Secondary battery and electric device

Abstract

The invention provides a secondary battery which comprises a positive pole piece, a positive active material is arranged on the positive pole piece, and the positive active material comprises an aggregate type positive pole material and a monocrystal-like positive pole material; the volume average particle size Dv50 of the aggregate type positive electrode material is 8-15 [mu] m, and the primary particle size of the aggregate type positive electrode material is 0.1-0.6 [mu] m; the volume average particle size Dv50 of the monocrystal-like positive electrode material is 2.5 mu m-4 mu m, and the particle size of primary particles of the monocrystal-like positive electrode material is 0.8 mu m-2 mu m; the mass ratio of the aggregate type positive electrode material to the monocrystal-like positive electrode material is greater than or equal to 1; the invention also relates to a corresponding electric device. The secondary battery has relatively high energy density and relatively long cycle life.

Description

Secondary batteries and electrical devices Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device. Background Art

[0002] In recent years, as the application scope of secondary batteries has become increasingly wider, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in many fields such as power tools, electric bicycles, electric motorcycles and electric vehicles.

[0003] As secondary batteries have made significant progress, higher performance requirements have been placed on them. High energy density and long cycle life in secondary batteries place very high demands on positive electrode plates. For example, the positive electrode plates of high energy density and long cycle life secondary batteries should have a high compaction density and a long service life.

[0004] Therefore, seeking a secondary battery with higher energy density and better cycle life is one of the key areas of focus for those skilled in the art.

[0005] Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and one of its purposes is to provide a secondary battery having a higher energy density and a better cycle life.

[0007] In order to achieve the above-mentioned object, the first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, wherein the positive electrode sheet has a positive electrode active material, wherein the positive electrode active material includes an agglomerate-type positive electrode material and a quasi-single crystal-type positive electrode material;

[0008] The volume average particle size Dv50 of the agglomerate-type positive electrode material is 8 μm to 15 μm, and the primary particle size of the agglomerate-type positive electrode material is 0.1 μm to 0.6 μm;

[0009] The volume average particle size Dv50 of the quasi-single-crystal positive electrode material is 2.5 μm to 4 μm, and the primary particle size of the quasi-single-crystal positive electrode material is 0.8 μm to 2 μm;

[0010] The mass ratio of the agglomerate-type positive electrode material to the single-crystal-like positive electrode material is greater than or equal to 1.

[0011] The present application adopts a quasi-single crystal positive electrode material with a Dv50 of 2.5μm to 4μm and a primary particle size of 0.8μm to 2μm, and a graded agglomerate positive electrode material with a Dv50 of 8μm to 15μm and a primary particle size of 0.1μm to 0.6μm in a mass ratio greater than or equal to 1. While ensuring the high pressure density of the positive electrode plate, the positive electrode plate can obtain a better life and capacity, so that the secondary battery using the positive electrode plate has a higher energy density and a longer cycle life.

[0012] In any embodiment, the mass ratio of the agglomerate-type positive electrode material to the single-crystal-like positive electrode material is 1 to 9:1.

[0013] In any embodiment, the mass ratio of the agglomerate-type positive electrode material to the quasi-single-crystal positive electrode material is 2.3 to 3: 1. In this way, the energy density and cycle life of the secondary battery can be further improved.

[0014] In any embodiment, the volume average particle size Dv50 of the quasi-monocrystalline positive electrode material is 3 μm to 3.5 μm, and / or the primary particle size of the quasi-monocrystalline positive electrode material is 1.2 μm to 1.5 μm. In this way, the energy density of the secondary battery can be further improved.

[0015] In any embodiment, the primary particle size of the agglomerate-type positive electrode material is 0.2 μm to 0.4 μm, thereby further improving the energy density of the secondary battery.

[0016] In any embodiment, the chemical formula of the aggregate-type positive electrode material is Li x1 Ni y1 Co z1 M 1-y1-z1 O2, wherein 0.9≤x1≤1, 0.9≤y1≤0.98, 0.05≤z1≤0.1, and M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, and Nb. In this way, the capacity of the positive electrode sheet can be further increased, thereby increasing the energy density of the secondary battery.

[0017] In any embodiment, 0.9≤y1≤0.96. In this way, the nickel content of the agglomerate-type positive electrode material is appropriately reduced while ensuring a high capacity of the positive electrode sheet.

[0018] In any embodiment, the chemical formula of the single crystal-like positive electrode material is Li x2 Ni y2 Co z2 M′ 1-y2-z2O2, wherein 0.9≤x2≤1, 0.9≤y2≤0.98, 0.05≤z2≤0.1, and M′ comprises one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, and Nb. In this way, the capacity of the positive electrode sheet can be further increased, thereby improving the energy density of the secondary battery.

[0019] In any embodiment, 0.92≤y2≤0.98. In this way, the capacity of the positive electrode sheet can be further increased, thereby improving the energy density of the secondary battery.

[0020] In any embodiment, y2>y1. In this way, the capacity of the positive electrode sheet can be improved while the overall nickel content of the positive electrode active material is relatively low, thereby improving the energy density of the secondary battery.

[0021] In any embodiment, the particle size distribution span of the agglomerate-type positive electrode material is (Dv90-Dv10) / Dv50≤1.5. This can provide sufficient filling space and specific capacity for the positive electrode sheet, thereby increasing the capacity of the positive electrode sheet and further increasing the energy density of the secondary battery.

[0022] In any embodiment, the particle size distribution span (Dv90-Dv10) / Dv50 of the agglomerated positive electrode material is 0.7 to 1.4. This can better provide sufficient filling space for the positive electrode sheet, better improve the capacity of the positive electrode sheet, and thus improve the energy density of the secondary battery.

[0023] In any embodiment, the BET specific surface area of ​​the agglomerate type positive electrode material is 0.2 m 2 / g~0.8m 2 In this way, it is possible to prevent excessive active surface of the agglomerate-type positive electrode material from contacting the electrolyte, thereby preventing the agglomerate-type positive electrode material from being excessively corroded by the electrolyte, thereby increasing the life of the positive electrode sheet and the cycle life of the secondary battery.

[0024] In any embodiment, the BET specific surface area of ​​the agglomerate type positive electrode material is 0.3 m 2 / g~0.6m 2 In this way, the life of the positive electrode sheet can be better improved, thereby increasing the cycle life of the secondary battery.

[0025] In any embodiment, the particle size distribution span of the quasi-single crystal positive electrode material is (Dv90-Dv10) / Dv50≥1.2. This can improve the compressive performance of the positive electrode sheet, thereby increasing the life of the positive electrode sheet and the cycle life of the secondary battery.

[0026] In any embodiment, the particle size distribution span of the quasi-single crystal positive electrode material (Dv90-Dv10) / Dv50 is 1.3 to 1.5. This can further improve the compressive performance of the positive electrode sheet, further improve the life of the positive electrode sheet, and improve the cycle life of the secondary battery.

[0027] In any embodiment, the BET specific surface area of ​​the single-crystal-like positive electrode material is 0.8 m 2 / g~1.3m 2 In this way, a highly dispersed morphology can be achieved, which is beneficial to improving the space utilization of the positive electrode sheet.

[0028] In any embodiment, the BET specific surface area of ​​the single-crystal-like positive electrode material is 0.85 m 2 / g~1.15m 2 In this way, the space utilization of the positive electrode sheet can be further improved.

[0029] In any embodiment, the particle size distribution span of the positive electrode active material (Dv90-Dv10) / Dv50 is 1.5 to 2.1. In this way, the positive electrode sheet can obtain higher compaction density and processing performance at a higher film loading.

[0030] In any embodiment, the BET specific surface area of ​​the positive electrode active material is 0.5 m 2 / g~0.7m 2 In this way, the positive electrode sheet can also obtain higher compaction density and processing performance at a higher film loading, thereby improving the energy density of the secondary battery.

