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 Dv99 of the negative electrode active material is 20 [mu] m to 80 [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 1.5 * Dv99 and smaller than or equal to 5mm. Through the arrangement, the secondary battery has good safety performance and rate capability in the later period of circulation.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry technology, and particularly 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 advantages such as high specific energy, high working voltage, low self-discharge rate, small size, and light weight. The rate performance of existing secondary batteries tends to deteriorate in the later stage of cycling. Based on this, how to improve the rate performance of secondary batteries in the later stage of cycling has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0003] The purpose of the present application is to provide a secondary battery and an electronic device, so as to improve the rate performance of the secondary battery in the later stage of cycling on the basis of having good safety performance.

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

[0005] In the first aspect of the present application, a secondary battery is provided. The secondary battery 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 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 Dv99 of the negative electrode active material is 20 μm to 80 μm. The negative electrode current collector includes opposite first and second surfaces. In the direction from the first surface to the second surface, at least one groove is provided in the region of the negative electrode current collector where the negative electrode active material layer is provided. The width of the groove is d, and 1.5×Dv99 ≤ d ≤ 5 mm. By selecting a negative electrode active material with a particle size Dv99 within the above range and providing 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 provided, when the negative electrode slurry is coated on the surface of the negative electrode current collector, the particles of the negative electrode active material in the negative electrode slurry can enter the groove, so as to improve the adhesion between the negative electrode active material layer and the negative electrode current collector in the negative electrode plate. In this way, during the cycling of the secondary battery, the negative electrode plate has a high adhesion, and the probability of the negative electrode active material layer peeling off from the negative electrode current collector is reduced, thereby improving the rate performance of the secondary battery in the later stage of cycling. Moreover, when the negative electrode plate has a high adhesion, the probability of short circuit caused by the contact between the negative electrode current collector and the positive electrode after the negative electrode active material layer peels off under working conditions such as impact of the secondary battery is also reduced, thereby improving the impact passing rate of the secondary battery and enabling the secondary battery to have good safety performance.

[0006] In one or more embodiments of the present application, 1.5×Dv99≤d≤2 mm. By regulating d within the above range, the secondary battery can further improve its rate performance on the basis of good safety performance.

[0007] In one or more embodiments of the present application, the depth h of the groove satisfies the following relationship with the thickness w of the negative electrode active material layer and the original thickness ε of the negative electrode current collector: w / 100≤h≤0.8ε, where 10 μm≤w≤300 μm and 4 μm≤ε≤40 μm. By regulating the relationship between the depth h of the groove, the thickness w of the negative electrode active material layer, and the original thickness ε of the negative electrode current collector, and regulating the thickness w of the negative electrode active material layer and the original thickness ε of the negative electrode current collector within the above range, the negative electrode tab has a high adhesive force, and the secondary battery has good safety performance and rate performance.

[0008] In one or more embodiments of the present application, w / 80≤h≤0.5ε, where 30 μm≤w≤200 μm and 6 μm≤ε≤40 μm. By regulating the relationship between the depth h of the groove, the thickness w of the negative electrode active material layer, and the original thickness ε of the negative electrode current collector, and regulating the thickness w of the negative electrode active material layer and the original thickness ε of the negative electrode current collector within the above range, the rate performance of the secondary battery can be further improved on the basis of good safety performance.

[0009] In one or more embodiments of the present application, the total volume V1 of the grooves and the total volume V2 of the portion of the negative electrode current collector provided with the negative electrode active material layer satisfy: 0.01%≤V1 / V2×100%≤60%, 1.5×10 -9 m 3 ≤V2≤9×10 - 4 m 3 . By regulating the relationship between the total volume V1 of the grooves and the total volume V2 of the portion of the negative electrode current collector provided with the negative electrode active material layer, and regulating the total volume V2 of the portion of the negative electrode current collector provided with the negative electrode active material layer within the above range, the secondary battery can have good safety performance and rate performance.

[0010] In one or more embodiments of the present application, 0.2%≤V1 / V2×100%≤40%. By regulating the relationship between the total volume V1 of the grooves and the total volume V2 of the portion of the negative electrode current collector provided with the negative electrode active material layer within the above range, the rate performance of the secondary battery can be further improved on the basis of good safety performance.

[0011] In one or more embodiments of the present application, the distance between two adjacent grooves is from 0.1 mm to 50 mm. By regulating the distance between two adjacent grooves within the above range, the secondary battery has good safety performance and rate performance.

[0012] In one or more embodiments of the present application, the distance between two adjacent grooves is 0.5 mm to 30 mm. By adjusting the distance between two adjacent grooves within the above range, the secondary battery can further improve its rate performance on the basis of good 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 0° to 90°. When the angle θ between the center line of the groove and the length direction of the negative electrode current collector itself is adjusted within the above range, the negative electrode plate has a high adhesive force, and the secondary battery has good safety performance and rate performance.

[0014] In one or more embodiments of the present application, the thickness ε1 of the thinnest region in the negative electrode current collector and the original thickness ε of the negative electrode current collector satisfy: ε1 ≥ 0.2ε. When the thickness of the thinnest region in the negative electrode current collector and the original thickness of the negative electrode current collector satisfy the above relationship, the secondary battery can have good safety performance and rate performance.

