments of this application provide a positive electrode active material, comprising: a nickel-cobalt-manganese ternary material and a lithium iron phosphate material, wherein the nickel-cobalt-manganese ternary material is LiNi. x Co y Mn z M1 1-x-y-z O2, x>0, y>0, z>0, 1-xyz≥0, M1 is selected from one or more of Zr, Al, Mg, Nb, Ti and Ba, the lithium iron phosphate material includes a lithium iron phosphate core and a conductive shell covering the surface of the lithium iron phosphate core, the conductive shell accounts for >0.2% of the mass of the lithium iron phosphate material, and the lithium iron phosphate core is LiFe m M2 n PO4, m>0, n≥0, M2 is selected from one or more of Mn, Ti, Mg, V, Cr, Zr, Nb and W, and the resistivity R1 of the nickel-cobalt-manganese ternary material and the resistivity R2 of the lithium iron phosphate material satisfy: R1 / R2≤60.

[0007] In the technical solution of this application embodiment, the lithium iron phosphate core is coated with a conductive shell of a specific mass ratio to avoid excessive polarization affecting capacity performance. Based on this, the ratio of the resistivity R1 of the nickel-cobalt-manganese ternary material to the resistivity R2 of the lithium iron phosphate material is controlled within a certain standard, making the conductivities of the lithium iron phosphate and nickel-cobalt-manganese ternary materials more matched. This improves the susceptibility of the nickel-cobalt-manganese ternary material surface to damage, thereby mitigating the problem of rapid capacity decay in the early stages during room temperature cycling.

[0008] In some embodiments, R1 / R2 ≤ 20. In this embodiment, the ratio of the resistivity R1 of the nickel-cobalt-manganese ternary material to the resistivity R2 of the lithium iron phosphate material is controlled to a smaller standard, so that the conductivities of the lithium iron phosphate material and the nickel-cobalt-manganese ternary material are more matched, which is beneficial to better improve the problem of rapid capacity decay in the early stage during room temperature cycling.

[0009] In some embodiments, under ambient temperature testing conditions with a test pressure of 8 MPa, at least one of the following conditions (a) and (b) is met: (a) R1 is 1000 Ω·m to 4000 Ω·m; (b) R2 is 100 Ω·m to 200 Ω·m. In this embodiment, the resistivity R1 of the nickel-cobalt-manganese ternary material and the resistivity R2 of the lithium iron phosphate material are each controlled within a specific range, which is convenient to implement and beneficial to the matching of the conductivity of the lithium iron phosphate material and the nickel-cobalt-manganese ternary material.

[0010] In some embodiments, the nickel-cobalt-manganese ternary material accounts for 10% to 30% of the mass of the positive electrode active material. In this embodiment, the nickel-cobalt-manganese ternary material has an appropriate mass ratio to avoid insufficient energy density improvement due to too little nickel-cobalt-manganese ternary material, while avoiding excessive nickel-cobalt-manganese ternary material leading to high costs.

[0011] In some embodiments, the nickel-cobalt-manganese ternary material is selected from one or more of small single-crystal materials, near-single-crystal materials, and polycrystalline materials; the Dv50 of the small single-crystal material is 0.5 μm to 3 μm; in the near-single-crystal material, the Dv50 of the secondary particles is 6 μm to 10 μm, and the Dv50 of the primary particles is 300 nm to 600 nm; in the polycrystalline material, the Dv50 of the secondary particles is 6 μm to 10 μm, and the Dv50 of the primary particles is 300 nm to 600 nm. In this embodiment, a specific type of nickel-cobalt-manganese ternary material is selected, which has better ionic conductivity than conventional single-crystal nickel-cobalt-manganese ternary materials, making the conductivity of the nickel-cobalt-manganese ternary material and lithium iron phosphate material more matched, which is beneficial to better improve the problem of rapid capacity decay in the early stage during room temperature cycling.

[0012] In some embodiments, the Dv50 of the lithium iron phosphate material is 1 μm to 2 μm. In this embodiment, the lithium iron phosphate material has a suitable particle size. On the one hand, this particle size is required to be increased to a certain extent compared to the conventional level, to avoid the lithium iron phosphate material being too small and forming an encapsulation on the nickel-cobalt-manganese ternary material, causing over-discharge. This can reduce the contact between the lithium iron phosphate material and the nickel-cobalt-manganese ternary material, which is beneficial to suppressing the over-discharge of the nickel-cobalt-manganese ternary material, thereby helping to better improve the problem of rapid capacity decay in the early stage during room temperature cycling. On the other hand, this particle size is required to avoid the lithium iron phosphate material being too large, which would lead to excessive polarization and affect the cycling stability.