[0031] In any embodiment, the mass percentage of the positive electrode active material in the positive electrode sheet to the positive electrode film layer is 95% to 99.5%. In this way, the specific capacity of the positive electrode active material in the secondary battery can be ensured, the capacity of the positive electrode sheet can be increased, and the energy density of the secondary battery can be increased.

[0032] In any embodiment, the coating area density of the positive electrode active material in the positive electrode sheet is 21.5 mg / cm 2 ~32.5mg / cm 2 In this way, the use of thick positive electrode coating combined with high compaction density can further increase the capacity of the positive electrode sheet and improve the energy density of the secondary battery.

[0033] A second aspect of the present application provides an electrical device, which includes the secondary battery according to the first aspect of the present application.

[0034] The positive electrode plate of the secondary battery of the present application adopts a single-crystal-type positive electrode material with a Dv50 of 2.5μm to 4μm and a primary particle size of 0.8μm to 2μm, and is graded with an agglomerate-type positive electrode material with a Dv50 of 8μm to 15μm and a primary particle size of 0.1μm to 0.6μm in a mass ratio greater than or equal to 1. While ensuring the high pressure density of the positive electrode plate, the positive electrode plate can obtain a better life and capacity, thereby making the secondary battery have a higher energy density and a longer cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to better describe and illustrate the embodiments and / or examples of the present application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the presently described embodiments and / or examples, and any of the best modes currently understood for these applications.

[0036] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0037] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0038] FIG3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0039] Description of reference numerals:

[0040] 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover; 6. Electrical device. DETAILED DESCRIPTION

[0041] Below, the embodiments of the positive electrode sheet and its preparation method, secondary battery and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0042] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0044] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0045] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0046] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0047] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0048] The weights described in this specification may be weight units known in the chemical industry, such as μg, mg, g, and kg.

[0049] At present, as the application scope of secondary batteries becomes wider and wider, higher requirements are also put forward for the performance of secondary batteries. Among them, energy density and cycle life are two very important performance indicators of secondary batteries. The energy density and cycle life of traditional secondary batteries need to be improved. Therefore, how to provide a secondary battery with high energy density and good cycle life has become one of the important research directions in this field. In this regard, the present application provides a secondary battery, which mainly through the selection and ratio of the positive electrode active material in the positive electrode plate can make the positive electrode plate have a higher compaction density and service life, and at the same time have a higher capacity, so that the secondary battery has a higher energy density and a longer cycle life.

[0050] In one aspect of the present application, a secondary battery is provided, comprising a positive electrode plate having a positive electrode active material thereon, the positive electrode active material comprising an agglomerate positive electrode material and a quasi-single crystal positive electrode material; wherein the volume average particle size Dv50 of the agglomerate positive electrode material is 8 μm to 15 μm, and the primary particle size of the agglomerate positive electrode material is 0.1 μm to 0.6 μm; the volume average particle size Dv50 of the quasi-single crystal positive electrode material is 2.5 μm to 4 μm, and the primary particle size of the quasi-single crystal positive electrode material is 0.8 μm to 2 μm; the mass ratio of the agglomerate positive electrode material to the quasi-single crystal positive electrode material is greater than or equal to 1.

[0051] In order to achieve a high energy density of 360Wh / kg to 500Wh / kg for secondary batteries, the design of secondary batteries requires the use of high nickel active materials for the positive electrode and a high coating area density. Correspondingly, the negative electrode uses graphite + high-content silicon-based materials as the negative electrode active material. However, the thick coating design of the positive electrode sheet will lead to the following two problems for secondary batteries: On the one hand, when the coating area density (CW) of the currently used positive electrode materials is large, the compaction density of the positive electrode sheet is limited, generally <3.3g / cm 3 On the other hand, if the positive electrode sheet is compressed less, the energy density of the battery will be reduced. On the other hand, when the positive electrode active material is made of polycrystalline material, the specific surface area is large, the side reactions increase, and the cycle performance of high energy density lithium-ion batteries is reduced.

[0052] The above-mentioned secondary battery of the present application, the positive electrode active material in its positive electrode plate includes an agglomerate positive electrode material and a quasi-single crystal positive electrode material; wherein, the volume average particle size Dv50 of the agglomerate positive electrode material is controlled to be 8μm~15μm, and the primary particle size of the agglomerate positive electrode material is 0.1μm~0.6μm; the volume average particle size Dv50 of the quasi-single crystal positive electrode material is controlled to be 2.5μm~4μm, and the primary particle size of the quasi-single crystal positive electrode material is 0.8μm~2μm; and the mass ratio of the agglomerate positive electrode material to the quasi-single crystal positive electrode material is controlled to be greater than or equal to 1.

[0053] In this way, by using agglomerate-type positive electrode materials with a specific volume average particle size Dv50 and a specific primary particle size and quasi-single crystal positive electrode materials with a specific volume average particle size Dv50 and a specific primary particle size, they are mixed in a specific mass ratio; the agglomerate-type positive electrode material has a larger particle size, plays a skeleton role, and can increase the capacity of the electrode sheet; the quasi-single crystal positive electrode material has a smaller particle size, which can fill the gaps between the particles of the agglomerate-type positive electrode material, thereby increasing the compaction density of the positive electrode sheet, and the quasi-single crystal positive electrode material has a longer life, which can extend the service life of the electrode sheet.

[0054] Combining the two different types and particle sizes of positive electrode active materials mentioned above can fully improve the pores and volume utilization between the particles, and improve the compressive resistance of the positive electrode sheet. Agglomerate-type positive electrode materials with a Dv50 of 8μm to 15μm can serve as the framework of the positive electrode sheet. Particle sizes that are too large are prone to cracks at the edges of the particles and limit the gram capacity. Particle sizes that are too small do not serve as a skeleton. Single-crystal-like positive electrode materials with a Dv50 of 2.5μm to 4μm serve as secondary fillers for agglomerate-type positive electrode materials, which can improve space utilization. Due to their high dispersibility and compressive resistance, they can fully fill the pores between the agglomerate-type positive electrode material particles.

[0055] Since the gram capacity of high-nickel single-crystal positive electrode materials is lower than that of agglomerate-type positive electrode materials, and the agglomerate-type positive electrode materials themselves are not pressure-resistant, controlling the mass ratio of the two to be greater than or equal to 1 can maximize the compatibility between gram capacity and compaction density, and such dense stacking is not prone to particle displacement / slip under high pressure, thereby avoiding large elongation of the electrode and increased brittleness.

[0056] In addition, the Dv50 of the single-crystal-like positive electrode material is 2.5μm~4μm, and its primary particle size is 0.8μm~2μm, which ensures the positive electrode capacity and life while achieving high positive electrode pressure density. When the Dv50 of the quasi-single-crystal positive electrode material is too large, the compaction density of the electrode sheet will decrease; when the primary particle size of the quasi-single-crystal positive electrode material is less than 0.8μm, the number of primary particles required to constitute the quasi-single-crystal positive electrode material is too large, and its morphology will be closer to that of agglomerates. The active specific surface of the quasi-single-crystal positive electrode material is exposed too much, which is easily corroded by the electrolyte, resulting in a decrease in the life of the positive electrode sheet and a decrease in the compressive resistance; when the primary particle size of the quasi-single-crystal positive electrode material is greater than 2μm, the number of primary particles required to constitute the quasi-single-crystal positive electrode material is too small, and only 2 to 3 primary particles may be needed to constitute the quasi-single-crystal positive electrode material. The active specific surface of the quasi-single-crystal positive electrode material is exposed too little, the lithium ion transmission path is limited, and the kinetic performance deteriorates, affecting the capacity and life of the positive electrode sheet.

