Secondary battery and electronic device

Abstract

The invention provides a secondary battery which comprises a positive pole piece, and the positive pole piece comprises a first positive pole material layer and a second positive pole material layer. The first positive electrode material layer comprises a first positive electrode active material and a first conductive agent, the first positive electrode active material comprises a first single crystal ternary material, the second positive electrode material layer comprises a second positive electrode active material and a second conductive agent, and the second positive electrode active material comprises a polycrystalline ternary material and a second single crystal ternary material; the second conductive agent includes a second zero-dimensional conductive material. Dv50 of the polycrystal ternary material is D1 [mu] m, Dv50 of the second single crystal ternary material is D2 [mu] m, Dv50 of the second zero-dimensional conductive material is D3 [mu] m, 5 < = D1 < = 30, 1 < = D2 < = 10, and 0.001 < = D3 < = 0.5. According to the present invention, the secondary battery meets the characteristics, such that the compaction density of the positive electrode plate can be improved while the secondary battery has good rate performance, and the energy density of the secondary battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and particularly relates to a secondary battery and an electronic device. BACKGROUND

[0002] With the exhaustion of fossil energy and the aggravation of environmental problems worldwide, constructing a green and sustainable new energy system has become a strategic direction of global scientific research. Under this background, lithium ion batteries have become an important pillar of new energy technology development due to their significant advantages of long cycle life, high energy density and strong environmental friendliness. At present, its application range has expanded from portable electronic products to new energy vehicle power systems and grid-level energy storage devices and other large-scale scenarios.

[0003] It is worth noting that as the "performance heart" of lithium ion batteries, the positive electrode material has a decisive influence on the upper limit of the energy density and the cycle life of the lithium ion battery. Among them, the ternary positive electrode material can provide higher specific capacity, and under the driving of the demand for high energy density of power batteries, it has become one of the most promising technical routes for industrialization. At present, ternary positive electrode materials can be divided into single-crystal ternary positive electrode materials and polycrystalline ternary positive electrode materials according to their morphology. Although the polycrystalline ternary positive electrode material can improve the rate performance of the lithium ion battery, the compaction density of the material is low; the secondary spherical particles are prone to structural collapse during the charging and discharging process and cause the lithium ion battery to produce gas. The single-crystal ternary positive electrode material has better cycle stability, but its production process is complex, the cost is high, and the rate performance is poor. SUMMARY

[0004] The purpose of the present application is to provide a secondary battery and an electronic device, which has good rate performance, and can also improve the compaction density of the positive electrode sheet and the energy density of the secondary battery. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides a secondary battery, which comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector, a first positive electrode material layer, and a second positive electrode material layer, the first positive electrode material layer being arranged between the positive electrode current collector and the second positive electrode material layer along the thickness direction of the positive electrode sheet. The first positive electrode material layer comprises a first positive electrode active material and a first conductive agent, the first positive electrode active material comprising a first single-crystal ternary material; the second positive electrode material layer comprises a second positive electrode active material and a second conductive agent, the second positive electrode active material comprising a polycrystalline ternary material and a second single-crystal ternary material, the second conductive agent comprising a second zero-dimensional conductive material. The Dv50 of the polycrystalline ternary material is D1 μm, the Dv50 of the second single-crystal ternary material is D2 μm, and the Dv50 of the second zero-dimensional conductive material is D3 μm, 5≤D1≤30, 1≤D2≤10, and 0.001≤D3≤0.5. Preferably, 0.05≤D3≤0.5. The secondary battery satisfies the above characteristics, and has good rate performance, and can improve the compaction density of the positive electrode sheet and the energy density of the secondary battery.

[0006] In one or more embodiments of the present application, D1>D2>D3. D1, D2, and D3 satisfy the above size relationship, which further improves the energy density of the secondary battery.

[0007] In one or more embodiments of the present application, 1≤D1 / D2≤10 and 5≤D2 / D3≤120. Preferably, 5≤D2 / D3≤20. By adjusting the values of D1 / D2 and D2 / D3 within the above ranges, the energy density of the secondary battery is further improved.

[0008] In one or more embodiments of the present application, the Dv50 of the first single-crystal ternary material is D4 μm, and 1≤D4≤10. By adjusting the value of D4 within the above range, the compaction density of the positive electrode sheet can be effectively improved, and the energy density of the secondary battery can be improved.

[0009] In one or more embodiments of the present application, the ratio of the maximum cross-sectional area of the particle of the first single-crystal ternary material to the maximum cross-sectional area of the minimum circumscribed sphere of the particle of the first single-crystal ternary material is S, and 0.9≤S≤1. By adjusting the value of S within the above range, the processing performance of the positive electrode sheet is further improved.

[0010] In one or more embodiments of the present application, at least one of the following features is satisfied: (1) the first single-crystal ternary material comprises a transition metal element, the transition metal element comprises a nickel element, a ratio of a molar amount of the nickel element in the first single-crystal ternary material to a total molar amount of the transition metal element in the first single-crystal ternary material is X1%, 50≤X1≤99, preferably, 85≤X1≤97; (2) the second single-crystal ternary material comprises a transition metal element, the transition metal element comprises a nickel element, a ratio of a molar amount of the nickel element in the second single-crystal ternary material to a total molar amount of the transition metal element in the second single-crystal ternary material is X2%, 50≤X2≤99, preferably, 85≤X2≤97; (3) the polycrystalline ternary material comprises a transition metal element, the transition metal element comprises a nickel element, a ratio of a molar amount of the nickel element in the polycrystalline ternary material to a total molar amount of the transition metal element in the polycrystalline ternary material is X3%, 50≤X3≤99, preferably, 85≤X3≤97.

[0011] In one or more embodiments of the present application, the first single-crystal ternary material, the second single-crystal ternary material are each independently selected from at least one of the following single-crystal materials: LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25 Mn 0.25 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.9 Co 0.05 Al 0.05 O2. The polycrystalline ternary material is selected from at least one of the following polycrystalline materials: LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25 Mn 0.25 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.9Co 0.05 Al 0.05 O2. By selecting the aforementioned first single-crystal ternary material, second single-crystal ternary material, and polycrystalline ternary material, the rate performance of secondary batteries can be improved.

[0012] In one or more embodiments of this application, the second zero-dimensional conductive material includes at least one of Super P, acetylene black, or Ketjen black. Using the aforementioned second zero-dimensional conductive material further improves the energy density of the secondary battery.

[0013] In one or more embodiments of this application, the oil absorption value of the second zero-dimensional conductive material is O2 mL / 100g, where 100≤O2≤500, preferably 150≤O2≤300. By adjusting the O2 value within the above range, the energy density and rate performance of the secondary battery are further improved.

[0014] In one or more embodiments of this application, the second conductive agent further includes a one-dimensional conductive material, which includes at least one of carbon nanotubes or carbon fibers. Using the aforementioned one-dimensional conductive material further improves the energy density of the secondary battery.

[0015] In one or more embodiments of this application, it satisfies at least one of the following features: (1) the diameter of the carbon nanotube is d1 nm, 1≤d1≤300, preferably, 5≤d1≤50; (2) the length of the carbon nanotube is L1 nm, 1000≤L1≤50000, preferably, 5000≤L1≤30000; (3) the diameter of the carbon nanotube is d1 nm, the length of the carbon nanotube is L1 nm, 50≤L1 / d1≤3000, preferably, 100≤L1 / d1≤1000; (4) the functional groups on the surface of the carbon nanotube include carboxyl groups, and the mass percentage of carboxyl groups is W% based on the mass of the carbon nanotube, 0.5≤W≤5.

[0016] In one or more embodiments of this application, it satisfies at least one of the following characteristics: (1) the diameter of the carbon fiber is d2 nm, 50≤d2≤200; (2) the length of the carbon fiber is L2 μm, 10≤L2≤50.

[0017] In one or more embodiments of this application, the first conductive agent comprises a first zero-dimensional conductive material and / or a two-dimensional conductive material. The first zero-dimensional conductive material comprises at least one of Super P, acetylene black, or Ketjen black, and the two-dimensional conductive material comprises graphene. Using the aforementioned first zero-dimensional conductive material and / or two-dimensional conductive material further improves the energy density of the secondary battery.

[0018] In one or more embodiments of the present application, at least one of the following characteristics is satisfied: (1) the Dv50 of the first zero-dimensional conductive material is D5 μm, 0.001≤D5≤0.5, preferably, 0.05≤D5≤0.5; (2) the oil absorption value of the first zero-dimensional conductive material is O1 mL / 100g, 100≤O1≤500, preferably, 150≤O1≤300.

[0019] In one or more embodiments of the present application, at least one of the following characteristics is satisfied: (1) the number of layers of the graphene is 1 layer to 8 layers; (2) the flake diameter of the graphene is G μm, 0.5≤G≤10; (3) the specific surface area of the graphene is B m 2 / g, 500≤B≤1500.

[0020] In one or more embodiments of the present application, the first positive electrode material layer further comprises a first binder, the mass percentage content of the first positive electrode active material is W 11 %, the mass percentage content of the first conductive agent is W 12 %, and the mass percentage content of the first binder is W 13 %, 90≤W 11 ≤99, 0.1≤W 12 ≤9.9, 0.1≤W 13 ≤9.9. By adjusting the values of W 11 , W 12 , and W 13 within the above ranges, the secondary battery has a higher energy density, and the secondary battery also has better rate performance.

[0021] In one or more embodiments of the present application, the first conductive agent comprises a first zero-dimensional conductive material and a two-dimensional conductive material, the first positive electrode material layer further comprises a first binder, the mass percentage content of the first positive electrode active material is W 11 %, the mass percentage content of the first zero-dimensional conductive material is W 121 %, the mass percentage content of the two-dimensional conductive material is W 122 %, and the mass percentage content of the first binder is W 13 %, 90≤W 11 ≤99, 0.05≤W 121 ≤5, 0.05≤W 122 ≤5, 0.1≤W 13 ≤9.9. By adjusting the values of W 11 , W 121 , W 122 , and W 13 within the above ranges, the secondary battery has a higher energy density, and the secondary battery also has better rate performance.

[0022] In one or more embodiments of the present application, the second positive electrode material layer further comprises a second binder, the mass percentage of the polycrystalline ternary material is W 211 %, the mass percentage of the second single-crystal ternary material is W 212 %, the mass percentage of the second conductive agent is W 22 %, the mass percentage of the second binder is W 23 %, 20≤W 211 ≤70, 20≤W 212 ≤70, 0.1≤W 22 ≤5, 0.1≤W 23 ≤5. By adjusting the values of W 211 , W 212 , W 22 , W 23 within the above ranges, the secondary battery has a higher energy density, and the secondary battery also has better rate performance.

[0023] In one or more embodiments of the present application, the second conductive agent further comprises a one-dimensional conductive material, the second positive electrode material layer further comprises a second binder, the mass percentage of the polycrystalline ternary material is W 211 %, the mass percentage of the second single-crystal ternary material is W 212 %, the mass percentage of the second zero-dimensional conductive material is W 221 %, the mass percentage of the one-dimensional conductive material is W 222 %, the mass percentage of the second binder is W 23 %, 20≤W 211 ≤70, 20≤W 212 ≤70, 0.1≤W 221 ≤5, 0.1≤W 222 ≤5, 0.1≤W 23 ≤5. By adjusting the values of W 211 , W 212 , W 221 , W 222 , W 23 within the above ranges, the secondary battery has a higher energy density, and the secondary battery also has better rate performance.

[0024] In one or more embodiments of the present application, the thickness of the first positive electrode material layer is H1 μm, 1≤H1≤200, preferably, 20≤H1≤50; and / or, the thickness of the second positive electrode material layer is H2 μm, 5≤H2≤200, preferably, 30≤H2≤100.

[0025] In one or more embodiments of the present application, H1≤H2. H1 and H2 satisfy the above size relationship, which can improve the rate performance and energy density of the secondary battery.

[0026] The second aspect of the present application provides an electronic device comprising the secondary battery in any of the foregoing embodiments. Therefore, the electronic device provided by the present application has good use performance.

[0027] Advantages of the present application:

[0028] The present application provides a secondary battery and an electronic device. The secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector, a first positive electrode material layer and a second positive electrode material layer, and along the thickness direction of the positive electrode sheet, the first positive electrode material layer is arranged between the positive electrode current collector and the second positive electrode material layer. The first positive electrode material layer comprises a first positive electrode active material and a first conductive agent, the first positive electrode active material comprises a first single-crystal ternary material, the second positive electrode material layer comprises a second positive electrode active material and a second conductive agent, the second positive electrode active material comprises a polycrystalline ternary material and a second single-crystal ternary material, and the second conductive agent comprises a second zero-dimensional conductive material. The Dv50 of the polycrystalline ternary material is D1 μm, the Dv50 of the second single-crystal ternary material is D2 μm, and the Dv50 of the second zero-dimensional conductive material is D3 μm, 5≤D1≤30, 1≤D2≤10, and 0.001≤D3≤0.5. The secondary battery satisfies the above characteristics, which can improve the rate performance of the secondary battery, and at the same time, can improve the compaction density of the positive electrode sheet and the energy density of the secondary battery.