[0013] In some embodiments, the conductive shell is made of carbon. In this embodiment, carbon material, as the conductive shell, has advantages such as low cost, ease of processing, and good conductivity.

[0014] In some embodiments, the conductive shell accounts for 0.5% to 1.5% of the mass of the lithium iron phosphate material. In this embodiment, the conductive shell has a suitable mass percentage in the lithium iron phosphate material. On the one hand, this mass percentage is reduced to a certain extent compared with the conventional level, which reduces the amount of electrons accumulating on the surface of the nickel-cobalt-manganese ternary material. This helps to suppress the over-discharge of the nickel-cobalt-manganese ternary material, thereby helping to better improve the problem of rapid capacity decay in the early stage during room temperature cycling. At the same time, it also reduces costs. On the other hand, it avoids the situation where the mass percentage is too low, which would lead to deterioration of rate performance and excessive polarization, thus affecting cycle stability.

[0015] Secondly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive active material layer located on at least one side surface of the positive current collector, wherein the positive active material layer contains a positive active material as described in the above embodiments.

[0016] In some embodiments, a conductive agent is distributed between the positive electrode active materials, and the mass percentage of the conductive agent in the positive electrode active material layer is 0.1% to 1%. In this embodiment, the conductive agent has a suitable mass percentage in the positive electrode active material layer, so that the positive electrode active material layer as a whole has suitable conductivity, which is beneficial to maintaining the room temperature cycling stability of the battery cell.

[0017] Thirdly, embodiments of this application provide an electrode assembly, including a negative electrode sheet, a separator, and a positive electrode sheet as described in the above embodiments, arranged sequentially.

[0018] Fourthly, embodiments of this application provide a battery cell, including a housing and an electrode assembly as described in the above embodiments; the electrode assembly is housed within the housing.

[0019] Fifthly, embodiments of this application provide a battery, including a housing and the battery cells described in the above embodiments; the battery cells are housed within the housing.

[0020] Sixthly, embodiments of this application provide an electrical device, including a battery cell as described in the above embodiments or a battery as described in the above embodiments.

[0021] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0024] Figure 2 Exploded views of batteries provided for some embodiments of this application;

[0025] Figure 3 for Figure 2 The exploded view of the battery cell shown;

[0026] Figure 4 A partial structural schematic diagram of an electrode assembly provided in some embodiments of this application;

[0027] Figure 5 This is a partial structural schematic diagram of the positive electrode sheet provided in some embodiments of this application.

[0028] icon:

[0029] 1000 vehicles;

[0030] Battery 100; Controller 200; Motor 300;

[0031] Box body 10; First part 11; Second part 12; Storage space 13;

[0032] Battery cell 20; casing 21; electrode assembly 22; electrode terminals 23; pressure relief structure 24;

[0033] 211 housing; 212 cover; 221 positive electrode plate; 222 negative electrode plate; 223 separator;

[0034] Positive electrode current collector 2211; Positive electrode active material layer 2212;

[0035] Negative electrode current collector 2221; negative electrode active material layer 2222. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0037] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0039] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0040] In the description of the embodiments of this application, the technical terms "inner" and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0041] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0042] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0043] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the height, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall height, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0044] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0045] In current cathode active material design, in order to balance discharge specific capacity, energy density and safety performance, active materials with high discharge specific capacity and active materials with high safety performance are usually mixed together.

[0046] In some current designs, lithium nickel cobalt aluminum oxide (NCA) is used as the main material, with lithium iron phosphate (LFP) adsorbed onto its surface. This approach leverages the superior safety and cycle performance of LFP to compensate for the poor safety of NCA, while maintaining the high discharge specific capacity of NCA. However, in this design, the LFP acts as a coating layer, isolating the NCA from direct contact with the electrolyte and air, leading to a sacrifice in energy density.

[0047] To address these issues, some current designs involve directly mixing specific types of active materials, such as lithium iron phosphate and nickel-cobalt-manganese ternary materials, to better balance energy density and safety performance.

[0048] However, the proposed cathode active material, which is a mixture of lithium iron phosphate and nickel-cobalt-manganese ternary materials, exhibits rapid capacity decay in the early stages of room temperature cycling, leading to capacity loss in the middle and later stages of battery cell cycling.