[0015] In one or more embodiments of the present application, at least one groove is provided in the region where the negative electrode active material layer is provided on the negative electrode current collector in the direction from the second surface to the first surface. By providing at least one groove in the region where the negative electrode active material layer is provided on the negative electrode current collector in the direction from the second surface to the first surface, the safety performance and rate performance of the secondary battery can be further improved.

[0016] 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 or intersect with each other. By setting the positional relationship between the above grooves, the secondary battery has good safety performance and rate performance.

[0017] The second aspect of the present application provides an electronic device, which includes the secondary battery described in any one of the foregoing embodiments. Thus, the electronic device has good use performance.

[0018] Beneficial effects of the embodiments of the present application:

[0019] In the secondary battery according to the embodiment of the present application, by selecting a negative electrode active material with a Dv99 particle size within the above range and providing a groove with a width within the above range in the area of the negative electrode current collector where the negative electrode active material layer is provided, when the negative electrode paste is coated on the surface of the negative electrode current collector, the particles of the negative electrode active material in the negative electrode paste can enter the groove, so as to improve the adhesion between the negative electrode active material layer and the negative electrode current collector in the negative electrode sheet. In this way, during the cycling process of the secondary battery, the negative electrode sheet has a high adhesion, and the probability of the negative electrode active material layer peeling off from the negative electrode current collector is reduced, thereby improving the rate performance of the secondary battery in the later stage of cycling. Moreover, when the negative electrode sheet has a high adhesion, in the case of impacts and other conditions of the secondary battery, the probability of short circuit caused by the contact between the negative electrode current collector and the positive electrode after the negative electrode active material layer peels off is also reduced, thereby improving the impact passing rate of the secondary battery and enabling the secondary battery to have good safety performance.

[0020] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application, and those of ordinary skill in the art can also obtain other embodiments according to these drawings.

[0022] Figure 1 It is a schematic cross-sectional structure view of a negative electrode sheet of an implementation solution of the present application along its thickness direction and length direction;

[0023] Figure 2 It is a top view of a negative electrode current collector of an implementation solution of the present application;

[0024] Figure 3 It is a schematic cross-sectional structure view of a negative electrode sheet of another implementation solution of the present application along its thickness direction and length direction;

[0025] Figure 4 It is a top view of a negative electrode current collector of another implementation solution of the present application;

[0026] Figure 5 It is a schematic cross-sectional structure view of a negative electrode current collector of some embodiments of the present application along its thickness direction and length direction;

[0027] Figure 6 It is a schematic cross-sectional structure view of a negative electrode current collector of some other embodiments of the present application along its thickness direction and length direction;

[0028] Figure 7Schematic diagram of the positional relationship of the negative electrode tab on the negative electrode sheet in some embodiments of the present application;

[0029] Figure 8 Schematic diagram of the positional relationship of the positive electrode tab on the positive electrode sheet in some embodiments of the present application.

[0030] Reference numerals: 10 - negative electrode sheet; 11 - negative current collector; 12 - negative active material layer; 13 - negative electrode tab; 14 - center line; 111 - first surface; 112 - second surface; 20 - groove; 21 - positive current collector; 22 - positive active material layer; 23 - positive electrode tab. Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a 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.

[0032] It should be noted that in the specific implementation manners of the present application, a lithium-ion battery is used as an example of a secondary battery to explain the present application, but the secondary battery of the present application is not limited to lithium-ion batteries.

[0033] In a first aspect of the present application, a secondary battery is provided. The secondary battery includes a positive electrode sheet, a negative electrode sheet, and a separator. The negative electrode sheet includes a negative current collector and a negative active material layer. The negative active material layer is disposed on at least one surface of the negative current collector. The negative active material layer includes a negative active material, and the particle size Dv99 of the negative active material is 20 μm to 80 μm. The negative current collector includes opposite first and second surfaces. In the direction from the first surface to the second surface, at least one groove is provided in the region where the negative active material layer is disposed on the negative current collector. The width of the groove is d, and 1.5×Dv99 ≤ d ≤ 5 mm.

[0034] For ease of understanding, in the present application, the self-length direction of the negative electrode sheet is defined as X, the self-width direction is defined as Y, and the self-thickness direction is defined as Z. It should be understood that the above definitions of directions are for the purpose of conveniently describing the present application, and the directions defined in the present application can be understood according to the relative positions of the accompanying drawings and the actual product elements. Moreover, the width direction, length direction, and thickness direction of the negative active material layer and the negative current collector itself are the same as those of the negative electrode sheet. The above "the negative active material layer is disposed on at least one surface of the negative current collector" means that the negative active material layer is disposed on one surface or two surfaces of the negative current collector, and the above "surface" can be a partial surface or the entire surface of the negative current collector. For example Figure 1As shown in the figure, the negative electrode plate 10 includes a negative electrode current collector 11 and a negative electrode active material layer 12. The negative electrode current collector 11 includes opposite first surface 111 and second surface 112. The negative electrode active material layer 12 is disposed on the first surface 111 of the negative electrode current collector 11. In the direction from the first surface 111 to the second surface 112, a groove 20 is provided in the area of the negative electrode current collector 11 where the negative electrode active material layer 12 is disposed, that is, along the thickness direction Z of the negative electrode current collector 11, a groove 20 is provided in the area of the first surface 111 of the negative electrode current collector 11 where the negative electrode active material layer 12 is disposed. The width of the groove 20 is d μm. Of course, in some other embodiments, the negative electrode active material layer 12 may be disposed on both the first surface 111 and the second surface 112 of the negative electrode current collector simultaneously. It should be noted that the shape, number, size, and spacing between adjacent grooves in the drawings of this application are only for illustrative purposes, and this application is not limited thereto. In this application, the above-mentioned "at least one groove" means that the number of grooves is more than 1 in the area of the negative electrode current collector where the negative electrode active material layer is disposed. This application does not particularly limit the specific number of grooves, and those skilled in the art can adjust according to the coating setting of the negative electrode active material layer and the setting of the grooves, as long as the purpose of this application can be achieved.