[0057] This application utilizes a quasi-single-crystal positive electrode material with a Dv50 of 2.5μm to 4μm and a primary particle size of 0.8μm to 2μm, and a gradation of an agglomerated positive electrode material with a Dv50 of 8μm to 15μm and a primary particle size of 0.1μm to 0.6μm in a mass ratio of 1 to 9:1. This ensures high pressure and density of the positive electrode while also providing a long lifespan and capacity for the positive electrode, thereby improving the energy density and cycle life of the secondary battery. The gram capacity of the positive electrode material in the secondary battery of this application can reach 215mAh / g to 230mAh / g, at 0.33C.

[0058] It should be noted that quasi-single-crystal cathode materials are irregular structures formed by the accumulation of several primary particles; whereas agglomerated cathode materials are regular spheres formed by a larger number of smaller spherical primary particles. It is understood that the volume average particle size Dv50 of the quasi-single-crystal cathode material can be, but is not limited to, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm, 3.0μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, or 4μm. The primary particle size of the quasi-single-crystal positive electrode material may be, but is not limited to, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm. The volume average particle size Dv50 of the agglomerate positive electrode material may be, but is not limited to, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, or 15 μm. The primary particle size of the agglomerate positive electrode material may be, but is not limited to, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, or 0.6 μm. The mass ratio of the agglomerate-type positive electrode material to the single-crystal-like positive electrode material can be, but is not limited to, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or 9:1.

[0059] In some embodiments, the mass ratio of the agglomerate-type positive electrode material to the single-crystal-like positive electrode material is 1 to 9: 1. In this way, the energy density and cycle life of the secondary battery can be further improved.

[0060] In some embodiments, the mass ratio of the agglomerate-type positive electrode material to the single-crystal-like positive electrode material is 2.3 to 3: 1. Using such a particle mass ratio gradation can further improve the energy density and cycle life of the secondary battery.

[0061] In some embodiments, the volume average particle size Dv50 of the quasi-single-crystal positive electrode material is 3 μm to 3.5 μm, and the primary particle size of the quasi-single-crystal positive electrode material is 1.2 μm to 1.5 μm. This is more conducive to improving the energy density of the secondary battery using the positive electrode sheet.

[0062] In some embodiments, the primary particle size of the agglomerate-type positive electrode material is 0.2 μm to 0.4 μm, which is more conducive to improving the energy density and cycle life of the secondary battery.

[0063] In some embodiments, the chemical formula of the aggregate-type cathode material is Li x1 Niy1 Co z1 M 1-y1- z1 O2, wherein 0.9≤x1≤1, 0.9≤y1≤0.98, 0.05≤z1≤0.1, and M comprises one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, and Nb. Thus, the agglomerate-type positive electrode material uses a high-nickel active material, which can increase the capacity of the positive electrode sheet and thereby improve the energy density of the secondary battery.

[0064] It can be understood that x1 in the chemical formula of the agglomerate type positive electrode material can be but not limited to 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1; y1 in the chemical formula of the agglomerate type positive electrode material can be but not limited to 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98; z1 in the chemical formula of the agglomerate type positive electrode material can be but not limited to 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0065] In some embodiments, the chemical formula of the agglomerate-type positive electrode material is 0.9≤y1≤0.96. Since the primary particle size of the agglomerate-type positive electrode material is relatively small and the agglomerates have more grain boundaries, which are more conducive to the transport of lithium ions, high capacity can be achieved even when the nickel content is not very high.

[0066] In some embodiments, the chemical formula of the single-crystal-like positive electrode material is Li x2 Ni y2 Co z2 M′ 1-y2- z2 O2, wherein 0.9≤x2≤1, 0.9≤y2≤0.98, 0.05≤z2≤0.1, and M′ comprises one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, and Nb. Thus, the quasi-single-crystal positive electrode material also uses a high-nickel active material, which can further increase the capacity of the positive electrode sheet and improve the energy density of the secondary battery.

[0067] It can be understood that x2 in the chemical formula of the quasi-single crystal positive electrode material can be but not limited to 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1; y2 in the chemical formula of the quasi-single crystal positive electrode material can be but not limited to 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98; z2 in the chemical formula of the quasi-single crystal positive electrode material can be but not limited to 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0068] In some embodiments, 0.92≤y2≤0.98. Because the primary particle size of the quasi-single-crystal positive electrode material is relatively larger, and the particle size of the secondary spheres of the quasi-single-crystal positive electrode material is smaller than that of the secondary spheres of the agglomerated positive electrode material, and there is no interface for rapid lithium ion transmission within the quasi-single-crystal positive electrode material, setting the nickel content y2 of the quasi-single-crystal positive electrode material to 0.92-0.98 can further increase the capacity of the positive electrode sheet and improve the energy density of the secondary battery.

[0069] In some embodiments, y2>y1. That is, the nickel content of the quasi-single-crystal positive electrode material is greater than the nickel content of the agglomerated positive electrode material. This arrangement can improve the capacity of the positive electrode sheet, thereby increasing the energy density of the secondary battery, even when the overall nickel content of the positive electrode active material is relatively low.

[0070] It should be noted that the element M in the chemical formula of the quasi-single crystal cathode material and the element M' in the chemical formula of the agglomerate cathode material differ, and their roles in the cathode material synthesis process are correspondingly different. For example, when M and M' are high-valent elements such as Sb and Nb, they can refine the grains, making the primary particle size of the cathode material even smaller, further improving the capacity and power performance of the cathode material. When M and M' are Sr, they can act as a co-solvent, allowing the cathode material to be sintered at a corresponding particle size without requiring too high a temperature, reducing the formation of the rock salt phase, and thus improving the capacity and cycle life of the cathode electrode. The element M and M' in the chemical formula of the cathode material can be determined according to actual needs.

[0071] In some embodiments, the particle size distribution span of the agglomerate-type positive electrode material (Dv90-Dv10) / Dv50 is ≤1.5. Controlling the particle size distribution span of the agglomerate-type positive electrode material (Dv90-Dv10) / Dv50 to ≤1.5 can provide sufficient filling space and specific capacity for the positive electrode sheet.

[0072] It can be understood that the particle size distribution span (Dv90-Dv10) / Dv50 of the agglomerate-type positive electrode material can be but is not limited to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5.

[0073] In some embodiments, the particle size distribution span (Dv90-Dv10) / Dv50 of the agglomerated positive electrode material is 0.7 to 1.4, thereby providing sufficient filling space for the positive electrode sheet, improving the specific capacity of the positive electrode sheet, and increasing the energy density of the secondary battery.

[0074] In some embodiments, the BET specific surface area of ​​the agglomerate-type positive electrode material is 0.2 m 2 / g~0.8m 2 / g. The BET specific surface area of ​​the agglomerate-type positive electrode material is controlled at 0.2m 2 / g~0.8m 2 / g, which can prevent excessive active surface of the agglomerate-type positive electrode material from contacting with the electrolyte, and avoid excessive corrosion of the agglomerate-type positive electrode material by the electrolyte, thereby increasing the life of the positive electrode sheet and the cycle life of the secondary battery.

[0075] It is understood that the BET specific surface area of ​​the agglomerate type positive electrode material can be but is not limited to 0.2 m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g.

[0076] In some embodiments, the BET specific surface area of ​​the agglomerate-type positive electrode material is 0.3 m 2 / g~0.6m 2 In this way, the life of the positive electrode sheet can be better improved, and the cycle life of the secondary battery can be increased.

[0077] In some embodiments, the particle size distribution span (Dv90-Dv10) / Dv50 of the quasi-single-crystal positive electrode material is ≥1.2. Controlling the particle size distribution span (Dv90-Dv10) / Dv50 of the quasi-single-crystal positive electrode material to ≥1.2 can improve the compressive performance of the positive electrode sheet, thereby increasing the life of the positive electrode sheet and the cycle life of the secondary battery. It is understood that the particle size distribution span (Dv90-Dv10) / Dv50 of the quasi-single-crystal positive electrode material can be, but is not limited to, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0.

