Composite cathode material, preparation method thereof, cathode sheet, and lithium secondary battery

Abstract

The application provides a composite positive electrode material, which comprises a positive electrode active material and a conductive material coated on the positive electrode active material, and the molar content of nickel element is higher than 85% based on the total molar number of transition metal elements in the positive electrode active material. By coating the conductive material on the surface of the high-nickel positive electrode active material, the electron transmission rate of the high-nickel positive electrode active material can be improved, and the synchronous improvement of the energy density and the power performance of the battery can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a composite positive electrode material, a preparation method thereof, a positive electrode sheet, a lithium secondary battery and an electric device. BACKGROUND

[0002] With the rapid development of the power automobile and energy storage technology industry, higher requirements are put forward for the energy density, cycle performance and cost of the secondary battery. The positive electrode material, as one of the core materials of the secondary battery, has a decisive influence on the comprehensive performance of the battery, including energy density, rate performance and cycle performance. Therefore, it is necessary to develop high-performance positive electrode materials to improve the comprehensive performance of the secondary battery. SUMMARY

[0003] The present application is made in view of the above-mentioned problems, and aims to provide a composite positive electrode material. By coating the surface of the positive electrode active material with a conductive material, the electronic conductivity of the high-nickel positive electrode material can be improved, and the simultaneous improvement of the power performance and energy density of the battery can be realized.

[0004] The first aspect of the present application provides a composite positive electrode material, which comprises a positive electrode active material and a conductive material coated on the positive electrode active material, and the molar content of nickel element is higher than 85% based on the total number of moles of transition metal elements in the positive electrode active material.

[0005] By coating the surface of the high-nickel positive electrode active material with a conductive material, the electronic transmission rate of the high-nickel positive electrode material can be improved, and the simultaneous improvement of the energy density and power performance of the battery can be realized.

[0006] In any embodiment, the general formula of the positive electrode active material is shown as formula I,

[0007] LiNi x Co y M 1-x-y O2formula I

[0008] Wherein, M comprises at least one of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, Mo, wherein 0.90≤x≤1.0, 0≤y≤0.10, optionally 0.95≤x<1.0, 0<y≤0.05.

[0009] The doping elements in the positive electrode active material of the present application improve the structural stability of the positive electrode active material, reduce the dissolution of nickel elements, alleviate the capacity decay during the cycle process, so that the battery can still maintain the stability of the structure under high-rate discharge, and further improve the power performance of the battery.

[0010] In any embodiment, the mass content M of the conductive material is 0.1% to 5%, optionally 0.5% to 3%, based on the total mass of the composite cathode material.

[0011] When the mass content of the conductive material is within the above range, based on the total mass of the composite cathode material, the battery can simultaneously achieve high energy density and power performance.

[0012] In any embodiment, the conductive material comprises at least one one-dimensional carbon material, and the aspect ratio of the one-dimensional carbon material is not less than 500:1.

[0013] The one-dimensional carbon material has a high aspect ratio, and the mutual lapping between one-dimensional materials easily forms a long and continuous conductive network, realizing long-range conduction, which is particularly suitable for high energy density batteries with high load capacity, and can effectively improve the transmission rate of electrons in the positive active material.

[0014] In any embodiment, the conductive material comprises at least two one-dimensional carbon materials with different tube diameter sizes.

[0015] Through the mutual matching of two one-dimensional carbon materials with different tube diameter sizes, the synergy of solid-phase transmission and liquid-phase mass transfer can be achieved, which can effectively improve the transmission efficiency of electrons and also realize electrolyte transmission by means of large tube diameter, thereby further optimizing the power performance of the battery.

[0016] In any embodiment, the ratio of the tube diameter sizes of at least two one-dimensional carbon materials in the at least two one-dimensional carbon materials with different tube diameter sizes is not less than 3, optionally not less than 100 or not less than 800.

[0017] The coating layer comprises at least two one-dimensional carbon materials with a tube diameter size ratio greater than 3, which can effectively improve the discharge time of the battery at high rate, i.e., optimize the power performance of the battery. The coating layer comprises at least two one-dimensional carbon materials with a tube diameter size ratio greater than 100, and the synergistic effect is more significant, further optimizing the power performance of the battery. The coating layer comprises at least two one-dimensional carbon materials with a tube diameter size ratio greater than 800, and the liquid-phase mass transfer function is obvious, further optimizing the power performance of the battery.

[0018] In any embodiment, the conductive material comprises at least one one-dimensional carbon material with a tube diameter size greater than 100 nm, optionally greater than 1 μm.

[0019] The one-dimensional carbon material with a tube diameter size greater than 100 nm can play a liquid-phase mass transfer role in the positive active material, improve the transmission rate of lithium ions in the electrode active material, thereby reducing the polarization resistance of the battery and improving the power performance of the battery.

[0020] In any embodiment, the mass content of the one-dimensional carbon material with a tube diameter size greater than 100 nm is 10%-80% based on the total mass of the conductive material.

[0021] In any embodiment, the conductive material comprises at least one of single-arm carbon nanotubes, vapor-grown carbon fibers, multi-arm carbon nanotubes, porous cross-linked carbon fibers, and hollow micron carbon fibers.