[0029] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0031] Figure 1 Schematic diagram of the extrusion of the positive electrode active material with high irregularity in the prior art on the positive electrode current collector during cold pressing;

[0032] Figure 2 Schematic diagram of the extrusion of the first single-crystal ternary material with high regularity in the present application on the positive electrode current collector during cold pressing;

[0033] Figure 3 Schematic diagram of the structure of the positive electrode sheet in one embodiment of the present application;

[0034] Figure 4 This is a schematic diagram of the electrode assembly according to one embodiment of this application. Detailed Implementation

[0035] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0036] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0037] In existing technologies, for ease of understanding, a two-dimensional Cartesian coordinate system is established with the length direction of the unfolded positive electrode sheet as the X-direction and the thickness direction of the positive electrode sheet as the Z-direction. For example... Figure 1 As shown, if the positive active material 111 in the positive material layer that is in direct contact with the positive current collector 100 has high irregularity, when the positive electrode sheet passes through the cold pressing roller during cold pressing, the positive active material exerts a larger force F1 on the positive current collector in the Z direction and a smaller force F2 on the positive current collector in the X direction, which greatly increases the frequency of strip breakage of the positive current collector during cold pressing, resulting in poor processing performance of the positive electrode sheet.

[0038] On the other hand, generally, ternary positive electrode materials can be divided into single-crystal ternary positive electrode materials and polycrystal ternary positive electrode materials according to their morphology. The particles of the single-crystal ternary positive electrode materials are single continuous crystals, have no grain boundaries or sub-grain boundaries, have a complete polyhedral surface, and have no micro-cracks inside. The polycrystal ternary positive electrode materials are generally spherical or spherical-like secondary particles formed by aggregation of nanoscale primary small particles. Although the polycrystal ternary positive electrode materials can provide more grain boundaries, increase the lithium ion diffusion channel, accelerate the lithium ion transmission speed, and improve the rate performance of the secondary battery, there are also certain disadvantages. For example, because the polycrystal ternary positive electrode materials exist in the form of aggregates, the bulk density of the material is low, and thus the compaction density of the material is low. The secondary spherical particles will be broken under high compaction density, increase the specific surface area of the material, cause the increase of side reactions, and reduce the electrochemical performance of the secondary battery. Under long cycle conditions, the secondary spherical particles will be cracked along the grain boundaries, expose new surfaces, cause uncontrollable side reactions between the active centers and the electrolyte, and cause the structure collapse of the secondary spherical particles and the gas production of the secondary battery under high pressure conditions. In comparison, the single-crystal ternary positive electrode material particles have few defects and good uniformity, can form a relatively smooth and uniform surface, and have a small specific surface area of the single particle. The contact area between the material and the electrolyte is reduced, and the single-crystal ternary positive electrode material has better cycle stability. However, the production process of the single-crystal ternary positive electrode material is complex, the cost is high, and because the single-crystal ternary positive electrode material has relatively few grain boundaries, the diffusion path of lithium ions in the material is long, which causes the rate performance (i.e., the fast charging and discharging ability) of the single-crystal ternary positive electrode material to be poorer than that of the polycrystal ternary positive electrode material. This makes the single-crystal ternary positive electrode material perform poorly in high-power applications.

[0039] Therefore, based on the advantages and disadvantages of the single-crystal ternary positive electrode material and the polycrystal ternary positive electrode material, the present application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode current collector, a first positive electrode material layer, and a second positive electrode material layer. Along the thickness direction of the positive electrode sheet, the first positive electrode material layer is arranged between the positive electrode current collector and the second positive electrode material layer. The first positive electrode active material includes a first single-crystal ternary material, the second positive electrode active material includes a polycrystal ternary material and a second single-crystal ternary material, and the second conductive agent includes a second zero-dimensional conductive material. By adjusting the Dv50 of the polycrystal ternary material, the Dv50 of the second single-crystal ternary material, and the Dv50 of the second zero-dimensional conductive material within the range of the present application, the secondary battery has good rate performance, and the compaction density of the positive electrode sheet and the energy density of the secondary battery are improved.

[0040] The first aspect of the present application provides a secondary battery, which includes a positive electrode sheet, as follows: Figure 3As shown, the positive electrode tab 10 includes a positive current collector 100, a first positive electrode material layer 101, and a second positive electrode material layer 102. The first positive electrode material layer 101 is arranged between the positive current collector 100 and the second positive electrode material layer 102 along the thickness direction of the positive electrode tab 10, i.e., the Z direction. The first positive electrode material layer includes a first positive electrode active material and a first conductive agent, and the first positive electrode active material includes a first single-crystal ternary material. The second positive electrode material layer includes a second positive electrode active material and a second conductive agent, and the second positive electrode active material includes a polycrystalline ternary material and a second single-crystal ternary material, and the second conductive agent includes a second zero-dimensional conductive material. The Dv50 of the polycrystalline ternary material is D1 μm, the Dv50 of the second single-crystal ternary material is D2 μm, and the Dv50 of the second zero-dimensional conductive material is D3 μm. 5≤D1≤30, and the value of D1 can be 5, 7, 9, 10, 11, 13, 15, 17, 19, 20, 21, 23, 25, 27, 29, or a range formed by any two of the above values. 1≤D2≤10, and the value of D2 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, or a range formed by any two of the above values. 0.001≤D3≤0.5, and preferably, 0.05≤D3≤0.5, and the value of D3 can be 0.001, 0.005, 0.01, 0.03, 0.05, 0.07, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a range formed by any two of the above values. In some embodiments of the present application, the first positive electrode material layer and the second positive electrode material layer can be arranged on one surface of the positive current collector, and the first positive electrode material layer is arranged between the positive current collector and the second positive electrode material layer along the thickness direction of the positive electrode tab. Alternatively, the first positive electrode material layer and the second positive electrode material layer can be arranged on two surfaces of the positive current collector in sequence, and the first positive electrode material layer is arranged between the positive current collector and the second positive electrode material layer along the thickness direction of the positive electrode tab. For example, as shown in FIG. 1A, the first positive electrode material layer 101 is arranged on one surface of the positive current collector 100, and the second positive electrode material layer 102 is arranged on the other surface of the positive current collector 100. As shown in FIG. 1B, the first positive electrode material layer 101 is arranged on one surface of the positive current collector 100, and the second positive electrode material layer 102 is arranged on the other surface of the positive current collector 100. Figure 3 The present application is not particularly limited as long as the purpose of the present application can be achieved.

[0041] In the present application, Dv50 refers to the particle size reaching 50% of the volume accumulation in the particle size distribution of the material on the volume basis.

[0042] The inventors have found that when the positive electrode tab includes a positive current collector, a first positive electrode material layer, and a second positive electrode material layer, the first positive electrode material layer is arranged between the positive current collector and the second positive electrode material layer along the thickness direction of the positive electrode tab, and the second positive electrode active material in the upper second positive electrode material layer includes a polycrystalline ternary material and a second single-crystal ternary material, and the first positive electrode active material in the lower first positive electrode material layer includes a first single-crystal ternary material. The lower layer uses a first single-crystal ternary material with higher particle regularity, such as Figure 2As shown, the first single-crystal ternary material 1011 particle has high regularity, the positive electrode plate passes through the cold-pressing roller during cold-pressing, the first single-crystal ternary material has a smaller force F1 on the positive electrode current collector in the Z direction and a larger force F2 on the positive electrode current collector in the X direction, effectively reducing the damage of the cold-pressing process to the positive electrode current collector and improving the processing performance of the positive electrode plate. The second positive electrode material layer in the upper layer is in direct contact with the electrolyte, the upper layer uses a mixture of the polycrystal ternary material and the second single-crystal ternary material, the polycrystal ternary material can provide more grain boundaries, increase the lithium ion diffusion channel and accelerate the lithium ion transmission speed; at the same time, the polycrystal ternary material has small grains, increases the specific surface area of the polycrystal ternary material and further increases the contact area of the second positive electrode material layer and the electrolyte, which is beneficial to the rapid embedding and extraction of lithium ions, thereby improving the rate performance of the secondary battery; and the polycrystal ternary material, the second single-crystal ternary material and the second zero-dimensional conductive material in the upper layer are mixed, the particle grading method is used to improve the compaction density of the positive electrode plate, thereby improving the energy density of the secondary battery; in addition, the second zero-dimensional conductive material is selected to be used with the second positive electrode active material in the upper layer, which can achieve better conductive effect at a lower addition amount of the second conductive agent, thereby saving space, increasing the mass percentage content of the second positive electrode active material and further improving the energy density of the secondary battery. Therefore, the positive electrode plate includes a positive electrode current collector, a first positive electrode material layer and a second positive electrode material layer, along the thickness direction of the positive electrode plate, the first positive electrode material layer is arranged between the positive electrode current collector and the second positive electrode material layer; the first positive electrode active material includes the first single-crystal ternary material, the second positive electrode active material includes the polycrystal ternary material and the second single-crystal ternary material, and the second conductive agent includes the second zero-dimensional conductive material; and by adjusting the Dv50 of the polycrystal ternary material, the Dv50 of the second single-crystal ternary material and the Dv50 of the second zero-dimensional conductive material within the range of the present application, the secondary battery has good rate performance, the compaction density of the positive electrode plate is further improved, and the energy density of the secondary battery is further improved.

[0043] In one or more embodiments of the present application, D1>D2>D3. D1, D2 and D3 satisfy the above size relationship, the polycrystal ternary material, the second single-crystal ternary material and the second zero-dimensional conductive material in the second positive electrode material layer are mixed, the particle grading method is used to further improve the compaction density of the positive electrode plate, thereby further improving the energy density of the secondary battery.

[0044] In one or more embodiments of the present application, 1≤D1 / D2≤10, for example, the value of D1 / D2 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range consisting of any two of the aforementioned values; 5≤D2 / D3≤120, preferably 5≤D2 / D3≤20, for example, the value of D2 / D3 can be 5, 7, 9, 10, 13, 15, 17, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, or a range consisting of any two of the aforementioned values. By adjusting the values of D1 / D2 and D2 / D3 within the above ranges, the particle sizes of the polycrystalline ternary material, the second single-crystal ternary material, and the second zero-dimensional conductive material are matched, the particle grading is better achieved, the compaction density of the positive electrode sheet is further improved, and thus the energy density of the secondary battery is further improved.

[0045] In one or more embodiments of the present application, the Dv50 of the first single-crystal ternary material is D4 μm, and 1≤D4≤10. For example, the value of D4 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range consisting of any two of the aforementioned values. By adjusting the value of D4 within the above range, the compaction density of the positive electrode sheet can be effectively improved, and the energy density of the secondary battery can be improved.

[0046] In one or more embodiments of the present application, the ratio of the maximum cross-sectional area of the particle of the first single-crystal ternary material to the maximum cross-sectional area of the smallest circumscribed sphere of the particle of the first single-crystal ternary material is S, and 0.9≤S≤1. For example, the value of S can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or a range consisting of any two of the aforementioned values. The ratio S of the maximum cross-sectional area of the particle of the first single-crystal ternary material to the maximum cross-sectional area of the smallest circumscribed sphere of the particle of the first single-crystal ternary material can reflect the regularity of the particle of the first single-crystal ternary material, also known as sphericity. The closer the value of S is to 1, the closer the particle is to a sphere, and the smoother the surface is. By adjusting the value of S within the above range, the regularity of the particle of the first single-crystal ternary material is higher. When the positive electrode sheet passes through the cold-pressing roller during cold-pressing, the force F1 of the first single-crystal ternary material on the positive electrode current collector in the Z direction is smaller, and the force F2 of the first single-crystal ternary material on the positive electrode current collector in the X direction is larger, further reducing the damage to the positive electrode current collector in the cold-pressing process and further improving the processability of the positive electrode sheet.

[0047] In one or more embodiments of the present application, the first single-crystal ternary material includes transition metal elements, the transition metal elements include nickel elements, the ratio of the amount of substance of the nickel elements in the first single-crystal ternary material to the total amount of substance of the transition metal elements in the first single-crystal ternary material is X1%, 50≤X1≤99, preferably 85≤X1≤97, and exemplarily the value of X1 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above-mentioned values. In the present application, the transition metal elements also include cobalt elements and manganese elements. By adjusting the value of X1 within the above-mentioned range, the content of nickel elements in the first single-crystal ternary material is relatively high, which can improve the specific capacity of the first single-crystal ternary material and increase the mass energy density of the secondary battery, thereby supporting longer endurance.