[0078] In some embodiments, the particle size distribution span (Dv90-Dv10) / Dv50 of the quasi-single-crystal positive electrode material is 1.3 to 1.5. This can further improve the compressive performance of the positive electrode sheet, further improve the life of the positive electrode sheet, and increase the cycle life of the secondary battery.

[0079] In some embodiments, the BET specific surface area of ​​the single-crystal-like positive electrode material is 0.8 m 2 / g~1.3m 2 / g. The BET specific surface area of ​​the single-crystal cathode material is controlled at 0.8m 2 / g~1.3m2 / g range, a highly dispersed morphology can be achieved, which is beneficial to improving the space utilization of the positive electrode sheet. It can be understood that the BET specific surface area of ​​the single-crystal positive electrode material can be but is not limited to 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g.

[0080] In some embodiments, the BET specific surface area of ​​the single-crystal-like positive electrode material is 0.85 m 2 / g~1.15m 2 In this way, the space utilization of the positive electrode sheet can be further improved.

[0081] In some embodiments, the particle size distribution span (Dv90-Dv10) / Dv50 of the positive electrode active material is 1.5 to 2.1. This allows the positive electrode sheet to achieve higher compaction density and processing performance at a higher membrane loading, thereby improving the energy density of the secondary battery. It is understood that the particle size distribution span (Dv90-Dv10) / Dv50 of the mixed positive electrode active material can be, but is not limited to, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or 2.1.

[0082] It should be noted that the volume average particle sizes Dv10, Dv50, and Dv90 of the positive electrode material are well-known concepts in the art. Specifically, Dv10 is the particle size at which the cumulative volume percentage of the powder particles, starting from the small particle size side, reaches 10%, and the unit is usually μm. Dv50 is the particle size at which the cumulative volume percentage of the powder particles, starting from the small particle size side, reaches 50%. Dv90 is the particle size at which the cumulative volume percentage of the powder particles, starting from the small particle size side, reaches 90%.

[0083] In some embodiments, the BET specific surface area of ​​the positive electrode active material is 0.5 m 2 / g~0.7m 2 / g. In this way, the positive electrode sheet can also obtain higher compaction density and processing performance at a higher film loading, thereby improving the energy density of the secondary battery. It is understood that the BET specific surface area of ​​the mixed positive electrode active material can be but is not limited to 0.5m 2 / g, 0.55m 2 / g, 0.6m 2 / g, 0.65m 2 / g, 0.7m 2By adopting the above-mentioned particle size distribution span and BET specific surface area of ​​the mixed positive electrode active material, the elongation of the positive electrode sheet after cold pressing can be made ≤0.8%.

[0084] In some embodiments, the mass percentage of the positive electrode active material in the positive electrode sheet to the positive electrode film layer is 95% to 99.5%. Controlling the mass percentage of the positive electrode active material in the positive electrode sheet to the positive electrode film layer to 95% to 99.5% can ensure that the gram capacity of the positive electrode active material in the secondary battery is fully utilized and improve the energy density of the secondary battery. It is understandable that the mass percentage of the positive electrode active material in the positive electrode sheet to the positive electrode film layer can be, but is not limited to, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, and 99.5%.

[0085] In some embodiments, the coating area density of the positive electrode active material in the positive electrode sheet is 21.5 mg / cm 2 ~32.5mg / cm 2 The positive electrode sheet of the present application can achieve a high compaction density of the positive electrode sheet at a higher surface density of the positive electrode active material coating, and the compaction density of the positive electrode sheet can reach 3.7g / cm 3 The above, and the elongation of the electrode sheet after cold pressing is small, the positive electrode sheet is not prone to breakage and other problems during later use. It can be understood that the coating area density of the positive electrode active material in the positive electrode sheet can be but is not limited to 21.5 mg / cm 2 , 22mg / cm 2 , 22.5mg / cm 2 , 23mg / cm 2 , 23.5mg / cm 2 , 24mg / cm 2 , 24.5mg / cm 2 , 25mg / cm 2 , 25.5mg / cm 2 , 26mg / cm 2 , 26.5mg / cm 2 , 27mg / cm 2 , 27.5mg / cm 2 , 28mg / cm 2 , 28.5mg / cm 2 , 29mg / cm 2 , 29.5mg / cm 2 、30mg / cm 2 、30.5mg / cm 2 、31mg / cm 2 、31.5mg / cm 2 、32mg / cm 2、32.5mg / cm 2 .

[0086] In some embodiments, the positive electrode plate includes a positive electrode current collector, which can be a metal foil or a composite current collector. The metal foil can be aluminum foil, and the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.

[0087] In some embodiments, a method for preparing a positive electrode sheet in a secondary battery comprises the following steps:

[0088] mixing the positive electrode active material with a conductive agent, a binder, and a solvent to form a slurry; and

[0089] The slurry is coated on the positive electrode current collector, dried and pressed to obtain the positive electrode sheet.

[0090] In some embodiments, the mass ratio of the positive electrode active material, conductive agent, and binder in the slurry is (90-96):(2-5):(2-5), and the solid content of the slurry is 70%-99.5%. Thus, by grading the size of the particles of the agglomerated positive electrode material and the quasi-single crystal positive electrode material in the positive electrode active material, the positive electrode active material, conductive agent, and binder are mixed in a specific mass ratio, and the slurry is adjusted to a specific solid content using a solvent. By combining the particle grading of the positive electrode active material with the specific positive electrode slurry formulation, the performance of the positive electrode active material can be fully utilized, and the compaction density of the positive electrode sheet can be further improved.

[0091] In some embodiments, the agglomerate-type positive electrode material and the single-crystal-like positive electrode material are put into a stirring tank according to a mass ratio, a conductive agent and a binder are added for pre-mixing, and a solvent is added for rapid stirring under a vacuum environment to form a positive electrode slurry; the positive electrode slurry is evenly coated on both sides of the positive electrode collector aluminum foil, and the electrode sheet coated with the slurry is dried at 100°C to 130°C, taken out and cold pressed to obtain a positive electrode sheet.

[0092] In some embodiments, the lithium source, high nickel ternary precursor, and additives are placed in a mixer according to a proportion, mixed evenly, and sintered at 550°C to 800°C in an oxygen atmosphere for 5h to 20h to obtain an agglomerate-type positive electrode material; the lithium source, high nickel ternary precursor, and additives are placed in a mixer according to a proportion, mixed evenly, and sintered at 600°C to 900°C in an oxygen atmosphere for 5h to 20h to obtain a single-crystal-type positive electrode material.

[0093] In some embodiments, the conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0094] In some embodiments, the binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0095] In some embodiments, the secondary battery further comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material, and the mass percentage of the silicon-based material in the negative electrode active material is 20% to 100%. In this way, the positive electrode plate of the first aspect of the present application and the negative electrode plate with a high silicon content are combined into a secondary battery, which can achieve a higher energy density of the secondary battery. It is understood that the mass percentage of the silicon-based material in the negative electrode active material can be, but is not limited to, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%.

[0096] In a second aspect of the present application, an electrical device is provided, comprising the secondary battery according to the first aspect of the present application.

[0097] The secondary battery and the electric device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0098] Unless otherwise specified, the components, material types, or contents of the batteries mentioned are applicable to both lithium-ion secondary batteries and sodium-ion secondary batteries.

[0099] In one embodiment of the present application, a secondary battery is provided.

[0100] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0101]

Positive electrode

[0102] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0103] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0104] In some embodiments, the positive electrode 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 material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc. Polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.)

[0105] In some embodiments, the positive electrode active material may include a positive electrode active material for a battery known in the art.