[0022] In any embodiment, the powder resistivity of the composite cathode material is 1x10 3 -1x10 4 Ω·cm.

[0023] Compared with the high-nickel cathode active material in the prior art, the powder resistivity of the composite cathode material is greatly reduced. In any embodiment, the particle Dv50 of the composite cathode material is 6-15 μm, and the particle Dv50 of the cathode active material is 8-12 μm.

[0024] When the particle Dv50 of the composite cathode material is within the above range, the composite cathode material has a large specific surface area and excellent kinetic performance, which is beneficial to improving the power performance of the cathode material.

[0025] In any embodiment, the span ratio of the composite cathode material is 1.12<(Dv90-Dv10) / Dv50<1.75.

[0026] When the span ratio of the composite cathode material meets the above range, the cathode active material can form a particle size matching, which is helpful to improve the compaction density of the electrode sheet and the energy density of the battery.

[0027] The second aspect of the present application provides a preparation method of a composite cathode material, comprising the following steps:

[0028] mixing and dispersing the cathode active material, the conductive material, and the dispersant, removing the dispersant, and sintering under an inert atmosphere to obtain the composite cathode material,

[0029] The molar content of nickel is higher than 85% based on the total number of moles of transition metal elements in the cathode active material.

[0030] Through the above method, uniform coating of the high-nickel cathode material can be achieved under oxygen-free conditions, the electronic conductivity of the high-nickel cathode material is improved, and the power performance of the battery is improved.

[0031] In any embodiment, the temperature of the low-temperature sintering is 120-200 °C, and the time is 2-6 h.

[0032] When the temperature and time of sintering are within the above range, the positive electrode active material does not have oxygen defects, and the adhesion between the conductive material and the positive electrode active material can be improved, so that the conductive material is coated and the structural stability of the composite positive electrode material is ensured.

[0033] In any embodiment, the positive electrode active material, the conductive material, and the dispersing agent are stirred and mixed to achieve dispersion.

[0034] The third aspect of the present application provides a positive electrode tab, a positive electrode current collector, and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the composite positive electrode material of the first aspect or the composite positive electrode material prepared by the preparation method of the second aspect.

[0035] In any embodiment, the area density I of the positive electrode film layer is 24-48 mg / cm 2 .

[0036] When the area density of the positive electrode film layer is within the above range, the battery can have high energy density. The composite positive electrode material of the present application is particularly suitable for thick-coated electrode tabs, and can significantly reduce the electrode resistance of the thick-coated electrode tab and improve the power performance of the battery through long-range conduction and liquid-phase mass transfer.

[0037] In any embodiment, the compaction density of the positive electrode tab is 2.9-3.6 g / cm 3 .

[0038] When the compaction density of the positive electrode tab is within the above range, the battery can have high energy density, and the electrolyte and the electrode tab can be mutually infiltrated to achieve high power performance.

[0039] In any embodiment, the elongation rate of the positive electrode tab in the length direction after cold pressing is not less than 0.5%, and can be 0.5%-0.9%.

[0040] The high-area-density electrode tab is prone to brittle fracture during cold pressing due to the large coating weight per unit area. The composite positive electrode material provided by the present application can coat a high content of conductive material, and the high content of conductive material can play a sliding role to increase the toughness of the electrode tab and improve the safety performance of the battery.

[0041] In any embodiment, the relationship between the mass content M of the conductive material relative to the composite positive electrode material and the area density I of the positive electrode film layer satisfies 500≤I / M≤40000.

[0042] When the relationship between the mass content M of the conductive material relative to the composite positive electrode material and the area density I of the positive electrode film layer satisfies the above range, the battery internal resistance can be reduced and the energy density of the battery can be improved.

[0043] The third aspect of the present application provides a lithium ion secondary battery comprising the positive electrode sheet of the second aspect.

[0044] In any embodiment, the energy density of the lithium ion secondary battery is 380-500 Wh / Kg.

[0045] The fourth aspect of the present application provides an electric device comprising the lithium ion secondary battery of the third aspect. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a scanning electron microscope image of the composite positive electrode material of an embodiment of the present application;

[0047] Figure 2 is a schematic diagram of a secondary battery of an embodiment of the present application;

[0048] Figure 3 is Figure 1 is an exploded view of the secondary battery of an embodiment of the present application shown in FIG. 8;

[0049] Figure 4 is a schematic diagram of an electric device using the secondary battery of an embodiment of the present application as a power source.

[0050] REFERENCE NUMERALS

[0051] 1 secondary battery; 11 housing; 12 electrode assembly; 13 cover plate. DETAILED DESCRIPTION

[0052] Hereinafter, embodiments of the binder, the production method, the electrode, the battery, and the electric device of the present application are specifically disclosed with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters that are already well known, repeated description of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0053] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0054] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0055] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0056] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0057] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0058] If not specifically stated, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0059] It is a common pursuit in the industry to improve the energy density of batteries, and using high-nickel positive electrode active materials and thick coating to increase the electrode loading can effectively improve the energy density of the battery. However, the increase of nickel content will greatly reduce the cobalt content, resulting in a significant decrease in battery power performance while the energy density is significantly improved; and the increase of electrode loading will further increase the difficulty of ion insertion and extraction in the active material, making it difficult to balance the energy density and power performance of the battery. Furthermore, the synthesis of high-nickel positive electrode active material is usually completed under oxygen-rich conditions, and it is difficult to directly perform high-temperature sintering under inert atmosphere to achieve carbon coating, so that the high-nickel positive electrode active material has poor conductivity and the electrons are difficult to transmit quickly, further reducing the power performance of the high-nickel positive electrode active material.