[0048] In one or more embodiments of the present application, the second single-crystal ternary material includes transition metal elements, the transition metal elements include nickel elements, the ratio of the amount of substance of the nickel elements in the second single-crystal ternary material to the total amount of substance of the transition metal elements in the second single-crystal ternary material is X2%, 50≤X2≤99, preferably 85≤X2≤97, and exemplarily the value of X2 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above-mentioned values. By adjusting the value of X2 within the above-mentioned range, the content of nickel elements in the second single-crystal ternary material is relatively high, which can improve the specific capacity of the second single-crystal ternary material, and the single-crystal structure reduces the grain boundaries and micro-cracks, thereby reducing the structural stress during the charging and discharging process and improving the cycle life of the secondary battery.

[0049] In one or more embodiments of the present application, the polycrystal ternary material includes transition metal elements, the transition metal elements include nickel elements, the ratio of the amount of substance of the nickel elements in the polycrystal ternary material to the total amount of substance of the transition metal elements in the polycrystal ternary material is X3%, 50≤X3≤99, preferably 85≤X3≤97, and exemplarily the value of X3 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above-mentioned values. By adjusting the value of X3 within the above-mentioned range, the content of nickel elements in the polycrystal ternary material is relatively high, which can effectively improve the mass energy density of the secondary battery, and the polycrystal ternary material is a spherical or spherical-like secondary particle formed by aggregation of nanoscale primary small particles, thereby providing a larger specific surface area and a shorter lithium ion diffusion path, which can enable the secondary battery to have longer endurance and better rate performance.

[0050] In one or more embodiments of the present application, the first single-crystal ternary material includes transition metal elements, the transition metal elements include nickel elements, the ratio of the amount of substance of the nickel elements in the first single-crystal ternary material to the total amount of substance of the transition metal elements in the first single-crystal ternary material is X1%, 50≤X1≤99, preferably, 85≤X1≤97, and exemplarily, the value of X1 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above-mentioned values. And, the second single-crystal ternary material includes transition metal elements, the transition metal elements include nickel elements, the ratio of the amount of substance of the nickel elements in the second single-crystal ternary material to the total amount of substance of the transition metal elements in the second single-crystal ternary material is X2%, 50≤X2≤99, preferably, 85≤X2≤97, and exemplarily, the value of X2 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above-mentioned values. By adjusting the values of X1 and X2 within the above-mentioned range, the content of nickel elements in the first single-crystal ternary material and the second single-crystal ternary material is high, which can reduce the dependence on cobalt elements and reduce the cost of the positive electrode material; at the same time, the nickel (Ni 2+ / Ni 4+ ) redox couple provides the main capacity, and the increase of the content of nickel elements can increase the number of de-intercalation ions and the lithium ion transmission speed, thereby improving the rate performance of the secondary battery.

[0051] In one or more embodiments of the present application, the first single-crystal ternary material includes transition metal elements, the transition metal elements include nickel elements, the ratio of the amount of substance of the nickel elements in the first single-crystal ternary material to the total amount of substance of the transition metal elements in the first single-crystal ternary material is X1%, 50≤X1≤99, preferably, 85≤X1≤97, and exemplarily, the value of X1 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above-mentioned values. And, the polycrystalline ternary material includes transition metal elements, the transition metal elements include nickel elements, the ratio of the amount of substance of the nickel elements in the polycrystalline ternary material to the total amount of substance of the transition metal elements in the polycrystalline ternary material is X3%, 50≤X3≤99, preferably, 85≤X3≤97, and exemplarily, the value of X3 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above-mentioned values. By adjusting the values of X1 and X3 within the above-mentioned range, the content of nickel elements in the first single-crystal ternary material and the polycrystalline ternary material is high, which can reduce the dependence on cobalt elements and reduce the cost of the positive electrode material; at the same time, the nickel (Ni 2+ / Ni 4+) The redox couple provides the main capacity, and the increased content of the nickel element can increase the number of extractable ions and the lithium ion transmission speed, thereby improving the rate performance of the secondary battery.

[0052] In one or more embodiments of the present application, the second single-crystal ternary material includes a transition metal element, the transition metal element includes a nickel element, and the ratio of the amount of substance of the nickel element in the second single-crystal ternary material to the total amount of substance of the transition metal element in the second single-crystal ternary material is X2%, 50≤X2≤99, preferably 85≤X2≤97, and exemplarily the value of X2 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above values. In addition, the polycrystalline ternary material includes a transition metal element, the transition metal element includes a nickel element, and the ratio of the amount of substance of the nickel element in the polycrystalline ternary material to the total amount of substance of the transition metal element in the polycrystalline ternary material is X3%, 50≤X3≤99, preferably 85≤X3≤97, and exemplarily the value of X3 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above values. By adjusting the values of X2 and X3 within the above range, the content of the nickel element in the second single-crystal ternary material and the polycrystalline ternary material is high, which can reduce the dependence on the cobalt element and reduce the cost of the positive electrode material. At the same time, the nickel (Ni 2+ / Ni 4+ ) The redox couple provides the main capacity, and the increased content of the nickel element can increase the number of extractable ions and the lithium ion transmission speed, thereby improving the rate performance of the secondary battery.

[0053] In one or more embodiments of the present application, the first single-crystal ternary material comprises transition metal elements, the transition metal elements comprise nickel elements, the ratio of the amount of substance of the nickel elements in the first single-crystal ternary material to the total amount of substance of the transition metal elements in the first single-crystal ternary material is X1%, 50≤X1≤99, preferably 85≤X1≤97, and exemplarily the value of X1 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above-mentioned values. And, the second single-crystal ternary material comprises transition metal elements, the transition metal elements comprise nickel elements, the ratio of the amount of substance of the nickel elements in the second single-crystal ternary material to the total amount of substance of the transition metal elements in the second single-crystal ternary material is X2%, 50≤X2≤99, preferably 85≤X2≤97, and exemplarily the value of X2 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above-mentioned values. And, the polycrystalline ternary material comprises transition metal elements, the transition metal elements comprise nickel elements, the ratio of the amount of substance of the nickel elements in the polycrystalline ternary material to the total amount of substance of the transition metal elements in the polycrystalline ternary material is X3%, 50≤X3≤99, preferably 85≤X3≤97, and exemplarily the value of X3 can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 99 or a range consisting of any two of the above-mentioned values. By adjusting the values of X1, X2 and X3 within the above-mentioned ranges, the content of nickel elements in the first single-crystal ternary material, the second single-crystal ternary material and the polycrystalline ternary material is relatively high, which can reduce the dependence on cobalt elements and further reduce the cost of the positive electrode material; at the same time, the nickel (Ni 2+ / Ni 4 + ) redox couple provides the main capacity, and the increase of the content of nickel elements can further improve the number of de-intercalation ions and the speed of lithium ion transmission, thereby further improving the rate performance of the secondary battery.

[0054] In one or more embodiments of the present application, the first single-crystal ternary material and the second single-crystal ternary material are each independently selected from at least one of the following single-crystal materials: LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25 Mn 0.25 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co0.05 Mn 0.05 O2, LiNi 0.9 Co 0.05 Al 0.05 O2. The polycrystalline ternary material is selected from at least one of the following polycrystalline materials: LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25 Mn 0.25 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.9 Co 0.05 Al 0.05 O2. The above-mentioned first single-crystal ternary material, the second single-crystal ternary material and the polycrystalline ternary material are selected, the ratio of the amount of substance of nickel element to the total amount of substance of transition metal elements in the above-mentioned materials is high, the content of nickel element is high, the dependence on cobalt element can be reduced, and the cost of the positive electrode material can be reduced; at the same time, the nickel (Ni 2+ / Ni 4+ ) redox couple provides main capacity, the increase of the content of nickel element can increase the number of deintercalation ions and the lithium ion transmission speed, and the rate performance of the secondary battery can be improved.

[0055] In one or more embodiments of the present application, the second zero-dimensional conductive material includes at least one of Super P, acetylene black or Ketjen black. The above-mentioned second zero-dimensional conductive material is selected, the above-mentioned substance can better coat the second single-crystal ternary material with smooth and uniform surface, the second zero-dimensional conductive material can be better matched with the second positive electrode active material, the second conductive agent can achieve better conductivity effect at a lower addition amount, thereby saving space, improving the mass percentage content of the second positive electrode active material, and further improving the energy density of the secondary battery.

[0056] In one or more embodiments of the present application, the oil absorption value of the second zero-dimensional conductive material is O2 mL / 100 g, 100≤O2≤500, preferably 150≤O2≤300. Exemplarily, the value of O2 can be 100, 130, 150, 170, 200, 230, 250, 270, 300, 330, 350, 370, 400, 430, 450, 470, 500 or a range formed by any two of the above values. By adjusting the value of O2 within the above range, the dispersibility of the second zero-dimensional conductive material is better, which is conducive to the construction of the conductive network in the second positive electrode material layer, conducive to electron transmission, and can make the second conductive agent achieve better conductivity effect at a lower addition amount, thereby saving space, increasing the mass percentage content of the second positive electrode active material, and further improving the energy density of the secondary battery; meanwhile, it can also improve the liquid retention capacity of the positive electrode sheet, which is conducive to lithium ion transmission and further improves the rate performance of the secondary battery.

[0057] In one or more embodiments of the present application, the second conductive agent further comprises a one-dimensional conductive material, and the one-dimensional conductive material comprises at least one of carbon nanotubes or carbon fibers. In the present application, the carbon nanotubes can include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes; and the carbon fibers can include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The second conductive agent further comprises a one-dimensional conductive material, and the use of the above one-dimensional conductive material has a more excellent effect of coating the relatively rough surface of the polycrystalline ternary material, and the one-dimensional conductive material can be better used with the second positive electrode active material, which can make the second conductive agent achieve better conductivity effect at a lower addition amount, thereby saving space, increasing the mass percentage content of the second positive electrode active material, and further improving the energy density of the secondary battery.

[0058] In one or more embodiments of the present application, the diameter of the carbon nanotube is d1 nm, 1≤d1≤300, preferably 5≤d1≤50, and exemplarily, the value of d1 can be 1, 3, 5, 7, 9, 10, 20, 30, 40, 50, 70, 100, 130, 150, 170, 200, 230, 250, 270, 300 or a range formed by any two of the above values. By adjusting the value of d1 within the above range, the dispersibility of the carbon nanotube is better, which makes the positive electrode slurry have better processing performance, is conducive to the construction of the conductive network in the second positive electrode material layer, conducive to electron transmission, and can make the second conductive agent achieve better conductivity effect at a lower addition amount, thereby saving space, increasing the mass percentage content of the second positive electrode active material, and further improving the energy density of the secondary battery.

[0059] In one or more embodiments of the present application, the length of the carbon nanotube is L1 nm, 1000≤L1≤50000, preferably, 5000≤L1≤30000, and exemplarily, the value of L1 can be 1000, 5000, 10000, 15000, 20000, 25000, 30000, 35000, 40000, 45000, 50000, or a range between any two of the above values. By adjusting the value of L1 within the above range, the dispersibility of the carbon nanotube is better, which makes the positive electrode slurry have better processing performance, and is conducive to the construction of the conductive network in the second positive electrode material layer, is conducive to electron transmission, can make the second conductive agent achieve better conductivity effect at a lower addition amount, thereby saving space, increasing the mass percentage content of the second positive electrode active material, and further improving the energy density of the secondary battery.

[0060] In one or more embodiments of the present application, the diameter of the carbon nanotube is d1 nm, the length of the carbon nanotube is L1 nm, and 50≤L1 / d1≤3000, preferably, 100≤L1 / d1≤1000, and exemplarily, the value of L1 / d1 can be 50, 100, 300, 500, 700, 900, 1000, 1300, 1500, 1700, 1900, 2000, 2500, 3000, or a range between any two of the above values. By adjusting the value of L1 / d1 within the above range, the dispersibility of the carbon nanotube is better, which makes the positive electrode slurry have better processing performance, and is more conducive to the construction of the conductive network in the second positive electrode material layer, is conducive to electron transmission, can make the second conductive agent achieve better conductivity effect at a lower addition amount, thereby saving space, increasing the mass percentage content of the second positive electrode active material, and further improving the energy density of the secondary battery.

