Positive electrode active material, secondary battery, and electric device

Abstract

The application provides a positive electrode active material, a secondary battery and a power utilization device, the positive electrode active material comprising: a nickel element, a mole percentage of the nickel element in total nickel, cobalt and manganese metal elements being 55% or more; a cobalt element, a mole percentage of the cobalt element in total nickel, cobalt and manganese metal elements being 20% or less; a first modified element Zr; a second modified element Al; a third modified element B; and a fourth modified element: at least one of Nb, Mo and W. The positive electrode active material provided by the application has excellent performance, and the battery prepared by the application can have good energy density and cycle performance.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and more particularly to a positive electrode active material, a secondary battery, and an electrical device. Background Technology

[0002] With the escalating energy crisis and environmental problems, the development of green, low-carbon, and environmentally friendly new energy sources is urgently needed. Lithium-ion batteries, as electrochemical energy storage devices, have advantages such as large capacity, no memory effect, and a wide application window, and have been widely used in various fields. In the transportation sector, new energy vehicles powered by lithium-ion batteries are gradually replacing traditional fuel vehicles, becoming the preferred mode of transportation for people in various countries. Currently, commonly used cathode active materials in the industry, such as lithium iron phosphate and low-nickel ternary materials, cannot meet the performance requirements of end customers due to inherent material limitations. Summary of the Invention

[0003] This application is made in view of the above-mentioned issues, and its purpose is to stabilize the crystal structure of the positive electrode active material by modifying it with multiple elements, so that the material has the advantages of high energy density and structural stability, and the battery prepared by it can achieve both good energy density and cycle performance.

[0004] To achieve the above objectives, a first aspect of this application provides a positive electrode active material containing a transition metal element, the positive electrode active material comprising: nickel, wherein the molar percentage of nickel in the total amount of nickel, cobalt, and manganese is 55% or more; cobalt, wherein the molar percentage of cobalt in the total amount of nickel, cobalt, and manganese is 20% or less; a first modifying element Zr; a second modifying element Al; a third modifying element B; and a fourth modifying element: at least one of Nb, Mo, and W; wherein, based on the total mass of the positive electrode active material, the mass percentage of the first modifying element is 0.01% to 0.5%, the mass percentage of the second modifying element is 0.01% to 1%, the mass percentage of the third modifying element is 0.01% to 0.4%, and the mass percentage of the fourth modifying element is 0.01% to 2.2%.

[0005] In ternary materials, as the proportion of nickel in the transition metal increases, the energy density of the material becomes increasingly higher. However, the higher energy density leads to a decrease in the electrochemical stability of the material. In the technical solution of this application, by adding modifying elements to the ternary material and coupling multiple different modifying elements with the ternary material, the capacity and cycle performance of the ternary material can be greatly improved. Specifically, the first and second modifying elements can react with the bulk phase of the ternary material, which helps to improve the structural stability of the material and optimize lithium-ion transport. They also help to reduce side reactions between the ternary material and the electrolyte, thereby significantly improving the cycle stability and power performance of the material. Simultaneously, the third and fourth modifying elements can enhance the capacity of the material, enabling the ternary material to achieve high capacity. When the mass ratio of these four modifying elements is combined within the aforementioned range, the positive electrode active material can achieve a good balance between capacity and stability, and the battery prepared from it can achieve a good balance between energy density and cycle performance.

[0006] In any embodiment, the mass ratio of (first modifying element + second modifying element) to (third modifying element + fourth modifying element) in the positive electrode active material is 1:(0.1~10).

[0007] In any embodiment, the mass ratio of (first modifying element + second modifying element) to (third modifying element + fourth modifying element) in the positive electrode active material is 1:(0.1~0.5).

[0008] In any embodiment, the mass ratio of (element Zr + element Al) to (element B + element W) in the positive electrode active material is 1:(0.1~0.5).

[0009] In any embodiment, the mass ratio of the first modifying element to the second modifying element in the positive electrode active material is 1:(0.1 to 30).

[0010] In any embodiment, the mass ratio of the first modifying element to the second modifying element in the positive electrode active material is 1:(0.1~1).

[0011] In any embodiment, the mass ratio of Zr to Al in the positive electrode active material is 1:(0.1~1).

[0012] In any embodiment, the mass ratio of the third modifying element to the fourth modifying element in the positive electrode active material is 1:(0.05-30).

[0013] In any embodiment, the mass ratio of the third modifying element to the fourth modifying element in the positive electrode active material is 1:(0.1~1).

[0014] In any embodiment, the mass ratio of element B to element W in the positive electrode active material is 1:(0.1~1).

[0015] By further precisely controlling the mass ratio among the first, second, third, and fourth modifying elements, the electrochemical performance and stability of the cathode active material can be further optimized, achieving the optimal solution for the overall performance of the material.

[0016] In any embodiment, the mass percentage of the first modifying element is 0.05% to 0.5% based on the total mass of the positive electrode active material.

[0017] In any embodiment, the mass percentage of the second modifying element is 0.05% to 0.3% based on the total mass of the positive electrode active material.

[0018] In any embodiment, the mass percentage of the third modifying element is 0.01% to 0.2% based on the total mass of the positive electrode active material.

[0019] In any embodiment, the mass percentage of the fourth modifying element is 0.01% to 0.3% based on the total mass of the positive electrode active material.

[0020] When the mass percentages of the first, second, third, and fourth modifying elements are within the above range, the energy density and cycle performance of the material can be further improved.

[0021] In any embodiment, the molar percentage of nickel in the total amount of nickel, cobalt, and manganese is 60% to 95%; and / or, the molar percentage of cobalt in the total amount of nickel, cobalt, and manganese is 3% to 10%.

[0022] In any embodiment, the molar percentage of nickel in the total amount of nickel, cobalt, and manganese metal elements is 80% to 95%.

[0023] When the proportions of nickel and cobalt in the transition metals of the positive electrode active material are within the above-mentioned range, the material has better specific capacity, and the battery prepared from it can better balance energy density and cycle performance.

[0024] In any embodiment, the positive electrode active material includes single-crystal particles and polycrystalline particles.

[0025] When the positive electrode active material includes both monocrystalline and polycrystalline particles, compared with a single-particle type system, the monocrystalline-polycrystalline mixed system is beneficial to further improve the compaction density of the material and improve its volumetric energy density and cycle stability.