[0035] For example, the volume median diameter Dv99 of the negative electrode active material is 20 μm, 26 μm, 33 μm, 41 μm, 46 μm, 50 μm, 53 μm, 56 μm, 59 μm, 64 μm, 70 μm, 72 μm, 76 μm, 77 μm, 80 μm or any value between any two of the above numerical ranges. When the volume median diameter Dv99 of the negative electrode active material is less than 20 μm, it indicates that the volume particle size of the negative electrode active material particles is too small, and the negative electrode active material particles are prone to agglomeration during the preparation of the negative electrode slurry. In this way, the probability of the negative electrode active material being uniformly dispersed in the negative electrode slurry is extremely small, and the distribution of the negative electrode active material particles in the formed negative electrode active material layer is uneven, which will affect the processing stability of the negative electrode plate and cause problems such as uneven coating during the coating process of the negative electrode slurry; moreover, the specific surface area of the negative electrode active material particles will be too large, resulting in an increase in the interface between the negative electrode active material particles and the electrolyte, and the side reactions will intensify, which will accelerate the consumption of the electrolyte and generate a large amount of side reaction products, thereby deteriorating the cycle performance, rate performance, and high-temperature stability of the secondary battery; when the volume median diameter Dv99 of the negative electrode active material is greater than 80 μm, it indicates that the volume particle size of the negative electrode active material particles is too large, the transmission path of lithium ions inside the negative electrode active material particles is too long, and the tortuosity of the transmission in the negative electrode plate is too large, which will affect the rate performance of the secondary battery, and it is easy to cause the thickness of the negative electrode active material layer to be too thick, thereby resulting in a loss of energy density of the secondary battery due to the increase in thickness.

[0036] The width d of the groove is less than 1.5×Dv99. If the width of the groove is too small, some negative active material particles cannot enter the groove, and the adhesion of the negative electrode sheet is not significantly improved. If the width d of the groove is greater than 5 mm, the number of grooves provided will be reduced, and the density of the grooves on the surface of the negative current collector is too small, so that the adhesion of the negative electrode sheet is not significantly improved. In the present application, the width d of the groove generally refers to the maximum horizontal distance of the groove measured along the length direction of the negative current collector.

[0037] In the present application, by selecting a negative active material with Dv99 within the above range and providing grooves with widths within the above range in the area of the negative current collector provided with the negative active material layer, when the negative electrode paste is coated on the surface of the negative current collector, the negative active material particles in the negative electrode paste can enter the grooves to improve the adhesion between the negative active material layer and the negative current collector in the negative electrode sheet. In this way, during the cycling process of the secondary battery, the negative electrode sheet has a high adhesion, and the probability of the negative active material layer peeling off from the negative current collector is reduced, thereby improving the rate performance of the secondary battery in the later stage of cycling. Moreover, when the negative electrode sheet has a high adhesion, during conditions such as impact of the secondary battery, the probability of short circuit caused by the contact between the negative current collector and the positive electrode after the negative active material layer peels off is also reduced, thereby improving the impact passing rate of the secondary battery and making the secondary battery have good safety performance.

[0038] In an embodiment of the present application, 1.5×Dv99≤d≤2 mm. By adjusting d within the above range, when all the negative active material particles in the negative electrode paste can enter the grooves, the grooves are provided with a more appropriate density, which is beneficial to further improving the adhesion of the negative electrode sheet, so that on the basis of the good safety performance of the secondary battery, its rate performance is further improved.

[0039] In the present application, the particle size Dv99 of the negative active material represents the particle size at which the cumulative volume of the negative active material particles reaches 99% starting from the small particle size side in the particle size distribution based on volume. The present application does not particularly limit the adjustment method of Dv99 of the negative active material, as long as the purpose of the present application can be achieved. For example, it can be achieved by directly purchasing a negative active material with Dv99 within the range of the present application, or by means such as crushing, grinding, and ball milling.