[0049] The applicant noted that during room temperature cycling, the surface of the nickel-cobalt-manganese ternary material is easily damaged, resulting in rapid capacity decay in the early stages, until the capacity decay rate gradually stabilizes after 200 to 300 cycles.

[0050] Further research by the applicant revealed that the resistivity of commonly used lithium iron phosphate materials ranges from 10 Ω·m to 50 Ω·m, while the resistivity of commonly used nickel-cobalt-manganese ternary materials exceeds 10,000 Ω·m. The main reason why the surface of nickel-cobalt-manganese ternary materials is easily damaged is the mismatch in conductivity between lithium iron phosphate and nickel-cobalt-manganese ternary materials. During room temperature cycling, the current distribution of nickel-cobalt-manganese ternary materials is greater, and electrons accumulate on the surface of nickel-cobalt-manganese ternary materials. At the end of the discharge, nickel-cobalt-manganese ternary materials are over-discharged, which makes the surface of nickel-cobalt-manganese ternary materials easily damaged.

[0051] Based on this, in order to improve the above problems, this application proposes a positive electrode active material that, when lithium iron phosphate material and nickel cobalt manganese ternary material are mixed, rationally adjusts the conductivity of lithium iron phosphate material and nickel cobalt manganese ternary material to improve the phenomenon that the surface of nickel cobalt manganese ternary material is easily damaged, thereby improving the problem of rapid capacity decay in the early stage during room temperature cycling.

[0052] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device according to an embodiment of this application.

[0053] See Figure 1 See Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0054] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0055] In this application, battery 100 refers to a single physical module comprising one or more battery cells 20 to provide higher voltage and capacity. Battery 100 generally includes a housing 10 for encapsulating one or more battery cells 20. The housing 10 prevents liquids or other foreign matter from affecting the charging or discharging of the battery cells 20.

[0056] See Figure 2 , Figure 2 The exploded view of a battery 100 provided in some embodiments of this application shows that the battery 100 may include a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 is used to house the battery cell 20 and may have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, defining a housing space 13 for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, overlapping the open side of the second portion 12 to form a housing 10 with the housing space 13. Alternatively, both the first portion 11 and the second portion 12 may be hollow structures with one open side, overlapping the open side of the second portion 12 to form a housing 10 with the housing space 13. Of course, the first portion 11 and the second portion 12 may have various shapes, such as cylinders, cuboids, etc.

[0057] In battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, they can be connected in series, in parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed configuration, and then the whole assembly of multiple battery cells 20 is housed in housing 10. Alternatively, multiple battery cells 20 can first be connected in series, in parallel, or in a mixed configuration to form modules, and then multiple modules can be connected in series, in parallel, or in a mixed configuration to form a whole, which is then housed in housing 10. Battery 100 may also include other structures. For example, multiple battery cells 20 can be electrically connected through a busbar component to achieve parallel, series, or mixed configuration of multiple battery cells 20.

[0058] Each battery cell 20 can be a secondary battery 100 or a primary battery 100; it can also be a lithium-sulfur battery 100, a sodium-ion battery 100 or a magnesium-ion battery 100, but is not limited to these.

[0059] See Figure 3 , Figure 3 for Figure 2The diagram shows an exploded view of a single battery cell 20. A single battery cell 20 refers to the smallest unit that makes up the battery 100. A single battery cell 20 may include a housing 21, an electrode assembly 22, and an electrolyte, with the electrode assembly 22 and electrolyte both housed within the housing 21.

[0060] The outer casing 21 may include a housing 211 and a cover 212. The housing 211 is an assembly that fits with the cover 212 to form an internal sealed space for the battery cell 20, wherein the formed sealed space can accommodate the electrode assembly 22, electrolyte, and other components. The cover 212 is a component that covers the opening of the housing 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 may be adapted to the shape of the housing 211 to fit the housing 211, and the cover 212 may also be provided with functional components such as electrode terminals 23 and pressure relief structures 24. A sealing ring may be provided between the opening of the housing 211 and the cover 212 to achieve a seal between the housing 211 and the cover 212.

[0061] The housing 211 and cover 212 can be of various shapes and sizes, such as cuboids, cylinders, and hexagonal prisms. Specifically, the shapes of the housing 211 and cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The materials of the housing 211 and cover 212 can be various, such as, but not limited to, metals like copper, iron, aluminum, stainless steel, and aluminum alloys. The materials of the sealing ring can be various, such as, but not limited to, materials resistant to electrolyte corrosion, high toughness, and fatigue resistance, such as PP (polypropylene), PC (polycarbonate), and PET (polyethylene terephthalate). A plating layer can be formed on the outer surface of the housing 211, and the plating layer material can be various, such as, but not limited to, corrosion-resistant materials like Ni and Cr.