[0106] As an example, the positive electrode active material of a lithium-ion secondary battery may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0107] As an example, the positive electrode active material of a sodium ion secondary battery may include at least one of the following materials: a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries may also be used.

[0108] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0109] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si; n represents (YO4) n- valence.

[0110] Polyanionic compounds can also be sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4) n- valence state; the halogen may be at least one of F, Cl and Br.

[0111] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y ) m+ and an optional halogen anion. Y can be at least one of P, S and Si, and n represents (YO4) n-Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and m represents (ZO y ) m+ valence state; the halogen may be at least one of F, Cl and Br.

[0112] Polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0113] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ) compounds. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0114] The weight ratio of the positive electrode active material in the positive electrode film layer is 80 to 100 weight percent based on the total weight of the positive electrode film layer.

[0115] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0 to 20 weight%, based on the total weight of the positive electrode film layer.

[0116] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0-20% by weight, based on the total weight of the positive electrode film layer.

[0117] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, wherein the positive electrode slurry has a solid content of 40% by mass (wt%) to 80% by weight, and the viscosity at room temperature is adjusted to 5000 millipascals seconds (mPa·s) to 25000 mPa·s, the positive electrode slurry is coated on the surface of the positive electrode collector, and after drying, it is cold-pressed by a cold rolling mill to form a positive electrode sheet.

[0118] The thickness T of the positive electrode film can be measured using a micrometer, for example, a Mitutoyo 293-100 with an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film described in this application refers to the thickness of the positive electrode film in the positive electrode sheet after cold pressing and used in battery assembly.

[0119]

Negative electrode

[0120] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0121] As an example, the negative electrode current collector has two surfaces opposite to each other in its 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.

[0122] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc., and the polymer material substrate includes but is not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) and other substrates.

[0123] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art.

[0124] As an example, the negative electrode active material of a lithium-ion secondary battery 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. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional 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.

[0125] As an example, the negative electrode active material of a sodium ion secondary battery is generally a hard carbon material, a two-dimensional metal carbide or a nitride. Preferably, the negative electrode active material of a sodium ion secondary battery is generally a hard carbon material.

[0126] The weight ratio of the negative electrode active material in the negative electrode film layer is 70 to 100 weight percent based on the total weight of the negative electrode film layer.

[0127] In some embodiments, the negative electrode film layer may further 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). The weight ratio of the binder in the negative electrode film layer is 0 to 30% by weight, based on the total weight of the negative electrode film layer.

[0128] In some embodiments, the negative electrode film layer may further 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. The weight ratio of the conductive agent in the negative electrode film layer is 0 to 20% by weight, based on the total weight of the negative electrode film layer.

[0129] In some embodiments, the negative electrode film layer may further include other additives, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)). The weight ratio of the other additives in the negative electrode film layer is 0 to 15% by weight, based on the total weight of the negative electrode film layer.

[0130] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30wt% to 70wt%, and the viscosity at room temperature is adjusted to 2000mPa·s to 10000mPa·s; the obtained negative electrode slurry is coated on the negative electrode current collector, and after a drying process, cold pressing, such as rolling, is performed to obtain the negative electrode sheet. The negative electrode powder coating unit area density is 75mg / m 2 ~220 mg / m 2 The compacted density of the negative electrode is 1.2 g / m3 (g / m 3 )~2.0g / m 3 .

[0131] The mass M of the negative electrode active material per unit area of ​​the negative electrode membrane can be obtained by weighing using a standard balance.

[0132] The thickness T of the negative electrode film can be measured using a micrometer, such as a Mitutoyo 293-100 with an accuracy of 0.1 μm. It should be noted that the thickness of the negative electrode film described in this application refers to the thickness of the negative electrode film after cold pressing and compaction and used in the negative electrode sheet assembled into the battery.

[0133] Electrolytes

[0134] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0135] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0136] In some embodiments, the electrolyte salt of the lithium ion secondary battery can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0137] The electrolyte salt of the sodium ion secondary battery can be selected from one or more of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, and sodium chloride.

[0138] The concentration of the electrolyte salt is generally 0.5 mol / L to 5 mol / L.

[0139] In some embodiments, the solvent can be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

[0140] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0141]

Isolation film

[0142] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0143] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0144] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may optionally be 12 μm to 20 μm.

[0145] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0146] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0147] 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. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0148] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0149] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0150] In some embodiments, the secondary batteries 5 can be assembled into a battery module. The number of secondary batteries 5 contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0151] In the battery module, the plurality of secondary batteries 5 can be arranged in sequence along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.

[0152] Optionally, the battery module may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0153] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0154] A battery pack may include a battery box and multiple battery modules disposed within the box. The battery box comprises an upper case and a lower case. The upper case can be placed over the lower case to form an enclosed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0155] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0156] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0157] Figure 3 shows an example of an electric device. This device can 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, a battery pack or battery module can be used.

[0158] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0159] The following are some examples.

[0160] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0161] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0162] 1. Implementation

[0163] Example 1:

[0164] 1) Positive electrode

[0165] The positive electrode active material is a mixture of an agglomerate-type positive electrode material (primary particle size of 0.4 μm) with a Dv50 of 12 μm and a quasi-single crystal-type positive electrode material (primary particle size of 1.2 μm) with a Dv50 of 3 μm in a mass ratio of 7:3.

[0166] Among them, the chemical formula of the aggregate type cathode material is Li x1 Ni y1 Co z1 M 1-y1-z1 O2; the chemical formula of the single-crystal positive electrode material is Li x2 Ni y2 Co z2 M′ 1-y2-z2 O2. x1 is 1, y1 is 0.93, z1 is 0.05, x2 is 1, y2 is 0.91, and z2 is 0.07; the particle size distribution span (Dv90-Dv10) / Dv50 of the agglomerate-type positive electrode material is 1.25, and the particle size distribution span (Dv90-Dv10) / Dv50 of the quasi-single crystal positive electrode material is 1.35; the BET specific surface area of ​​the agglomerate-type positive electrode material is 0.56m 2 / g, and the BET specific surface area of ​​the single-crystal cathode material is 1.05m 2 / g; the particle size distribution span (Dv90-Dv10) / Dv50 of the mixed positive electrode active material is 1.78, and the BET specific surface area is 0.66m 2 / g.

[0167] The above-mentioned positive electrode active materials were placed in a 5L stirring tank. Acetylene black (SP), a conductive agent, and polyvinylidene fluoride (PVDF), a binder, were then added and pre-mixed for 30 minutes. N-methylpyrrolidone (NMP) was then added and rapidly stirred under vacuum to form a positive electrode slurry. The mass ratio of positive electrode active material: acetylene black: PVDF was 96:2:2, and the solids content of the slurry was 70%.

[0168] The positive electrode slurry is evenly coated on both sides of the positive electrode current collector aluminum foil with a thickness of 12μm. The coated electrode is dried in an oven at 100℃~130℃ for half an hour, then taken out and cold-pressed by rollers to prepare the positive electrode sheet. The active material loading of the positive electrode film on the electrode sheet is 21.5mg / cm 2 .

[0169] 2) Negative electrode

[0170] The negative electrode active materials, graphite + silicon-carbon material, carbon black (SP), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC), are dissolved in deionized water at a weight ratio of 95:2:2:1. A uniformly dispersed negative electrode slurry is obtained by stirring. The negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil. After drying, cold pressing, and cutting, the negative electrode sheet is obtained. The silicon-carbon material accounts for 30% of the negative electrode active material by weight.

[0171] 3) Isolation film

[0172] Polyethylene (PE) porous polymer film is used as the isolation membrane.