[0040] In an embodiment of the present application, as Figure 1As shown, the depth h of the groove 20 satisfies the following relationship with the thickness w of the negative electrode active material layer 12 and the original thickness ε of the negative electrode current collector 11: w / 100 ≤ h ≤ 0.8ε, where 10 μm ≤ w ≤ 300 μm and 4 μm ≤ ε ≤ 40 μm. For example, w is 10 μm, 60 μm, 100 μm, 139 μm, 160 μm, 200 μm, 210 μm, 243 μm, 267 μm, 280 μm, 300 μm, or any value between any two of the above numerical ranges. For example, ε is 4 μm, 10 μm, 13 μm, 16 μm, 18 μm, 22 μm, 26 μm, 30 μm, 33 μm, 38 μm, 40 μm, or any value between any two of the above numerical ranges. By controlling the relationship between the depth h of the groove, the thickness w of the negative electrode active material layer, and the original thickness ε of the negative electrode current collector within the above ranges, while the groove has an appropriate depth to improve the adhesion of the negative electrode plate, the probability of the negative electrode plate breaking due to the relatively deep groove depth is reduced, and the negative electrode plate has good production reliability. Thus, the negative electrode plate has a high adhesion, and the secondary battery has good safety performance and rate performance.

[0041] See Figure 1 , in this application, the "depth h of the groove 20" refers to the vertical distance from the surface of the negative electrode current collector 11 to the lowest point of the groove 20. The "original thickness ε of the negative electrode current collector 11" refers to the thickness of the area of the negative electrode current collector 11 where no groove 20 is provided. The "thickness w of the negative electrode active material layer 12" refers to the vertical distance from the surface of the negative electrode current collector 11 to the surface of the negative electrode active material layer 12, that is, the partial thickness of the negative electrode active material layer 12 that falls into the groove is not included in the thickness of the negative electrode active material layer 12.

[0042] In an embodiment of this application, w / 80 ≤ h ≤ 0.5ε, where 30 μm ≤ w ≤ 200 μm and 6 μm ≤ ε ≤ 40 μm. For example, w is 30 μm, 60 μm, 100 μm, 139 μm, 160 μm, 200 μm, or any value between any two of the above numerical ranges. For example, ε is 6 μm, 10 μm, 13 μm, 16 μm, 18 μm, 22 μm, 26 μm, 30 μm, 33 μm, 38 μm, 40 μm, or any value between any two of the above numerical ranges. By controlling the relationship between the depth h of the groove, the thickness w of the negative electrode active material layer, and the original thickness ε of the negative electrode current collector within the above ranges, on the basis of the secondary battery having good safety performance, its rate performance can be further improved.

[0043] In an embodiment of the present application, the total volume V1 of the grooves and the total volume V2 of the part of the negative electrode current collector provided with the negative electrode active material layer satisfy: 0.01% ≤ V1 / V2 × 100% ≤ 60%, 1.5×10 -9 m 3 ≤ V2 ≤ 9×10 -4 m 3 . For example, the value of V1 / V2 × 100% is 0.01%, 0.05%, 0.2%, 2%, 5%, 9%, 15%, 19%, 20%, 25%, 30%, 35%, 37%, 40%, 41%, 48%, 52%, 55%, 60% or any value between any two of the above numerical ranges. For example, V2 is 1.5×10 -9 m 3 、7×10 -9 m 3 、1.5×10 -8 m 3 、8×10 -8 m 3 、1.5×10 -7 m 3 、1.5×10 -6 m 3 、5×10 -6 m 3 、1.5×10 -5 m 3 、6×10 -5 m 3 、1.5×10 -4 m 3 、9×10 -4 m 3 or any value between any two of the above numerical ranges. By controlling the relationship between the total volume V1 of the grooves and the total volume V2 of the part of the negative electrode current collector provided with the negative electrode active material layer, and the total volume V2 of the part of the negative electrode current collector provided with the negative electrode active material layer within the above range, the grooves can play their role to the fullest, improve the adhesion of the negative electrode plate, and reduce the probability of the negative electrode plate breaking during use. Thus, the secondary battery can have good safety performance and rate performance. In the present application, "the total volume V2 of the part of the negative electrode current collector provided with the negative electrode active material layer" refers to the total volume of the original negative electrode current collector provided with the negative electrode active material layer without grooves.

[0044] In an embodiment of the present application, 0.2% ≤ V1 / V2 × 100% ≤ 40%. For example, the value of V1 / V2 × 100% is 0.2%, 5%, 9%, 15%, 19%, 20%, 25%, 30%, 35%, 37%, 40%, or any value between any two of the above numerical ranges. By regulating the relationship between the total volume V1 of the grooves and the total volume V2 of the part of the negative electrode current collector provided with the negative electrode active material layer within the above range, the secondary battery can further improve its rate performance on the basis of having good safety performance.

[0045] Further, 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 volume V1 of the grooves is 9×10 -10 m 3 to 3.6×10 -4 m 3 and the total volume V2 of the part of the negative electrode current collector provided with the negative electrode active material layer is 1.6×10 -6 m 3 to 9×10 -4 m 3 When the secondary battery of the present application is applied as a small-sized portable battery to portable devices such as mobile phones, laptop computers, and cameras, the total volume V1 of the grooves is 7.5×10 -13 m 3 to 9.6×10 -7 m 3 and the total volume V2 of the part of the negative electrode current collector provided with the negative electrode active material layer is 1.5×10 -9 m 3 to 1.6×10 -6 m 3 .