[0026] In any embodiment, the specific surface area of ​​the single crystal particles is 0.9–1.5 m². 2 / g, wherein the specific surface area of ​​the polycrystalline particles is 0.3–1.0 m² / g. 2 / g.

[0027] When the specific surface area of ​​the positive electrode active material is within the above range, it is beneficial to increase the contact area between the positive electrode material and the electrolyte, thereby further enhancing the electrochemical activity of the material.

[0028] In any embodiment, the mass ratio of the single crystal particles to the polycrystalline particles in the positive electrode active material is 1:9 to 5:5.

[0029] In any embodiment, the volume average particle size Dv50 of the single crystal particles is 3 to 5 μm, and the volume average particle size Dv50 of the polycrystalline particles is 4 to 13 μm.

[0030] When single-crystal and polycrystalline particles in the positive electrode active material are matched with the above-mentioned mass ratio and particle size, the energy density and cycle performance of the battery can be further improved.

[0031] In any embodiment, the positive electrode active material has the molecular formula Li a (Ni b Co c Mn 1-b-c ) 1-x-y-z- q Zr x Al y B z Q q O e Where Q includes at least one of Nb, Mo, and W, 0.9≤a≤1.2, 0.55≤b≤0.95, 0≤c≤0.20, 1.8≤e≤2.2, 0 <x≤0.04,0<y≤0.02,0<z≤0.09,0<q≤0.03。

[0032] In any embodiment, the positive electrode active material further includes strontium (Sr), and the mass percentage of strontium is 0.05% to 0.2% based on the total mass of the positive electrode active material.

[0033] In any embodiment, the positive electrode active material further includes yttrium (Y), and the mass percentage of yttrium is 0.05% to 0.2% based on the total mass of the positive electrode active material.

[0034] Adding strontium and / or yttrium to ternary materials can further improve their capacity and cycle performance.

[0035] In any embodiment, the powder resistivity of the positive electrode active material at 12 MPa is 100–8000 Ω·cm.

[0036] When the resistivity of the powder material is within the above range, the power performance of the material can be further improved.

[0037] In any embodiment, the tap density of the positive electrode active material is 1.9–2.6 g / cm³. 3 .

[0038] A second aspect of this application provides a lithium secondary battery, including the positive electrode active material described in the first aspect of this application.

[0039] In any embodiment, the specific capacity of the positive electrode active material in the lithium secondary battery is 193–210 mAh / g at 25°C and a 1 / 3C discharge rate.

[0040] In any embodiment, the specific capacity of the positive electrode active material in the lithium secondary battery is 202-210 mAh / g at 25°C and a discharge rate of 1 / 3C.

[0041] A third aspect of this application provides an electrical device including the lithium secondary battery described in the second aspect of this application. Attached Figure Description

[0042] Figure 1A and Figure 1B This is a single-crystal morphology diagram of the positive electrode active material prepared in Example 1.

[0043] Figure 2 This is a polycrystalline morphology diagram of the positive electrode active material prepared in Example 1.

[0044] Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0045] Figure 4 yes Figure 3 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0046] Figure 5 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0047] Explanation of reference numerals in the attached figures:

[0048] 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover plate. Detailed Implementation

[0049] The following describes in detail embodiments of the positive electrode active material, secondary battery, and power device of this application, as well as methods for manufacturing the same. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0050] 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 understood that ranges of 60–110 and 80–120 are also expected. 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 "a–b" 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.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0052] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0053] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, optionally 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 method may also include step (c), indicating 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.

[0054] 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.

[0055] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0056] Currently, improving the energy density of materials has become a major research direction in the development of cathode active materials, and increasing nickel content to improve capacity is a common approach. However, with the increase of nickel content in ternary materials, the phase transition intensifies and the lattice contraction and expansion rate increases, leading to a deterioration in the cycle life of the material. This application provides a cathode active material with good structural stability and specific capacity, thus enabling the fabricated battery to achieve both good energy density and cycle performance.

[0057] [Positive electrode active material]

[0058] To achieve the above objectives, this application provides a positive electrode active material containing transition metal elements, the positive electrode active material comprising: nickel, wherein the molar percentage of nickel in the total amount of nickel, cobalt, and manganese metal elements is 55% or more; cobalt, wherein the molar percentage of cobalt in the total amount of nickel, cobalt, and manganese metal elements is 20% or less; a first modifying element Zr; a second modifying element Al; a third modifying element B; and a fourth modifying element: at least one of Nb, Mo, and W; wherein, based on the total mass of the positive electrode active material, the mass percentage of the first modifying element is 0.01% to 0.5%, the mass percentage of the second modifying element is 0.01% to 1%, the mass percentage of the third modifying element is 0.01% to 0.4%, and the mass percentage of the fourth modifying element is 0.01% to 2.2%.

[0059] In ternary materials, as the proportion of nickel in the transition metal increases, the energy density of the material becomes higher and higher. However, the higher energy density leads to a decrease in the electrochemical stability of the material. In the technical solution of this application, by adding modifying elements to the ternary material and coupling multiple different modifying elements with the ternary material, the capacity and cycle performance of the ternary material can be greatly improved. Among them, the first and second modifying elements can react with the bulk phase of the ternary material, which helps to improve the structural stability of the material and optimize lithium-ion transport. They also help to reduce the side reactions between the ternary material and the electrolyte, thereby significantly improving the cycle stability and power performance of the material. At the same time, the third and fourth modifying elements can improve the capacity of the material, enabling the ternary material to achieve high capacity. When the mass ratio of these four modifying elements is combined within the above range, the positive electrode active material can achieve both good capacity and stability, and the battery prepared from it can achieve both good energy density and cycle performance.

[0060] In some embodiments, the positive electrode active material includes nickel, wherein the molar percentage of nickel in the total amount of nickel, cobalt, and manganese is 55% or more, such as 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or other unlisted values. In some preferred embodiments, the molar percentage of nickel in the total amount of nickel, cobalt, and manganese is 60%, 80%, or 95%.

[0061] In some embodiments, the positive electrode active material further includes cobalt, wherein the molar percentage of cobalt in the total amount of nickel, cobalt, and manganese is less than 20%, for example, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or other unlisted values ​​less than 20%. In some preferred embodiments, the molar percentage of cobalt in the total amount of nickel, cobalt, and manganese is 3% or 10%.

[0062] In some embodiments, the positive electrode active material further includes: a first modifying element Zr; a second modifying element Al; a third modifying element B; and a fourth modifying element, which is at least one of Nb, Mo, and W.

