Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a positive pole piece, a negative pole piece and a diaphragm, the negative pole piece comprises a negative pole current collector and a negative pole active material layer, the negative pole active material layer is arranged on at least one surface of the negative pole current collector, the negative pole active material layer comprises a negative pole active material, the particle size Dv50 of the negative electrode active material is 0.2 mu m to 20 mu m; the negative electrode current collector comprises a first surface and a second surface which are opposite to each other, at least one groove is formed in the area, provided with the negative electrode active material layer, of the negative electrode current collector in the direction from the first surface to the second surface, the width of the groove is d, and d is larger than or equal to 0.1 micrometer and smaller than or equal to Dv50. Through the arrangement, the cycle performance and the safety performance of the secondary battery are both considered.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have been widely used in the field of consumer electronics due to their advantages such as high specific energy, high operating voltage, low self-discharge rate, small size and light weight. Existing secondary batteries have the problem of difficulty in electrolyte infiltration, and are prone to problems such as diving during the cycle, which reduces the cycle performance of the secondary battery. In order to solve the above problems, the existing technology often increases the thickness of the diaphragm to improve the liquid retention capacity between the pole pieces to alleviate the problem of insufficient electrolyte in the later stage of the secondary battery cycle, but the increase in the thickness of the diaphragm will reduce the energy density of the secondary battery. Therefore, it is necessary to develop a new technical solution to improve the cycle performance of secondary batteries. Summary of the invention

[0003] The purpose of the present application is to provide a secondary battery and an electronic device to improve the cycle performance of the secondary battery while taking into account its safety performance.

[0004] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate and a separator, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, and the particle size Dv50 of the negative electrode active material is 0.2μm to 20μm; the negative electrode current collector includes a first surface and a second surface opposite to each other, and from the first surface to the second surface, at least one groove is arranged in the region where the negative electrode current collector is provided with the negative electrode active material layer, and the width of the groove is d (the unit of d is μm), 0.1μm≤d≤Dv50. The present application selects a negative electrode active material with a particle size Dv50 within the above range, and arranges a groove with a width within the above range in the region of the negative electrode current collector where the negative electrode active material layer is arranged, so that the number of negative electrode active material particles entering the groove is greatly reduced, and a pore for the electrolyte to flow is reserved. In this way, the flow rate of the electrolyte in the negative electrode sheet can be increased, and the electrolyte's wetting performance on the negative electrode sheet can be improved. And the probability that the setting of the above groove affects the mechanical properties of the negative electrode current collector is small. As a result, the electrolyte has good wetting performance on the secondary battery, and the secondary battery has a high impact pass rate, thereby improving the cycle performance of the secondary battery and taking into account its safety performance.

[0006] In one or more embodiments of the present application, 1 μm≤d≤0.5×Dv50. By adjusting d within the above range, the cycle performance of the secondary battery can be further improved while taking into account its safety performance.

[0007] In one or more embodiments of the present application, the depth h μm of the groove is related to the original thickness ε μm of the negative electrode current collector and the coating area density CW mg / 1540 mm 2 Between: 0.5≤h≤(0.9ε-4×10 -3 CW), wherein 4≤ε≤30, 20≤CW≤400. The relationship between the depth h of the groove and the original thickness ε of the negative electrode current collector and the coating surface density of the negative electrode active material layer, as well as the original thickness ε of the negative electrode current collector and the coating surface density of the negative electrode active material layer are regulated within the above range, and the secondary battery has good safety performance on the basis of good cycle performance.

[0008] In one or more embodiments of the present application, 1≤h≤(0.9ε-6×10 -3 CW). By regulating the relationship between the depth h of the groove, the original thickness ε of the negative electrode current collector, and the coating surface density of the negative electrode active material layer within the above range, the cycle performance and safety performance of the secondary battery are further improved.

[0009] In one or more embodiments of the present application, on the plane formed by the length and width of the negative electrode current collector itself, the total area of ​​the groove is S1 m 2 The total area of ​​the negative electrode active material layer is S2 m 2 Satisfy: 0.1% ≤ S1 / S2×100% ≤ 70%, 3×10 -4 ≤S2≤12. By adjusting the relationship between the total area of ​​the grooves and the total area of ​​the negative electrode active material layer, and the total area of ​​the negative electrode active material layer within the above range, the secondary battery can have good cycle performance and safety performance.

[0010] In one or more embodiments of the present application, 0.2%≤S1 / S2×100%≤50%. Adjusting the relationship between the total area of ​​the grooves and the total area of ​​the negative electrode active material layer within the above range can further improve the cycle performance and safety performance of the secondary battery.

[0011] In one or more embodiments of the present application, the distance between the center lines of two adjacent grooves is σ, 1.5d≤σ≤5cm. By adjusting the distance between the center lines of two adjacent grooves within the above range, the safety performance of the secondary battery is further improved on the basis of having good cycle performance.

[0012] In one or more embodiments of the present application, 5d≤σ≤3 cm. When the distance between the center lines of two adjacent grooves is adjusted within the above range, the secondary battery has good cycle performance and safety performance.

[0013] In one or more embodiments of the present application, the angle θ between the center line of the groove and the length direction of the negative electrode current collector itself is 30° to 90°. By adjusting the angle θ between the center line of the groove and the length direction of the negative electrode current collector itself within the above range, the secondary battery can have good safety performance and improve the cycle performance of the secondary battery.

[0014] In one or more embodiments of the present application, the angle θ between the center line of the groove and the length direction of the negative electrode current collector itself is 45° to 90°. By adjusting the angle θ between the center line of the groove and the length direction of the negative electrode current collector itself within the above range, the secondary battery can have good safety performance and further improve the cycle performance of the secondary battery.

[0015] In one or more embodiments of the present application, the thickness of the thinnest region in the negative electrode current collector ε1 μm is equal to the original thickness of the negative electrode current collector εμm and the coating area density CW of the negative electrode active material layer mg / 1540 mm 2 Satisfy between: ε1≥0.1ε+4×10 -4 CW. The relationship between the thickness of the thinnest area in the negative electrode current collector, the original thickness of the negative electrode current collector and the coating surface density of the negative electrode active material layer is regulated within the above range, so that the secondary battery has good safety performance on the basis of good cycle performance.

[0016] In one or more embodiments of the present application, at least one groove is provided in the region where the negative electrode current collector is provided with the negative electrode active material layer from the second surface to the first surface. At least one groove is provided in the region where the negative electrode current collector is provided with the negative electrode active material layer from the second surface to the first surface, so that the secondary battery can take into account both its safety performance and cycle performance.