[0062] See Figure 4 The electrode assembly 22 can be composed of a positive electrode 221, a negative electrode 222, and a separator 223. The battery cell 20 mainly functions by the movement of metal ions between the positive electrode 221 and the negative electrode 222. The separator 223 can be made of PP (polypropylene) or PE (polyethylene), etc. See also... Figure 5The positive electrode 221 includes a positive current collector 2211 and a positive active material layer 2212. Taking a lithium-ion battery cell 20 as an example, the material of the positive current collector 2211 can be aluminum, and the main component of the positive active material layer 2212 is the positive active material. The negative electrode 222 includes a negative current collector 2221 and a negative active material layer 2222. The material of the negative current collector 2221 can be copper, and the negative active material in the negative active material layer 2222 can be carbon, silicon, etc. Furthermore, the electrode assembly 22 can be a wound structure or a stacked structure; the embodiments of this application are not limited to these.

[0063] The positive electrode active material proposed in the embodiments of this application will now be described in detail.

[0064] In a first aspect, embodiments of this application provide a positive electrode active material, comprising: a nickel-cobalt-manganese ternary material and a lithium iron phosphate material, wherein the nickel-cobalt-manganese ternary material is LiNi. x Co y Mn z M1 1-x-y-z O2, x>0, y>0, z>0, 1-xyz≥0, M1 is selected from one or more of Zr, Al, Mg, Nb, Ti and Ba, the lithium iron phosphate material includes a lithium iron phosphate core and a conductive shell 211 covering the surface of the lithium iron phosphate core, the conductive shell 211 accounts for >0.2% of the mass of the lithium iron phosphate material, and the lithium iron phosphate core is LiFe m M2 n PO4, m>0, n≥0, M2 is selected from one or more of Mn, Ti, Mg, V, Cr, Zr, Nb and W, and the resistivity R1 of the nickel-cobalt-manganese ternary material and the resistivity R2 of the lithium iron phosphate material satisfy: R1 / R2≤60.

[0065] Lithium iron phosphate material has a core-shell-like structure. The lithium iron phosphate core is the core part mainly made of lithium iron phosphate, and the conductive shell 211 is the shell part mainly made of conductive material. The conductive shell 211 can completely cover the lithium iron phosphate core or partially cover it.

[0066] In this application, the resistivity test method can employ a test method known in the art. As an example, the test method includes: weighing a certain mass of powder sample, adjusting the depth of the feeding chamber, adding the sample into the feeding chamber, applying pressure at room temperature, with the pressure value selected from 4 MPa, 8 MPa, 12 MPa, and 16 MPa, recording the powder resistivity test results at different pressure points, and the test range being <100000 Ω·m.

[0067] As an example, the ratio of R1 / R2 may satisfy, but is not limited to: ≤60, ≤50, ≤45, ≤40, ≤35, ≤30, ≤25, or ≤20.

[0068] In the technical solution of this application embodiment, the lithium iron phosphate core is coated with a conductive shell 211 of a specific mass ratio to avoid excessive polarization affecting capacity performance. Based on this, the ratio of the resistivity R1 of the nickel-cobalt-manganese ternary material to the resistivity R2 of the lithium iron phosphate material is controlled within a certain standard, making the conductivities of the lithium iron phosphate material and the nickel-cobalt-manganese ternary material more matched. This improves the susceptibility of the nickel-cobalt-manganese ternary material surface to damage, thereby mitigating the problem of rapid capacity decay in the early stages during room temperature cycling.

[0069] In some embodiments, R1 / R2 ≤ 20.

[0070] In this embodiment, the ratio of the resistivity R1 of the nickel-cobalt-manganese ternary material to the resistivity R2 of the lithium iron phosphate material is controlled at a smaller standard, so that the conductivity of the lithium iron phosphate material and the nickel-cobalt-manganese ternary material are more matched, which is beneficial to better improve the problem of rapid capacity decay in the early stage during room temperature cycling.

[0071] In some embodiments, under normal temperature test conditions with a test pressure of 8 MPa, at least one of the following conditions (a) and (b) is met: (a) R1 is 1000 Ω·m to 4000 Ω·m; (b) R2 is 100 Ω·m to 200 Ω·m.