[0046] There is no particular limitation on the regulation method of the total volume V1 of the grooves 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 grooves, the depth h of the grooves, the spacing between adjacent grooves, etc. Generally, when the depth h of the grooves and the spacing between adjacent grooves are constant, the larger the width d of the grooves, the larger V1; the smaller the width d of the grooves, the smaller V1. The larger the depth h of the grooves, the larger V1; when the width d of the grooves and the spacing between adjacent grooves are constant, the smaller the depth h of the grooves, the smaller V1. When the width d of the grooves and the depth h of the grooves are constant, the larger the spacing σ between adjacent grooves, the smaller V1; the smaller the spacing σ between adjacent grooves, the larger V1.

[0047] In an embodiment of the present application, the spacing σ between adjacent grooves is 0.1 mm to 50 mm. It can be understood that the "spacing σ between adjacent grooves" refers to the shortest distance between the edges of two adjacent grooves. As Figure 2As shown, the spacing between two adjacent grooves 20 is σ. For example, the spacing σ between two adjacent grooves is 0.1mm, 0.5mm, 1mm, 5mm, 10mm, 13mm, 16mm, 20mm, 26mm, 30mm, 36mm, 40mm, 43mm, 47mm, 50mm or any value between any two of the above numerical ranges. The spacing between two adjacent grooves is regulated within the above range so that the grooves provided in the negative electrode current collector region where the negative electrode active material layer is provided have a suitable spacing and density, which is conducive to the grooves to fully play their role and improve the bonding force of the negative electrode sheet. Thereby, the secondary battery has good safety performance and rate performance.

[0048] In one embodiment of the present application, the spacing σ between two adjacent grooves is 0.5 mm to 30 mm. For example, the spacing σ between two adjacent grooves is 0.5 mm, 1 mm, 5 mm, 10 mm, 13 mm, 16 mm, 20 mm, 26 mm, 30 mm, or any value between any two of the above numerical ranges. By adjusting the spacing between two adjacent grooves within the above range, the distance between adjacent grooves is further reduced, which can further improve the bonding force of the negative electrode sheet, so that the secondary battery can further improve the rate performance on the basis of having good safety performance.

[0049] In one embodiment 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 0° to 90°. Figure 2 As shown, the angle between the center line 14 of the groove 20 and the length direction X of the negative electrode current collector 11 itself is θ. For example, θ is 0°, 5°, 9°, 10°, 12°, 15°, 20°, 25°, 30°, 36°, 42°, 46°, 50°, 55°, 60°, 66°, 71°, 75°, 80°, 86°, 90° or any value between any two of the above numerical ranges. When the angle θ between the center line of the groove and the length direction of the negative electrode current collector itself is regulated within the above range, the negative electrode sheet has a higher bonding force, and the secondary battery has good safety performance and rate performance. In the present application, the "center line of the groove" is a line used to mark the center of the groove, that is, a set of line segments representing the midpoint of the groove.

[0050] In one embodiment of the present application, from the second surface to the first surface, at least one groove is provided in the region where the negative electrode active material layer is provided in the negative electrode current collector, 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. Figure 3As shown, the negative electrode current collector 11 includes opposite first and second surfaces 111 and 112, and the negative electrode active material layer 12 is disposed 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 disposed 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 disposed 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 the two surfaces of the negative electrode current collector are provided with the negative electrode active material layer. When the negative electrode paste is coated on the two surfaces of the negative electrode current collector, the particles of the negative electrode active material in the negative electrode paste can enter the grooves, thereby further improving the adhesion of the negative electrode plate and further improving the safety performance and rate performance of the secondary battery.

[0051] 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 2 shown, in one embodiment, the six grooves 20 located on the first surface 111 are parallel to each other. As Figure 4 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 particles of the negative electrode active material in the negative electrode paste to enter the grooves, improve the adhesion of the negative electrode plate, and enable the secondary battery to have good safety performance and rate performance.

[0052] In an embodiment of the present application, the thickness ε1 of the thinnest region in the negative electrode current collector and the original thickness ε of the negative electrode current collector satisfy: ε1≥0.2ε. Further, 0.2ε≤ε1≤39.9 μm. Exemplarily, Figure 5 shows a schematic cross-sectional structure diagram of the negative electrode current collector in the longitudinal direction and the thickness direction in some embodiments. As Figure 5 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 5 In, the original thickness of the negative electrode current collector 11 is shown as ε. From Figure 5 it can be seen that the original thickness ε of the negative electrode current collector 11 refers to the thickness of the negative electrode current collector 11 where no groove 20 is provided. The thickness of the thinnest region in the negative electrode current collector 11 is shown as ε1. From Figure 5 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 6The schematic cross-sectional structure of the negative electrode current collector in some other embodiments along its own length direction and thickness direction is shown. For example, Figure 6 As 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. 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 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 of the negative electrode current collector 11 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 where the groove 20 is provided. For example, Figure 6 At the rightmost side in [reference], 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. When the relationship between the thickness of the thinnest region in the negative electrode current collector and the original thickness of the negative electrode current collector is satisfied, and when all the negative active material particles in the negative electrode slurry enter the grooves, the negative electrode current collector has a relatively high hardness, and during the preparation of the negative electrode plate or during the use of the negative electrode plate, the probability of the negative electrode current collector breaking is relatively low, thereby enabling the secondary battery to have good safety performance and rate performance.

[0053] 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 circular arc, rectangular, triangular, etc.