[0061] In one or more embodiments of the present application, the functional groups on the surface of the carbon nanotube include carboxyl groups (-COOH), and the mass percentage content of the carboxyl groups is W% based on the mass of the carbon nanotube, 0.5≤W≤5, and exemplarily, the value of W can be 0.5, 0.7, 1, 1.5, 1.7, 2, 2.5, 2.7, 3, 3.5, 3.7, 4, 4.5, 4.7, 5, or a range between any two of the above values. The functional groups on the surface of the carbon nanotube include carboxyl groups, and by adjusting the value of W within the above range, the dispersibility of the carbon nanotube can be better, which makes the positive electrode slurry have better processing performance, is conducive to the construction of the conductive network in the second positive electrode material layer, is conducive to electron transmission, can make the second conductive agent achieve better conductivity effect at a lower addition amount, thereby saving space, increasing the mass percentage content of the second positive electrode active material, and further improving the energy density of the secondary battery.

[0062] In one or more embodiments of the present application, the carbon fiber has a diameter of d2 nm, 50≤d2≤200, and exemplary values of d2 can be 50, 70, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, or a range defined by any two of the aforementioned values. By adjusting the value of d2 within the above range, the carbon fiber has good dispersibility, the positive electrode slurry has good processability, the conductive network in the second positive electrode material layer is built, electron transmission is facilitated, the second conductive agent can achieve better conductivity at a lower addition amount, thereby saving space, increasing the mass percentage of the second positive electrode active material, and further improving the energy density of the secondary battery.

[0063] In one or more embodiments of the present application, the carbon fiber has a length of L2 μm, 10≤L2≤50, and exemplary values of L2 can be 10, 15, 20, 25, 30, 35, 40, 45, 50, or a range defined by any two of the aforementioned values. By adjusting the value of L2 within the above range, the carbon fiber has good dispersibility, the positive electrode slurry has good processability, the conductive network in the second positive electrode material layer is built, electron transmission is facilitated, the second conductive agent can achieve better conductivity at a lower addition amount, thereby saving space, increasing the mass percentage of the second positive electrode active material, and further improving the energy density of the secondary battery.

[0064] In one or more embodiments of the present application, the first conductive agent comprises a first zero-dimensional conductive material and / or a two-dimensional conductive material, the first zero-dimensional conductive material comprises at least one of Super P, acetylene black, or Ketjen black, and the two-dimensional conductive material comprises graphene. The first conductive agent comprises the first zero-dimensional conductive material and / or the two-dimensional conductive material, and the first zero-dimensional conductive material and / or the two-dimensional conductive material is selected to better coat the first single-crystal ternary material with a smooth and uniform surface. The first conductive agent can be better matched with the first positive electrode active material, the first conductive agent can achieve better conductivity at a lower addition amount, thereby saving space, increasing the mass percentage of the first positive electrode active material, and further improving the energy density of the secondary battery.

[0065] In one or more embodiments of the present application, the Dv50 of the first zero-dimensional conductive material is D5 μm, 0.001≤D5≤0.5, preferably 0.05≤D5≤0.5, and exemplarily the value of D5 can be 0.001, 0.005, 0.01, 0.03, 0.05, 0.07, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or a range between any two of the above values. By adjusting the value of D5 within the above range, the particle size of the first zero-dimensional conductive material matches the particle size of the first single-crystal ternary material, the first zero-dimensional conductive material can better coat the first single-crystal ternary material with a smooth and uniform surface, the first conductive agent can be better matched with the first positive electrode active material, and the first conductive agent can achieve better conductivity at a lower addition amount, thereby saving space, increasing the mass percentage of the first positive electrode active material, and further improving the energy density of the secondary battery.

[0066] In one or more embodiments of the present application, the oil absorption value of the first zero-dimensional conductive material is O1 mL / 100g, 100≤O1≤500, preferably 150≤O1≤300, and exemplarily the value of O1 can be 100, 130, 150, 170, 200, 230, 250, 270, 300, 330, 350, 370, 400, 430, 450, 470, 500 or a range between any two of the above values. By adjusting the value of O1 within the above range, the first zero-dimensional conductive material has good dispersibility, which is conducive to the construction of the conductive network in the first positive electrode material layer, conducive to electron transmission, and enables the first conductive agent to achieve better conductivity at a lower addition amount, thereby saving space, increasing the mass percentage of the first positive electrode active material, and further improving the energy density of the secondary battery. At the same time, it can also improve the liquid retention capacity of the positive electrode sheet, which is conducive to lithium ion transmission and further improves the rate performance of the secondary battery.

[0067] In one or more embodiments of the present application, the number of layers of graphene is 1 to 8 layers, and exemplarily the number of layers of graphene can be 1 layer, 2 layers, 3 layers, 4 layers, 5 layers, 6 layers, 7 layers, 8 layers or a range between any two of the above values. By adjusting the number of layers of graphene within the above range, the graphene has good conductivity, which is conducive to the construction of the conductive network in the first positive electrode material layer, conducive to electron transmission, and enables the first conductive agent to achieve better conductivity at a lower addition amount, thereby saving space, increasing the mass percentage of the first positive electrode active material, and further improving the energy density of the secondary battery.

[0068] In one or more embodiments of the present application, the graphene has a sheet diameter of G μm, 0.5≤G≤10, and exemplary values of G can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or a range defined by any two of the aforementioned values. By adjusting the value of G within the aforementioned range, the graphene can have both good dispersibility and long-range conductivity, so that the positive electrode slurry has good processability, and the conductive network in the first positive electrode material layer can be built, which is conducive to electron transport, and the first conductive agent can achieve better conductivity at a lower addition amount, thereby saving space, increasing the mass percentage of the first positive electrode active material, and further improving the energy density of the secondary battery.

[0069] In one or more embodiments of the present application, the graphene has a specific surface area of B m 2 / g, 500≤B≤1500, and exemplary values of B can be 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, or a range defined by any two of the aforementioned values. By adjusting the value of B within the aforementioned range, the graphene has a suitable specific surface area, which can enable the graphene to have good contact with the first positive electrode active material, and the graphene can be better matched with the first positive electrode active material, which can enable the first conductive agent to achieve better conductivity at a lower addition amount, thereby saving space, increasing the mass percentage of the first positive electrode active material, and further improving the energy density of the secondary battery.

[0070] In one or more embodiments of the present application, the first positive electrode material layer further comprises a first binder, and the mass percentage of the first positive electrode active material is W 11 %, the mass percentage of the first conductive agent is W 12 %, and the mass percentage of the first binder is W 13 %, 90≤W 11 ≤99, and exemplary values of W 11 may be 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or a range defined by any two of the aforementioned values; 0.1≤W 12 ≤9.9, and exemplary values of W 12 may be 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9.9, or a range defined by any two of the aforementioned values; 0.1≤W 13 ≤9.9, and exemplary values of W 13 may be 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9.9, or a range defined by any two of the aforementioned values. By adjusting the value of W11 , W 12 , W 13 , W 11 , W 121 , W 122 , W 13 , W 11 , W 11 , W 121 , W 121 , W 122 , W 122 , W 13 , W 13 , W 11 , W 121 , W 122 , W 13 , W

[0071] The first binder is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, the first binder can include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, polyamide-imide, styrene butadiene rubber or polyvinylidene fluoride.

[0072] In one or more embodiments of the present application, the first conductive agent includes a first zero-dimensional conductive material and a two-dimensional conductive material, the first positive electrode material layer further includes a first binder, the mass percentage of the first positive electrode active material is W 11 %, the mass percentage of the first zero-dimensional conductive material is W 121 %, the mass percentage of the two-dimensional conductive material is W 122 %, and the mass percentage of the first binder is W 13 %, 90≤W 11 ≤99, for example, W 11 may be 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or a range composed of any two of the above values; 0.05≤W 121 ≤5, for example, W 121 may be 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range composed of any two of the above values; 0.05≤W 122 ≤5, for example, W 122 may be 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range composed of any two of the above values; 0.1≤W 13 ≤9.9, for example, W 13 may be 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9.9 or a range composed of any two of the above values. By adjusting the value of W 11 , W 121 , W 122 , W 13 , the mass percentage of the first positive electrode active material in the first positive electrode material layer is higher, the secondary battery has a higher energy density, and the secondary battery also has better rate performance.

[0073] In one or more embodiments of the present application, the second positive electrode material layer further comprises a second binder, the mass percentage of the polycrystalline ternary material is W 211 %, the mass percentage of the second single-crystal ternary material is W 212 %, the mass percentage of the second conductive agent is W 22 %, the mass percentage of the second binder is W 23 %, 20≤W 211 ≤70, and exemplary values of W 211 may be 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 or a range defined by any two of the above values; 20≤W 212 ≤70, and exemplary values of W 212 may be 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 or a range defined by any two of the above values; 0.1≤W 22 ≤5, and exemplary values of W 22 may be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range defined by any two of the above values; 0.1≤W 23 ≤5, and exemplary values of W 23 may be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range defined by any two of the above values. By adjusting the values of W 211 , W 212 , W 22 , W 23 , the mass percentage of the second positive electrode active material in the second positive electrode material layer is higher, the secondary battery has a higher energy density, and the secondary battery also has better rate performance.

[0074] The second binder is not particularly limited in the present application, as long as it can achieve the purpose of the present application. For example, the second binder can include at least one of the above-mentioned first binders.

[0075] In one or more embodiments of the present application, the second conductive agent further comprises a one-dimensional conductive material, the second positive electrode material layer further comprises a second binder, the mass percentage of the polycrystalline ternary material is W 211 %, the mass percentage of the second single-crystal ternary material is W 212 %, the mass percentage of the second zero-dimensional conductive material is W 221 %, the mass percentage of the one-dimensional conductive material is W 222 %, the mass percentage of the second binder is W 23 %, 20≤W211 ≤70, exemplary, W 211 The value of W can be 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 or a range between any two of the above values; 20≤W 212 ≤70, exemplary, W 212 The value of W can be 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 or a range between any two of the above values; 0.1≤W 221 ≤5, exemplary, W 221 The value of W can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range between any two of the above values; 0.1≤W 222 ≤5, exemplary, W 222 The value of W can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range between any two of the above values; 0.1≤W 23 ≤5, exemplary, W 23 The value of W can be 0.1, 0.3, 0.5, 0.7, 0.9, 1, 1.3, 1.5, 1.7, 1.9, 2, 2.3, 2.5, 2.7, 2.9, 3, 3.5, 4, 4.5, 5 or a range between any two of the above values. By adjusting the value of W 211 , W 212 , W 221 , W 222 , W 23 The value of W is within the above range, the mass percentage of the second positive active material in the second positive material layer is higher, the secondary battery has higher energy density, and the secondary battery also has better rate performance.

[0076] In one or more embodiments of the present application, the thickness of the first positive material layer is H1 μm, 1≤H1≤200, preferably, 20≤H1≤50, exemplary, the value of H1 can be 1, 3, 5, 7, 10, 13, 15, 17, 20, 25, 30, 35, 40, 45, 50, 70, 90, 100, 150, 170, 190, 200 or a range between any two of the above values. The above "thickness of the first positive material layer" refers to the thickness of the first positive material layer after coating. By adjusting the value of H1 within the above range, the thickness of the first positive material layer is relatively appropriate, so that the secondary battery has higher volume energy density.

[0077] In one or more embodiments of the present application, the thickness of the second positive electrode material layer is H2μm, 5≤H2≤200, preferably 30≤H2≤100, and exemplarily the value of H2 can be 5, 7, 10, 15, 17, 20, 25, 27, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 150, 170, 200 or a range between any two of the above values. The "thickness of the second positive electrode material layer" refers to the thickness of the second positive electrode material layer after coating. By adjusting the value of H2 within the above range, the thickness of the second positive electrode material layer is relatively appropriate, so that the secondary battery has a higher volumetric energy density.

[0078] In one or more embodiments of the present application, the thickness of the first positive electrode material layer is H1μm, 1≤H1≤200, preferably 20≤H1≤50, and exemplarily the value of H1 can be 1, 3, 5, 7, 10, 13, 15, 17, 20, 25, 30, 35, 40, 45, 50, 70, 90, 100, 150, 170, 190, 200 or a range between any two of the above values. And, the thickness of the second positive electrode material layer is H2μm, 5≤H2≤200, preferably 30≤H2≤100, and exemplarily the value of H2 can be 5, 7, 10, 15, 17, 20, 25, 27, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 150, 170, 200 or a range between any two of the above values. By adjusting the values of H1 and H2 within the above ranges, the thicknesses of the first positive electrode material layer and the second positive electrode material layer are relatively appropriate, so that the secondary battery has a higher volumetric energy density.