[0072] As an example, the value of R1 may be, for example but not limited to, any one of 1000Ω·m, 1500Ω·m, 2000Ω·m, 2500Ω·m, 3000Ω·m, 3500Ω·m and 4000Ω·m or a range between any two.

[0073] As an example, the value of R2 is, for example, but not limited to, any one of 100Ω·m, 110Ω·m, 120Ω·m, 130Ω·m, 140Ω·m, 150Ω·m, 160Ω·m, 170Ω·m, 180Ω·m, 190Ω·m and 200Ω·m, or a range between any two.

[0074] In this embodiment, the resistivity R1 of the nickel-cobalt-manganese ternary material and the resistivity R2 of the lithium iron phosphate material are each controlled within a specific range, which is convenient to implement and facilitates the matching of the electrical conductance of the lithium iron phosphate material and the nickel-cobalt-manganese ternary material.

[0075] In some embodiments, the nickel-cobalt-manganese ternary material accounts for 10% to 30% of the mass of the positive electrode active material.

[0076] As an example, the mass percentage of nickel-cobalt-manganese ternary materials in the positive electrode active material is, for example, but not limited to, any one of 10%, 15%, 20%, 25%, and 30%, or a range between any two.

[0077] In this embodiment, the nickel-cobalt-manganese ternary material has a suitable mass ratio to avoid insufficient energy density improvement due to too little nickel-cobalt-manganese ternary material, while avoiding excessive nickel-cobalt-manganese ternary material leading to high costs.

[0078] In some embodiments, the nickel-cobalt-manganese ternary material is selected from one or more of small single-crystal materials, near-single-crystal materials, and polycrystalline materials; the Dv50 of the small single-crystal material is 0.5μm to 3μm; in the near-single-crystal material, the Dv50 of the secondary particles is 6μm to 10μm, and the Dv50 of the primary particles is 300nm to 600nm; in the polycrystalline material, the Dv50 of the secondary particles is 6μm to 10μm, and the Dv50 of the primary particles is 300nm to 600nm.

[0079] Small single-crystal materials refer to single-crystal materials that meet the above-mentioned small particle size standard, while single-crystal materials refer to materials composed of a single crystal.

[0080] Single-crystal-like materials refer to crystalline materials that are close to single crystals, with large crystal size and a small number of grains.

[0081] Polycrystalline materials are materials composed of randomly oriented grains that may have textured properties.

[0082] Dv50 represents the particle size corresponding to 50% of the volume distribution.

[0083] When crystals are very small, due to the high surface energy of the grains, these small grains easily bond together due to weak interaction forces, leading to grain agglomeration. In other words, many small grains clump together to form larger particles. The small grains before agglomeration are called primary particles, and the larger particles formed after agglomeration are called secondary particles.

[0084] As an example, the Dv50 of small single-crystal materials can be, for example but not limited to, a point value of 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm and 3 μm or a range of values ​​between any two.

[0085] As an example, the Dv50 of the secondary particles of the quasi-single-crystal material and the polycrystalline material is, for example, but not limited to, a point value of 6μm, 7μm, 8μm, 9μm and 10μm or a range of values ​​between any two; the Dv50 of the primary particles of the quasi-single-crystal material and the polycrystalline material is, for example, but not limited to, a point value of 300nm, 400nm, 500nm and 600nm or a range of values ​​between any two.

[0086] In this embodiment, a specific type of nickel-cobalt-manganese ternary material is selected. Compared with conventional single-crystal nickel-cobalt-manganese ternary materials, it has better ionic conductivity, making the conductivity of nickel-cobalt-manganese ternary materials and lithium iron phosphate materials more compatible. This is beneficial to better improve the problem of rapid capacity decay in the early stage during room temperature cycling.

[0087] In some embodiments, the Dv50 of the lithium iron phosphate material is 1 μm to 2 μm.

[0088] As an example, the Dv50 of lithium iron phosphate materials is, for example, but not limited to, a point value or a range of any two of 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm and 2μm.

[0089] In this embodiment, the lithium iron phosphate material has a suitable particle size. On the one hand, the particle size is required to be increased to a certain extent compared with the conventional level to avoid the lithium iron phosphate material being too small and forming a coating on the nickel cobalt manganese ternary material, causing over-discharge. This can reduce the contact between the lithium iron phosphate material and the nickel cobalt manganese ternary material, which is beneficial to suppress the over-discharge of the nickel cobalt manganese ternary material, thereby helping to better improve the problem of rapid capacity decay in the early stage during room temperature cycling. On the other hand, the particle size is required to avoid the lithium iron phosphate material being too large, which would lead to excessive polarization and affect the cycling stability.