[0017] In one or more embodiments of the present application, at least two of the grooves located on the first surface and the second surface are parallel to or intersect each other. The above arrangement of the positional relationship between the grooves enables the secondary battery to have good cycle performance and safety performance.

[0018] The second aspect of the present application provides an electronic device, which comprises the secondary battery described in any one of the above embodiments, so that the electronic device has good performance.

[0019] Beneficial effects of this application:

[0020] The secondary battery of the embodiment of the present application selects negative electrode active materials with a particle size Dv50 of 0.2μm to 20μm, and a groove with a width d satisfying 0.1μm≤d≤Dv50 is provided in the negative electrode current collector area provided with the negative electrode active material layer, so that the number of negative electrode active material particles entering the groove is greatly reduced, and a channel for the electrolyte to flow is reserved. In this way, the circulation speed of the electrolyte in the negative electrode pole piece can be increased, and the wetting performance of the electrolyte on the negative electrode pole piece can be improved. And the probability that the setting of the above-mentioned groove affects the mechanical properties of the negative electrode current collector is small. As a result, the electrolyte has good wetting performance on the secondary battery, and the secondary battery has a high impact pass rate, thereby improving the cycle performance of the secondary battery and taking into account its safety performance.

[0021] Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0023] Figure 1 A schematic diagram of the cross-sectional structure of a negative electrode sheet along its thickness direction and length direction according to an embodiment of the present application;

[0024] Figure 2 A schematic diagram of the effect of coating negative electrode active material particles on a negative electrode current collector according to an embodiment of the present application;

[0025] Figure 3 for Figure 1 A top view of the negative electrode current collector;

[0026] Figure 4 A schematic diagram of the cross-sectional structure of a negative electrode sheet along its thickness direction and length direction according to another embodiment of the present application;

[0027] Figure 5 A top view of a negative electrode current collector in some other embodiments of the present application;

[0028] Figure 6 for Figure 1 Schematic diagram of the cross-sectional structure of the negative electrode current collector along its thickness direction and length direction;

[0029] Figure 7 for Figure 4 Schematic diagram of the cross-sectional structure of the negative electrode current collector along its thickness direction and length direction;

[0030] Figure 8 A schematic diagram of the positional relationship of the negative electrode tabs provided on the negative electrode plates in some embodiments of the present application;

[0031] Fig. 9 This is a schematic diagram of the positional relationship of the positive electrode tabs in the positive electrode sheets in some embodiments of the present application.

[0032] Reference numerals:

[0033] Negative electrode sheet 10; negative electrode current collector 11; first surface 111; second surface 112; negative electrode active material layer 12; negative electrode tab 13; groove 20; center line 14; positive electrode current collector 21; positive electrode active material layer 22; positive electrode tab 23. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0035] It should be noted that in the specific implementation manner of the present application, the present application is explained by taking a lithium-ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium-ion battery.

[0036] The first aspect of the present application provides a secondary battery, including a positive electrode plate, a negative electrode plate and a separator, the negative electrode plate includes a negative current collector and a negative active material layer, the negative active material layer is arranged on at least one surface of the negative current collector, the negative active material layer includes a negative active material, and the particle size Dv50 of the negative active material is 0.2μm to 20μm. The negative current collector includes a first surface and a second surface relative to each other, and in the direction from the first surface to the second surface, at least one groove is arranged in the region where the negative active material layer is arranged in the negative current collector, that is, at least one groove is arranged in the region where the negative active material layer is arranged on the first surface of the negative current collector, and the width of the groove is d (the unit of d is μm), 0.1μm≤d≤Dv50.

[0037] For ease of understanding, in this application, the negative electrode sheet’s own length direction is defined as X, its own width direction is defined as Y, and its own thickness direction is defined as Z. It should be understood that the above definition of direction is for the purpose of convenient description of this application, and the directions defined in this application can be understood based on the relative positions of the drawings and actual product elements. Moreover, the width direction, length direction and thickness direction of the negative electrode active material layer and the negative electrode current collector themselves are the same as those of the negative electrode sheet. The above-mentioned “negative electrode active material layer is disposed on at least one surface of the negative electrode current collector” means that the negative electrode active material layer is disposed on one surface or two surfaces of the negative electrode current collector, and the above-mentioned “surface” may be a partial surface of the negative electrode current collector or the entire surface of the negative electrode current collector. Figure 1 As shown, the negative electrode sheet 10 includes a negative electrode collector 11 and a negative electrode active material layer 12. The negative electrode collector 11 includes a first surface 111 and a second surface 112 opposite to each other. The negative electrode active material layer 12 is arranged on the first surface 111 of the negative electrode collector 11. From the first surface 111 to the second surface 112, a groove 20 is arranged in the region where the negative electrode active material layer 12 is arranged on the negative electrode collector 11, that is, along the thickness direction Z of the negative electrode collector 11, a groove 20 is arranged in the region where the negative electrode active material layer 12 is arranged on the first surface 111 of the negative electrode collector 11, and the width of the groove 20 is dμm. Of course, in other embodiments, the negative electrode active material layer can be arranged on the first surface 111 and the second surface 112 of the negative electrode collector at the same time. It should be noted that the shape, number, size, and spacing between adjacent grooves in the drawings of the present application are only exemplary, and the present application is not limited thereto. In the present application, the above-mentioned "at least one groove" means that the number of grooves in the region where the negative electrode current collector is provided with the negative electrode active material layer is one or more. The present application does not particularly limit the specific number of grooves, and those skilled in the art can adjust it according to the coating arrangement of the negative electrode active material layer and the arrangement of the grooves, as long as the purpose of the present application can be achieved.

[0038] For example, the particle size Dv50 of the negative electrode active material is 0.2 μm, 2 μm, 4 μm, 5 μm, 7 μm, 10 μm, 13 μm, 16 μm, 20 μm or any value between any two of the above numerical ranges. The particle size Dv50 of the negative electrode active material is less than 0.2 μm. The particle size Dv50 of the negative electrode active material is too small. When the negative electrode active material is prepared to obtain the negative electrode slurry, the negative electrode active material is easy to agglomerate. After the negative electrode slurry is coated on the surface of the negative electrode current collector to form the negative electrode sheet, the negative electrode active material is unevenly distributed in the negative electrode active material layer, which will affect the normal function of the negative electrode active material, and further affect the performance of the secondary battery, such as cycle performance, safety performance, energy density, etc. The particle size Dv50 of the negative electrode active material is greater than 20μm. If the particle size Dv50 of the negative electrode active material is too large, the gaps between the negative electrode active material particles in the negative electrode active material layer will be too large, resulting in poor contact between the particles. The conductivity of the negative electrode active material layer is poor, which will affect the cycle performance of the secondary battery. In addition, as the thickness of the negative electrode active material layer increases, the volume of the secondary battery increases, which will result in a loss of energy density.