[0079] In one or more embodiments of the present application, H1≤H2. H1 and H2 satisfy the above size relationship, the thickness of the second positive electrode material layer is relatively large, the mass percentage content of the polycrystalline ternary material is high, the polycrystalline ternary material can provide more grain boundaries, increase the lithium ion diffusion channel, speed up the lithium ion transmission speed, and can improve the rate performance of the secondary battery; and the polycrystalline ternary material, the second single-crystal ternary material and the second zero-dimensional conductive material in the second positive electrode material layer are mixed, the particle grading method is used to improve the compaction density of the positive electrode sheet, thereby improving the energy density of the secondary battery.

[0080] The application does not have special restrictions on the method for regulating the Dv50 of the polycrystalline ternary material, the second monocrystalline ternary material, and the first monocrystalline ternary material, as long as the purpose of the application can be achieved. Illustratively, the Dv50 of the polycrystalline ternary material, the second monocrystalline ternary material, and the first monocrystalline ternary material can be regulated by grinding the polycrystalline ternary material, the second monocrystalline ternary material, and the first monocrystalline ternary material. For example, the Dv50 of the polycrystalline ternary material, the second monocrystalline ternary material, and the first monocrystalline ternary material can be regulated by regulating the grinding time. Illustratively, when other conditions are unchanged, the Dv50 of the polycrystalline ternary material decreases as the grinding time is extended; the Dv50 of the polycrystalline ternary material increases as the grinding time is shortened. Illustratively, when other conditions are unchanged, the Dv50 of the second monocrystalline ternary material decreases as the grinding time is extended; the Dv50 of the second monocrystalline ternary material increases as the grinding time is shortened. Illustratively, when other conditions are unchanged, the Dv50 of the first monocrystalline ternary material decreases as the grinding time is extended; the Dv50 of the first monocrystalline ternary material increases as the grinding time is shortened.

[0081] The application does not have special restrictions on the method for regulating the Dv50 of the second zero-dimensional conductive material and the first zero-dimensional conductive material, as long as the purpose of the application can be achieved. Illustratively, the Dv50 of the second zero-dimensional conductive material and the first zero-dimensional conductive material can be regulated by grinding the second zero-dimensional conductive material and the first zero-dimensional conductive material. For example, the Dv50 of the second zero-dimensional conductive material and the first zero-dimensional conductive material can be regulated by regulating the grinding time. Illustratively, when other conditions are unchanged, the Dv50 of the second zero-dimensional conductive material decreases as the grinding time is extended; the Dv50 of the second zero-dimensional conductive material increases as the grinding time is shortened. Illustratively, when other conditions are unchanged, the Dv50 of the first zero-dimensional conductive material decreases as the grinding time is extended; the Dv50 of the first zero-dimensional conductive material increases as the grinding time is shortened.

[0082] The application does not have special restrictions on the method for regulating D1 / D2, as long as the purpose of the application can be achieved. For example, the value of D1 / D2 can be regulated by regulating the value of D1 and D2 respectively, and the regulation method is as described above.

[0083] The application does not have special restrictions on the method for regulating D2 / D3, as long as the purpose of the application can be achieved. For example, the value of D2 / D3 can be regulated by regulating the value of D2 and D3 respectively, and the regulation method is as described above.

[0084] The application does not have special restrictions on the method for regulating the value of S, as long as the purpose of the application can be achieved. Illustratively, the value of S can be regulated by grinding the first monocrystalline ternary material with a planetary ball mill.

[0085] The application does not have special restrictions on the way to regulate the value of X1, as long as the purpose of the application can be achieved. Illustratively, during the synthesis of the first single-crystal ternary material, the value of X1 can be regulated by controlling the molar ratio of the precursor raw materials (such as nickel salt, cobalt salt, manganese salt or aluminum salt).

[0086] The application does not have special restrictions on the way to regulate the value of X2, as long as the purpose of the application can be achieved. Illustratively, during the synthesis of the second single-crystal ternary material, the value of X2 can be regulated by controlling the molar ratio of the precursor raw materials (such as nickel salt, cobalt salt, manganese salt or aluminum salt).

[0087] The application does not have special restrictions on the way to regulate the value of X3, as long as the purpose of the application can be achieved. Illustratively, during the synthesis of the polycrystalline ternary material, the value of X3 can be regulated by controlling the molar ratio of the precursor raw materials (such as nickel salt, cobalt salt, manganese salt or aluminum salt).

[0088] The application does not have special restrictions on the way to regulate the value of O2, as long as the purpose of the application can be achieved. Illustratively, the value of O2 can be regulated by regulating the branching degree, primary particle size or aggregation degree of the second zero-dimensional conductive material.

[0089] The application does not have special restrictions on the way to regulate the value of O1, as long as the purpose of the application can be achieved. Illustratively, the value of O1 can be regulated by regulating the branching degree, primary particle size or aggregation degree of the first zero-dimensional conductive material.

[0090] The application does not have special restrictions on the way to regulate the value of W, as long as the purpose of the application can be achieved. Illustratively, carboxyl groups can be grafted on the surface of carbon nanotubes by adding concentrated nitric acid for reaction in carbon nanotubes. Specifically, the value of W can be regulated by regulating the proportion of the added reactant concentrated nitric acid and the reaction time.

[0091] The application does not have special restrictions on the way to regulate the value of B, as long as the purpose of the application can be achieved. Illustratively, the value of B can be regulated by regulating the number of layers and the flake diameter of graphene.

[0092] The application does not have special restrictions on the way to regulate the value of H1, as long as the purpose of the application can be achieved. Illustratively, the value of H1 can be regulated by regulating the coating weight of the first positive electrode material layer.

[0093] The application does not have special restrictions on the way to regulate the value of H2, as long as the purpose of the application can be achieved. Illustratively, the value of H2 can be regulated by regulating the coating weight of the second positive electrode material layer.

[0094] The positive electrode current collector is not particularly limited in the present application as long as the object of the present application can be achieved, and for example, can include an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, an aluminum-carbon composite current collector), and the like. The thickness of the positive electrode current collector is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm.

[0095] In the present application, the secondary battery further includes a negative electrode tab including a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The above-mentioned "the negative electrode material layer is provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector in the thickness direction thereof, or can be provided on both surfaces of the negative electrode current collector in the thickness direction thereof. It should be noted that the "surface" herein can be the entire region of the surface of the negative electrode current collector, or can be a partial region of the surface of the negative electrode current collector, and the present application is not particularly limited as long as the object of the present application can be achieved.

[0096] The negative electrode current collector is not particularly limited in the present application as long as the object of the present application can be achieved, and for example, can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector, and exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, and the like.

[0097] The negative electrode material layer includes a negative electrode active material, and the negative electrode active material is not particularly limited in the present application as long as the object of the present application can be achieved, and for example, the negative electrode active material can include, but is not limited to, at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 or Li-Al alloy.

[0098] In some embodiments of the present application, the negative electrode material layer can further include a conductive agent and a binder, and the types of the conductive agent and the binder are not particularly limited in the present application as long as the object of the present application can be achieved, and for example, can be at least one of the above-mentioned first conductive agent and the above-mentioned first binder. The mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode material layer is not particularly limited in the present application, and a person skilled in the art can select according to the actual needs as long as the object of the present application can be achieved.

[0099] In some embodiments of the present application, the negative electrode material layer can further include a conductive agent, a binder, and a thickening agent, and the present application does not particularly limit the kind of the conductive agent, the binder, and the thickening agent as long as the purpose of the present application can be achieved, for example, the conductive agent and the binder can be at least one of the above-described first conductive agent and the above-described first binder. The thickening agent can include, but is not limited to, at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, or lithium carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickening agent in the negative electrode material layer, and a person skilled in the art can select according to the actual needs as long as the purpose of the present application can be achieved.

[0100] The present application does not particularly limit the thickness of the negative electrode material layer as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode material layer is 30 μm to 120 μm.

[0101] The present application does not particularly limit the thickness of the negative electrode current collector as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0102] In the present application, the secondary battery further includes a separator. The present application does not particularly limit the separator as long as the purpose of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendered film, or a spunlaced film.

[0103] In some embodiments of the present application, the separator can include a base material layer and a surface treatment layer. The base material layer can be a non-woven fabric or a composite film having a porous structure, and the material of the base material layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0104] Optionally, a surface treatment layer is provided on at least one surface of the base material layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0105] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited in the present application, and for example, the inorganic particles can include at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited in the present application, and for example, the binder can be at least one of the above-described first binders. In some embodiments of the present application, the polymer layer includes a polymer, and a material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0106] In the present application, the thickness of the separator is not particularly limited as long as the object of the present application is achieved, and for example, the thickness of the separator can be 3 μm to 30 μm.

[0107] In the present application, the secondary battery further includes an electrolyte including a lithium salt and a non-aqueous solvent. The lithium salt is not particularly limited in the present application as long as the object of the present application is achieved. For example, the lithium salt can include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate.

[0108] The non-aqueous solvent is not particularly limited in the present application as long as the object of the present application is achieved, and for example, the non-aqueous solvent can include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents.

[0109] The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro-carbonate compound. The chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The cyclic carbonate compound can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluoro-carbonate compound can include, but is not limited to, at least one of fluoro-ethylene carbonate (FEC), 1,2-difluoro-ethylene carbonate, 1,1-difluoro-ethylene carbonate, 1,1,2-trifluoro-ethylene carbonate, 1,1,2,2-tetrafluoro-ethylene carbonate, 1-fluoro-2-methyl-ethylene carbonate, 1-fluoro-1-methyl-ethylene carbonate, 1,2-difluoro-1-methyl-ethylene carbonate, 1,1,2-trifluoro-2-methyl-ethylene carbonate, or trifluoromethyl-ethylene carbonate. The carboxylic acid ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or caprolactone. The ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvent can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the non-aqueous solvent in the electrolyte is not particularly limited in the present application, as long as the object of the present application is achieved.

[0110] The secondary battery further includes a case for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art of secondary batteries, which are not limited in the present application. The case is not particularly limited in the present application, and can be a case known in the art, as long as the object of the present application is achieved. For example, the case can be a hard case or a flexible case. The material of the hard case can be a metal, and the kind of the metal is not limited in the present application, and a metal hard case known in the art can be used, as long as the object of the present application is achieved. The flexible case can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0111] The kind of the secondary battery according to the present application is not particularly limited, and it can include any device in which an electrochemical reaction occurs. In the present application, the secondary battery can include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, and the like.

[0112] The preparation process of the secondary battery according to the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, it can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and winding, folding, or the like as needed to obtain an electrode assembly of a wound structure, such as Figure 4 As shown, the positive electrode sheet 10, the separator 30, and the negative electrode sheet 20 are stacked in order, wound to obtain an electrode assembly of a wound structure; the electrode assembly is placed in a packaging bag, electrolyte is injected into the packaging bag and sealed to obtain a secondary battery; or the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, and then the four corners of the entire stack structure are fixed with adhesive tape to obtain an electrode assembly of a stack structure, the electrode assembly is placed in a packaging bag, electrolyte is injected into the packaging bag and sealed to obtain a secondary battery. The packaging bag is a packaging bag known in the art, and the present application does not limit it.

[0113] The second aspect of the present application provides an electronic device comprising the secondary battery according to any one of the preceding embodiments. Therefore, the electronic device provided by the present application has good use performance.

[0114] The kind of the electronic device according to the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, and the like.

[0115] Embodiments

[0116] Hereinafter, embodiments and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations were carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0117] Test methods and equipment:

[0118] Particle size test of the second single-crystal ternary material, the second zero-dimensional conductive material:

[0119] Disassemble the lithium ion battery to obtain the positive electrode sheet. The positive electrode sheet is cleaned with dimethyl carbonate (DMC) for 5 times to clean the residual electrolyte, and then the positive electrode sheet is baked at a baking temperature of 100°C for 60 min to obtain a dried positive electrode sheet. A scraper is used to scrape the powder on the surface layer of the positive electrode sheet to obtain a second positive electrode material layer powder. The above surface layer refers to a region with a depth of 30 pm from the surface of the positive electrode sheet. The second positive electrode material layer powder is dispersed in chloroform, and then centrifuged. The solution after centrifugation is divided into three layers from bottom to top, which are the second positive electrode active material, the second binder and the second conductive agent. Each layer is taken out with a pipette, and after vacuum drying, the second positive electrode active material, the second binder and the second conductive agent can be obtained.

[0120] A scanning electron microscope (SEM, model: Thermo Fisher FEI-Apreo S) is used to observe the particle size distribution of the second positive electrode active material and the second conductive agent.