[0173] 4) Electrolyte

[0174] In an argon atmosphere glove box, 8% lithium hexafluorophosphate (LiPF6), 2% vinylene carbonate (VC), 0.5% hexamethylene diisocyanate (HDI), 25% ethylene carbonate (EC), 10% dimethyl carbonate (DMC), 20% ethyl methyl carbonate (EMC), and the remainder was supplemented with diethyl carbonate (DEC) to 100%, and mixed to obtain the corresponding electrolyte.

[0175] 5) Battery assembly

[0176] The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in sequence to form a bare cell, which is then placed in a battery casing, injected with electrolyte, and formed to obtain a secondary battery.

[0177] Example 2:

[0178] This embodiment is substantially the same as embodiment 1, with the only difference being that the Dv50 of the agglomerate-type positive electrode material in the positive electrode active material is different. In this embodiment, the Dv50 of the agglomerate-type positive electrode material is 8.2 μm.

[0179] Example 3:

[0180] This embodiment is substantially the same as embodiment 1, with the only difference being that the primary particles of the agglomerate-type positive electrode material in the positive electrode active material have a different particle size. In this embodiment, the primary particles of the agglomerate-type positive electrode material have a particle size of 0.2 μm.

[0181] Example 4:

[0182] This embodiment is substantially the same as embodiment 1, differing only in that the particle size distribution span (Dv90-Dv10) / Dv50 (i.e., SPAN) of the agglomerated positive electrode material in the positive electrode active material is different. In this embodiment, the particle size distribution span (SPAN) of the agglomerated positive electrode material is 1.39.

[0183] Example 5:

[0184] This embodiment is substantially the same as embodiment 1, with the only difference being that the molecular formula of the agglomerate-type positive electrode material in the positive electrode active material is different. In this embodiment, the molecular formula of the agglomerate-type positive electrode material is 0.98 and z1 is 0.01.

[0185] Example 6:

[0186] This embodiment is basically the same as embodiment 1, except that the BET specific surface area of ​​the agglomerate type positive electrode material in the positive electrode active material is different. The BET specific surface area of ​​the agglomerate type positive electrode material in this embodiment is 0.78 m 2 / g.

[0187] Example 7:

[0188] This embodiment is substantially the same as embodiment 1, with the only difference being that the Dv50 of the quasi-single-crystal positive electrode material in the positive electrode active material is different. In this embodiment, the Dv50 of the quasi-single-crystal positive electrode material is 3.8 μm.

[0189] Example 8:

[0190] This embodiment is substantially the same as embodiment 1, with the only difference being that the particle size of the primary particles of the quasi-single-crystal positive electrode material in the positive electrode active material is different. In this embodiment, the particle size of the primary particles of the quasi-single-crystal positive electrode material is 0.9 μm.

[0191] Example 9:

[0192] This embodiment is substantially the same as Example 1, differing only in that the particle size distribution span (Dv90 - Dv10) / Dv50 (i.e., SPAN) of the quasi-single-crystal positive electrode material in the positive electrode active material is different. In this embodiment, the particle size distribution span (SPAN) of the quasi-single-crystal positive electrode material is 1.47.

[0193] Example 10:

[0194] This embodiment is substantially the same as embodiment 1, with the only difference being that the molecular formula of the quasi-single-crystal positive electrode material in the positive electrode active material is different. In this embodiment, the molecular formula of the quasi-single-crystal positive electrode material is y2, which is 0.97, and z2, which is 0.02.

[0195] Example 11:

[0196] This embodiment is basically the same as embodiment 1, except that the BET specific surface area of ​​the single-crystal positive electrode material in the positive electrode active material is different. The BET specific surface area of ​​the single-crystal positive electrode material in this embodiment is 0.85 m 2 / g.

[0197] Example 12:

[0198] This embodiment is substantially the same as embodiment 1, except that the mass ratio of the agglomerate-type positive electrode material to the quasi-single-crystal positive electrode material in the positive electrode active material is different. In this embodiment, the mass ratio of the agglomerate-type positive electrode material to the quasi-single-crystal positive electrode material is 8:2.

[0199] Example 13:

[0200] This embodiment is substantially the same as embodiment 1, except that the particle size distribution span (Dv90-Dv10) / Dv50 (i.e., SPAN) of the mixed positive electrode active material is different. In this embodiment, the particle size distribution span SPAN of the positive electrode active material is 2.03.

[0201] Example 14:

[0202] This embodiment is basically the same as embodiment 1, except that the BET specific surface area of ​​the mixed positive electrode active material is different. The BET specific surface area of ​​the positive electrode active material in this embodiment is 0.52 m 2 / g.

[0203] Example 15:

[0204] This embodiment is substantially the same as embodiment 1, with the only difference being the content of the silicon-based material in the negative electrode active material of the negative electrode plate. In this embodiment, the mass content of the silicon-based material in the negative electrode active material is 90%.

[0205] Example 16:

[0206] In this embodiment, the Dv50 of the agglomerate type positive electrode material is 14.9 μm, the particle size of the primary particles of the agglomerate type positive electrode material is 0.3 μm, the particle size distribution span SPAN of the agglomerate type positive electrode material is 0.72, y1 in the molecular formula of the agglomerate type positive electrode material is 0.94, z1 is 0.05, and the BET specific surface area of ​​the agglomerate type positive electrode material is 0.3 m 2 / g; the Dv50 of the quasi-single-crystal positive electrode material is 3.5μm, the particle size of the primary particles of the quasi-single-crystal positive electrode material is 1.5μm, the particle size distribution span SPAN of the quasi-single-crystal positive electrode material is 1.44, y2 in the molecular formula of the quasi-single-crystal positive electrode material is 0.92, z2 is 0.06, and the BET specific surface area of ​​the quasi-single-crystal positive electrode material is 0.9m 2 / g; the mass ratio of agglomerate-type positive electrode material to single-crystal-type positive electrode material is 65:35, the particle size distribution span SPAN of the positive electrode active material is 1.55, and the BET specific surface area of ​​the positive electrode active material is 0.53m 2 / g, the mass content of the silicon-based material in the negative electrode active material is 50%, and the rest is the same as in Example 1.

[0207] Example 17:

[0208] In this embodiment, the Dv50 of the agglomerate-type positive electrode material is 9.5 μm, the particle size of the primary particles of the agglomerate-type positive electrode material is 0.13 μm, the particle size distribution span SPAN of the agglomerate-type positive electrode material is 1.33, y1 in the molecular formula of the agglomerate-type positive electrode material is 0.94, z1 is 0.05, and the BET specific surface area of ​​the agglomerate-type positive electrode material is 0.2 m 2 / g; the Dv50 of the quasi-single-crystal positive electrode material is 3.5μm, the particle size of the primary particles of the quasi-single-crystal positive electrode material is 1.5μm, the particle size distribution span SPAN of the quasi-single-crystal positive electrode material is 1.44, y2 in the molecular formula of the quasi-single-crystal positive electrode material is 0.92, z2 is 0.06, and the BET specific surface area of ​​the quasi-single-crystal positive electrode material is 0.83m 2 / g; the mass ratio of agglomerate-type positive electrode material to single-crystal-type positive electrode material is 75:25, the particle size distribution span SPAN of the positive electrode active material is 1.9, and the BET specific surface area of ​​the positive electrode active material is 0.53m 2 / g, the mass content of the silicon-based material in the negative electrode active material is 50%, and the rest is the same as in Example 1.