[0039] The width d of the groove is less than 0.1. If the width of the groove is too small, the flow channel provided for the electrolyte flow is too small to play the role of the groove. If the width d of the groove is greater than Dv50, too many negative electrode active material particles enter the groove, causing the groove to be filled, and the role of the groove cannot be played. Figure 2 A schematic diagram showing the effect of coating negative electrode active material particles with negative electrode current collector in one embodiment of the present application is shown. Figure 2 It can be seen that there is a correlation between the width d of the groove 20 and the number of negative electrode active material particles 121 in the groove 20. If the width d of the groove 20 is greater than Dv50, the number of negative electrode active material particles 121 entering the groove 20 will increase. In the present application, the width d of the groove generally refers to the maximum width of the groove measured along the length direction of the negative electrode current collector.

[0040] The present application selects negative electrode active materials with a particle size Dv50 within the above range, and provides grooves with a width within the above range in the negative electrode current collector region where the negative electrode active material layer is provided, so that the number of negative electrode active material particles entering the grooves is greatly reduced, and channels for the electrolyte to flow are reserved. In this way, the circulation speed of the electrolyte in the negative electrode pole piece can be increased, and the wetting performance of the electrolyte on the negative electrode pole piece can be improved. And the probability that the setting of the above grooves affects the mechanical properties of the negative electrode current collector is small. As a result, the electrolyte has good wetting performance on the secondary battery, and the secondary battery has a high impact pass rate, thereby improving the cycle performance of the secondary battery and taking into account its safety performance.

[0041] In one embodiment of the present application, 1 μm ≤ d ≤ 0.5 × Dv50. By regulating d within the above range, the number of negative electrode active material particles entering the groove can be further reduced, and the flow channel reserved for the electrolyte is larger, thereby further increasing the flow rate of the electrolyte in the negative electrode sheet and further improving the wetting performance of the electrolyte on the negative electrode sheet. The negative electrode current collector still has good mechanical properties. As a result, the cycle performance of the secondary battery can be further improved while taking into account its safety performance.

[0042] In this application, the particle size Dv50 of the negative electrode active material represents the particle size of the negative electrode active material particles in the volume-based particle size distribution, starting from the small particle size side, reaching 50% of the volume accumulation. This application does not specifically limit the method of regulating the Dv50 of the negative electrode active material, as long as the purpose of this application can be achieved. For example, it can be achieved by directly purchasing negative electrode active materials with a Dv50 within the range of this application, or by crushing, grinding, ball milling, etc.

[0043] In one embodiment of the present application, Figure 1 As shown, the depth h μm of the groove 20 is related to the original thickness ε μm of the negative electrode current collector 11 and the coating area density CW mg / 1540 mm 2 Between: 0.5≤h≤(0.9ε-4×10 -3 CW), wherein 4≤ε≤30, 20≤CW≤400. For example, ε is 4, 7, 10, 13, 16, 19, 21, 23, 25, 27, 30 or any value between any two of the above numerical ranges. For example, CW is 20, 60, 77, 80, 95, 100, 120, 150, 163, 190, 210, 230, 252, 261, 277, 300, 320, 340, 370, 400 or any value between any two of the above numerical ranges. The relationship between the depth h of the groove and the original thickness ε of the negative electrode collector and the coating surface density of the negative electrode active material layer, as well as the original thickness ε of the negative electrode collector and the coating surface density of the negative electrode active material layer are controlled within the above range, and the groove has a suitable depth to increase the electrolyte flux. On the basis of the lower probability of the negative electrode sheet being broken due to the deeper depth of the groove, the negative electrode sheet has good production reliability. Therefore, the secondary battery has good electrolyte wettability, and thus has good safety performance on the basis of good cycle performance. In the present application, "original thickness of the negative electrode current collector" refers to the thickness of the negative electrode current collector without grooves.

[0044] In one embodiment of the present application, 1≤h≤(0.9ε-6×10 -3CW). By controlling the relationship between the depth h of the groove, the original thickness ε of the negative electrode current collector, and the coating surface density of the negative electrode active material layer within the above range, the cycle performance and safety performance of the secondary battery can be further improved.

[0045] In an embodiment of the present application, as Figure 1 and Figure 3 shown, on the plane XOY formed by the length and width of the negative electrode current collector 11 itself, the total area S1 m of the grooves 20 2 and the total area S2 m of the negative electrode active material layer 12 2 satisfy: 0.1% ≤ S1 / S2×100% ≤ 70%, 3×10 -4 ≤ S2 ≤ 12. It can be understood that the area of a single groove is the area of the positive projection of the groove on the negative electrode current collector, and the total area of the grooves is the product of the area of a single groove and the number of grooves. For example, S1 / S2×100% is 0.1%, 1%, 5%, 12%, 20%, 28%, 35%, 40%, 50%, 54%, 59%, 70% or any value between any two of the above numerical ranges. For example, S2 is 3×10 -4 , 10 -3 , 2×10 -3 , 4×10 -2 , 0.1, 0.7, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or any value between any two of the above numerical ranges. By controlling the relationship between the total area of the grooves and the total area of the negative electrode active material layer, and the total area of the negative electrode active material layer within the above range, on the basis that the grooves on the negative electrode current collector have little influence on the fracture of the negative electrode plate, sufficient channels can be reserved for the electrolyte to flow, so that the electrolyte has good wettability for the negative electrode plate. Thus, the secondary battery can have good cycle performance and safety performance.

[0046] In an embodiment of the present application, 0.2% ≤ S1 / S2×100% ≤ 50%. For example, S1 / S2×100% is 0.2%, 1%, 5%, 12%, 20%, 28%, 35%, 37%, 40%, 43%, 50% or any value between any two of the above numerical ranges. By controlling the relationship between the total area of the grooves and the total area of the negative electrode active material layer within the above range, it is beneficial to make the negative electrode plate have good production reliability, and the provided grooves can also reserve sufficient channels for the electrolyte to flow, so that the cycle performance and safety performance of the secondary battery can be further improved.

[0047] When the secondary battery of the present application is applied as a large-sized power battery to power equipment such as automobiles and motorcycles, the total area S1 m of the grooves 2 is 0.105 m 2Up to 8.4 m 2 , the total area S2 of the negative electrode active material layer is m 2 0.15 m 2 Up to 12 m 2 . When the secondary battery of the present application is applied to portable devices such as laptops and cameras as a small-sized portable battery, the total area of the grooves is 3×10 -7 m 2 Up to 0.105 m 2 . The total area S2 of the negative electrode active material layer is m 2 3×10 -4 m 2 Up to 0.15 m 2 .