[0121] The second positive electrode active material powder is uniformly dispersed on the conductive tape, and the second positive electrode active material powder sample is treated by gold spraying with a thickness of about 10 nm to increase the conductivity of the powder sample. Ensure that the powder sample is clean and clean during sample preparation. The prepared gold sprayed powder sample is placed on the SEM sample stage, set the voltage to 20 kV, and observe at a magnification of 5000. High-resolution secondary electron images are captured in multiple areas (at least 5 different fields of view) to cover the representative particle distribution. Among them, the particles of the single-crystal ternary material are single continuous particles with complete polyhedral morphology on the surface and no microcracks inside. The polycrystalline ternary material is a spherical or spherical secondary particle formed by the aggregation of nanoscale primary small particles. Then use image analysis software to process the selected area, select at least 200 single-crystal ternary material or polycrystalline ternary material particles for measurement, draw a histogram and a cumulative distribution curve to obtain the Dv50 (i.e. D2) of the second single-crystal ternary material, the particle size distribution width, and the Dv50 (i.e. D1) of the polycrystalline ternary material, the particle size distribution width.

[0122] The second conductive agent powder is uniformly dispersed on the conductive tape, and then the second conductive agent powder sample is placed on the SEM sample stage, set the voltage to 20 kV, and observe at a magnification of 10000. High-resolution secondary electron images are captured in multiple areas (at least 5 different fields of view) to cover the representative particle distribution. Among them, the particulate conductive agent is the second zero-dimensional conductive material. Then use image analysis software to process the selected area, select at least 200 second zero-dimensional conductive material particles for measurement, draw a histogram and a cumulative distribution curve to obtain the Dv50 (i.e. D3) of the second zero-dimensional conductive material, the particle size distribution width.

[0123] Test of particle size of the first single-crystal ternary material and the first zero-dimensional conductive material:

[0124] The lithium ion battery was disassembled to obtain a positive electrode sheet. The positive electrode sheet was cleaned with dimethyl carbonate (DMC) for 5 times to clean the residual electrolyte, and then the positive electrode sheet was baked at a baking temperature of 100°C for 60 min to obtain a dried positive electrode sheet. The cross section of the positive electrode sheet was observed by SEM (model: Thermo Fisher FEI-Apreo S), and the interface between the first positive electrode material layer and the second positive electrode material layer was observed to obtain the thicknesses of the first positive electrode material layer and the second positive electrode material layer. The second positive electrode material layer with a corresponding thickness was scraped off with a small knife to obtain a positive electrode sheet sample coated only with the first positive electrode material layer. The first positive electrode material layer powder was scraped off with a scraper, and then dispersed in trichloromethane, and then centrifuged. The solution after centrifugation was divided into three layers from bottom to top, namely the first positive electrode active material, the first binder and the first conductive agent. Each layer was taken out with a pipette, and after vacuum drying, the first positive electrode active material, the first binder and the first conductive agent were obtained. The particle size distribution of the first positive electrode active material and the first conductive agent was observed by scanning electron microscopy (SEM, model: Thermo Fisher FEI-Apreo S).

[0125] The first positive electrode active material powder was uniformly dispersed on the conductive tape, and the first positive electrode active material powder sample was treated by gold spraying with a thickness of about 10 nm to increase the conductivity of the powder sample. Ensure that the powder sample is clean and clean during sample preparation. The prepared powder sample after gold spraying was placed on the SEM sample stage, the voltage was set to 20 kV, and the observation was carried out at a magnification of 5000. High-resolution secondary electron images were captured in multiple areas (at least 5 different fields of view) to cover the representative particle distribution. Among them, the single-crystal ternary material particles are single continuous particles with complete polyhedral morphology on the surface and no microcracks inside. Then the selected areas were processed using image analysis software, at least 200 single-crystal ternary material particles were selected for measurement, and a histogram and a cumulative distribution curve were drawn to obtain the Dv50 (i.e. D4) and the particle size distribution width of the first single-crystal ternary material.

[0126] The first conductive agent powder was uniformly dispersed on the conductive tape, and then the first conductive agent powder sample was placed on the SEM sample stage, the voltage was set to 20 kV, and the observation was carried out at a magnification of 10000. High-resolution secondary electron images were captured in multiple areas (at least 5 different fields of view) to cover the representative particle distribution. Among them, the particulate conductive agent is the first zero-dimensional conductive material. Then the selected areas were processed using image analysis software, at least 200 first zero-dimensional conductive material particles were selected for measurement, and a histogram and a cumulative distribution curve were drawn to obtain the Dv50 (i.e. D5) and the particle size distribution width of the first zero-dimensional conductive material.

[0127] The ratio of the maximum cross-sectional area of the first single-crystal ternary material particle to the maximum cross-sectional area of the smallest circumscribed sphere of the first single-crystal ternary material particle is tested:

[0128] The ratio of the maximum cross-sectional area of the first single-crystal ternary material particle to the maximum cross-sectional area of the smallest circumscribed sphere of the first single-crystal ternary material particle (i.e., the sphericity) is tested using a dynamic image analyzer (manufacturer: Sympatec; model: QICPIC). The first single-crystal ternary material particle sample is vacuum-dried at 80°C for 2h to remove moisture to prevent particle agglomeration, a reference sample sphericity calibration system is used to ensure an error <0.03. The gas pressure is set to 1.0 bar, and the sample feeding rate is 0.8g / min. In the test, at least 50,000 particle samples are captured to ensure the reliability of the data. After the test is completed, the software WINDOX 5 is used to automatically perform the test sphericity, and the projected area A and the circumference p of each particle sample are extracted, and the sphericity S = 4πA / p is automatically calculated according to the following formula 2 , and the three-dimensional sphericity is fitted by multi-angle projection (based on the equivalent surface area / volume ratio).

[0129] The ratio of the amount of substance of the nickel element to the total amount of substance of the transition metal elements in the positive electrode active material is tested:

[0130] The mass percentage content of the nickel element and other transition metal elements in the positive electrode active material is determined using an inductively coupled plasma emission spectrometer (ICP-OES, PE7000DV spectrometer produced by American Platinum Elmer). High-purity reverse aqua regia (HNO3 and HCl in a volume ratio of 3:1) is configured, 0.1000g of the positive electrode active material sample is accurately weighed into a digestion tank, 10mL of the configured digestion reagent is added, after cooling after complete digestion, the solution is transferred to a beaker, the acid is chased to 1mL using a 150°C hot plate, and 1wt% HNO3 is used to dilute to a 50mL volumetric flask, and then filtered through a 0.22μm nylon filter. At the same time, the standard solution of the nickel element or other transition metal elements X (X is cobalt element or manganese element) (concentration of 1000mg / L, solvent is the above high-purity reverse aqua regia) is diluted into a series of solutions with concentrations of 0mg / L, 2mg / L, 5mg / L, 10mg / L, and 20mg / L, and the medium is 1wt% HNO3, and the linear correlation coefficient R 2 of the calibration curve is required to be ≥0.9995. After the mass percentage content of the nickel element and other transition metal elements in the positive electrode active material is measured using ICP-OES, the mass and amount of substance of the nickel element and other transition metal elements are calculated, and then the ratio of the amount of substance of the nickel element to the total amount of substance of the transition metal elements is calculated.

[0131] Oil absorption value test:

[0132] The oil absorption value of the second zero-dimensional conductive material and the first zero-dimensional conductive material is tested by using a DABS-H type oil absorption meter, and the oil absorption value of the second zero-dimensional conductive material and the first zero-dimensional conductive material is tested according to the national standard "Carbon Black Part 2: Determination of Oil Absorption" (GB / T 3780.2-2007). The sample is added to the mixing tank of the oil absorption meter, and the paraffin oil is added to the sample at a speed of 4 mL / min by using a titrator. As the oil absorption value of the sample increases, the mixture changes from a free-flowing state to a semi-plastic agglomerate, and the viscosity of the mixture continuously increases. The viscosity is transmitted to the torque sensing system of the oil absorption meter, and when the viscosity of the mixture reaches a predetermined torque value, the oil absorption meter and the titrator are automatically turned off at the same time. The volume of oil added is directly read from the reading burette, and the volume of oil absorbed per unit mass of the sample is the oil absorption value of the sample.

[0133] Diameter and length test of carbon nanotubes and carbon fibers:

[0134] The carbon nanotube slurry or carbon fiber slurry is dispersed by gradient dilution method. The specific steps of gradient dilution method are as follows: 1.00 g of carbon nanotube slurry or carbon fiber slurry (accurate to 0.1 mg) is mixed with 10.00 g of N-methyl pyrrolidone (NMP), and is treated by ultrasonic for 30 min at a power of 300 W, and the water bath temperature is controlled at 25°C. First dilution is completed to obtain a first diluted carbon nanotube solution or carbon fiber solution. 1.00 g of the first diluted carbon nanotube solution or carbon fiber solution is repeatedly diluted to achieve 100 times dispersion by secondary dilution, and the above dilution operation is repeated to achieve 1000 times dispersion by tertiary dilution to obtain a finally dispersed carbon nanotube solution or carbon fiber solution. 5 μL of the finally dispersed carbon nanotube solution or carbon fiber solution is dropped on the surface of aluminum foil, and vacuum drying is performed at 60°C for 2 h to obtain a carbon nanotube sample or a carbon fiber sample. The carbon nanotube sample or the carbon fiber sample is observed by field emission scanning electron microscope (FESEM, model JSM-7900F) at an acceleration voltage of 5 kV and a magnification of 50,000 times. The diameter (accuracy ±0.2 nm) and length of 20 randomly selected carbon nanotubes or carbon fibers are measured, and the average value is the final diameter and length of the carbon nanotubes or carbon fibers. The ratio of the diameter to the length (aspect ratio) of each carbon nanotube is calculated, and the average value of the aspect ratios of the 20 carbon nanotubes is the final aspect ratio of the carbon nanotubes.

[0135] Mass percentage content test of carboxyl group:

[0136] The carboxyl group will undergo decarboxylation at 200-350°C, and the mass percentage of carboxyl group (-COOH) in carbon nanotubes (CNTs) is determined by using thermogravimetric analysis-mass spectrometry (TGA-MS). The carbon nanotube slurry sample to be tested is dried at 80°C under vacuum for 24h to remove the solvent and adsorbed water, and a ball mill is used for 5min to uniformly disperse the CNTs powder. After dispersion, 10±0.1mg of the CNTs powder sample is placed in an alumina crucible, the temperature range of the TGA device module is set to 30-800°C, the heating rate is 10°C / min, the atmosphere is high-purity He, and the gas flow rate is 50mL / min; the ion source temperature of the MS device module is set to 200°C, the ion peaks of CO2 (m / z=44) and H2O (m / z=18) are tested, and a group of empty crucibles is tested at the same time to deduct the background signal of CO2. After testing, the temperature signal of m / z=44 at 200-350°C is extracted, and the release amount of CO2 mCO2 is calculated according to the following formula:

[0137]

[0138] wherein the unit of mCO2 is μg; A simple is the peak area integral value of the CNTs powder sample to be tested, A blank is the peak area integral value of the empty crucible; and K is the CO2 calibration factor.

[0139] The calculation formula of the mass percentage of carboxyl group W is as follows:

[0140]

[0141] wherein mCOOH is the mass of the carboxyl group, in mg.

[0142] Layer number test:

[0143] The graphene slurry sample to be tested is dried at 80°C under vacuum for 24h to remove the solvent and adsorbed water, and a graphene powder sample is obtained. The graphene powder sample is tested by Raman spectroscopy, and the number of layers of graphene is determined according to the peak shape, full width at half maximum (FWHM), peak position, and peak intensity ratio of G peak to 2D peak (IG / I2D) of 2D peak (~2700cm -1 ). A SiO2 / Si sheet with a thickness of 300nm is used as a substrate, and the substrate is cleaned with acetone. Then the graphene sample to be tested is transferred to the substrate, the laser wavelength is set to 532nm, the laser power is set to <1mW, the objective magnification is set to 100× (numerical aperture NA=0.9), the grating is set to 1800gr / mm, and the spectral range is set to 1200cm -1 -3200cm -1The Raman spectrum test results and the number of layers of graphene correspond to the following table:

[0144]

[0145]

[0146] Sheet diameter test:

[0147] The graphene slurry is centrifuged, and after drying to remove the solvent, a graphene powder sample is obtained. The graphene powder sample is added to the solvent NMP to obtain a solution with a concentration of 0.01 mg / mL. The above solution is subjected to ultrasonic treatment, the ultrasonic power is 200 W, and the ultrasonic time is 20 min. After ultrasonic treatment, a dispersion liquid is prepared. The dispersion liquid is dropped onto a copper mesh of a transmission electron microscope (TEM, model JEOL JEM-2100plus), and vacuum dried for 2 h. The acceleration voltage is set to 100 kV, and the magnification is set to 100,000 times. After observing and finding the graphene region, the software Image J is used for threshold segmentation to identify the sheet layer contour, and the maximum projection size (i.e. sheet diameter) of each sheet layer is measured. The maximum projection size data of ≥500 sheet layers are counted, and a size distribution histogram is generated. The size data is arranged from small to large, and the size value corresponding to the cumulative distribution of 50% is the sheet diameter G of the graphene.