[0060] Based on this, the present application provides a composite positive electrode material to realize the simultaneous optimization of battery energy density and power performance.

[0061] In some embodiments, the composite positive electrode material comprises a positive electrode active material and a conductive material coated on the positive electrode active material, and the molar content of nickel element is higher than 85% based on the total moles of transition metal elements in the positive electrode active material.

[0062] In some embodiments, the molar content of nickel element can be selected as 86%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or any value therein based on the total moles of transition metal elements in the positive electrode active material.

[0063] In some embodiments, the molar content of nickel element can be obtained by scanning electron microscopy and energy spectrum analysis. In some embodiments, the scanning electron microscopy image of the composite positive electrode material is as shown in Figure 1 It can be seen that a large amount of conductive material is uniformly and closely coated on the surface of the positive electrode active material, realizing the effective compounding of the positive electrode active material and the conductive material.

[0064] By coating the conductive material on the surface of the high-nickel positive electrode active material, the electron transmission rate of the high-nickel positive electrode material can be improved, realizing the simultaneous improvement of the energy density and power performance of the battery.

[0065] In some embodiments, the general formula of the positive electrode active material is as shown in formula I,

[0066] LiNi x Coy M 1-x-y O2Formula I

[0067] wherein M comprises at least one of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, Mo, wherein 0.90≤x≤1.0, 0≤y≤0.10, optionally 0.95≤x<1.0, 0<y≤0.05.

[0068] In some embodiments, M comprises Mn. In some embodiments, M comprises Mn, Zr. In some embodiments, M comprises Mn, W. In some embodiments, M comprises Mn, Mo. In some embodiments, M comprises Mn, Zr, Mo. In some embodiments, M comprises Mn, Zr, W. In some embodiments, x is selected from 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 1.0. In some embodiments, y is selected from 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 1.0.

[0069] The doping element in the positive electrode active material of the present application improves the structural stability of the positive electrode active material, reduces the dissolution of nickel element and the capacity decay caused thereby, so that the battery can still maintain the stability of the structure under high rate discharge, further improving the power performance of the battery.

[0070] In some embodiments, the mass content M of the conductive material is 0.1% to 5%, optionally 0.5% to 3%, based on the total mass of the composite positive electrode material.

[0071] In some embodiments, the mass content M of the conductive material is optionally 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.6%, 4.8%, or 5%, based on the total mass of the composite positive electrode material.

[0072] In the prior art, conductive material is often added during the slurry mixing process. However, too high a content of conductive material can cause the slurry to gel and the conductive material to agglomerate, resulting in a decrease in the performance of the slurry. The composite positive electrode material provided by the present application has a high content of conductive material, and the conductive material can be uniformly distributed on the surface and in the bulk phase of the positive electrode active material, and can provide enough conductive paths, so that the power performance of the positive electrode material is greatly improved.

[0073] Based on the total mass of the composite cathode material, when the mass content M of the conductive material is 0.5% to 3%, the battery can simultaneously achieve high energy density and power performance.

[0074] In some embodiments, the conductive material includes at least one one-dimensional carbon material, said one-dimensional carbon material having an aspect ratio of not less than 500:1.

[0075] In this article, "one-dimensional carbon material" refers to carbon material whose length dimension is greater than its radial dimension. As examples, one-dimensional carbon materials include, but are not limited to, fibrous carbon materials and needle-like carbon materials.

[0076] One-dimensional carbon materials have a high aspect ratio, and the interlocking of one-dimensional materials can easily form a long and continuous conductive network, achieving long-range conductivity. They are especially suitable for high-energy-density batteries with large loads and can effectively improve the electron transport rate in the positive electrode active material.

[0077] In some embodiments, the conductive material comprises at least two one-dimensional carbon materials with different tube diameters.

[0078] By combining two one-dimensional carbon materials with different tube diameters, solid-phase transport and liquid-phase mass transfer can be synergistically achieved. This can effectively improve electron transport efficiency and, with the help of the large tube diameter, electrolyte transport can be realized, thereby improving ion transport efficiency and further optimizing the power performance of the battery.

[0079] In some embodiments, the ratio of the diameters of at least two one-dimensional carbon materials with different diameters is not less than 3, and can be selected as not less than 100 or not less than 800.

[0080] In some embodiments, the ratio of the diameters of the at least two one-dimensional carbon materials with different diameters is 3, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, or any value thereof.

[0081] The coating layer contains at least two one-dimensional carbon materials with a diameter-to-size ratio of not less than 3. Compared to a single one-dimensional carbon material, this effectively improves the discharge time at high rates, thus optimizing the battery's power performance. When the coating layer contains at least two one-dimensional carbon materials with a diameter-to-size ratio of not less than 100, the synergistic effect becomes even more significant, further optimizing the battery's power performance. When the coating layer contains at least two one-dimensional carbon materials with a diameter-to-size ratio of not less than 800, the liquid-phase mass transfer function is significantly enhanced, further optimizing the battery's power performance.