[0048] There is no particular limitation on the regulation method of the value of S1 / S2×100% in the present application, as long as the purpose of the present application can be achieved. For example, it can be achieved by regulating the width d of the groove, the distance σ between the center lines of two adjacent grooves, etc. Generally speaking, when the distance σ between the center lines of two adjacent grooves is fixed, the larger the width d of the groove, the larger the value of S1 / S2×100%; the smaller the width d of the groove, the smaller the value of S1 / S2×100%. When the width d of the groove is fixed, the larger the distance σ between the center lines of two adjacent grooves, the smaller the value of S1 / S2×100%; the smaller the distance σ between the center lines of two adjacent grooves, the larger the value of S1 / S2×100%.

[0049] In an embodiment of the present application, the distance between the center lines of two adjacent grooves is σ, and 1.5d ≤ σ ≤ 5 cm. As Figure 3 shown, the distance between the center lines 14 of two adjacent grooves 20 is σ. By regulating the distance between the center lines of two adjacent grooves within the above range, a suitable gap is provided between the adjacent grooves in the negative electrode current collector region provided with the negative electrode active material layer, so that the hardness of the negative electrode current collector is not lost due to the setting of the grooves, which is beneficial to the transmission of the electrolyte, increases the transmission driving force of the electrolyte, reduces the diffusion resistance of the electrolyte, and thus improves the wetting performance of the electrolyte on the negative electrode plate. And it can further keep the negative electrode current collector in good mechanical properties. Thereby, on the basis of the secondary battery having good cycle performance, its safety performance is further improved.

[0050] In an embodiment of the present application, 5d ≤ σ ≤ 3 cm. Further, 5d ≤ σ ≤ 2000 μm. By controlling the distance between the centerlines of two adjacent grooves within the above range, and further reducing the distance between adjacent grooves, the density of the grooves on the negative current collector is greater, which is more conducive to the transmission of the electrolyte, further increasing the driving force for the transmission of the electrolyte and reducing the diffusion resistance of the electrolyte, thereby further improving the wetting performance of the electrolyte on the negative electrode sheet. Moreover, the probability of the mechanical properties of the negative current collector being reduced is low, resulting in a high impact passing rate of the secondary battery. Thus, the secondary battery has good cycle performance and safety performance.

[0051] In an embodiment of the present application, the angle θ between the centerline of the groove and the length direction of the negative current collector itself is 30° to 90°. For example, θ is 30°, 36°, 42°, 46°, 50°, 55°, 60°, 66°, 71°, 75°, 80°, 86°, 90° or any value between any two of the above numerical ranges. As Figure 3 shown, the angle between the centerline 14 of the groove 20 and the length direction X of the negative current collector 11 itself is θ. The flow of the electrolyte is mainly along the width direction of the negative electrode sheet. When the secondary battery is a cylindrical secondary battery, it is usually placed upright along the axis of the cylindrical secondary battery for use. Therefore, by controlling the angle θ between the centerline of the groove and the length direction of the negative current collector itself within the above range, the flow efficiency of the electrolyte can be improved, thereby improving the wetting performance of the electrolyte on the secondary battery. Moreover, the negative current collector has good mechanical properties, resulting in a high impact passing rate of the secondary battery. Thus, on the basis of good safety performance, the cycle performance of the secondary battery can be improved. In the present application, the "centerline of the groove" is a line used to identify the center of the groove, that is, a set of line segments representing the midpoint of the groove.

[0052] In an embodiment of the present application, the angle θ between the centerline of the groove and the length direction of the negative current collector itself is 45° to 90°. For example, θ is 45°, 50°, 55°, 60°, 66°, 71°, 75°, 80°, 86°, 90° or any value between any two of the above numerical ranges. By controlling the angle θ between the centerline of the groove and the length direction of the negative current collector itself within the above range, the flow efficiency of the electrolyte can be further improved, thereby further improving the wetting performance of the electrolyte on the secondary battery. Moreover, the negative current collector has good mechanical properties, resulting in a high impact passing rate of the secondary battery. Thus, on the basis of good safety performance, the cycle performance of the secondary battery can be further improved.

[0053] In an embodiment of the present application, in the direction from the second surface to the first surface, at least one groove is provided in the region where the negative electrode current collector is provided with the negative electrode active material layer, that is, at least one groove is provided in the region where the negative electrode active material layer is provided on the second surface of the negative electrode current collector. As Figure 4 shown, the negative electrode current collector 11 includes opposite first surface 111 and second surface 112, and the negative electrode active material layer 12 is provided on the first surface 111 and the second surface 112. In the direction from the first surface 111 to the second surface 112, a groove 20 is provided in the region where the negative electrode active material layer 12 is provided on the first surface 111 of the negative electrode current collector 11. In the direction from the second surface 112 to the first surface 111, a groove 20 is provided in the region where the negative electrode active material layer 12 is provided on the second surface 112 of the negative electrode current collector 11. In the direction from the second surface to the first surface, at least one groove is provided in the region where the negative electrode current collector is provided with the negative electrode active material layer, that is, grooves are provided in the regions where both surfaces of the negative electrode current collector are provided with the negative electrode active material layer, which can further improve the flow effect of the electrolyte, improve the wettability of the electrolyte to the secondary battery, and the probability that the mechanical properties of the negative electrode current collector are affected is small, so that on the basis of the good safety performance of the secondary battery, the cycle performance of the secondary battery is further improved.

[0054] In an embodiment of the present application, at least two of the grooves located on the first surface and the second surface are parallel or intersect with each other. As Figure 3 shown, in one embodiment, the six grooves 20 located on the first surface 111 are parallel to each other. As Figure 5 shown, in another embodiment, among the six grooves 20 located on the second surface, three grooves 20 are parallel to each other and three grooves 20 intersect. The setting of the positional relationship between the above grooves can also enable the electrolyte to flow quickly and uniformly in the negative electrode plate, thereby improving the wettability of the electrolyte to the secondary battery. And the negative electrode current collector has good mechanical properties, so that the impact passing rate of the secondary battery is relatively high. Thus, the secondary battery has good cycle performance and safety performance.