[0063] In some embodiments, the mass percentage of the first modifying element, based on the total mass of the positive electrode active material, is 0.01% to 0.5%, for example, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or other unlisted values ​​within the range of 0.01% to 0.5%. In some preferred embodiments, the mass percentage of the first modifying element is 0.01% or 0.5%.

[0064] In some embodiments, the mass percentage of the second modifying element, based on the total mass of the positive electrode active material, is 0.01% to 1%, for example, 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or other unlisted values ​​within the range of 0.01% to 1%. In some preferred embodiments, the mass percentage of the second modifying element is 0.01%, 0.05%, 0.3%, or 1%.

[0065] In some embodiments, the third modifying element comprises 0.01% to 0.4% of the total mass of the positive electrode active material, for example, 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, or other unlisted values ​​within the range of 0.01% to 0.4%. In some preferred embodiments, the third modifying element comprises 0.01%, 0.1%, 0.2%, or 0.4% of the mass.

[0066] In some embodiments, the mass percentage of the fourth modifying element, based on the total mass of the positive electrode active material, is 0.01% to 2.2%, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, or other unlisted values ​​within the range of 0.01% to 2.2%. In some preferred embodiments, the mass percentage of the fourth modifying element is 0.01%, 0.3%, 2.0%, or 2.2%.

[0067] In some embodiments, the mass ratio of (first modifying element + second modifying element) to (third modifying element + fourth modifying element) in the positive electrode active material is 1:(0.1 to 10), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or other unlisted values ​​within the range of 1:(0.1 to 10). In some preferred embodiments, the mass ratio of (first modifying element + second modifying element) to (third modifying element + fourth modifying element) in the positive electrode active material is 1:0.625, 1:0.5, 1:3, 1:0.91, 1:0.33, 1:2.75, 1:0.3875, 1:0.875, 1:1.61, 1:0.15, 1:0.98, 1:0.2, 1:1.625, or 1:0.26.

[0068] In some embodiments, the mass ratio of (first modifying element + second modifying element) to (third modifying element + fourth modifying element) in the positive electrode active material is 1:(0.33~3).

[0069] In some embodiments, the mass ratio of (first modifying element + second modifying element) to (third modifying element + fourth modifying element) in the positive electrode active material is 1:(0.1 to 0.5).

[0070] In some embodiments, the mass ratio of the first modifying element to the second modifying element in the positive electrode active material is 1:(0.1 to 30), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:15, 1:20, 1:25, 1:30, or other unlisted values ​​within the range of 1:(0.1 to 30). In some preferred embodiments, the mass ratio of the first modifying element to the second modifying element in the positive electrode active material is 1:0.6, 1:0.1, 1:2, 1:30, 1:0.1, 1:0.02, or 1:4.

[0071] In some embodiments, the mass ratio of the first modifying element to the second modifying element in the positive electrode active material is 1:(0.1-2).

[0072] In some embodiments, the mass ratio of the first modifying element to the second modifying element in the positive electrode active material is 1:(0.1~1).

[0073] In some embodiments, the mass ratio of the third modifying element to the fourth modifying element in the positive electrode active material is 1:(0.05-30), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:15, 1:20, 1:25, 1:30, or other unlisted values ​​within the range of 1:(0.05-30). In some preferred embodiments, the mass ratio of the third modifying element to the fourth modifying element in the positive electrode active material is 1:1.5, 1:3, 1:11, 1:1, 1:10, 1:30, 1:0.75, 1:0.3, or 1:0.05.

[0074] In some embodiments, the mass ratio of the third modifying element to the fourth modifying element in the positive electrode active material is 1:(1-10).

[0075] In some embodiments, the mass ratio of the third modifying element to the fourth modifying element in the positive electrode active material is 1:(0.1 to 1).

[0076] In some embodiments, the fourth modifying element is W. In some embodiments, the mass ratio of (Zr + Al) to (B + W) in the positive electrode active material is 1:(0.1 to 0.5), for example, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, or other unlisted values ​​within the range of 1:(0.1 to 0.5).

[0077] In some embodiments, the mass ratio of element Zr to element Al in the positive electrode active material is 1:(0.1 to 1), for example 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, or other unlisted values ​​within the range of 1:(0.1 to 1).

[0078] In some embodiments, the fourth modifying element is W. In some embodiments, in the positive electrode active material, the mass ratio of the third modifying element B to the fourth modifying element W is 1:(0.1 to 1), for example 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, or other unlisted values ​​within the range of 1:(0.1 to 1).

[0079] By further precisely controlling the mass ratio among the first, second, third, and fourth modifying elements, the electrochemical performance and stability of the positive electrode active material can be further optimized, achieving the optimal solution for material performance.

[0080] In some embodiments, the mass percentage of the first modifying element is 0.05% to 0.5% based on the total mass of the positive electrode active material.

[0081] In some embodiments, the second modifying element accounts for 0.05% to 0.3% of the total mass of the positive electrode active material.

[0082] In some embodiments, the third modifying element accounts for 0.01% to 0.2% of the total mass of the positive electrode active material.

[0083] In some embodiments, the mass percentage of the fourth modifying element is 0.01% to 0.3% based on the total mass of the positive electrode active material.

[0084] When the mass percentages of the first, second, third, and fourth modifying elements are within the above range, the energy density and cycle performance of the material can be further improved.

[0085] In some embodiments, the molar percentage of nickel in the total amount of nickel, cobalt, and manganese is 60% to 95%.

[0086] In some embodiments, the molar percentage of nickel in the total amount of nickel, cobalt, and manganese metals is 80% to 95%.

[0087] In some embodiments, the cobalt element accounts for 3% to 10% of the total amount of nickel, cobalt, and manganese.

[0088] When the proportions of nickel and cobalt in the transition metals of the positive electrode active material are within the above-mentioned range, the material has better specific capacity, and the battery prepared from it can better balance energy density and cycle performance.

[0089] In some embodiments, the positive electrode active material includes single-crystal particles and polycrystalline particles.

[0090] As used herein, "single crystal" refers to a single, complete particle, or an aggregate of 2 to 9 primary particles, or an aggregate of 10 to 49 primary particles, or a mixture of particles and / or aggregates of the above types. See Appendix. Figure 1A and 1B .