[0082] In some embodiments, the conductive material includes at least one one-dimensional carbon material with a diameter greater than 100 nm, optionally with a diameter greater than 1 μm.

[0083] In some embodiments, the conductive material includes at least one-dimensional carbon material with a tube diameter greater than 100 nm, which may be selected as having a tube diameter of 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any value thereof.

[0084] One-dimensional carbon materials with a diameter greater than 100 nm can play a role in liquid-phase mass transfer in positive electrode active materials, thereby increasing the transport rate of lithium ions in the electrode active materials, reducing the polarization internal resistance of the battery, and improving the power performance of the battery.

[0085] In some implementations, based on the total mass of conductive materials, the mass content of one-dimensional carbon materials with a tube diameter greater than 100 nm is 10%-80%.

[0086] In some embodiments, the conductive material includes at least one of single-arm carbon nanotubes, vapor-grown carbon fibers, multi-arm carbon nanotubes, porous cross-linked carbon fibers, and hollow micron-sized carbon fibers.

[0087] In some embodiments, the conductive material includes single-arm carbon nanotubes. Single-arm carbon nanotubes have excellent conductivity, which can effectively improve the power performance of the battery.

[0088] In some embodiments, the conductive material further includes at least one of vapor-grown carbon fibers, multi-arm carbon nanotubes, porous cross-linked carbon fibers, and hollow micron-sized carbon fibers.

[0089] Although the conductivity of the aforementioned conductive materials is not as good as that of single-arm carbon nanotubes, their large diameter can synergize with single-arm carbon nanotubes, improving the battery's electron transport capability while optimizing the battery's mass transfer rate, thereby further enhancing the battery's power performance.

[0090] Vapor-grown carbon fiber refers to fibrous carbon produced by high-temperature pyrolysis of low-carbon hydrocarbons or carbon oxides under the action of a catalyst, with a tube diameter typically ranging from 5 to 10 nm.

[0091] Porous cross-linked carbon fiber refers to hollow carbon fiber prepared by template method, with a tube diameter generally ranging from 3 to 10 μm.

[0092] Hollow micron-sized carbon fiber refers to a carbon fiber structure with a hollow tube diameter and a micron-sized diameter. Its preparation method is mainly electrospinning, and its tube diameter is generally 3-8μm.

[0093] In some embodiments, the powder resistivity of the composite cathode material is 1×10⁻⁶. 3 -1×10 4 Ω·cm.

[0094] Compared to existing high-nickel cathode active materials, composite cathode materials exhibit significantly lower powder resistivity.

[0095] In some embodiments, the powder resistivity of the composite cathode material can be selected as 1×10⁻⁶. 3 Ω·cm, 2×10 3 Ω·cm, 3×10 3 Ω·cm, 4×10 3 Ω·cm, 5×10 3 Ω·cm, 6×10 3 Ω·cm, 7×10 3 Ω·cm, 8×10 3 Ω·cm, 9×10 3 Ω·cm, 1×10 4 Ω·cm.

[0096] In some embodiments, the particle size Dv50 of the composite cathode material is 6–15 μm, and the particle size Dv50 of the cathode active material is 8–12 μm.

[0097] In some embodiments, the particle size Dv50 of the composite cathode material can be selected as 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm, and the particle size Dv50 of the cathode active material can be selected as 8μm, 9μm, 10μm, 11μm or 12μm.

[0098] When the particle Dv50 of the composite cathode material is within the above range, the composite cathode material has a large specific surface area and excellent kinetic performance, which is beneficial to improving the power performance of the cathode material.

[0099] In some embodiments, the aspect ratio of the composite cathode material is 1.12≤(Dv90-Dv10) / Dv50≤1.75.

[0100] When the aspect ratio of the composite cathode material meets the above range, the cathode active material can form a particle size distribution, which helps to improve the compaction density of the electrode and increase the energy density of the battery.

[0101] [Preparation methods for composite cathode materials]

[0102] One embodiment of this application discloses a method for preparing a composite cathode material, comprising the following steps:

[0103] The positive electrode active material, conductive material, and dispersant are mixed and dispersed, the dispersant is removed, and then low-temperature sintering is performed under an inert atmosphere to obtain the composite positive electrode material.

[0104] Based on the total molar number of transition metal elements in the positive electrode active material, the molar content of nickel is higher than 85%.

[0105] The above method can achieve uniform coating of high-nickel cathode materials under oxygen-free conditions, thereby improving the electronic conductivity of high-nickel cathode materials and enhancing the power performance of the battery.

[0106] In some embodiments, the low-temperature sintering temperature is 120–200°C and the time is 2–6 hours.

[0107] When the sintering temperature and time are within the above range, oxygen defects will not occur in the positive electrode active material, and the bonding force between the conductive material and the positive electrode active material can be improved, so as to achieve the structural stability of the composite positive electrode material while coating the conductive material.

[0108] In some embodiments, the positive electrode active material, conductive material, and dispersant are stirred and mixed to achieve dispersion.

[0109] [Positive electrode plate]

[0110] One embodiment of this application provides a positive electrode sheet, including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a composite positive electrode material of any embodiment or a composite positive electrode material prepared by any embodiment of the preparation method.