[0054] The present application does not particularly limit the type of the negative active material, as long as the purpose of the present application can be achieved. For example, the negative 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, spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloy or metallic lithium.

[0055] The present application does not particularly limit the thickness of the negative active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative active material layer is 30 μm to 130 μm.

[0056] This application has no particular limitation on the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the negative electrode current collector may include a copper foil, a copper alloy foil, or the like.

[0057] In one embodiment of this 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. This application has no particular limitation on 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 purpose of this application can be achieved. This application has no particular limitation on 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 purpose of this 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).

[0058] 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-mentioned "surface" can 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 can include aluminum foil, 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 can 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 can also contain non-metallic elements, and the non-metallic elements can include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. These elements can further improve the stability of the positive electrode active material. In the present application, there are no particular restrictions on the thickness 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 can 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. 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 - 97.9):(0.8 - 1.7):(1.0 - 2.0).

[0059] 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 can 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 can 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.

[0060] 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 has 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 purpose of the present application can be achieved.

[0061] The secondary battery of the present application is not particularly limited, and it may include any device that generates 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.

[0062] The present application has no particular limitation on the shape of the secondary battery as long as the purpose of the present application can be achieved. For example, the shape of the secondary battery is cylindrical, square, etc.

[0063] 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 it 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 them 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 it 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.

[0064] 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, and 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.

[0065] 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.

[0066] 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, mobile phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal TVs, 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 batteries, and lithium-ion capacitors.

[0067] Examples

[0068] Hereinafter, examples and comparative examples are given to illustrate the embodiments of the present application more specifically. Various tests and evaluations are carried out according to the following methods.

[0069] Testing methods and equipment:

[0070] Test of the particle size Dv99 of the negative electrode active material:

[0071] The Dv99 of the negative electrode active material is measured using a laser particle size analyzer.

[0072] Test of the adhesion of the negative electrode sheet:

[0073] The negative electrode sheet is cut into strip-shaped specimens with a width × length = 2 cm × 5 cm, and then the negative electrode current collector and the negative electrode active material layer in the strip-shaped specimens are slowly separated using a universal tensile testing machine at a separation angle of 90°, and the force value at the time of separation is recorded. Finally, the adhesion strength of the negative electrode sheet is calculated by software and recorded as the adhesion of the negative electrode sheet.

[0074] Test of the rate performance of the secondary battery in the later stage of cycling:

[0075] (1) The lithium-ion batteries of each example and comparative example are subjected to the following rate performance tests: 1) The test temperature is 25 °C; 2) Stand for 10 min; 3) Charge at a constant current of 1C to 4.2V and charge at a constant voltage of 4.2V to 0.025C; 4) Stand for 30 min; 5) Discharge at a constant current of 0.2C to 2.5V, and record the discharge capacity as the reference capacity C 01; 6) Let it stand for 15 min; 7) Charge at a constant current of 1C to 4.2V and then charge at a constant voltage of 4.2V to 0.025C; 8) Let it stand for 60 min; 9) Discharge at a constant current of 10C to 2.5V and record the discharge capacity as the rate capacity C 11 ; The rate capacity retention rate CR1 = C 01 / C 11 ×100%.

[0076] (2) Then conduct a cycle test: 1) The test temperature is 25°C; 2) Let it stand for 30 min; 3) Charge at a constant current of 8A to 4.2V and then charge at a constant voltage of 4.2V to 0.05C; 4) Let it stand for 30 min; 5) Discharge at a constant current of 30A to 2.5V; 6) Let it stand for 60 min; 7) Repeat steps 3) to 6) 400 times;

[0077] (3) Then conduct the following rate performance test: 1) The test temperature is 25°C; 2) Let it stand for 10 min; 3) Charge at a constant current of 1C to 4.2V and then charge at a constant voltage of 4.2V to 0.025C; 4) Let it stand for 30 min; 5) Discharge at a constant current of 0.2C to 2.5V and record the discharge capacity as the reference capacity C 02 ; 6) Let it stand for 15 min; 7) Charge at a constant current of 1C to 4.2V and then charge at a constant voltage of 4.2V to 0.025C; 8) Let it stand for 60 min; 9) Discharge at a constant current of 10C to 2.5V and record the discharge capacity as the rate capacity C 12 ; The rate capacity retention rate CR2 = C 02 / C 12 ×100%.

[0078] The rate performance = CR2 / CR1×100%, and the higher the rate performance data, the better the rate performance.

[0079] Test of the impact passing rate:

[0080] After charging the lithium-ion batteries of each example and comparative example at a constant current of 2C to 4.2V and then charging at a constant voltage of 4.2V to 0.05C to reach the full charge state. Place the fully charged lithium-ion battery on the test bench, place a round bar with a diameter of φ15.8mm and a length of 15.8cm at the center position of the wide surface of the lithium-ion battery. The longitudinal axes of both the lithium-ion battery and the round bar are parallel to the surface of the test bench 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 9.1kg weight to drop vertically from a height of 610mm in a free state and fall on the intersection of the round bar and the lithium-ion battery. The above lithium-ion battery is a cylindrical lithium-ion battery.

[0081] Judgment criterion: Pass if there is no fire, no explosion, and no leakage.