[0091] When used in this document, "polycrystalline" refers to secondary particles formed by the agglomeration of multiple primary particles. "Multiple" here typically means 10 or more, or 50 or more, or 100 or more, or a mixture of agglomerates of the above types. See Appendix. Figure 2 .

[0092] When used in this article, if "single crystal" and "polycrystalline" appear together, "single crystal" refers to particles with a polygonal or irregular outer contour. See Appendix. Figure 1A and 1B "Polycrystalline" refers to particles with a circular or nearly circular outer contour; see appendix. Figure 2 .

[0093] When the positive electrode active material includes both single-crystal and polycrystalline particles, compared with a single-particle type system, the single-crystal mixed with polycrystalline system is beneficial to further improve the volumetric energy density and cycle stability of the material.

[0094] In some embodiments, the specific surface area of ​​the single crystal particles is 0.9–1.5 m². 2 / g, for example 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, or 0.9–1.5m 2 Other unlisted values ​​within the range of / g. In some preferred embodiments, the specific surface area of ​​the single crystal particles is 0.9–1.2 m². 2 / g. In some preferred embodiments, the specific surface area of ​​the single crystal particles is 0.9m². 2 / g.

[0095] In some embodiments, the specific surface area of ​​the polycrystalline particles is 0.3–1.0 m². 2 / g, for example 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, or 0.3~1.0m 2 Other unlisted values ​​within the range of / g. In some preferred embodiments, the specific surface area of ​​the polycrystalline particles is 0.3m². 2 / g, 0.5m 2 / g, 1.0m 2 / g.

[0096] In this article, "specific surface area" refers to the total surface area per unit mass of material. The determination method can be found in GB / T19587-2017, using the nitrogen adsorption specific surface area analysis method and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0097] When the specific surface area of ​​the positive electrode active material is within the above range, it is beneficial to increase the contact area between the positive electrode material and the electrolyte, thereby further enhancing the electrochemical activity of the material.

[0098] In some embodiments, the mass ratio of the single crystal particles to the polycrystalline particles in the positive electrode active material is 1:9 to 5:5, for example, 1:9, 2:8, 3:7, 4:6, 5:5, or other unlisted values ​​within the range of 1:9 to 5:5.

[0099] In some embodiments, the mass ratio of the single crystal particles to the polycrystalline particles in the positive electrode active material is 1:9 to 3:7.

[0100] In some embodiments, the volume average particle size Dv50 of the single crystal particles is 3 to 5 μm, for example 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, or other unlisted values ​​within the range of 3 to 5 μm. In some preferred embodiments, the volume average particle size Dv50 of the single crystal particles is 4 μm.

[0101] In some embodiments, the volume average particle size Dv50 of the polycrystalline particles is 4–13 μm, for example, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, or other unlisted values ​​within the range of 4–13 μm. In some preferred embodiments, the volume average particle size Dv50 of the polycrystalline particles is 4 μm, 10 μm, or 13 μm.

[0102] In this paper, "volume average particle size Dv50" refers to the particle size that, in the particle size distribution, reaches 50% of the cumulative volume distribution percentage, starting from the smallest particle size. The determination method can be found in GB / T19077-2016 / ISO 13320:2009, using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer.

[0103] When single-crystal and polycrystalline particles in the positive electrode active material are matched with the above-mentioned mass ratio and particle size, the energy density and cycle performance of the battery can be further improved.

[0104] In some embodiments, the positive electrode active material has the molecular formula Li a (Ni b Co c Mn 1-b-c ) 1-x-y-z- q Zr x Al y B z Q q O e Q includes at least one of Nb, Mo, and W, and 0.9≤a≤1.2, 0.55≤b≤0.95, 0≤c≤0.20, 1.8≤e≤2.2, 0≤x≤0.04, 0≤y≤0.02, 0≤z≤0.09, and 0≤q≤0.03.

[0105] When used herein, "having a molecular formula" is not limited to the substances represented by the molecular formula, but also includes other substances formed by further appropriate modifications based on the molecular formula, without limitation. The use of "having a molecular formula" is for ease of description only and is not intended to limit this application. It is understood that new materials or substances obtained by appropriate modifications based on the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modifications refer to acceptable modification methods for positive electrode active materials, and non-limiting examples include coating modification.

[0106] In this application, unless otherwise specified, the Li content in the listing of positive electrode active materials refers to the initial state of the material. When positive electrode active materials are applied to the positive electrode sheet in a battery system, the Li content in the positive electrode active material typically changes after charge-discharge cycles. The Li content can be measured using atomic molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry.

[0107] In the enumeration of positive electrode active materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the atomic molar content of oxygen, and the actual O content will fluctuate. The O content can be measured using atomic molar content, but is not limited to this.

[0108] In some embodiments, the positive electrode active material further includes strontium (Sr), and the mass percentage of strontium is 0.05% to 0.2% based on the total mass of the positive electrode active material, for example, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, or other unlisted values ​​within the range of 0.05% to 0.2%.

[0109] In some embodiments, the positive electrode active material further includes yttrium (Y), and the mass percentage of yttrium is 0.05% to 0.2% based on the total mass of the positive electrode active material, for example, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, or other unlisted values ​​within the range of 0.05% to 0.2%.

[0110] Adding strontium and / or yttrium to ternary materials can further improve their capacity and cycle performance.

[0111] In some embodiments, the powder resistivity of the positive electrode active material at 12 MPa is 100–8000 Ω·cm, for example, 100 Ω·cm, 500 Ω·cm, 1000 Ω·cm, 1500 Ω·cm, 2000 Ω·cm, 2500 Ω·cm, 3000 Ω·cm, 3500 Ω·cm, 4000 Ω·cm, 4500 Ω·cm, 5000 Ω·cm, 6000 Ω·cm, 7000 Ω·cm, 8000 Ω·cm, or other unlisted values ​​within the range of 100–8000 Ω·cm. In some preferred embodiments, the powder resistivity of the positive electrode active material at 12 MPa is 2000 Ω·cm, 1500 Ω·cm, 2200 Ω·cm, 1900 Ω·cm, 8000 Ω·cm, 1600 Ω·cm, 100 Ω·cm, or 5000 Ω·cm.

[0112] When used in this article, "powder resistivity" is a parameter describing the electrical conductivity of powder materials, usually referring to the resistance per unit length and unit area, measured in ohm-cm (Ω·cm). The measurement method follows standard GB / T 30835-2014 and is performed using a powder resistivity tester (ST2722).