[0111] In some embodiments, the areal density I of the positive electrode film is 24–48 mg / cm³. 2 .

[0112] When the areal density of the positive electrode film is within the above-mentioned range, the battery can be guaranteed to have a high energy density. The composite positive electrode material of this application is particularly suitable for thick-coated electrodes. Through long-range conductivity and liquid-phase mass transfer, it can significantly reduce the electrode resistance of thick-coated electrodes and improve the power performance of the battery.

[0113] In some embodiments, the compaction density of the positive electrode sheet is 2.9–3.6 g / cm³. 3 .

[0114] In cathode sheets with high compaction density, the cathode and active materials are tightly packed, resulting in short ion movement paths, small pores, and a small contact area with the electrolyte, leading to increased internal resistance of the battery. Conversely, cathode sheets with low compaction density cannot effectively improve energy density. The composite cathode material provided in this application achieves increased battery compaction density while maintaining battery power performance.

[0115] In some embodiments, the elongation of the positive electrode sheet in the length direction after cold pressing is not less than 0.5%, and can be selected as 0.5% to 0.9%.

[0116] In some embodiments, the elongation of the positive electrode sheet in the length direction after cold pressing is 0.5%, 0.6%, 0.7%, 0.8%, or 0.9%.

[0117] High areal density electrodes are prone to brittle fracture during cold pressing due to their large coating weight per unit area. The composite cathode material provided in this application can achieve coating with a high content of conductive material. The high content of conductive material plays a sliding role, thereby increasing the toughness of the electrode and improving the battery safety performance.

[0118] In some embodiments, the relationship between the mass content M of the conductive material relative to the composite cathode material and the areal density I of the cathode film satisfies 500 ≤ I / M ≤ 40000.

[0119] In some embodiments, the relationship between the mass content M of the conductive material relative to the composite cathode material and the areal density I of the cathode film, I / M, is 500, 720, 900, 980, 1000, 1200, 1800, 2400, 5000, 6000, 6200, 7200, 7800, 10000, 20000, 30000, 36000, 40000, or any value therein.

[0120] To improve battery energy density, it is often necessary to increase the areal density of the positive electrode film. However, a high areal density of the electrode is not conducive to ion transport, resulting in a decrease in battery power performance. This application achieves simultaneous optimization of battery energy density and power performance by matching the content of conductive material in the positive electrode composite material with the areal density of the positive electrode film. When the relationship between the mass content M of the conductive material relative to the composite positive electrode material and the areal density I of the positive electrode film meets the above-mentioned range, it is beneficial to reduce the battery internal resistance and improve the battery power performance.

[0121] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0122] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0124] [Negative electrode plate]

[0125] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0126] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0127] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0128] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: lithium metal and its alloys, artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0129] In some implementations, the negative electrode material includes a silicon-based material. The combination of silicon-based materials and composite positive electrode materials can effectively improve the energy density of the battery.

[0130] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0131] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0132] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0133] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0134] [Isolation membrane]

[0135] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0136] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0137] [Lithium-ion rechargeable battery]

[0138] One embodiment of this application provides a lithium secondary battery, including a positive electrode sheet according to any embodiment.

[0139] In some implementations, the energy density of the lithium secondary battery is 380-500Wh / Kg.

[0140] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 1.

[0141] In some implementations, refer toFigure 3 The outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The secondary battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to specific practical needs.

[0142] Electrical devices include the secondary batteries provided in this application. The secondary battery can be the power source of the electrical device or the energy storage unit of the electrical device. Electrical devices may include, but are 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.

[0143] Figure 4 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0144] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0145] Examples

[0146] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0147] I. Preparation Method

[0148] Example 1

[0149] (1) Preparation of composite cathode materials

[0150] A high-nickel ternary cathode material precursor was mixed with lithium hydroxide (lithium source) and Zr(OH)4 (dopant), and then calcined at 750°C for 13 hours to obtain a high-nickel ternary cathode material with a nickel content of 98%.

[0151] The high-nickel ternary cathode material was washed with water, filtered, and vacuum dried to obtain powder of the high-nickel ternary cathode material. The water washing time was 5 minutes, and the solid-liquid ratio of the high-nickel ternary cathode material to water was 0.5:1.

[0152] The powder, with a porosity of 50%, was distributed in a sintering container sagger and then fed into an atmosphere furnace. The volume of the powder occupied 15% of the sagger capacity. Sintering was carried out under an oxygen atmosphere at a flow rate of 5 L / min, a heating rate of 2 °C / min, a holding temperature of 600 °C, and a holding time of 5 h. The positive electrode active material was then obtained after furnace cooling under an oxygen atmosphere.

[0153] The prepared positive electrode active material was mixed with a carbon nanotube dispersion (N-methylpyrrolidone (NMP) as the dispersing agent) using a high-speed disperser at a stirring rate of 4000 r / min for 2 h to obtain a mixed dispersion. The conductive carbon nanotubes used in the preparation process included single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), and the mass ratio of SWCNTs to MWCNTs was 4:1 based on the total mass of the conductive agents.