[0148] Specific surface area test:

[0149] The specific surface area of graphene is determined by gas adsorption method (BET method). First, 100 mg of graphene powder sample is taken and placed in a sample tube, and the degassing conditions are set, i.e. vacuum degassing at 150°C for ≥6 h to remove water or organic matter adsorbed on the surface of the graphene powder sample to avoid blocking the nano-pores. Then, the degassed graphene powder sample is tested, the adsorbate is high-purity N2, the relative pressure (P / P0) range is 0.05 to 0.30 (BET linear interval), and the equilibrium time is 10 s per point. After the test is completed, the specific surface area of the graphene is calculated according to the BET equation and the specific surface area formula.

[0150] The BET equation is as follows:

[0151]

[0152] Wherein, V is the adsorption amount; Vm is the monolayer adsorption amount; C is the BET constant;

[0153] The specific surface area formula is as follows:

[0154]

[0155] Wherein, N Awherein A is Avogadro's number; σ is the gas molecular cross-sectional area; M is the gas molar mass; and m is the sample mass.

[0156] Rate performance test:

[0157] The lithium ion battery was placed in a constant temperature environment of 25°C and rested for 30 min to allow the lithium ion battery to reach a constant temperature. The lithium ion battery that reached a constant temperature was charged at 0.5C constant current to 4.3V, charged at constant voltage to 0.05C at 4.3V, rested for 5 min, and then discharged at 0.5C constant current to 3.0V to obtain the 0.5C discharge capacity of the lithium ion battery.

[0158] The lithium ion battery was charged at 0.5C constant current to 4.3V, charged at constant voltage to 0.05C at 4.3V, rested for 5 min, and then discharged at 2C constant current to 3.0V to obtain the 2C discharge capacity of the lithium ion battery. The 2C discharge capacity was divided by the 0.5C discharge capacity to obtain the 2C capacity retention rate.

[0159] 2C capacity retention rate (%) = 2C discharge capacity / 0.5C discharge capacity x 100%.

[0160] Volume energy density test:

[0161] At 25°C, the lithium ion battery in the example or the comparative example was charged at 0.2C constant current to 4.3V, charged at constant voltage to 0.05C at 4.3V, rested for 5 min, and then discharged at 0.2C constant current to 3.0V, and rested for 5 min. The energy of the above discharge process was recorded as the discharge energy E. The volume V (mm 3 ) of the lithium ion battery was calculated.

[0162] Volume energy density (Wh / L) = E / V x 10 6 .

[0163] Example 1-1

[0164] Preparation of the positive electrode sheet

[0165] The first single-crystal ternary material LiNi 0.9 Co 0.05 Mn 0.05 O2, the first binder polyvinylidene fluoride (PVDF), the first zero-dimensional conductive material Super P, and the two-dimensional conductive material graphene were mixed in a weight ratio of 97:2:0.7:0.3, N-methyl pyrrolidone (NMP) was added as a solvent, and the mixture was stirred and mixed uniformly to obtain a first positive electrode material layer slurry, wherein the solid content of the first positive electrode material layer slurry was 70wt%.

[0166] The second single-crystal ternary material LiNi 0.9 Co 0.05Mn 0.05 O2, polycrystalline ternary material LiNi 0.9 Co 0.05 Mn 0.05 O2, second binder polyvinylidene fluoride (PVDF), second zero-dimensional conductive material Super P, one-dimensional conductive material single-walled carbon nanotube are mixed in a weight ratio of 48.5:48.5:2:0.3:0.7, N-methyl pyrrolidone (NMP) is added as a solvent, and the mixture is stirred and mixed uniformly to obtain a second positive electrode material layer slurry, wherein the solid content of the second positive electrode material layer slurry is 71.5wt%.

[0167] The first positive electrode material layer slurry is uniformly coated on one surface of the positive electrode current collector aluminum foil with a thickness of 12 μm, and is subjected to drying treatment at 120 °C for 1 h to obtain a positive electrode tab coated with a first positive electrode material layer with a thickness of 25 μm on one surface; then the second positive electrode material layer slurry is uniformly coated on the surface of the first positive electrode material layer, and is subjected to drying treatment at 120 °C for 1 h to obtain a positive electrode tab coated with a first positive electrode material layer and a second positive electrode material layer on one surface; wherein the thickness of the second positive electrode material layer is 50 μm. Then the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode tab coated with a first positive electrode material layer and a second positive electrode material layer on both surfaces. After drying at 120 °C under vacuum conditions for 1 h, cold pressing, cutting and slitting, a positive electrode tab with a specification of 74 mm x 867 mm is obtained. The compaction density in the cold pressing process is 4.2 g / cm 3 .

[0168] <Preparation of negative electrode tab>

[0169] The negative electrode active material artificial graphite, thickening agent carboxymethyl cellulose (CMC), binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 97.5:1:1.5, deionized water is added as a solvent, and the mixture is stirred and mixed uniformly to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry is 75wt%; the negative electrode slurry is uniformly coated on one surface of the negative electrode current collector copper foil with a thickness of 12 μm, and is subjected to drying at 120 °C to obtain a negative electrode tab coated with a negative electrode material layer with a thickness of 120 μm on one surface. Repeat the above steps on the other surface of the copper foil to obtain a negative electrode tab coated with a negative electrode material layer on both surfaces. After drying at 120 °C under vacuum conditions for 1 h, cold pressing, cutting and slitting, a negative electrode tab with a specification of 78 mm x 875 mm is obtained. The compaction density in the cold pressing process is 1.75 g / cm 3 .

[0170] <Preparation of electrolyte>

[0171] In an argon atmosphere glove box with water content less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC) were mixed in a weight ratio of 1:1 to obtain a base solvent, then lithium salt lithium hexafluorophosphate (LiPF6) was added and mixed uniformly to obtain an electrolyte. The mass percentage of lithium salt in the electrolyte was 12.5%, and the balance was the base solvent.

[0172] <Preparation of the separator>

[0173] A polyethylene (PE) film with a thickness of 15 μm was used.

[0174] <Preparation of the lithium ion battery>

[0175] The positive electrode sheet, the separator, the negative electrode sheet, and the separator prepared above were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to serve as a separator, and wound to obtain an electrode assembly. After welding the tabs, the electrode assembly was placed in an aluminum-plastic film packaging bag, and subjected to the processes of hot pressing, molding, top sealing, vacuum drying, injection of electrolyte, high-temperature standing, degassing, formation, and capacity distribution to obtain a lithium ion battery.

[0176] Examples 1-2 to 1-35

[0177] Except for adjusting the relevant preparation parameters according to Table 1, the rest was the same as Example 1-1.

[0178] Examples 2-1 to 2-9

[0179] Except for adjusting the relevant preparation parameters according to Table 2, the rest was the same as Example 1-1.

[0180] Examples 3-1 to 3-31

[0181] Except for adjusting the relevant preparation parameters according to Table 3, the rest was the same as Example 1-1.

[0182] Comparative Example 1

[0183] Except for adjusting the relevant preparation parameters according to Table 1, the rest was the same as Example 1-1.

[0184] Comparative Example 2

[0185] Except for replacing the first single-crystal ternary material LiNi0.8Co0.1Mn0.1O2 in the first positive electrode material layer with the polycrystalline ternary material LiNi0.8Co0.1Mn0.1O2 in the <Preparation of the positive electrode sheet>, the rest was the same as Example 1-1. 0.9 Co 0.05 Mn 0.05 O2 in the first positive electrode material layer with the polycrystalline ternary material LiNi0.8Co0.1Mn0.1O2 in the <Preparation of the positive electrode sheet>, the rest was the same as Example 1-1. 0.9 Co 0.05 Mn 0.05 O2 in the first positive electrode material layer with the polycrystalline ternary material LiNi0.8Co0.1Mn0.1O2 in the <Preparation of the positive electrode sheet>, the rest was the same as Example 1-1.

[0186] Comparative Examples 3 to 10

[0187] The rest is the same as Example 1-1 except that the relevant preparation parameters are adjusted according to Table 1.

[0188] The preparation parameters and electrical performance parameters of each example and comparative example are shown in Tables 1 to 3.

[0189]

[0190]

[0191]

[0192]

[0193]

[0194] As can be seen from Examples 1-1 to 1-35 and Comparative Examples 1 to 10, by adjusting the structure of the positive electrode sheet and the Dv50 of the polycrystalline ternary material, the Dv50 of the second single-crystal ternary material, and the Dv50 of the second zero-dimensional conductive material within the scope of the present application, the lithium ion battery has a higher 2C capacity retention rate and a higher volumetric energy density, indicating that the lithium ion battery has good rate performance and a high energy density. In Comparative Example 1, the second positive electrode material layer does not include the second zero-dimensional conductive material, in Comparative Example 2, the first positive electrode active material of the first positive electrode material layer is selected to be the polycrystalline ternary material LiNi 0.9 Co 0.05 Mn 0.05 O2, in Comparative Example 3, the second positive electrode material layer does not include the second single-crystal ternary material, and in Comparative Examples 4 to 10, at least one of the Dv50 of the polycrystalline ternary material, the Dv50 of the second single-crystal ternary material, and the Dv50 of the second zero-dimensional conductive material is not within the scope of the present application, the lithium ion battery has a lower 2C capacity retention rate and a lower volumetric energy density, indicating that the lithium ion battery has poor rate performance and a low energy density.

[0195] D4 will affect the rate performance and energy density of the lithium ion battery. As can be seen from Examples 1-1 to 1-3, when the value of D4 is within the scope of the present application, the lithium ion battery has a higher 2C capacity retention rate and a higher volumetric energy density, indicating that the lithium ion battery has good rate performance and a high energy density.

[0196] W 11 , W 121 , W 122 , W 13 will affect the rate performance and energy density of the lithium ion battery. As can be seen from Examples 1-1, 1-4 to 1-6, when W 11 , W 121 , W122 W 13 When the value is within the range of this application, the lithium-ion battery has a high 2C capacity retention rate and a high volumetric energy density, indicating that the lithium-ion battery has good rate performance and high energy density.

[0197] The type of first zero-dimensional conductive material, second zero-dimensional conductive material, and one-dimensional conductive material affects the rate performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-7, 1-22, and 1-27, when the type of first zero-dimensional conductive material, second zero-dimensional conductive material, and one-dimensional conductive material are within the scope of this application, the lithium-ion battery exhibits higher 2C capacity retention and higher volumetric energy density, indicating that the lithium-ion battery has better rate performance and higher energy density.

[0198] H1 affects the rate performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-8 to 1-12, when the value of H1 is within the range of this application, the lithium-ion battery has a higher 2C capacity retention rate and a higher volumetric energy density, indicating that the lithium-ion battery has better rate performance and higher energy density.

[0199] W 211 W 212 W 221 W 222 W 23 It will affect the rate performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-15 to 1-19, when W... 211 W 212 W 221 W 222 W 23 When the value is within the range of this application, the lithium-ion battery has a high 2C capacity retention rate and a high volumetric energy density, indicating that the lithium-ion battery has good rate performance and high energy density.

[0200] H2 affects the rate performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-28 to 1-31, when the value of H2 is within the range of this application, the lithium-ion battery has a higher 2C capacity retention rate and a higher volumetric energy density, indicating that the lithium-ion battery has better rate performance and higher energy density.

[0201] The ratios D1 / D2 and D2 / D3 affect the rate performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-13, 1-14, 1-20, 1-21, 1-23 to 1-26, and 1-32 to 1-35, when the values ​​of D1 / D2 and D2 / D3 are within the range of this application, the lithium-ion battery exhibits higher 2C capacity retention and higher volumetric energy density, indicating that the lithium-ion battery has better rate performance and higher energy density.

[0202] Table 2

[0203]

[0204] The types of first monocrystalline ternary materials, second monocrystalline ternary materials, and polycrystalline ternary materials affect the rate performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-3, and 2-7 to 2-9, when the types of first monocrystalline ternary materials, second monocrystalline ternary materials, and polycrystalline ternary materials are within the scope of this application, the lithium-ion batteries exhibit higher 2C capacity retention and higher volumetric energy density, indicating that the lithium-ion batteries have better rate performance and higher energy density.