[0090] In some embodiments, the conductive housing 211 is made of carbon.

[0091] In this embodiment, carbon material is used as the conductive shell 211, which has the advantages of low cost, easy processing, and good conductivity.

[0092] In some embodiments, the conductive housing 211 accounts for 0.5% to 1.5% of the mass of the lithium iron phosphate material.

[0093] As an example, the mass percentage of the conductive casing 211 in the lithium iron phosphate material is, for example, but not limited to, any one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, and 1.5%, or a range between any two.

[0094] In this embodiment, the conductive shell 211 has a suitable mass ratio in the lithium iron phosphate material. On the one hand, this mass ratio is reduced to a certain extent compared with the conventional level, which reduces the amount of electrons accumulating on the surface of the nickel-cobalt-manganese ternary material. This helps to suppress the over-discharge of the nickel-cobalt-manganese ternary material, thereby helping to better improve the problem of rapid capacity decay in the early stage during room temperature cycling. At the same time, it also reduces costs. On the other hand, it avoids the deterioration of rate performance and excessive polarization caused by the mass ratio being too low, which would affect the cycle stability.

[0095] See Figure 5 Secondly, embodiments of this application provide a positive electrode 221, including a positive current collector 2211 and a positive active material layer 2212 located on at least one side surface of the positive current collector 2211, wherein the positive active material layer 2212 contains the positive active material as described in the above embodiments.

[0096] In some embodiments, a conductive agent is distributed between the positive electrode active materials, and the mass percentage of the conductive agent in the positive electrode active material layer 2212 is 0.1% to 1%.

[0097] As an example, the mass percentage of the conductive agent in the positive electrode active material layer 2212 may be, for example, but not limited to, any one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1%, or a range between any two.

[0098] In this embodiment, the conductive agent has a suitable mass ratio in the positive electrode active material layer 2212, so that the positive electrode active material layer 2212 as a whole has suitable conductivity, which is beneficial to maintaining the room temperature cycling stability of the battery cell 20.

[0099] See Figure 4 Thirdly, embodiments of this application provide an electrode assembly 22, including a negative electrode 222, a separator 223, and a positive electrode 221 as described in the above embodiments, arranged sequentially.

[0100] See Figure 3 Fourthly, embodiments of this application provide a battery cell 20, including a housing 21 and an electrode assembly 22 as described in the above embodiments; the electrode assembly 22 is housed within the housing 21.

[0101] See Figure 2 Fifthly, embodiments of this application provide a battery 100, including a housing 10 and a battery cell 20 as described above; the battery cell 20 is housed within the housing 10.

[0102] Sixthly, embodiments of this application provide an electrical device, such as a vehicle 1000, including a battery cell 20 as described above or a battery 100 as described above.

[0103] According to some embodiments of this application, R1 / R2≤20; the nickel-cobalt-manganese ternary material is selected from one of small single crystal materials, near-single crystal materials, and polycrystalline materials; the conductive shell 211 is made of carbon, and the mass percentage of the conductive shell 211 in the lithium iron phosphate material is 0.5% to 1.5%.

[0104] The following specific embodiments are provided to better illustrate this application.

[0105] I. Preparation of battery cells

[0106] (1) Preparation of negative electrode sheet

[0107] The negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are mixed in a weight ratio of 95:2:2:1. An appropriate amount of deionized water is added and the mixture is stirred thoroughly to form a uniform negative electrode slurry. The negative electrode slurry is coated onto the negative electrode current collector copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0108] (2) Preparation of positive electrode sheet

[0109] The positive electrode active material and (conductive agent + binder) are mixed at a mass ratio of 95:5 and dispersed in a solvent to obtain a positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet.

[0110] (3) Electrolyte preparation

[0111] The electrolytes were prepared according to the following method:

[0112] In an argon atmosphere glove box with a water content of <10ppm, a certain mass of fully dried lithium salt LiPF6 is dissolved in a mixed solvent, and then an inorganic lithium salt additive is added. After stirring evenly, an electrolyte is obtained.

[0113] (4) Battery manufacturing

[0114] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up to obtain an electrode assembly. The electrode assembly is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried outer packaging foil. The battery cell is then obtained through vacuum sealing, settling, formation, and shaping processes.