[0055] In an embodiment of the present application, the thickness ε1 μm of the thinnest region in the negative electrode current collector, the original thickness ε μm of the negative electrode current collector, and the coating surface density CW mg / 1540 mm of the negative electrode active material layer 2 satisfy: ε1 ≥ 0.1ε + 4×10 - 4 CW. Exemplarily, Figure 6 shows the cross-sectional structure schematic diagrams of the negative electrode current collector in the longitudinal direction and the thickness direction in some embodiments. As Figure 6As shown, in the direction from the first surface 111 to the second surface 112, a groove 20 is provided on the first surface 111 of the negative electrode current collector 11. Figure 6 In [reference], the original thickness of the negative electrode current collector 11 is shown as ε. From Figure 6 it can be seen that the original thickness ε of the negative electrode current collector 11 refers to the thickness without the groove 20 being provided. The thickness of the thinnest region in the negative electrode current collector 11 is shown as ε1. From Figure 6 it can be seen that the thickness ε1 of the thinnest region in the negative electrode current collector 11 refers to the distance between the bottom of the groove 20 with the largest depth h among the grooves 20 and the second surface 112 of the negative electrode current collector 11. Figure 7 [Figure] shows a schematic cross-sectional structure diagram of the negative electrode current collector in the longitudinal direction and thickness direction in some other embodiments. As shown in Figure 7 it, in the direction from the first surface 111 to the second surface 112, a groove 20 is provided on the first surface 111 of the negative electrode current collector 11. At the same time, in the direction from the second surface 112 to the first surface 111, a groove 20 is provided on the second surface 112 of the negative electrode current collector 11. Figure 7 In [reference], the original thickness of the negative electrode current collector 11 is shown as ε. From Figure 7 it can be seen that the original thickness ε of the negative electrode current collector 11 refers to the thickness without the groove 20 being provided. The thickness of the thinnest region in the negative electrode current collector 11 is shown as ε1. From Figure 7 it can be seen that the thickness ε1 of the thinnest region in the negative electrode current collector 11 refers to the thinnest thickness in the region of the negative electrode current collector 11 provided with the groove 20. For example, Figure 7 in the rightmost part of [figure], grooves 20 are respectively provided on the first surface 111 and the second surface 112 of the negative electrode current collector 11, and the bottoms of the two grooves 20 are opposite to each other. Then, the thickness ε1 of the thinnest region in the negative electrode current collector 11 is the distance between the bottoms of the two opposite grooves 20. By controlling the relationship between the thickness of the thinnest region in the negative electrode current collector, the original thickness of the negative electrode current collector, and the coating surface density of the negative electrode active material layer within the above range, on the basis that the groove on the negative electrode current collector can enable the electrolyte to have good wetting performance for the negative electrode plate, the negative electrode plate has good processing reliability, and the probability of the negative electrode plate breaking during the preparation process of the secondary battery is reduced. Thus, on the basis of the secondary battery having good cycle performance, it also has good safety performance.

[0056] The present application does not particularly limit the shape of the groove, as long as the purpose of the present application can be achieved. For example, when observing along the width direction of the negative electrode current collector, the cross-sectional shape of the groove is an arc, a rectangle, a triangle, etc.

[0057] The present application does not particularly limit the type of the negative electrode active material, as long as the object of the present application can be achieved. For example, the negative electrode active material may include at least one of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate Li4Ti5O with a spinel structure 12 , Li-Al alloy or metallic lithium.

[0058] The present application does not particularly limit the thickness of the negative electrode active material layer, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode active material layer is 30 μm to 130 μm.

[0059] The present application does not particularly limit the negative electrode current collector, as long as the object of the present application can be achieved. For example, the negative electrode current collector may include a copper foil or a copper alloy foil, etc.

[0060] In one embodiment of the present application, the negative electrode active material layer may further include at least one of a negative electrode conductive agent, a dispersant or a negative electrode binder. The present application does not particularly limit the types of the negative electrode conductive agent, the dispersant and the negative electrode binder in the negative electrode active material layer, as long as the object of the present application can be achieved. The present application does not particularly limit the mass ratio of the negative electrode active material, the negative electrode conductive agent, the dispersant and the negative electrode binder in the negative electrode active material layer, as long as the object of the present application can be achieved. For example, the mass ratio of the negative electrode active material, the negative electrode conductive agent, the dispersant and the negative electrode binder in the negative electrode active material layer is (94 to 98):(0.5 to 2.0):(0 to 1.5):(1.0 to 2.5).

[0061] The present application places no particular restrictions on the positive electrode sheet, as long as the object of the present application can be achieved. In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is disposed on one surface or both surfaces of the positive electrode current collector. The above "surface" may be a partial surface or the entire surface of the positive electrode current collector. The present application places no particular restrictions on the positive electrode current collector, as long as the object of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil or aluminum alloy foil, etc. The positive electrode active material layer of the present application contains a positive electrode active material. The present application places no particular restrictions on the type of the positive electrode active material, as long as the object of the present application can be achieved. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate, etc. In the present application, the positive electrode active material may further contain a non-metallic element, and the non-metallic element may include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur, and these elements can further improve the stability of the positive electrode active material. In the present application, there are no particular restrictions on the thicknesses of the positive electrode current collector and the positive electrode active material layer, 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. The thickness of a single-layer positive electrode active material layer is 30 μm to 120 μm. Optionally, the positive electrode active material layer may further include at least one of a positive electrode conductive agent or a positive electrode binder. The present application places no particular restrictions on the types of the positive electrode conductive agent and the positive electrode binder in the positive electrode active material layer, as long as the object of the present application can be achieved. The present application places no particular restrictions on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active material layer, and those skilled in the art can select according to actual needs, as long as the object of the present application can be achieved. For example, the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active material layer is (97.5 to 97.9):(0.8 to 1.7):(1.0 to 2.0).

[0062] The present application places no particular restrictions on the separator, as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film, or a spun film. The present application places no particular restrictions on the thickness of the separator, as long as the object of the present application can be achieved.

[0063] The secondary battery of the present application further includes a housing and an electrolyte. The positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte are accommodated in the housing. The present application places no particular limitation on the housing and the electrolyte, and the well-known housing and electrolyte in the present application can be selected according to actual needs, as long as the object of the present application can be achieved.

[0064] The secondary battery of the present application is not particularly limited, and it may include any device that undergoes an electrochemical reaction. For example, the secondary battery may 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.

[0065] In one embodiment of the present application, the secondary battery of the present application is a cylindrical secondary battery.