[0113] When the resistivity of the powder material is within the above range, the power performance of the material can be further improved.

[0114] In some embodiments, the tap density of the positive electrode active material is 1.9–2.6 g / cm³. 3 For example, 1.9 g / cm³ 3 2.0g / cm 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 2.5g / cm 3 2.6g / cm 3 Or 1.9–2.6 g / cm³ 3 Other values ​​not listed within the range. In some preferred embodiments, the tap density of the positive electrode active material is 2.52 g / cm³. 3 2.55g / cm 3 2.50g / cm 3 2.60g / cm 3 .

[0115] In some preferred embodiments, the tap density of the positive electrode active material is 2.5–2.6 g / cm³. 3 .

[0116] In this article, "tapered density" refers to the density obtained by dividing the mass of a certain amount of powder in a container by the volume after tapping, using a vibrating device to vibrate and rotate the powder until its volume no longer decreases. The determination method can refer to GB / T5162-2006, using a powder tapped density tester (such as Dandong Baite BT-301) with the following parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 5000 times, and graduated cylinder volume 25mL.

[0117] In some embodiments, the specific capacity of the positive electrode active material in the lithium secondary battery at 25°C and a 1 / 3C discharge rate is 193–210 mAh / g, for example, 193 mAh / g, 194 mAh / g, 195 mAh / g, 196 mAh / g, 197 mAh / g, 198 mAh / g, 199 mAh / g, 200 mAh / g, 201 mAh / g, 202 mAh / g, 203 mAh / g, 204 mAh / g, 205 mAh / g, 206 mAh / g, 207 mAh / g, 208 mAh / g, 209 mAh / g, 210 mAh / g, or other unlisted values ​​within the range of 193–210 mAh / g.

[0118] In some preferred embodiments, the specific capacity of the positive electrode active material in the lithium secondary battery is 202-210 mAh / g at 25°C and a 1 / 3C discharge rate.

[0119] [Positive electrode plate]

[0120] This application also provides a positive electrode sheet, characterized in that it includes a positive current collector and a positive active material disposed on at least one surface of the positive current collector, wherein the positive active material is the positive active material described in this application.

[0121] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] In some embodiments, the positive electrode may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin.

[0123] In some embodiments, the positive electrode 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.

[0124] 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.

[0125] [Negative electrode plate]

[0126] 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.

[0127] 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.

[0128] 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.).

[0129] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. 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.

[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] [Electrolytes]

[0135] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0136] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0137] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0138] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0139] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0140] [Isolation membrane]

[0141] 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.

[0142] 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.

[0143] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0144] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0145] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0146] [Lithium-ion rechargeable battery]

[0147] This application also provides a lithium secondary battery, characterized in that it includes the positive electrode sheet described in this application.

[0148] This application does not impose any particular limitation on the shape of the lithium secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0149] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0150] [Electrical appliances]

[0151] In addition, this application also provides an electrical device, which includes the lithium secondary battery provided in this application. The lithium secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0152] As the electrical device, a lithium secondary battery can be selected according to its usage requirements.

[0153] Figure 5 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 lithium-ion battery for this device, a battery pack or battery module can be used.

[0154] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a lithium-ion battery as their power source.

[0155] Example

[0156] 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.

[0157] I. Preparation Method

[0158] Example 1

[0159] 1.1. Preparation of positive electrode active materials

[0160] (1) Polycrystalline preparation method:

[0161] Ternary polycrystalline precursor (Ni 0.80 Co 0.10 Mn 0.10 OH2 (volume average particle size Dv50 = 10 μm), LiOH·H2O, ZrO2, Al2O3, and MoO3 were mixed in a mixer according to the molar ratio of the corresponding elements in the molecular formula. Then, the mixture was sintered at 800℃ for 20 h in an oxygen atmosphere (oxygen volume concentration > 99.9%) to obtain material 1. After mechanical crushing, the crushed material 1 was washed in deionized water (material-to-liquid mass ratio 0.5:1 to ensure that the material does not sink to the bottom during stirring) for 1 min.

[0162] Then, the water-washed material 1 was mixed with H3BO3 in the molar ratio of the corresponding elements in the molecular formula, and sintered at 400℃ for 10 hours in an oxygen atmosphere (oxygen volume concentration > 99.9%) to obtain a polycrystalline positive electrode active material. The molecular formula of the obtained polycrystalline positive electrode active material is Li(Ni) 0.8 Co 0.1 Mn 0.1 ) 0.963 Zr 0.005 Al 0.011 B 0.018 Mo 0.003 O2 has a specific surface area of ​​0.5 m². 2 / g, with a volume average particle size Dv50 of 10μm.

[0163] (2) Single crystal preparation method:

[0164] Ternary single crystal precursor (Ni 0.80 Co 0.10 Mn 0.10OH2 (volume average particle size Dv50 = 3 μm), LiOH·H2O, ZrO2, Al2O3, and MoO3 were mixed in a mixer in the molar ratio of the corresponding elements in the molecular formula, and then sintered at 850℃ for 25 h in an oxygen atmosphere (oxygen volume concentration > 99.9%). After air jet pulverization, material 2 was obtained.

[0165] Then, material 2 was mixed with H3BO3 in the molar ratio of the corresponding elements in the molecular formula, and sintered at 400℃ for 10 h in an oxygen atmosphere (oxygen volume concentration > 99.9%) to obtain a single-crystal positive electrode active material. The molecular formula of the obtained single-crystal positive electrode active material is Li(Ni) 0.8 Co 0.1 Mn 0.1 ) 0.963 Zr 0.005 Al 0.011 B 0.018 Mo 0.003 O2 has a specific surface area of ​​0.9 m². 2 / g, with a volume average particle size Dv50 of 4μm.

[0166] (3) Method for preparing polycrystalline hybrid single crystals:

[0167] The polycrystalline cathode active material and the monocrystalline cathode active material were physically mixed at a mass ratio of 5:5 to obtain a polycrystalline-monocrystalline cathode active material. The resulting polycrystalline-monocrystalline cathode active material had a powder resistivity of 2000 Ω·cm at 12 MPa.

[0168] 1.2. Preparation of the positive electrode sheet

[0169] The polycrystalline mixed single-crystal positive electrode active material prepared in 1.1, polyvinylidene fluoride and conductive carbon black were mixed at a mass ratio of 90:5:5. Then N-methylpyrrolidone (NMP) was added and stirred for 2 hours. Then it was stirred in a homogenizer at 1200 r / min until it was uniformly mixed. Then it was uniformly coated on both sides of a 13-micron thick aluminum foil current collector. After coating, it was dried in a drying oven at 120℃, cold-pressed and cut to obtain the positive electrode sheet.