[0154] The above-mentioned mixed dispersion was dried in a forced-air drying oven at 80℃ for 4 hours. Then, the powder material of the mixed dispersion was calcined in a protective argon atmosphere at 200℃ for 60 minutes to obtain the composite cathode material. The Dv50 of the composite cathode material was 12 μm. The aspect ratio (Dv90-Dv10) / Dv50 of the composite cathode material was 1.56.

[0155] (2) Preparation of positive electrode sheet

[0156] The composite cathode material prepared above, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone at a mass ratio of 97:1:2, and the mixture was stirred for 0.5-6 hours to obtain a cathode slurry. The cathode slurry was then uniformly coated onto a cathode current collector, and after drying, cold pressing, and slitting, a cathode sheet was obtained.

[0157] (3) Preparation of negative electrode sheet

[0158] A negative electrode active material, conductive agent carbon black, carbon nanotubes (CNTs), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are added to deionized water in a weight ratio of 0.945:0.01:0.00375:0.028:1.325 and mixed and stirred for 0.5-6 hours to obtain a slurry. The negative electrode active material includes graphite and SiO in a mass ratio of 5:5. The slurry is then uniformly coated onto a negative electrode current collector in layers, dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0159] (4) Preparation of electrolyte

[0160] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and fluoroethylene carbonate (FEC) were mixed uniformly in a volume ratio of 1:1:1:1. LiPF6 and LIFSI were mixed and dissolved in the organic solvent in a mass ratio of 7:3 and stirred uniformly to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0161] (5) Separating membrane

[0162] Polypropylene film is used as the separator.

[0163] (6) Battery manufacturing

[0164] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are wound in sequence to obtain a bare cell. The bare cell is placed in a packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, the lithium-ion battery of Example 1 is obtained.

[0165] Examples 2-6

[0166] The preparation methods of Examples 2 to 6 are basically the same as those of Example 1, except that the type of conductive material is adjusted. The specific parameters are shown in Table 1.

[0167] Among them, vapor-grown carbon fiber (VGCF) was purchased from Showa Denko, porous cross-linked carbon fiber was purchased from Wuxi Dongheng, and hollow microfiber was purchased from Qingdao Haoxin.

[0168] Examples 7-9

[0169] The preparation methods of Examples 7-9 are basically the same as those of Example 1, except that the types and molar contents of the dopant elements are changed. The specific parameters are shown in Table 1.

[0170] Examples 10-13

[0171] The preparation methods of Examples 10-13 are basically the same as those of Example 1, except that the mass content of the conductive material is adjusted. The specific parameters are shown in Table 1.

[0172] Examples 14-15

[0173] The preparation methods of Examples 14 and 15 are basically the same as those of Example 1, except that the mass content of the conductive material and the film thickness are adjusted. The specific parameters are shown in Table 1.

[0174] Comparative Example 1

[0175] In Comparative Example 1, LiNi was used. 0.8Co 0.1 Mn 0.05 Zr 0.05 O2 is used as the positive electrode active material, and other methods are the same as in Example 1. Specific parameters are shown in Table 1.

[0176] Comparative Example 2

[0177] In Comparative Example 2, the positive electrode active material was prepared in the same way as in Example 1, except that it was not coated with conductive material. Specific parameters are shown in Table 1.

[0178] Comparative Example 3

[0179] Other preparation methods are the same as in Comparative Example 2, except that the preparation method of the positive electrode sheet is as follows: The positive electrode material, conductive agent carbon black, single-walled carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:1:2:2 with N-methylpyrrolidone and stirred for 0.5-6 hours to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0180] II. Performance Testing

[0181] 1. Characterization of the properties of composite cathode materials

[0182] (1) Powder resistivity of composite cathode material

[0183] The composite cathode material powder was dried, an appropriate amount of powder was weighed, and then the powder resistivity of the sample was measured using a powder resistivity tester. The equipment model was Yuanneng Resistivity Tester.

[0184] (2) Particle size testing of composite cathode materials

[0185] Referring to GB / T 19077-2016 / ISO 13320:2009, the particle size distribution was determined by laser diffraction. 0.1g–0.13g of the composite cathode material was weighed into a 50ml beaker. 5g of deionized water was added to the beaker containing the composite cathode material. A stir bar approximately 2.5mm in length was placed inside, and the beaker was sealed with plastic wrap. The sample was sonicated for 5 minutes, then transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples were taken from each batch for testing. The particle size distribution (Dv10, Dv50, and Dv90) of the composite cathode material was measured using a laser particle size analyzer, such as the Mastersizer 3000 from Malvern Instruments Ltd. (UK). The particle size distribution (Dv90 – Dv10) / Dv50 of the composite cathode material was calculated using the formula SPAN = (Dv90 – Dv10) / Dv50.

[0186] 2. Performance testing of the positive electrode sheet

[0187] (1) Compacted density of the positive electrode sheet

[0188] The compaction density of the positive electrode sheet can be calculated using the formula PD=M / (d×A), where M is the mass of a 40mm diameter positive electrode sheet, which can be obtained by taking the average of 10 weighings; d is the thickness of the positive electrode sheet after cold pressing, which can be obtained by measuring the thickness of small 40mm positive electrode sheet pieces and taking the average; and A is the area of ​​the small 40mm positive electrode sheet pieces.