[0209] Example 18:

[0210] In this embodiment, the Dv50 of the agglomerate-type positive electrode material is 9.5 μm, the particle size of the primary particles of the agglomerate-type positive electrode material is 0.3 μm, the particle size distribution span SPAN of the agglomerate-type positive electrode material is 1.33, y1 in the molecular formula of the agglomerate-type positive electrode material is 0.94, z1 is 0.05, and the BET specific surface area of ​​the agglomerate-type positive electrode material is 0.45 m 2 / g; the Dv50 of the quasi-single-crystal positive electrode material is 3.5μm, the particle size of the primary particles of the quasi-single-crystal positive electrode material is 1.5μm, the particle size distribution span SPAN of the quasi-single-crystal positive electrode material is 1.44, y2 in the molecular formula of the quasi-single-crystal positive electrode material is 0.92, z2 is 0.06, and the BET specific surface area of ​​the quasi-single-crystal positive electrode material is 1.14m 2 / g; the mass ratio of agglomerate-type positive electrode material to single-crystal-type positive electrode material is 7:3, the particle size distribution span SPAN of the positive electrode active material is 1.9, and the BET specific surface area of ​​the positive electrode active material is 0.68m 2 / g, the mass content of the silicon-based material in the negative electrode active material is 50%, and the rest is the same as in Example 1.

[0211] Example 19:

[0212] In this embodiment, the Dv50 of the agglomerate-type positive electrode material is 9.5 μm, the particle size of the primary particles of the agglomerate-type positive electrode material is 0.56 μm, the particle size distribution span SPAN of the agglomerate-type positive electrode material is 1.33, y1 in the molecular formula of the agglomerate-type positive electrode material is 0.94, z1 is 0.05, and the BET specific surface area of ​​the agglomerate-type positive electrode material is 0.45 m 2 / g; the Dv50 of the quasi-single-crystal positive electrode material is 3.5μm, the particle size of the primary particles of the quasi-single-crystal positive electrode material is 1.9μm, the particle size distribution span SPAN of the quasi-single-crystal positive electrode material is 1.44, y2 in the molecular formula of the quasi-single-crystal positive electrode material is 0.92, z2 is 0.06, and the BET specific surface area of ​​the quasi-single-crystal positive electrode material is 0.9m 2 / g; the mass ratio of agglomerate-type positive electrode material to single-crystal-type positive electrode material is 8:2, the particle size distribution span SPAN of the positive electrode active material is 1.9, and the BET specific surface area of ​​the positive electrode active material is 0.53m 2 / g, the mass content of the silicon-based material in the negative electrode active material is 50%, and the rest is the same as in Example 1.

[0213] Example 20:

[0214] In this embodiment, the Dv50 of the agglomerate-type positive electrode material is 9.5 μm, the particle size of the primary particles of the agglomerate-type positive electrode material is 0.3 μm, the particle size distribution span SPAN of the agglomerate-type positive electrode material is 1.33, y1 in the molecular formula of the agglomerate-type positive electrode material is 0.94, z1 is 0.05, and the BET specific surface area of ​​the agglomerate-type positive electrode material is 0.45 m 2 / g, the Dv50 of the quasi-single-crystal positive electrode material is 2.6μm, the particle size of the primary particles of the quasi-single-crystal positive electrode material is 1.5μm, and the particle size distribution span SPAN of the quasi-single-crystal positive electrode material is 1.44; in the molecular formula of the quasi-single-crystal positive electrode material, y2 is 0.92, z2 is 0.06, and the BET specific surface area of ​​the quasi-single-crystal positive electrode material is 1.26m 2 / g, the mass ratio of agglomerate-type positive electrode material to single-crystal-type positive electrode material is 7:3, the particle size distribution span SPAN of the positive electrode active material is 2.07, and the BET specific surface area of ​​the positive electrode active material is 0.53m 2 / g, the mass content of the silicon-based material in the negative electrode active material is 50%, and the rest is the same as in Example 1.

[0215] Comparative Example 1:

[0216] In this comparative example, the Dv50 of the agglomerate-type positive electrode material is 9 μm, the particle size of the primary particles of the agglomerate-type positive electrode material is 0.2 μm, the particle size distribution span SPAN of the agglomerate-type positive electrode material is 1.2, y1 in the molecular formula of the agglomerate-type positive electrode material is 0.94, z1 is 0.05, and the BET specific surface area of ​​the agglomerate-type positive electrode material is 0.45 m 2 / g; the Dv50 of the quasi-single-crystal positive electrode material is 3.3μm, the particle size of the primary particles of the quasi-single-crystal positive electrode material is 0.7μm, and the particle size distribution span SPAN of the quasi-single-crystal positive electrode material is 1.4; in the molecular formula of the quasi-single-crystal positive electrode material, y2 is 0.93, z2 is 0.06, and the BET specific surface area of ​​the quasi-single-crystal positive electrode material is 0.95m 2 / g; the mass ratio of agglomerate-type positive electrode material to single-crystal-type positive electrode material is 8:2, the particle size distribution span SPAN of the positive electrode active material is 1.94, and the BET specific surface area of ​​the positive electrode active material is 0.61m 2 / g, the mass content of the silicon-based material in the negative electrode active material is 40%, and the rest is the same as in Example 1.

[0217] Comparative Example 2:

[0218] This comparative example is basically the same as comparative example 1, with the only difference being that: the positive electrode active material uses only agglomerated positive electrode material, and does not use quasi-single crystal positive electrode material; the total amount of positive electrode active material remains unchanged; and the compaction density of the positive electrode sheet is different.

[0219] Comparative Example 3:

[0220] This comparative example is basically the same as comparative example 1, with the only difference being that: the positive electrode active material only uses a quasi-single crystal positive electrode material, and does not use an agglomerate positive electrode material, and the primary particle size of the quasi-single crystal positive electrode material is 1.2 μm, the total amount of the positive electrode active material remains unchanged; and the compaction density of the positive electrode sheet is different.

[0221] 2. Test Method

[0222] 1) Dv10, Dv50, and Dv90 tests

[0223] The volume average particle size Dv10, Dv50, and Dv90 of the particles can be measured using methods known in the art. For example, the particle size distribution laser diffraction method according to GB / T 19077-2016 / ISO 13320:2009 can be used, and the measurement can be performed using a Malvern 3000 instrument.

[0224] 2) BET specific surface area test

[0225] The BET surface area of ​​particles can be determined using methods known in the art. For example, the BET surface area of ​​particles can be determined using a TriStar II 3020 instrument, as described in GB / T 19587-2017, "Determination of the Specific Surface Area of ​​Solids by Gas Adsorption BET Method."

[0226] 3) Primary particle size test

[0227] In a 3000-times magnified photograph, a scanning electron microscope measures the length of each particle in its longest direction (for regular spheres, the diameter is measured; for irregular particles, the length is measured in the opposite direction of the longest direction). Approximately 300 particles are measured, and the average value is calculated to obtain the primary particle size.

[0228] 4) Compaction density calculation

[0229] The compaction density of the positive electrode sheet can be calculated by the formula PD=M / (d×A), where M is the mass of a small disc with a diameter of 40 mm, which can be obtained by taking the average value of 10 weighings; d is the thickness of the positive electrode sheet after cold pressing, which can be obtained by cutting it into 40 mm small discs and measuring the thickness and taking the average value; A is the area of ​​the 40 mm small disc.

[0230] 5) Lengthwise elongation test

[0231] The elongation of the positive electrode in the longitudinal 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.

[0232] 6) Energy density test

[0233] Battery cell capacity test: Allow the battery cell to rest at 25°C for 2 hours, ensuring the battery cell temperature is 25°C. At 25°C, charge the battery cell at 0.1C to the charge cutoff voltage. Continue constant voltage charging at the same charge cutoff voltage until the current reaches 0.05C, at which point the charge is cutoff (where C represents the rated capacity of the battery cell). Allow the battery cell to rest at 25°C for 1 hour. At 25°C, discharge the battery cell at 0.1C to the discharge cutoff voltage. Record the total discharge capacity (C0) of the battery cell. The total discharge energy (E0) is recorded.

[0234] Battery cell weight measurement: Place the battery cell on an electronic balance until the weight stabilizes, and read the battery cell weight value M0.