[0205] S affects the rate performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 2-4 to 2-6, when the value of S is within the range specified in this application, the lithium-ion battery exhibits higher 2C capacity retention and higher volumetric energy density, indicating that the lithium-ion battery has better rate performance and higher energy density. Compared with Example 1-1, the particles of the first single-crystal ternary material in Example 2-6 have a larger S value, resulting in better processing performance of the positive electrode sheet in Example 2-6.

[0206] Table 3

[0207]

[0208]

[0209] Note: " / " in Table 3 indicates that there is no corresponding parameter.

[0210] O2 affects the rate performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 3-1 to 3-4, when the value of O2 is within the range of this application, the lithium-ion battery has a higher 2C capacity retention rate and a higher volumetric energy density, indicating that the lithium-ion battery has better rate performance and higher energy density.

[0211] d1 will affect the rate capability and energy density of the lithium ion battery. As can be seen from Example 1-1, Example 3-5 to Example 3-8, when the value of d1 is within the range of the present application, the 2C capacity retention rate and the volume energy density of the lithium ion battery are higher, which indicates that the lithium ion battery has better rate capability and higher energy density.

[0212] L1 will affect the rate capability and energy density of the lithium ion battery. As can be seen from Example 1-1, Example 3-9 to Example 3-12, when the value of L1 is within the range of the present application, the 2C capacity retention rate and the volume energy density of the lithium ion battery are higher, which indicates that the lithium ion battery has better rate capability and higher energy density.

[0213] L1 / d1 will affect the rate capability and energy density of the lithium ion battery. As can be seen from Example 1-1, Example 3-5 to Example 3-12, when the value of L1 / d1 is within the range of the present application, the 2C capacity retention rate and the volume energy density of the lithium ion battery are higher, which indicates that the lithium ion battery has better rate capability and higher energy density.

[0214] W will affect the rate capability and energy density of the lithium ion battery. As can be seen from Example 1-1, Example 3-13 to Example 3-14, when the value of W is within the range of the present application, the 2C capacity retention rate and the volume energy density of the lithium ion battery are higher, which indicates that the lithium ion battery has better rate capability and higher energy density.

[0215] d2 will affect the rate capability and energy density of the lithium ion battery. As can be seen from Example 3-15 to Example 3-17, when the value of d2 is within the range of the present application, the 2C capacity retention rate and the volume energy density of the lithium ion battery are higher, which indicates that the lithium ion battery has better rate capability and higher energy density.

[0216] L2 will affect the rate capability and energy density of the lithium ion battery. As can be seen from Example 3-16, Example 3-18 to Example 3-20, when the value of L2 is within the range of the present application, the 2C capacity retention rate and the volume energy density of the lithium ion battery are higher, which indicates that the lithium ion battery has better rate capability and higher energy density.

[0217] D5 will affect the rate capability and energy density of the lithium ion battery. As can be seen from Example 1-1, Example 3-21 to Example 3-23, when the value of D5 is within the range of the present application, the 2C capacity retention rate and the volume energy density of the lithium ion battery are higher, which indicates that the lithium ion battery has better rate capability and higher energy density.

[0218] O1 will affect the rate performance and energy density of the lithium ion battery. As can be seen from Example 1-1, Example 3-24 to Example 3-27, when the value of O1 is within the range of the present application, the 2C capacity retention rate and the volume energy density of the lithium ion battery are higher, which indicates that the lithium ion battery has better rate performance and higher energy density.

[0219] The number of layers of graphene will affect the rate performance and energy density of the lithium ion battery. As can be seen from Example 1-1, Example 3-28 to Example 3-29, when the number of layers of graphene is within the range of the present application, the 2C capacity retention rate and the volume energy density of the lithium ion battery are higher, which indicates that the lithium ion battery has better rate performance and higher energy density.

[0220] G will affect the rate performance and energy density of the lithium ion battery. As can be seen from Example 1-1, Example 3-30 to Example 3-31, when the value of G is within the range of the present application, the 2C capacity retention rate and the volume energy density of the lithium ion battery are higher, which indicates that the lithium ion battery has better rate performance and higher energy density.

[0221] It should be noted that the relational terms herein such as first and second, and the like are used merely to distinguish one entity or action from another entity or action, without necessarily requiring or implying that the entities or actions are in any way mutually exclusive or mutually related, unless such a relationship is explicitly indicated. Also, the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusion, such that processes, methods, or articles including a series of elements not only include those elements, but also include other elements not explicitly listed, or other elements inherent to such processes, methods, or articles.

[0222] Each of the embodiments in the specification is described in a relevant manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the difference from other embodiments.

[0223] The above only describes the preferred embodiments of the present application, and does not limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet including a positive electrode current collector, a first positive electrode material layer, and a second positive electrode material layer, the first positive electrode material layer being disposed between the positive electrode current collector and the second positive electrode material layer in a thickness direction of the positive electrode sheet; the first positive electrode material layer including a first positive electrode active material and a first conductive agent, the first positive electrode active material including a first single-crystal ternary material, the second positive electrode material layer including a second positive electrode active material and a second conductive agent, the second positive electrode active material including a polycrystalline ternary material and a second single-crystal ternary material, the second conductive agent including a second zero-dimensional conductive material; a Dv50 of the polycrystalline ternary material is D1 μm, a Dv50 of the second single-crystal ternary material is D2 μm, and a Dv50 of the second zero-dimensional conductive material is D3 μm, 5 ≤ D1 ≤ 30, 1 ≤ D2 ≤ 10, and 0.001 ≤ D3 ≤ 0.

5.

2. The secondary battery according to claim 1, wherein 0.05≤D3≤0.5。 3. The secondary battery according to claim 1, wherein D1 > D2 > D3.

4. The secondary battery according to claim 1, wherein 1 ≤ D1 / D2 ≤ 10 and 5 ≤ D2 / D3 ≤ 120;preferably, 5 ≤ D2 / D3 ≤ 20.

5. The secondary battery according to claim 1, wherein a Dv50 of the first single-crystal ternary material is D4 μm, 1 ≤ D4 ≤ 10.

6. The secondary battery according to claim 1, wherein a ratio of a maximum cross-sectional area of a particle of the first single-crystal ternary material to a maximum cross-sectional area of a minimum circumscribed sphere of the particle of the first single-crystal ternary material is S, 0.9 ≤ S ≤ 1. 7.The secondary battery according to claim 1, satisfying at least one of the following characteristics: (1) the first single-crystal ternary material includes a transition metal element, the transition metal element including a nickel element, a ratio of a molar amount of the nickel element in the first single-crystal ternary material to a total molar amount of the transition metal element in the first single-crystal ternary material is X1 %, 50 ≤ X1 ≤ 99, and preferably, 85 ≤ X1 ≤ 97; (2) the second single-crystal ternary material includes a transition metal element, the transition metal element including a nickel element, a ratio of a molar amount of the nickel element in the second single-crystal ternary material to a total molar amount of the transition metal element in the second single-crystal ternary material is X2 %, 50 ≤ X2 ≤ 99, and preferably, 85 ≤ X2 ≤ 97; (3) the polycrystalline ternary material includes a transition metal element, the transition metal element including a nickel element, a ratio of a molar amount of the nickel element in the polycrystalline ternary material to a total molar amount of the transition metal element in the polycrystalline ternary material is X3 %, 50 ≤ X3 ≤ 99, and preferably, 85 ≤ X3 ≤ 97.

8. The secondary battery according to claim 1, wherein the first single-crystalline ternary material, the second single-crystalline ternary material are each independently selected from at least one of the following single-crystalline materials: LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25 Mn 0.25 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.9 Co 0.05 Al 0.05 O2; the polycrystalline ternary material is selected from at least one of the following polycrystalline materials: LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25 Mn 0.25 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.9 Co 0.05 Al 0.05 O2.

9. The secondary battery according to claim 1, wherein the second zero-dimensional conductive material includes at least one of Super P, acetylene black, or Ketjen black.

10. The secondary battery according to claim 1, wherein an oil absorption value of the second zero-dimensional conductive material is O2 mL / 100 g, 100 ≤ O2 ≤ 500, and preferably, 150 ≤ O2 ≤ 300.

11. The secondary battery according to claim 1, wherein the second conductive agent further includes a one-dimensional conductive material, the one-dimensional conductive material including at least one of a carbon nanotube or a carbon fiber. 12.The secondary battery according to claim 11, satisfying at least one of the following characteristics: (1) the diameter of the carbon nanotube is d1 nm, 1≤d1≤300, preferably, 5≤d1≤50; (2) the length of the carbon nanotube is L1 nm, 1000≤L1≤50000, preferably, 5000≤L1≤30000; (3) the diameter of the carbon nanotube is d1 nm, the length of the carbon nanotube is L1 nm, 50≤L1 / d1≤3000, preferably, 100≤L1 / d1≤1000; (4) the functional group on the surface of the carbon nanotube includes carboxyl, the mass percentage of the carboxyl is W%, 0.5≤W≤5, based on the mass of the carbon nanotube.

13. The secondary battery according to claim 11, which satisfies at least one of the following characteristics: (1) the diameter of the carbon fiber is d2 nm, 50≤d2≤200; (2) the length of the carbon fiber is L2 μm, 10≤L2≤50.

14. The secondary battery according to claim 1, wherein The first conductive agent includes a first zero-dimensional conductive material and / or a two-dimensional conductive material, the first zero-dimensional conductive material includes at least one of Super P, acetylene black or Ketjen black, and the two-dimensional conductive material includes graphene.

15. The secondary battery according to claim 14, which satisfies at least one of the following characteristics: (1) the Dv50 of the first zero-dimensional conductive material is D5 μm, 0.001≤D5≤0.5, preferably, 0.05≤D5≤0.5; (2) the oil absorption value of the first zero-dimensional conductive material is O1 mL / 100g, 100≤O1≤500, preferably, 150≤O1≤300.

16. The secondary battery according to claim 14, which satisfies at least one of the following characteristics: (1) the number of layers of the graphene is 1 layer to 8 layers; (2) the flake diameter of the graphene is G μm, 0.5≤G≤10; (3) the specific surface area of the graphene is B m2 / g, 500≤B≤1500. 2 / g, 500≤B≤1500.

17. The secondary battery according to claim 1, wherein The first positive electrode material layer further includes a first binder, a mass percentage content of the first positive electrode active material is W 11 %, a mass percentage content of the first conductive agent is W 12 %, and a mass percentage content of the first binder is W 13 %, 90≤W 11 ≤99, 0.1≤W 12 ≤9.9, 0.1≤W 13 ≤9.

9.

18. The secondary battery according to claim 1, wherein The first conductive agent includes a first zero-dimensional conductive material and a two-dimensional conductive material, the first positive electrode material layer further includes a first binder, a mass percentage content of the first positive electrode active material is W 11 %, a mass percentage content of the first zero-dimensional conductive material is W 121 %, a mass percentage content of the two-dimensional conductive material is W 122 %, and a mass percentage content of the first binder is W 13 %, 90≤W 11 ≤99, 0.05≤W 121 ≤5, 0.05≤W 122 ≤5, 0.1≤W 13 ≤9.

9.

19. The secondary battery according to claim 1, wherein The second positive electrode material layer further comprises a second binder, a mass percentage content of the polycrystal ternary material is W 211 %, a mass percentage content of the second single-crystal ternary material is W 212 %, a mass percentage content of the second conductive agent is W 22 %, and a mass percentage content of the second binder is W 23 %, 20≤W 211 ≤70, 20≤W 212 ≤70, 0.1≤W 22 ≤5, 0.1≤W 23 ≤5.

20. The secondary battery of claim 1, wherein, The second conductive agent further comprises a one-dimensional conductive material, the second positive electrode material layer further comprises a second binder, a mass percentage content of the polycrystal ternary material is W 211 %, a mass percentage content of the second single-crystal ternary material is W 212 %, a mass percentage content of the second zero-dimensional conductive material is W 221 %, a mass percentage content of the one-dimensional conductive material is W 222 %, and a mass percentage content of the second binder is W 23 %, 20≤W 211 ≤70, 20≤W 212 ≤70, 0.1≤W 221 ≤5, 0.1≤W 222 ≤5, 0.1≤W 23 ≤5.

21. The secondary battery according to claim 1, wherein The thickness of the first positive electrode material layer is H1 μm, 1≤H1≤200, preferably, 20≤H1≤50; and / or, the thickness of the second positive electrode material layer is H2 μm, 5≤H2≤200, preferably, 30≤H2≤100.

22. The secondary battery of claim 21, wherein, H1≤H2.

23. An electronic device comprising the secondary battery according to any one of claims 1 to 22.

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