[0115] II. Testing individual battery cells

[0116] Detection method:

[0117] Material resistivity test: Weigh a certain mass of powder sample, adjust the depth of the feeding chamber, add the sample into the feeding chamber, apply pressure at room temperature with a pressure value of 8 MPa, and record the powder resistivity test results at different pressure points. The test range is <100000 Ω·m.

[0118] Battery cell cycle performance test: At 25 / 45℃, the battery cell is first charged to 4.3V with a constant current of 1C, then further charged to 0.05C with a constant voltage of 4.3V, and then discharged to 3V with a constant current of 1C. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The battery cell is subjected to multiple charge-discharge cycles in the above manner, and the discharge capacity of the 200th cycle is obtained. The capacity retention rate of the battery after cycles is calculated using the following formula 1.

[0119] Formula 1: Battery capacity retention rate (%) after 200 cycles = (Discharge capacity of the 200th cycle / Discharge capacity of the 1st cycle) × 100%.

[0120] The performance parameters of the nickel-cobalt-manganese ternary material and lithium iron phosphate material used in each experiment are shown in Table 1. The parameter conditions of the battery cells in each experiment are shown in Table 2. The cycle performance test results of the battery cells in each experiment are shown in Table 3.

[0121] Table 1.

[0122]

[0123]

[0124] For materials other than single-crystal quasi-materials and multi-crystal materials, Dv50 is understood according to the conventional particle size, that is, Dv50 is relative to the material as a whole, without distinguishing between primary and secondary particles; for single-crystal quasi-materials and multi-crystal materials, Dv50 refers to the Dv50 of secondary particles, and the particle size of primary particles refers to the Dv50 of primary particles.

[0125] Table 2.

[0126]

[0127]

[0128] The conductive agent ratio refers to the mass percentage of the conductive agent in the positive electrode active material layer. In Experiment 11, the resistivity R2 of the lithium iron phosphate material was not obtained because it exceeded the range, so the specific ratio of R1 / R2 is not shown.

[0129] Table 3.

[0130]

[0131]

[0132] According to Tables 1-3:

[0133] Compared with Experiment 1, Experiments 2-4 replaced the conventional single crystal nickel-cobalt-manganese ternary material with one of the following: small single crystal material, near-single crystal material, and polycrystalline material. This reduced R1 / R2, improved the room temperature cycling stability of the battery cells, and improved the capacity decay in the early stage, as well as the capacity retention rate.

[0134] Compared to Experiment 1, Experiments 5-8 show different carbon coating amounts in the lithium iron phosphate materials. The comparison between Experiments 5-7 and Experiment 1 shows that appropriately reducing the carbon coating amount in the lithium iron phosphate material decreases R1 / R2, resulting in better room-temperature cycle stability of the battery cells, improved capacity decay in the early stages, and increased capacity retention. The comparison between Experiment 8 and Experiment 1 shows that if the carbon coating amount in the lithium iron phosphate material is too low, R1 / R2 decreases, but due to excessive polarization, the room-temperature cycle stability of the battery cells decreases to some extent, the capacity decay in the early stages worsens, and the capacity retention is slightly reduced.

[0135] Compared with Experiment 1, Experiment 9 showed that the lithium iron phosphate material was not coated with carbon. Due to excessive polarization, the capacity could not be fully utilized, resulting in a significant decrease in the room temperature cycling stability of the battery cells. The capacity decay in the early stage was severely worsened, and the capacity retention rate was significantly reduced.

[0136] Compared to Experiment 1, Experiments 10-12 increased the particle size of the lithium iron phosphate material, resulting in a smaller R1 / R2 ratio and better room temperature cycle stability of the battery cells. This improved early-stage capacity decay and increased capacity retention. However, a comparison between Experiment 10 and Experiments 11-12 shows that the lithium iron phosphate material in Experiment 10 had a higher particle size and greater polarization, leading to decreased stability of the battery cells at 45℃, worsened early-stage capacity decay, and reduced capacity retention.

[0137] Compared with Experiment 1, Experiment 13 reduced the particle size of lithium iron phosphate material, increased R1 / R2, reduced the room temperature cycling stability of the battery cells, worsened the early capacity decay, and reduced the capacity retention rate.

[0138] Compared with Experiment 6, Experiment 14 reduced the mass ratio of the conductive agent in the positive electrode active material layer, resulting in better room temperature cycling stability of the battery cells, improved capacity decay in the early stage, and increased capacity retention.