[0082] Fifteen lithium-ion batteries were tested for each example or comparative example, and the impact passing rate was expressed as "number of passes / 15". The more passes, the better the safety performance of the lithium-ion battery.

[0083] Example 1-1

[0084] <Preparation of negative electrode sheet>

[0085] 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; 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 6 shown, which is arc-shaped. The width d of the groove is 45 μm, the depth h of the groove is 2 μm, and the length of the groove is 60 mm. The grooves are equally spaced and parallelly distributed. The spacing σ between two adjacent grooves is 0.5 mm, 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 first surface and the second surface of the negative electrode current collector are staggered in the thickness direction of the negative electrode current collector.

[0086] Mix the negative electrode active material artificial graphite, negative electrode conductive agent conductive carbon black (Super P), dispersant carboxymethyl cellulose (CMC), and negative electrode binder styrene-butadiene rubber (SBR, weight average molecular weight of 5×10 6 ) in a mass ratio of 96:1.3:1.7:1, 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 sheet with a single-sided coated negative electrode active material layer. Then, repeat the above steps on the second surface of the copper foil to obtain a negative electrode sheet with a double-sided coated negative electrode active material layer. After cold pressing and slitting, a negative electrode sheet with a specification of 1500 mm × 65 mm is obtained for use. Among them, the thickness w of the single-layer negative electrode active material layer is 50 μm. For the setting of the negative electrode tab, refer to Figure 7 . 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 Dv99 of the negative electrode active material is 30 μm. The total volume V1 of the grooves is 3.2×10 -8 m 3 , and the total volume V2 of the part of the negative electrode current collector where the negative electrode active material layer is provided is 1.17×10 -6 m 3, V1 / V2 × 100% = 2.8%.

[0087] <Preparation of the positive electrode sheet>

[0088] Mix the positive electrode active material lithium nickel cobalt manganese oxide NCM811, the positive electrode binder polyvinylidene fluoride (PVDF, weight average molecular weight is 5 × 10 5 ), and the positive electrode 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 slurry with a solid content of 75 wt% and a homogeneous system is obtained. Coat the positive electrode slurry evenly on one surface of a positive electrode current collector aluminum foil with a thickness of 13 μm, and dry it at 100 °C to obtain a positive electrode sheet with a single-sided coated positive electrode active material layer. Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode active material layer. After that, through cold pressing and slitting, a positive electrode sheet with a specification of 1450 mm × 63 mm is obtained for use. Among them, the thickness of the single-layer positive electrode active material layer is 50 μm. Among them, for the setting of the positive electrode tab, refer to Figure 8 , when setting the positive electrode active material layer 22 on the surface of the positive electrode current collector 21, along the width direction Y of the positive electrode current collector 21, reserve the area shown by the dotted box B as the positive electrode tab 23 for use.

[0089] <Preparation of the separator>

[0090] Use a polyethylene (PE) porous film with a thickness of 8 μm as the separator.

[0091] <Preparation of the electrolyte>

[0092] 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. 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.

[0093] <Preparation of the lithium-ion battery>

[0094] Stack and wind the separator, negative electrode sheet, separator, and positive electrode sheet 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 after standing at a high temperature of 45 °C, perform formation and capacity testing to obtain a full-tab cylindrical lithium-ion battery (model 21700).

[0095] Examples 1-2 to Examples 1-8

[0096] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Example 1-1.

[0097] Among them, when the value of V1 / V2×100% changes, V1 changes while V2 remains unchanged.

[0098] Examples 1-9 to Examples 1-11

[0099] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Examples 1-4.

[0100] Examples 1-12 to Examples 1-16

[0101] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Examples 1-4.

[0102] Among them, when the value of V1 / V2×100% changes, V1 changes while V2 remains unchanged.

[0103] Examples 2-1 to Examples 2-21

[0104] Except for adjusting the relevant preparation parameters according to Table 2, the rest are the same as in Examples 1-3.

[0105] Example 2-22

[0106] <Preparation of the negative electrode plate>

[0107] Select a negative electrode current collector with a structure as Figure 5 shown, but not limited to Figure 5 . 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 grooves is as Figure 5 shown, which is arc-shaped. The thickness ε1 of the thinnest area in the negative electrode current collector is ε - h = 10 μm. No grooves are provided on the second surface of the negative electrode current collector.

[0108] The rest are the same as in Examples 1-3.

[0109] Examples 3-1 to Examples 3-3

[0110] Except for adjusting the relevant preparation parameters according to Table 4, the rest are the same as in Examples 1-3.

[0111] Comparative Example 1

[0112] Except for not providing grooves in <Preparation of the negative electrode plate>, the rest are the same as in Examples 1-10.

[0113] Comparative Examples 2 to Comparative Example 4

[0114] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Examples 1-10.

[0115] The preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 to 4.

[0116] Table 1

[0117]

[0118]

[0119] Note: The "\\" in Table 1 indicates no corresponding parameter.

[0120] It can be seen from Examples 1-1 to 1-11 and Comparative Examples 1 to 4 that when the negative electrode active material with a Dv99 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 negative electrode tab has higher adhesion, and the secondary battery has higher rate performance and impact passing rate, indicating that the secondary battery of this application has improved rate performance on the basis of good safety performance. In the secondary battery of the comparative example, the Dv99 particle size of the negative electrode active material is not within the scope of this application, no groove is provided or the groove width is not within the scope of this application, the negative electrode tab has lower adhesion, and the secondary battery has lower rate performance or safety performance, indicating that the secondary battery of the comparative example cannot balance safety performance and rate performance.