[0189] (2) Elongation of the positive electrode sheet

[0190] The elongation of the positive electrode sheet in the length direction after cold pressing can be calculated by the formula ΔEL%=(L2-L1) / L1×100%, where L1 is the marked length before cold pressing, which is generally fixed at 100mm; L2 is the distance of the L1 marked length after cold pressing.

[0191] (3) Bending test

[0192] The cold-pressed positive electrode sheet is cut into 20×100mm pieces. 2 Test specimens for size; fold them in half forward, flatten them with a 2kg roller, unfold them and check the gap against the light to see if light passes through. If no light passes through, fold them in the opposite direction, flatten them with a 2kg roller, and check again against the light. Repeat this process until light passes through the gap. Record the number of folds. Take at least three specimens for testing and take the average value as the test result of the bending test.

[0193] (4) Diaphragm resistance

[0194] Cut the dried electrode sheet into small round pieces with a diameter of 10mm from the left, center, and right sides of the positive electrode sheet. Turn on the Yuaneng Technology electrode resistance meter, place it at the appropriate position of the "probe" of the electrode resistance meter, and click the "start" button. After the reading stabilizes, take the reading. Test two positions for each small round piece, and finally calculate the average of the six measurements, which is the film resistance of the electrode sheet.

[0195] (5) Surface density of the positive electrode film

[0196] The areal density of the positive electrode film can be obtained by dividing the mass of the positive electrode film by its area.

[0197] 3. Battery performance testing

[0198] (1) Energy density

[0199] The method for measuring the discharge energy of a single battery cell is as follows: The battery cell is left to stand at 25°C for 2 hours to ensure the temperature remains at 25°C; then, at 25°C, the battery cell is charged at 0.1C to the charging cutoff voltage, and then charged at this voltage under constant voltage until the current reaches 0.05C, at which point charging is stopped (where C represents the rated capacity of the battery cell); the battery cell is left to stand at 25°C for 1 hour; then, at 25°C, the battery cell is discharged at 0.1C to the discharge cutoff voltage, and the total discharge capacity C0 and total discharge energy E0 of the battery cell are recorded.

[0200] Battery cell weight measurement: Place the battery cell on an electronic balance until the weight stabilizes, and read the battery cell weight value M0.

[0201] Energy density calculation: The energy density of a battery cell is calculated as the discharge energy E0 of the battery cell divided by the weight M0 of the battery cell.

[0202] (2) Discharge time at 4C rate when battery is 40% SOC

[0203] Let the battery cells stand at 25°C for 10 minutes to ensure the temperature of the battery cells is 25°C; charge the battery cells at 1 / 3C0 at 25°C with a constant current until they reach 4.25V, then charge with a constant voltage until the current reaches 0.05C, at which point charging is stopped (where C represents the rated capacity of the battery cell); let the battery cells stand at 25°C for 10 minutes; discharge the battery cells at 1 / 3C0 at 25°C to 0.6C0, i.e., adjust the battery's SOC to 40%; after standing at 25°C for 30 minutes, discharge at a constant current at a rate of 4C0, and record the discharge time until the protection voltage is triggered.

[0204] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0205] The positive electrode materials, positive electrode sheets, and secondary batteries of each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in Table 1 and Table 2 below.

[0206] Table 1

[0207]

[0208] Table 2

[0209]

[0210] Based on the above results, the composite cathode materials of Examples 1-15 include a cathode active material and a conductive material coated on the cathode active material. Based on the total number of moles of transition metal elements in the cathode active material, the molar content of nickel is higher than 85%.

[0211] Figure 1This is a scanning electron microscope (SEM) image of the composite cathode material from Example 1. Figure 1 As can be seen, a large amount of conductive material is uniformly and tightly coated on the surface of the positive electrode active material, realizing the effective combination of the positive electrode active material and the conductive material.

[0212] In Comparative Example 1, the positive electrode active material used was an existing high-nickel positive electrode active material without a conductive coating layer. In Comparative Example 2, the positive electrode active material used was the same high-nickel positive electrode active material as in Example 1, but without a conductive coating layer. Compared to Comparative Examples 1-2, the powder resistivity of the composite positive electrode materials in Examples 1-15 was significantly reduced, resulting in longer discharge time and greater discharge capacity at 4C rate. The positive electrode composite material provided by this application enables lithium ions to rapidly insert and extract into the positive electrode active material at high rates, resulting in higher discharge time and discharge capacity at high rates, i.e., better power performance. In Comparative Example 3, single-arm carbon nanotubes were physically mixed with the positive electrode active material. Excessive single-arm carbon nanotubes would agglomerate and cause slurry gelation. Therefore, the maximum addition amount of single-arm carbon nanotubes could only reach 2%, limiting further improvement in battery power performance.

[0213] As can be seen from the comparison between Examples 1-6 and Comparative Examples 1-3, the coating of one-dimensional carbon materials on the positive electrode active material significantly improves the long-range conductivity of the composite material, greatly reduces the powder resistivity of the composite positive electrode material, effectively improves the electron transport rate, increases the discharge time of the battery at 4C rate, and optimizes the power performance of the battery.

[0214] As can be seen from the comparison between Examples 1-6, when the conductive material includes at least two kinds of one-dimensional carbon materials with different tube diameters, compared with the conductive material containing only single-arm carbon nanotubes, although the powder resistivity is further reduced, the discharge time of the battery at high rate is further increased and the power performance is further improved.