[0235] Energy density calculation: discharge energy E0 of battery cell / battery cell weight M0, which is the energy density of battery cell.

[0236] 7) Cycle test

[0237] (1) Place the full battery in a thermostat at 45°C for 30 minutes, then discharge it at a constant current of 0.33C to 2.8V. (2) Allow it to stand for 5 minutes, charge it at a constant current of 0.33C to 4.25V, then charge it at a constant current of 0.05C to 4.25V, and allow it to stand for 5 minutes. (3) Discharge it at a constant current of 0.33C to 2.8V. The capacity value at this point is recorded as the initial capacity C0. Repeat steps (2) to (3) to obtain the second cycle capacity data C1. C1 / C0 can be used to calculate the cycle retention rate. The number of test cycles when the cycle retention rate reaches 80% is the number of cycles.

[0238] The parameters and performance test results of the positive electrode sheets and secondary batteries in the above embodiments and comparative examples are shown in Tables 1, 2 and 3. In the following tables, A represents agglomerate-type positive electrode material, and B represents a quasi-single-crystal positive electrode material.

[0239] It should be noted that, since the results of multiple particle size tests of the same material may fluctuate to a certain extent, the small fluctuations in particle size (e.g., ±0.1 μm) in the embodiments of this application are within the normal error range. Similarly, the small fluctuations in the BET specific surface area of ​​the same positive electrode material (e.g., ±0.01 μm) 2 / g) is also within the normal error range.

[0240] Table 1

[0241] Table 2

[0242] Table 3

[0243] From the data in the above tables, we can see that:

[0244] The secondary batteries of Examples 1 to 20 of the present application have high energy density, good cycle performance, and excellent overall performance. The primary particle size of the single-crystal-like positive electrode material in the positive electrode active material in Comparative Example 1 is not within the scope of this application; the positive electrode active material in Comparative Example 2 uses only agglomerated positive electrode materials, and does not use single-crystal-like positive electrode materials; the positive electrode active material in Comparative Example 3 uses only single-crystal-like positive electrode materials, and does not use agglomerated positive electrode materials. The overall performance of the secondary batteries of Examples 1 to 20 of the present application is significantly better than that of Comparative Examples 1, 2, and 3.

[0245] The primary difference between the secondary battery of Example 7 and Example 1 lies in the Dv50 of the quasi-single-crystal positive electrode material. The Dv50 of the quasi-single-crystal positive electrode material in Example 7 is 3.8, while the Dv50 of the quasi-single-crystal positive electrode material in Example 1 is 3. While the cycling performance of these secondary batteries is comparable, Example 1 has a higher energy density.

[0246] The primary difference between the secondary battery of Example 8 of the present application and Example 1 lies in the difference in the primary particle size of the quasi-single-crystal positive electrode material. The primary particle size of the quasi-single-crystal positive electrode material in Example 8 is 0.9, while the primary particle size of the quasi-single-crystal positive electrode material in Example 1 is 1.2. The energy density and cycle performance of the secondary battery of Example 1 are significantly improved compared to those of Example 8.

[0247] The secondary battery of Example 12 of the present application differs primarily from that of Example 1 in the mixing ratio of the agglomerate-type positive electrode material to the quasi-single-crystal positive electrode material. In Example 12, the mixing ratio of the agglomerate-type positive electrode material to the quasi-single-crystal positive electrode material is 8:2, while in Example 1, the mixing ratio is 7:3. The energy density and cycle performance of the secondary battery of Example 1 are significantly improved compared to those of Example 12.

[0248] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, comprising a positive electrode plate, wherein the positive electrode plate has a positive electrode active material, wherein the positive electrode active material comprises an aggregate type positive electrode material and a quasi-single crystal type positive electrode material; The volume average particle size Dv50 of the agglomerate type positive electrode material is 8 μm to 15 μm, and the primary particle size of the agglomerate type positive electrode material is 0.1 μm to 0.6 μm; The volume average particle size Dv50 of the quasi-single-crystal positive electrode material is 2.5 μm to 4 μm, and the primary particle size of the quasi-single-crystal positive electrode material is 0.8 μm to 2 μm; The mass ratio of the agglomerate-type positive electrode material to the quasi-single-crystal positive electrode material is greater than or equal to 1.

2. The secondary battery according to claim 1, It is characterized in that The mass ratio of the agglomerate-type positive electrode material to the quasi-single-crystal positive electrode material is 1 to 9:1, and can be optionally 2.3 to 3:

1.

3. The secondary battery according to claim 1 or 2, It is characterized in that The volume average particle size Dv50 of the quasi-single-crystal positive electrode material is 3 μm to 3.5 μm, and / or the primary particle size of the quasi-single-crystal positive electrode material is 1.2 μm to 1.5 μm.

4. The secondary battery according to any one of claims 1 to 3, It is characterized in that The primary particle size of the agglomerate-type positive electrode material is 0.2 μm to 0.4 μm.

5. The secondary battery according to any one of claims 1 to 4, It is characterized in that The chemical formula of the aggregate type positive electrode material is Li x1 Ni y1 Co z1 M 1-y1-z1 O 2 , wherein 0.9≤x1≤1, 0.9≤y1≤0.98, 0.05≤z1≤0.1, and M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg and Nb; Optionally, 0.9≤y1≤0.

96.

6. The secondary battery according to claim 5, It is characterized in that The chemical formula of the single-crystal-like positive electrode material is Li x2 Ni y2 Co z2 M′ 1-y2-z2 O 2 , wherein 0.9≤x2≤1, 0.9≤y2≤0.98, 0.05≤z2≤0.1, and M′ includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg and Nb; Optionally, 0.92≤y2≤0.

98.

7. The secondary battery according to claim 6, It is characterized in that y2>y1.

8. The secondary battery according to any one of claims 1 to 7, It is characterized in that The particle size distribution span of the agglomerate-type positive electrode material is (Dv90-Dv10) / Dv50≤1.5, and can be optionally 0.7 to 1.

4.

9. The secondary battery according to any one of claims 1 to 8, It is characterized in that The BET specific surface area of ​​the agglomerate-type positive electrode material is 0.2 m 2 / g~0.8m 2 / g; optional: 0.3m 2 / g~0.6m 2 / g.

10. The secondary battery according to any one of claims 1 to 9, It is characterized in that The particle size distribution span of the single-crystal-like positive electrode material is (Dv90-Dv10) / Dv50≥1.2, and can be optionally 1.3 to 1.

5.

11. The secondary battery according to any one of claims 1 to 10, It is characterized in that The BET specific surface area of ​​the single-crystal-like positive electrode material is 0.8 m 2 / g~1.3m 2 / g; optional: 0.85m 2 / g~1.15m 2 / g.

12. The secondary battery according to any one of claims 1 to 11, It is characterized in that The particle size distribution span of the positive electrode active material is (Dv90-Dv10) / Dv50 of 1.5 to 2.

1.

13. The secondary battery according to any one of claims 1 to 12, It is characterized in that The BET specific surface area of ​​the positive electrode active material is 0.5 m 2 / g~0.7m 2 / g.

14. The secondary battery according to any one of claims 1 to 13, It is characterized in that The mass percentage of the positive electrode active material in the positive electrode plate to the positive electrode film layer is 95% to 99.5%.

15. The secondary battery according to any one of claims 1 to 14, It is characterized in that The coating surface density of the positive electrode active material in the positive electrode sheet is 21.5 mg / cm 2 ~32.5mg / cm 2 .

16. The secondary battery according to any one of claims 1 to 15, It is characterized in that It also includes a negative electrode plate, on which a negative electrode active material is disposed, wherein the mass percentage of silicon-based material in the negative electrode active material is 20% to 100%.

17. An electrical device comprising the secondary battery according to any one of claims 1 to 16.

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