[0066] The present application does not particularly limit the method for preparing the negative electrode sheet, as long as the object of the present application can be achieved. For example, in one embodiment, the method for preparing the negative electrode sheet includes, but is not limited to, the following steps: (1) arranging a groove within the scope of the present application in the area where the negative electrode active material layer is provided on the first surface of the negative electrode current collector in the direction from the first surface to the second surface; (2) coating a negative electrode slurry on the first surface of the negative electrode current collector and drying it to form a negative electrode active material layer; (3) coating a negative electrode slurry on the second surface of the negative electrode current collector, drying it, cold pressing, and slitting to obtain a negative electrode sheet with a negative electrode active material layer provided on both sides. In another embodiment, the method for preparing the negative electrode sheet includes, but is not limited to, the following steps: (1) arranging a groove within the scope of the present application in the area where the negative electrode active material layer is provided on the first surface of the negative electrode current collector in the direction from the first surface to the second surface; (2) coating a negative electrode slurry on the first surface of the negative electrode current collector, drying it, cold pressing, and slitting to obtain a negative electrode sheet with a negative electrode active material layer provided on one side. In still another embodiment, the method for preparing the negative electrode sheet includes, but is not limited to, the following steps: (1) arranging a groove within the scope of the present application in the area where the negative electrode active material layer is provided on the first surface of the negative electrode current collector in the direction from the first surface to the second surface; arranging a groove within the scope of the present application in the area where the negative electrode active material layer is provided on the second surface of the negative electrode current collector in the direction from the second surface to the first surface; (2) coating a negative electrode slurry on the first surface of the negative electrode current collector and drying it to form a negative electrode active material layer; (3) coating a negative electrode slurry on the second surface of the negative electrode current collector, drying it, cold pressing, and slitting to obtain a negative electrode sheet with a negative electrode active material layer provided on both sides. The present application does not particularly limit the solid content of the above-mentioned negative electrode slurry, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved. The present application does not particularly limit the process parameters of the above-mentioned drying, cold pressing, and slitting, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved. The present application does not particularly limit the method for preparing the groove, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved. For example, it can be achieved by an etching process.

[0067] The present application does not particularly limit the method for preparing the secondary battery, and a well-known preparation method in the art can be selected as long as the object of the present application can be achieved. For example, the method for preparing the secondary battery includes, but is not limited to, the following steps: stacking a separator, a positive electrode sheet, a separator, and a negative electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly, placing the electrode assembly into a housing, injecting an electrolyte into the housing and sealing it to obtain a secondary battery; or stacking a separator, a positive electrode sheet, a separator, and a negative electrode sheet in sequence, then fixing the four corners of the entire laminated structure to obtain a laminated electrode assembly, placing the electrode assembly into a housing, injecting an electrolyte into the housing and sealing it to obtain a secondary battery.

[0068] The second aspect of the present application provides an electronic device, which includes the secondary battery described in any of the foregoing embodiments. Therefore, the electronic device has good performance in use.

[0069] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device may include but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, minidiscs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries, and lithium-ion capacitors.

[0070] Examples

[0071] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods.

[0072] Test methods and equipment:

[0073] Measurement of the particle size Dv50 of the negative electrode active material:

[0074] The Dv50 of the negative electrode active material is measured using a laser particle size analyzer.

[0075] Measurement of the coating surface density CW of the negative electrode active material layer:

[0076] After discharging the lithium-ion batteries of each example and comparative example to 2.5V, the negative electrode plates are disassembled. After cleaning the surface of the negative electrode plates with DMC, the negative electrode plates are punched into small circular pieces with a radius of 22.14 mm (area 1540.25 mm 2 ) and then weighed, and the weight of the negative electrode current collector with the same area is subtracted, which is the coating surface density CW of the negative electrode plate.

[0077] Measurement of cycle performance:

[0078] The specific test process is as follows: 1) The test temperature is 25°C; 2) Stand still for 30 min; 3) Charge at a constant current of 8 A until 4.2 V, and then charge at a constant voltage of 4.2 V until 0.05C; 4) Stand still for 30 min; 5) Discharge at a constant current of 40 A for more than 600 min; 6) If the temperature ≥ 75°C, jump to step 8; 7) If the voltage ≤ 2.5 V, jump to step 10; 8) Stand still for 20000 min; 9) If the temperature ≤ 50°C, jump to step 5; 10) Stand still for 60 min; 11) Repeat steps 3 to 10 for 400 times.

[0079] Calculation of capacity retention rate: The capacity retention rate (%) of the Xth cycle = (discharge capacity of the Xth cycle / discharge capacity of the second cycle) × 100%.

[0080] Recording of the number of cycles: Record X as the number of cycles.

[0081] Recording of the number of diving cycles: The number of cycles when the capacity attenuation accelerates during cycling. The number of cycles at the attenuation acceleration point (inflection point) of the cycling trend is the number of diving cycles; it should be noted that when the diving phenomenon occurs, there will be an obvious difference in the slope of the cycling trend, and the attenuation acceleration point can be judged.

[0082] When the diving phenomenon does not occur during cycling, the cycling performance is characterized by the capacity retention rate. The higher the capacity retention rate, the better the cycling performance of the lithium-ion battery. When the diving phenomenon occurs during cycling, the cycling performance is characterized by the number of diving cycles. The larger the number of diving cycles, the later the cycling performance of the lithium-ion battery deteriorates, indicating that the cycling performance of the lithium-ion battery is better.

[0083] Test of impact passing rate:

[0084] After charging the lithium-ion batteries of each example and comparative example at a constant current of 2C to 4.2 V, charge at a constant voltage of 4.2 V until 0.05C to reach the full charge state. Place the fully charged lithium-ion battery on the test table, place a round bar with a diameter of φ15.8 mm and a length of 15.8 cm at the center position of the wide surface of the lithium-ion battery. The longitudinal axes of the lithium-ion battery and the round bar are both parallel to the surface of the test table and the longitudinal axis of the lithium-ion battery is perpendicular to the longitudinal axis of the round bar (in a cross shape). Use a 9.1 kg weight to fall vertically freely from a height of 610 mm and drop on the intersection of the round bar and the lithium-ion battery. The above lithium-ion battery is a cylindrical lithium-ion battery.

[0085] Judgment criterion: Pass if there is no fire, explosion, or liquid leakage.

[0086] Test 15 lithium-ion batteries for each example or comparative example, and represent the impact passing rate as "number of passes / 15". The more the number of passes, the better the safety performance of the lithium-ion battery.

[0087] Example 1-1

[0088] <Preparation of Negative Electrode Plate>

[0089] Select a negative electrode current collector with a structure as Figure 7 shown, but not limited to Figure 7 . The original thickness ε of the negative electrode current collector is 12 μm. In the direction from the first surface to the second surface, grooves are provided in the area of the first surface of the negative electrode current collector where the negative electrode active material layer is provided. In the direction from the second surface to the first surface, grooves are also provided in the area of the second surface of the negative electrode current collector where the negative electrode active material layer is provided. The shape of the groove is as Figure 7 shown, which is arc-shaped. The width d of the groove is 0.7 μm, the depth h of the groove is 2 μm, and the length of the groove is 60 mm. The thickness ε1 of the thinnest area in the negative electrode current collector is ε - h = 10 μm. The grooves are equally spaced and parallelly distributed. The distance σ between the center lines of two adjacent grooves is 40 μm, and the angle θ between the center line of the groove and the length direction of the negative electrode current collector itself is 90°. The grooves on the second surface of the negative electrode current collector and the grooves on the first surface of the negative electrode current collector are staggered in the thickness direction of the negative electrode current collector.