[0170] 1.3. Preparation of Electrolyte

[0171] A mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) was prepared by mixing them at a volume ratio of 1:2 to obtain a mixed solvent. Then, thoroughly dried lithium hexafluorophosphate was dissolved in the mixed solvent and mixed thoroughly in an argon-atmospheric glove box to obtain an electrolyte. The lithium salt concentration in the electrolyte was 1 mol / L.

[0172] 1.4. Preparation of negative electrode sheet

[0173] The negative electrode active materials graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber and acetylene black were mixed in a mass ratio of 96:1:1:2, deionized water was added, and the mixture was stirred evenly in a mixer. The slurry was then coated on both sides of an 8-micron thick copper foil, dried in an oven at 120°C, cold-pressed, and slit to obtain the negative electrode sheet.

[0174] 1.5. Preparation of battery cells

[0175] The positive electrode, separator, and negative electrode are stacked in sequence from top to bottom, ensuring that the positive and negative electrode plates do not come into contact with each other. Then, they are wound into a bare cell using a winding needle, placed in a square aluminum shell, injected with electrolyte, and subjected to steps such as settling, formation, and capacity testing to produce the battery cell.

[0176] Examples 2-20, 22

[0177] The secondary batteries in Examples 2-20 and 22 are prepared using a similar method to those in Example 1, but the types and contents of elements in the positive electrode active material are adjusted, or the BET and powder resistivity of the positive electrode active material are adjusted, or the mass ratio of single crystal particles, DV50 (single crystal particles, polycrystalline particles), and tap density of the positive electrode active material are adjusted. The different preparation parameters are detailed in Tables 1-5. Based on the different types and mass proportions of elements in Tables 1-5, the chemical formulas of the positive electrode active materials prepared in Examples 2-20 and 22 can be calculated.

[0178] Example 21

[0179] The secondary battery of Example 21 is prepared in a similar manner to that of Example 1, but by adjusting the types of raw materials, the types of elements in the positive electrode active material are changed. The difference between this and the preparation method of Example 1 is as follows:

[0180] (1) Polycrystalline preparation method:

[0181] Ternary polycrystalline precursor (Ni 0.80 Co 0.10 Mn 0.10 OH2 (volume average particle size Dv50 = 10 μm), LiOH·H2O, ZrO2, Al2O3, MoO3, SrO, and Y2O3 were mixed in a mixer in the molar ratio of the corresponding elements in the molecular formula, and then the same preparation steps as in Example 1 were performed.

[0182] (2) Single crystal preparation method:

[0183] Ternary single crystal precursor (Ni 0.80 Co 0.10 Mn 0.10OH2 (volume average particle size Dv50 = 3 μm), LiOH·H2O, ZrO2, Al2O3, MoO3, SrO, and Y2O3 were mixed in a mixer in the molar ratio of the corresponding elements in the molecular formula, and then the same preparation steps as in Example 1 were performed.

[0184] Other different preparation parameters are detailed in Tables 1 to 5. Based on the types and mass ratios of different elements in Tables 1 to 5, the chemical formula of the positive electrode active material prepared in Example 21 can be calculated.

[0185] Comparative Examples 1-6

[0186] The secondary batteries of Comparative Examples 1 to 6 were prepared using a similar method to those of Example 1, but the types and contents of the modifying elements in the positive electrode active material were adjusted. The different preparation parameters are detailed in Tables 1 to 5.

[0187] II. Performance Testing

[0188] 1. Test methods for relevant parameters of positive electrode active materials

[0189] (1) Material composition testing methods

[0190] Inductively coupled plasma atomic emission spectrometry (ICP-AES) was employed. The specific testing equipment was a Thermo Scientific iCAP 7400 ICP-AES spectrometer.

[0191] (2) Test method for BET specific surface area

[0192] The nitrogen adsorption specific surface area was tested using the nitrogen adsorption specific surface area analysis method and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using the TriStar II specific surface area and porosity analyzer from Micromeritics, USA. The test procedure can refer to GB / T 19587-2004.

[0193] The detailed steps are as follows: Dry the sample to be tested in a vacuum drying oven at 200℃ for 2 hours; weigh 1g of the sample to be tested and place it in the test tube; fill the liquid nitrogen cup with liquid nitrogen and insert it into the test tube; use nitrogen as the adsorption gas; plot the adsorption-desorption curve with relative pressure P / P0 of 0 to 0.99 using a specific surface area and porosity analyzer; P is the equilibrium adsorption pressure and P0 is the saturated vapor pressure; calculate the BET specific surface area of ​​the positive electrode active material using the BET method.

[0194] (3) Powder resistivity testing method

[0195] On a four-probe powder resistivity meter, 2.4g of positive electrode active material was placed in a feeding cup, a pressure of 12MPa was applied, and the powder resistivity of the material was recorded.

[0196] (4) Scanning electron microscopy testing methods

[0197] The cathode material was tested using SEM to obtain its microstructure.

[0198] (5) Test method for volume average particle size Dv50

[0199] Equipment model: MasterSizer 2000 laser particle size analyzer; reference standard procedure: GB / T19077-2016 / ISO 13320:2009.

[0200] Detailed test procedure: Take an appropriate amount of washed sample (ensuring a sample concentration of 8% to 12% opacity), add 20 mL of anhydrous ethanol, and sonicate for 5 min (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to GB / T19077-2016 / ISO13320:2009 standard.

[0201] (6) Tap density test method

[0202] Using a Dandong BT-300 measuring cylinder with a 25ml capacity, the material was filled to 20ml. The material was then vibrated 5000 times at a frequency of 250 times / min to measure its compaction density.

[0203] (7) Electrode compaction density test method

[0204] 1) Cut the above positive electrode sheet into a 1000mm long film;

[0205] 2) The positive electrode film is rolled under a certain pressure. Due to the ductility of aluminum foil, the length of the film is 1006 mm.

[0206] 3) The punching area is 1540.25 mm. 2 The compaction density can be calculated by measuring the weight and thickness of the small disc: (weight of small disc - weight of substrate) / 1540.25 / (coating thickness - substrate thickness).