[0215] As can be seen from the comparison between Examples 1-6, when the ratio of the diameter of the two one-dimensional carbon materials in the conductive material is greater than 100 or greater than 800, the large-diameter one-dimensional carbon material provides a long-distance conduction path for lithium ions, and the power performance of the battery at 4C rate is further improved.

[0216] As can be seen from Examples 1 and 7-9, when the high-nickel cathode active material contains doped elements Nb, Zr, and W, the structural stability of the cathode active material is improved, the discharge time of the battery at 4C rate is further improved, and the battery power performance is further improved.

[0217] A comparison of Examples 1, 10-15 and Comparative Examples 1-3 shows that, based on the total mass of the composite cathode material, when the mass content M of the conductive material is 0.1% to 5%, the discharge time of the battery at a 4C rate can be improved, and the power performance of the battery can be optimized. Based on the total mass of the composite cathode material, when the mass content M of the conductive material is 0.5% to 3%, both the power performance and energy density of the battery can be achieved.

[0218] As can be seen from Examples 14-15, the mass content M of the conductive material can be adjusted with the change of the surface density of the positive electrode sheet. The relationship between the mass content M of the conductive material relative to the composite positive electrode material and the surface density I of the positive electrode film layer satisfies 500≤I / M≤40000, which can improve the battery power performance.

[0219] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A composite cathode material, characterized in that, The composite cathode material includes a cathode active material and a conductive material coated on the cathode active material. Based on the total molar number of transition metal elements in the cathode active material, the molar content of nickel is higher than 85%. The conductive material includes at least two one-dimensional carbon materials with different tube diameters, and the ratio of the tube diameters of at least two one-dimensional carbon materials with different tube diameters is not less than 100. The aspect ratio of the composite cathode material is 1.12≤(Dv90-Dv10) / Dv50≤1.

75.

2. The composite cathode material according to claim 1, characterized in that, The general formula of the positive electrode active material is shown in Formula I. LiNi x Co y M 1-x-y O2 type I Wherein, M includes at least one of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, Nb, and Mo, wherein 0.90≤x≤1.0 and 0≤y≤0.

10.

3. The composite cathode material according to claim 2, characterized in that, 0.95≤x<1.0, 0 <y≤0.05。 4. The composite cathode material according to any one of claims 1 to 3, characterized in that, Based on the total mass of the composite cathode material, the mass content M of the conductive material is 0.1%-5%.

5. The composite cathode material according to claim 4, characterized in that, Based on the total mass of the composite cathode material, the mass content M of the conductive material is 0.5%-3%.

6. The composite cathode material according to any one of claims 1 to 5, characterized in that, The aspect ratio of the one-dimensional carbon material is not less than 500:

1.

7. The composite cathode material according to any one of claims 1 to 6, characterized in that, The ratio of the diameters of at least two one-dimensional carbon materials with different diameters is not less than 800.

8. The composite cathode material according to any one of claims 1 to 7, characterized in that, The conductive material includes at least one one-dimensional carbon material with a tube diameter greater than 100 nm.

9. The composite cathode material according to claim 8, characterized in that, The conductive material includes at least one one-dimensional carbon material with a tube diameter greater than 1 μm.

10. The composite cathode material according to any one of claims 1 to 9, characterized in that, The conductive material includes at least one of single-walled carbon nanotubes, vapor-grown carbon fibers, multi-walled carbon nanotubes, porous cross-linked carbon fibers, and hollow micron-sized carbon fibers.

11. The composite cathode material according to any one of claims 1 to 10, characterized in that, The resistivity of the composite cathode material is 1×10⁻⁶. 3 -1×10 4 Ω·cm.

12. The composite cathode material according to any one of claims 1 to 11, characterized in that, The particle size Dv50 of the composite cathode material is 6-15 μm, and the particle size Dv50 of the cathode active material is 8-12 μm.

13. A positive electrode plate, characterized in that, It includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer comprising the composite positive electrode material according to any one of claims 1 to 12.

14. The positive electrode sheet according to claim 13, characterized in that, The areal density I of the positive electrode film is 24-48 mg / cm³. 2 .

15. The positive electrode sheet according to claim 13 or 14, characterized in that, The compaction density of the positive electrode sheet is 2.9-3.6 g / cm³. 3 .

16. The positive electrode sheet according to any one of claims 13 to 15, characterized in that, The elongation of the positive electrode sheet in the length direction after cold pressing is not less than 0.5%.

17. The positive electrode sheet according to claim 16, characterized in that, The elongation of the positive electrode sheet in the length direction after cold pressing is 0.5%-0.9%.

18. The positive electrode sheet according to any one of claims 13 to 17, characterized in that, The relationship between the mass content M of the conductive material relative to the composite cathode material and the areal density I of the cathode film layer satisfies 500≤I / M≤40000.

19. A lithium secondary battery, characterized in that, The positive electrode sheet includes any one of claims 13 to 18.

20. The lithium secondary battery according to claim 19, characterized in that, The energy density of the lithium secondary battery is 380-500 Wh / Kg.

21. An electrical appliance, characterized in that, Includes the lithium secondary battery as described in claim 19 or 20.

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