[0139] Compared with Experiment 6, Experiment 15 increased the mass ratio of conductive agent in the positive electrode active material layer, resulting in a decrease in the room temperature cycling stability of the battery cell, a worsening of the early capacity decay, and a decrease in capacity retention.

[0140] Compared with Experiment 1, Experiments 16-18 replaced the conventional single crystal nickel-cobalt-manganese ternary material with one of the following: small single crystal material, near-single crystal material, and polycrystalline material. At the same time, the carbon coating in the lithium iron phosphate material was appropriately reduced. The room temperature cycle stability of the battery cells was significantly better, the capacity decay in the early stage was significantly improved, and the capacity retention rate was significantly increased.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode active material, characterized by, The nickel-cobalt-manganese ternary material and the lithium iron phosphate material include a lithium iron phosphate core and a conductive shell coated on the surface of the lithium iron phosphate core, the mass ratio of the conductive shell in the lithium iron phosphate material is >0.2%, the resistivity R1 of the nickel-cobalt-manganese ternary material and the resistivity R2 of the lithium iron phosphate material satisfy: R1 / R2≤60, the resistivity R1 of the nickel-cobalt-manganese ternary material is the resistivity value measured under the normal temperature test condition with a test pressure of 8 MPa, and the resistivity R2 of the lithium iron phosphate material is the resistivity value measured under the normal temperature test condition with a test pressure of 8 MPa.

2. The positive electrode active material according to claim 1, characterized by The resistivity R1 of the nickel-cobalt-manganese ternary material and the resistivity R2 of the lithium iron phosphate material satisfy any one of conditions (1) and (7): (1) R1 / R2≤50; (2) R1 / R2≤45; (3) R1 / R2≤40; (4) R1 / R2≤35; (5) R1 / R2≤30; (6) R1 / R2≤25 (7) R1 / R2≤20.

3. The positive electrode active material according to claim 1, characterized by Under the normal temperature test condition with a test pressure of 8 MPa, at least one of conditions (a) and (b) is satisfied: (a) R1 is 1000 Ω·m ~4000 Ω·m; (b) R2 is 100 Ω·m ~200 Ω·m.

4. The positive electrode active material according to claim 1, characterized by The nickel-cobalt-manganese ternary material is LiNi x Co y Mn z M1 1-x-y-z O2, x > 0, y > 0, z > 0, 1 - x - y - z > 0, M1 is selected from one or more of Zr, Al, Mg, Nb, Ti and Ba; and / or The lithium iron phosphate core is LiFe m M2 n PO4, m > 0, n > 0, M2 is selected from one or more of Mn, Ti, Mg, V, Cr, Zr, Nb and W.

5. The positive electrode active material according to claim 1, characterized by The mass ratio of the nickel-cobalt-manganese ternary material in the positive electrode active material is 10% ~30%.

6. The positive electrode active material according to claim 1, characterized by The nickel-cobalt-manganese ternary material is selected from one or more of small single crystal materials, single crystal-like materials and polycrystalline materials; The Dv50 of the small single crystal material is 0.5 μm ~3 μm; In the single crystal-like material, the Dv50 of secondary particles is 6 μm ~10 μm, and the Dv50 of primary particles is 300 nm ~600 nm; In the polycrystalline material, the Dv50 of secondary particles is 6 μm ~10 μm, and the Dv50 of primary particles is 300 nm ~600 nm.

7. The positive electrode active material according to claim 1, characterized by The Dv50 of the lithium iron phosphate material is 1 μm ~2 μm.

8. The positive electrode active material according to claim 1, characterized by The material of the conductive shell is carbon.

9. The positive electrode active material according to claim 1, characterized by The mass ratio of the conductive shell in the lithium iron phosphate material is 0.5% ~1.5%.

10. A positive electrode sheet characterized by comprising: The positive electrode active material layer includes the positive electrode active material layer and the positive electrode current collector.

11. The cathode electrode of claim 10, wherein, The conductive agent is distributed between the positive electrode active materials, and the mass ratio of the conductive agent in the positive electrode active material layer is 0.1% ~1%.

12. An electrode assembly, characterized by, The electrode assembly includes a negative electrode sheet, a separator film and the positive electrode sheet.

13. A battery cell, characterized by The electrode assembly is accommodated in the shell. The battery cell includes the battery cell and the shell.

14. A battery, characterized by The battery cell is accommodated in the shell. The battery includes the battery cell or the battery.

15. An electrical device, characterized by ​

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