[0207] 2. Battery performance testing methods

[0208] (1) Method for testing gram capacity

[0209] At 25°C, the battery is first discharged at a 1 / 3C rate to a voltage of 2.80V and held for 30 minutes. Then, it is charged at a constant current at a 1 / 3C rate to a voltage of 4.25V, followed by a 1 / 3C discharge to a voltage of 2.80V. The discharge capacity of the battery in the first cycle is recorded as C0. Finally, C0 is divided by the mass of the positive electrode active material to obtain the specific capacity.

[0210] (2) Cyclic performance testing method

[0211] At 25℃, the battery is charged at a constant current rate of 1 / 3C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a rate of 0.05C, and discharged at a rate of 1 / 3C to a voltage of 2.80V. This is the first cycle, and the discharge capacity of the first cycle is denoted as C0. The cycle is repeated as described above, and the discharge capacity of the nth cycle is denoted as Cn. The capacity retention rate for each cycle is Cn / C0*100%. Calculate the capacity retention rate after 100 cycles.

[0212] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0213] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 5 below.

[0214] Table 1 Preparation parameters

[0215]

[0216] Table 2 Preparation parameters

[0217]

[0218] Table 3 Preparation parameters

[0219]

[0220] Table 4 Preparation parameters

[0221]

[0222] Table 5 Preparation parameters and performance parameters

[0223]

[0224] In Examples 1 to 22, the positive electrode active materials all contained the first modifying element Zr, the second modifying element Al, the third modifying element B, and the fourth modifying element (at least one of Nb, Mo, and W). The batteries prepared from these materials all exhibited excellent specific capacity and cycle performance.

[0225] No modifying elements were added to the positive electrode active material in Comparative Example 1. A comparison between Comparative Example 1 and Examples 1-22 shows that adding the first modifying element Zr, the second modifying element Al, the third modifying element B, and the fourth modifying element (at least one of Nb, Mo, and W) to the positive electrode active material can effectively improve the specific capacity of the positive electrode active material and improve the cycle performance of the lithium secondary battery.

[0226] In Comparative Example 2, only the first modifying element Zr and the second modifying element Al were added to the positive electrode active material. In Comparative Example 3, only the third modifying element B and the fourth modifying element Mo were added to the positive electrode active material. In Comparative Example 6, only the first modifying element Zr, the second modifying element Al, and the fourth modifying element Mo were added to the positive electrode active material. A comparison of Comparative Examples 2-3 and 6 with Examples 1-22 shows that adding all four modifying elements simultaneously to the positive electrode active material can effectively improve the specific capacity of the positive electrode active material and enhance the cycle performance of the lithium secondary battery. However, adding only two or three of the four modifying elements to the positive electrode active material has limited improvement on the overall battery performance.

[0227] As can be seen from Examples 1 to 6, when the mass ratio of (first modifying element + second modifying element) to (third modifying element + fourth modifying element) in the positive electrode active material is controlled to be 1:(0.1 to 10), or when the mass ratio of the first modifying element to the second modifying element is controlled to be 1:(0.1 to 30), or when the mass ratio of the third modifying element to the fourth modifying element is controlled to be 1:(0.05 to 30), the positive electrode active material can have a high specific capacity, and the lithium secondary battery can have excellent cycle performance.

[0228] As can be seen from Examples 1 to 22, based on the total mass of the positive electrode active material, when the mass percentage of the first modifying element is controlled to be 0.01% to 0.5%, or the mass percentage of the second modifying element is controlled to be 0.01% to 1%, or the mass percentage of the third modifying element is controlled to be 0.01% to 0.4%, or the mass percentage of the fourth modifying element is controlled to be 0.01% to 2.2%, the positive electrode active material can have a high specific capacity, and the lithium secondary battery can have excellent cycle performance.

[0229] In the positive electrode active material of Comparative Example 4, the mass percentage of the first modifying element exceeded the range of 0.01% to 0.5%, and the mass percentage of the second modifying element exceeded the range of 0.01% to 1%. In the positive electrode active material of Comparative Example 5, the mass percentage of the third modifying element exceeded the range of 0.01% to 0.4%, and the mass percentage of the fourth modifying element exceeded the range of 0.01% to 2.2%. A comparison of Comparative Examples 4-5 with Examples 1-22 shows that controlling the mass percentage of modifying elements in the positive electrode active material within a certain range is necessary to effectively improve the specific capacity of the positive electrode active material and enhance the cycle performance of the lithium secondary battery; however, when the mass percentage of modifying elements exceeds the aforementioned range, the improvement in battery performance is relatively small.

[0230] As can be seen from Examples 1 and 7-8, when various types of fourth modifying elements (such as Nb, Mo, and W) are added to the positive electrode active material, the prepared batteries all have excellent specific capacity and cycle performance.

[0231] As can be seen from Examples 1 and 9-11, when the molar percentage of nickel in the total transition metal elements in the positive electrode active material is above 55% (preferably in the range of 60% to 95%), the batteries prepared with it all exhibit excellent specific capacity and cycle performance. Meanwhile, when the molar percentage of cobalt in the total transition metal elements in the positive electrode active material is below 20% (preferably in the range of 3% to 10%), the batteries prepared with it all exhibit excellent specific capacity and cycle performance.

[0232] As can be seen from Examples 1 and 21, the addition of Sr and Y elements to the positive electrode active material, in addition to the addition of four modifying elements, can further improve the cycle performance of the battery.

[0233] As can be seen from Examples 1-21, the positive electrode active material adopts a single-crystal mixed-polycrystalline system, and the prepared battery has good specific capacity and cycle performance. Figure 1 and Figure 2 The images show the morphology of single-crystal and polycrystalline particles of the positive electrode active material. Furthermore, when the mass ratio of single-crystal to polycrystalline particles in the positive electrode active material is controlled to be 1:9 to 5:5 (preferably within the range of 1:9 to 3:7), the prepared batteries exhibit excellent specific capacity and cycle performance.

[0234] The positive electrode active material in Example 22 uses only a single-crystal system and does not contain any polycrystalline components. A comparison of Example 22 with Examples 1-21 shows that the compaction density of the positive electrode active material in the single-crystal system is worse than that in the single-crystal mixed-polycrystalline system. The use of a single-crystal mixed-polycrystalline system in the positive electrode active material of this application can further improve the compaction density of the active material, thereby comprehensively improving its performance.