[0090] Mix artificial graphite as the negative electrode active material, conductive carbon black (Super P) as the negative electrode conductive agent, carboxymethyl cellulose (CMC) as the dispersant, and styrene-butadiene rubber (SBR, weight average molecular weight is 5×10 6 ) in a mass ratio of 96:1.3:1.7:1, and then add deionized water as a solvent and stir in a vacuum mixer until a negative electrode slurry with a solid content of 50 wt% and a uniform system is obtained. The negative electrode slurry is uniformly coated on the first surface of the negative electrode current collector copper foil and dried at 90°C to obtain a negative electrode plate with a negative electrode active material layer coated on one side. Then, repeat the above steps on the second surface of the copper foil to obtain a negative electrode plate with negative electrode active material layers coated on both sides. After cold pressing and slitting, a negative electrode plate with a specification of 1500 mm × 65 mm is obtained for use. For the setting of the negative electrode tab, refer to Figure 8 . When setting the negative electrode active material layer 12 on the surface of the negative electrode current collector 11, a region (width 5 mm) shown by the dotted box A is reserved along the width direction Y of the negative electrode current collector 11 as the negative electrode tab 13. Among them, the particle size Dv50 of the negative electrode active material is 10 μm, and the coating surface density CW of the negative electrode active material layer is 240 mg / 1540 mm 2 . On the plane formed by the length and width of the negative electrode current collector itself, the total area S1 of the grooves is 1.55×10 -3 m 2 , the total area S2 of the negative electrode active material layer is 0.09 m 2 , and S1 / S2×100% = 2%.

[0091] <Preparation of the positive electrode tab>

[0092] Mix the positive active material lithium nickel cobalt manganese oxide NCM811, the positive binder polyvinylidene fluoride (PVDF, weight average molecular weight of 5×10 5 ) and the positive conductive agent conductive carbon black in a mass ratio of 94.8:2.8:2.4, add N-methylpyrrolidone (NMP) as a solvent, and stir in a vacuum mixer until a positive electrode paste with a solid content of 75 wt% and a uniform system is obtained. Coat the positive electrode paste evenly on one surface of a positive current collector aluminum foil with a thickness of 13 μm, and dry it at 100 °C to obtain a positive electrode tab with a single-sided coated positive active material layer (thickness 50 μm). Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode tab with a double-sided coated positive active material layer. After cold pressing and slitting, a positive electrode tab with a specification of 1450 mm×63 mm is obtained for use. Among them, for the setting of the positive electrode tab, refer to Fig. 9 , when setting the positive active material layer 22 on the surface of the positive current collector 21, along the width direction Y of the positive current collector 21, reserve the area shown by the dotted box B as the positive electrode tab 23 for use.

[0093] <Preparation of the separator>

[0094] Use a polyethylene (PE) porous film with a thickness of 8 μm as the separator.

[0095] <Preparation of the electrolyte>

[0096] In a dry argon atmosphere, mix the organic solvents ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a mass ratio of 30:50:20 to obtain an organic solution, and then add lithium hexafluorophosphate as a lithium salt to the organic solvent, dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0097] <Preparation of the lithium-ion battery>

[0098] Stack and wind the separator, negative electrode tab, separator and positive electrode tab prepared above in sequence to obtain a wound electrode assembly. Place the electrode assembly in a cylindrical shell, perform vacuum drying, welding, electrolyte injection and sealing, and perform formation and capacity testing after standing at 45 °C for a high temperature to obtain a full-tab cylindrical lithium-ion battery (model 21700).

[0099] Examples 1-2 to Examples 1-9

[0100] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Example 1-1.

[0101] Among them, when the value of S1 / S2×100% changes, S1 changes and S2 remains unchanged.

[0102] Examples 2-1 to 2-15

[0103] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Example 1-2.

[0104] Example 2-16

[0105] <Preparation of negative electrode sheet>

[0106] Select a negative electrode current collector with a structure as Figure 6 shown, but not limited to Figure 6 . The original thickness ε of the negative electrode current collector is 12 μm. In the direction from the first surface to the second surface, grooves are provided in the area of the first surface of the negative electrode current collector where the negative electrode active material layer is provided. The shape of the groove is as Figure 6 shown, being arc-shaped, and the thickness ε1 of the thinnest area in the negative electrode current collector is ε - h = 10 μm.

[0107] The rest is the same as in Example 1-2.

[0108] Examples 3-1 to 3-11

[0109] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Example 1-2.

[0110] Among them, when the value of S1 / S2×100% changes, S1 changes and S2 remains unchanged.

[0111] Examples 4-1 to 4-4

[0112] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as in Example 1-2.

[0113] Comparative Example 1

[0114] Except for not providing grooves in <Preparation of negative electrode sheet>, the rest is the same as in Example 1-1.

[0115] Comparative Examples 2 and 3

[0116] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0117] The preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 to 4.

[0118] Table 1

[0119]

[0120]

[0121] Note: The "\ " in Table 1 indicates no corresponding parameter.

[0122] It can be seen from Examples 1-1 to 1-9 and Comparative Examples 1 to 3 that when the negative electrode active material with a Dv50 particle size within the scope of this application is selected in the secondary battery of this application, a groove with a width within the scope of this application is provided in the negative electrode current collector region where the negative electrode active material layer is provided. The secondary battery has a higher cycle capacity retention rate and number of cycles, no diving occurs during the cycling process, and has a higher impact passing rate, indicating that the secondary battery of this application has improved cycling performance on the basis of good safety performance. For the secondary batteries of the comparative examples, no groove is provided or the groove width is not within the scope of this application, and they have a lower cycle capacity retention rate and diving occurs earlier during the cycling process., indicating that the cycling performance of the secondary batteries of the comparative examples is poor.

[0123] The width d of the groove usually affects the cycling performance and safety performance of the secondary battery. It can be seen from Examples 1-1 to 1-7, Comparative Example 2 and Comparative Example 3 that for the secondary battery with the groove width d within the scope of this application, it has a higher cycle capacity retention rate when the number of cycling turns is 400, no diving occurs during the cycling process, and has a higher impact passing rate, indicating that the secondary battery has good cycling performance and safety performance.

[0124] The Dv50 particle size of the negative electrode active material usually affects the cycling performance and safety performance of the secondary battery. It can be seen from Examples 1-4, 1-8 and 1-9 that for the secondary battery with the Dv50 particle size of the negative electrode active material within the scope of this application, it has a higher cycle capacity retention rate when the number of cycling turns is 400, no diving occurs during the cycling process, and has a higher impact passing rate, indicating that the secondary battery has good cycling performance and safety performance.

[0125] Table 2

[0126]

[0127]

[0128] Note: The difference between Example 1-2 and Example 2-16 in Table 2 is that: the negative electrode current collector in Example 1-2 is provided with grooves on both surfaces, and the negative electrode current collector in Example 2-16 is provided with grooves on only one surface.

[0129] The depth h of the groove, the original thickness ε of the negative current collector, and the coating areal density CW of the negative active material layer generally also affect the cycle performance and safety performance of the secondary battery. It can be seen from Examples 1-2, Examples 2-1 to Examples 2-15 that for secondary batteries with the depth h of the groove, the original thickness ε of the negative current collector, and the coating areal density CW of the negative active material layer within the scope of this application, they have a high cycle capacity retention rate when the number of cycles is 400, no diving occurs during the cycling process or diving occurs relatively late during the cycling process, and they have a high impact passing rate, indicating that the secondary battery has good cycle performance and safety performance. Among them, in Example 2-7, no diving occurred during the cycling process, and its cycle performance was better than that of Example 2-1. However, its impact passing rate was 5 / 15, far lower than the impact passing rate of 15 / 15 of Example 2-1. Therefore, Example 2-1 is more capable of balancing the cycle performance and safety performance of the secondary battery. The cycle performance and impact passing rate of Example 2-14 are better than or equivalent to those of Example 1-2, Example 2-11, and Example 2-3. However, due to the low coating areal density CW of Example 2-14, the energy density of the secondary battery in Example 2-14 is low, which is not conducive to the practical utilization of the secondary battery. Therefore, it is not within the preferred scope of this application.

[0130] The groove being provided on one surface or two surfaces of the negative current collector generally also affects the cycle performance and safety performance of the secondary battery. It can be seen from Examples 1-2 and Example 2-16 that for secondary batteries with the groove provided within the position range of this application, they have a high cycle capacity retention rate when the number of cycles is 400, no diving occurs during the cycling process, and they have a high impact passing rate, indicating that the secondary battery has good cycle performance and safety performance.

[0131] Table 3

[0132]

[0133]

[0134] The value of S1 / S2×100% and the distance σ between the centerlines of two adjacent grooves generally also affect the cycle performance and safety performance of the secondary battery. It can be seen from Examples 1-2, Examples 3-1 to Examples 3-11 that for secondary batteries with the value of S1 / S2×100% and the distance σ between the centerlines of two adjacent grooves within the scope of this application, they have a high cycle capacity retention rate when the number of cycles is 400, no diving occurs during the cycling process or diving occurs relatively late during the cycling process, and they have a high impact passing rate, indicating that the secondary battery has good cycle performance and safety performance.

[0135] Table 4

[0136]

[0137] The included angle θ between the center line of the groove and the length direction of the negative current collector itself usually affects the cycle performance and safety performance of the secondary battery. It can be seen from Examples 1-2, Examples 4-1 to 4-4 that for the secondary battery with the included angle θ between the center line of the groove and the length direction of the negative current collector itself within the scope of this application, it has a high cycle capacity retention rate when the number of cycles is 400, no diving occurs during the cycling process or diving occurs relatively late during the cycling process, and it has a high impact passing rate, indicating that the secondary battery has good cycle performance and safety performance.

[0138] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0139] Each embodiment in this specification is described in a related manner. The same or similar parts between each embodiment can be referred to each other, and the differences between each embodiment and other embodiments are emphasized.

[0140] The above description is only the preferred embodiment of this application and is not intended to limit this application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the scope of protection of this application.

Claims

1. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, and the particle size Dv50 of the negative electrode active material is 0.2 μm to 20 μm; The negative electrode current collector includes opposite first and second surfaces, and in a direction from the first surface to the second surface, at least one groove is provided in a region where the negative electrode active material layer is provided on the negative electrode current collector, and the width of the groove is d, 0.1 μm ≤ d ≤ Dv50.

2. The secondary battery according to claim 1, wherein, The depth h μm of the groove, the original thickness ε μm of the negative current collector, and the coating areal density CW mg / 1540 mm of the negative active material layer satisfy: 0.5 ≤ h ≤ (0.9 2 between them satisfy: 0.5 ≤ h ≤ (0.9 ε - 4×10 -3 (CW), where 4 ≤ ε ≤ 30 and 20 ≤ CW ≤ 400.

3. The secondary battery according to claim 2, wherein, 1 ≤ h ≤ (0.9ε - 6×10 -3 CW).

4. The secondary battery according to claim 1, wherein, On the plane formed by the length and width of the negative electrode current collector itself, the total area S1 m of the grooves 2 and the total area S2 m of the negative electrode active material layer 2 satisfy: 0.1% ≤ S1 / S2 × 100% ≤ 70%, 3×10 -4 ≤ S2 ≤ 12.

5. The secondary battery according to claim 1, wherein, The distance between the centerlines of two adjacent grooves is σ, 1.5d ≤ σ ≤ 5 cm.

6. The secondary battery according to claim 1, wherein, The angle θ between the centerline of the groove and the length direction of the negative electrode current collector itself is 30° to 90°.

7. The secondary battery according to claim 1, wherein, The secondary battery satisfies at least one of the following characteristics: (1) 1 μm ≤ d ≤ 0.5×Dv50; (2) On the plane formed by the length and width of the negative electrode current collector itself, the total area S1 m of the grooves 2 and the total area S2 m of the negative electrode active material layer 2 satisfy: 0.2% ≤ S1 / S2 × 100% ≤ 50%; (3) The distance between the centerlines of two adjacent grooves is σ, 5d ≤ σ ≤ 3 cm; (4) The angle θ between the centerline of the groove and the length direction of the negative electrode current collector itself is 45° to 90°.

8. The secondary battery according to claim 1, wherein, The thickness ε1 μm of the thinnest region in the negative electrode current collector, the original thickness ε μm of the negative electrode current collector, and the coating surface density CW mg / 1540 mm of the negative electrode active material layer satisfy: ε1 ≥ 0.1ε + 4×10 2 CW. -4 ​ 9. The secondary battery according to any one of claims 1 to 8, wherein, In a direction from the second surface to the first surface, at least one such groove is provided in a region where the negative electrode active material layer is provided on the negative electrode current collector.

10. The secondary battery according to claim 9, wherein, At least two of the grooves located on the first surface and the second surface are parallel or intersect with each other.

11. An electronic device, wherein, The electronic device includes the secondary battery according to any one of claims 1 to 10.

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