[0235] As can be seen from Examples 1-22, the specific surface area of ​​the single-crystal particles in the positive electrode active material is controlled to be 0.9-1.5 m². 2 When / g, or control the specific surface area of ​​the polycrystalline particles to be 0.3–1.0m². 2 When the resistivity of the positive electrode active material is controlled within the range of 100–5000 Ω·cm at 12 MPa, the prepared batteries all exhibit excellent specific capacity and cycle performance.

[0236] It should be noted that this application is not limited to the described embodiments. The described 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, are also included in the scope of this application without departing from the spirit of this application.

Claims

1. A positive electrode active material containing a transition metal element, characterized in that, The positive electrode active material includes: Nickel element, wherein the molar percentage of nickel element in the total amount of nickel, cobalt and manganese metal elements is more than 55%; The element cobalt, wherein the molar percentage of cobalt in the total amount of nickel, cobalt and manganese is less than 20%; The first modifying element is Zr; The second modifying element is Al; The third modifying element B; and The fourth modifying element is at least one of Nb, Mo, and W. Specifically, based on the total mass of the positive electrode active material, the mass percentage of the first modifying element is 0.01%~0.5%, the mass percentage of the second modifying element is 0.01%~1%, the mass percentage of the third modifying element is 0.01%~0.4%, and the mass percentage of the fourth modifying element is 0.01%~2.2%. The positive electrode active material includes single crystal particles and polycrystalline particles, and the mass ratio of the single crystal particles to the polycrystalline particles is 1:9 to 5:

5.

2. The positive electrode active material according to claim 1, characterized in that, In the positive electrode active material, the mass ratio of (first modifying element + second modifying element) to (third modifying element + fourth modifying element) is 1:(0.1~10).

3. The positive electrode active material according to claim 2, characterized in that, In the positive electrode active material, the mass ratio of (first modifying element + second modifying element) to (third modifying element + fourth modifying element) is 1:(0.1~0.5).

4. The positive electrode active material according to claim 3, characterized in that, In the positive electrode active material, the mass ratio of (element Zr + element Al) to (element B + element W) is 1:(0.1~0.5).

5. The positive electrode active material according to claim 1, characterized in that, In the positive electrode active material, the mass ratio of the first modifying element to the second modifying element is 1:(0.1~30).

6. The positive electrode active material according to claim 5, characterized in that, In the positive electrode active material, the mass ratio of the first modifying element to the second modifying element is 1:(0.1~1).

7. The positive electrode active material according to claim 6, characterized in that, In the positive electrode active material, the mass ratio of element Zr to element Al is 1:(0.1~1).

8. The positive electrode active material according to claim 1, characterized in that, In the positive electrode active material, the mass ratio of the third modifying element to the fourth modifying element is 1:(0.05~30).

9. The positive electrode active material according to claim 8, characterized in that, In the positive electrode active material, the mass ratio of the third modifying element to the fourth modifying element is 1:(0.1~1).

10. The positive electrode active material according to claim 9, characterized in that, In the positive electrode active material, the mass ratio of element B to element W is 1:(0.1~1).

11. The positive electrode active material according to claim 1, characterized in that, Based on the total mass of the positive electrode active material, the mass percentage of the first modifying element is 0.05% to 0.5%.

12. The positive electrode active material according to claim 1, characterized in that, Based on the total mass of the positive electrode active material, the mass percentage of the second modifying element is 0.05% to 0.3%.

13. The positive electrode active material according to claim 1, characterized in that, Based on the total mass of the positive electrode active material, the mass percentage of the third modifying element is 0.01% to 0.2%.

14. The positive electrode active material according to claim 1, characterized in that, Based on the total mass of the positive electrode active material, the mass percentage of the fourth modifying element is 0.01% to 0.3%.

15. The positive electrode active material according to claim 1, characterized in that, The molar percentage of nickel in the total amount of nickel, cobalt, and manganese is 60% to 95%; and / or, the molar percentage of cobalt in the total amount of nickel, cobalt, and manganese is 3% to 10%.

16. The positive electrode active material according to claim 15, characterized in that, The molar percentage of nickel in the total amount of nickel, cobalt, and manganese is 80% to 95%.

17. The positive electrode active material according to claim 1, characterized in that, The specific surface area of ​​the single crystal particles is 0.9~1.5 m². 2 / g, wherein the specific surface area of ​​the polycrystalline particles is 0.3~1.0 m² / g. 2 / g.

18. The positive electrode active material according to claim 1, characterized in that, The volume average particle size Dv50 of the single crystal particles is 3~5 μm, and the volume average particle size Dv50 of the polycrystalline particles is 4~13 μm.

19. The positive electrode active material according to any one of claims 1-18, characterized in that, The positive electrode active material has the molecular formula Li a (Ni b Co c Mn 1-b-c ) 1-x-y-z-q Zr x Al y B z Q q O e Where Q includes at least one of Nb, Mo, and W, 0.9≤a≤1.2, 0.55≤b≤0.95, 0≤c≤0.20, 1.8≤e≤2.2, 0 <x≤0.04,0<y≤0.02,0<z≤0.09,0<q≤0.03。 20. The positive electrode active material according to claim 19, characterized in that, The positive electrode active material also includes strontium (Sr), and the mass percentage of strontium is 0.05% to 0.2% based on the total mass of the positive electrode active material.

21. The positive electrode active material according to claim 19, characterized in that, The positive electrode active material also includes yttrium (Y), and the mass percentage of yttrium is 0.05% to 0.2% based on the total mass of the positive electrode active material.

22. The positive electrode active material according to any one of claims 1-18, characterized in that, The resistivity of the positive electrode active material at 12 MPa is 100~8000 Ω·cm.

23. The positive electrode active material according to any one of claims 1-18, characterized in that, The tap density of the positive electrode active material is 1.9~2.6 g / cm³. 3 .

24. A lithium secondary battery, characterized in that, The positive electrode active material includes any one of claims 1-23.

25. The lithium secondary battery according to claim 24, characterized in that, The specific capacity of the positive electrode active material in the lithium secondary battery is 193~210mAh / g at 25℃ and 1 / 3C discharge rate.

26. The lithium secondary battery according to claim 24, characterized in that, The specific capacity of the positive electrode active material in the lithium secondary battery is 202~210mAh / g at 25℃ and 1 / 3C discharge rate.

27. An electrical appliance, characterized in that, The lithium secondary battery comprising any one of claims 24-26.

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