[0121] The width d of the groove usually affects the rate performance and safety performance of the secondary battery. It can be seen from Examples 1-1 to 1-8 and Comparative Examples 2 to 4 that for the secondary battery with the width d of the groove within the scope of this application, the value of V1 / V2×100% is within the scope of this application, the negative electrode tab has higher adhesion, and the secondary battery has higher rate performance and impact passing rate, indicating that the secondary battery has good rate performance and safety performance.

[0122] The Dv99 particle size of the negative electrode active material usually affects the rate performance and safety performance of the secondary battery. It can be seen from Examples 1-4, 1-9 to 1-11 that for the secondary battery with the Dv99 particle size of the negative electrode active material within the scope of this application, the negative electrode tab has higher adhesion, and the secondary battery has higher rate performance and impact passing rate, indicating that the secondary battery has good rate performance and safety performance.

[0123] The spacing σ between two adjacent grooves generally affects the rate performance and safety performance of the secondary battery. It can be seen from Examples 1-4, Examples 1-12 to Examples 1-16 that for a secondary battery with the spacing σ between two adjacent grooves within the scope of this application, the value of V1 / V2×100% is within the scope of this application, the negative electrode tab has a high adhesion, and the secondary battery has high rate performance and impact passing rate, indicating that the secondary battery has good rate performance and safety performance.

[0124] Table 2

[0125]

[0126]

[0127] Note: The difference between Example 1-3 and Example 2-22 in Table 2 is that the negative electrode current collector in Example 1-3 has grooves on both surfaces, while the negative electrode current collector in Example 2-22 has grooves on only one surface.

[0128] Table 3

[0129] Adhesion force of the negative electrode tab (N / m) Rate performance (%) Impact passing rate Examples 1 - 3 10.1 88.55 15 / 15 Example 2 - 1 8.3 82.60 15 / 15 Example 2 - 2 8.5 83.93 15 / 15 Example 2 - 3 9.0 84.59 15 / 15 Example 2 - 4 10.6 89.54 15 / 15 Example 2 - 5 11.4 91.08 15 / 15 Example 2 - 6 13.0 90.86 15 / 15 Example 2 - 7 13.2 91.19 15 / 15 Example 2 - 8 13.4 92.51 13 / 15 Example 2 - 9 8.0 82.00 15 / 15 Example 2 - 10 - 91.30 10 / 15 Example 2 - 11 13.0 92.80 15 / 15 Example 2 - 12 11.4 90.90 15 / 15 Example 2 - 13 9.0 82.77 15 / 15 Example 2 - 14 9.4 83.30 15 / 15 Example 2 - 15 7.9 82.10 15 / 15 Example 2 - 16 10.2 99.00 15 / 15 Example 2 - 17 7.4 81.30 15 / 15 Example 2 - 18 9.9 81.62 9 / 15 Example 2 - 19 10.5 86.57 15 / 15 Example 2 - 20 10.2 90.86 15 / 15 Example 2 - 21 9.6 89.76 15 / 15 Example 2 - 22 9.4 81.50 15 / 15

[0130] Note: The "-" in Table 3 indicates that the depth of the groove provided on the surface of the negative electrode current collector is etched too deep relative to the thickness of the negative electrode current collector. When testing the adhesion of the negative electrode tab, the negative electrode current collector cannot be normally separated from the negative electrode active material layer, so the adhesion of the negative electrode tab cannot be measured, but it does not affect the normal use of the negative electrode tab in the secondary battery.

[0131] The depth h of the groove, the thickness w of the negative electrode active material layer, and the original thickness ε of the negative electrode current collector generally also affect the rate performance and safety performance of the secondary battery. As can be seen from Examples 1-3, Examples 2-1 to Examples 2-21, for the secondary battery with the depth h of the groove, the thickness w of the negative electrode active material layer, and the original thickness ε of the negative electrode current collector within the scope of this application, the value of V1 / V2×100% is within the scope of this application, the negative electrode plate has a high adhesive force, and the secondary battery has high rate performance and impact passing rate, indicating that the secondary battery has good rate performance and safety performance. Among them, the negative electrode plate of Example 2-8 has a high adhesive force and high rate performance, but its impact passing rate is 12 / 15. Compared with Examples 1-3, Examples 2-2 to Examples 2-7, the impact passing rate shows a decreasing trend, so it is not within the preferred scope of this application. The secondary battery of Example 2-16 has good rate performance and safety performance, but the thickness w of its negative electrode active material layer is small, which will result in a low energy density of the secondary battery and is not conducive to the actual utilization of the secondary battery. Therefore, it is not within the preferred scope of this application. Compared with Examples 1-3, Examples 2-18, and Examples 2-19, Example 2-21 has better rate performance, but the thickness of its negative electrode active material layer is relatively thick, which will cause an increase in the volume of the secondary battery, resulting in a loss of the energy density of the secondary battery. Therefore, it is not within the preferred scope of this application.

[0132] The groove being provided on one surface or both surfaces of the negative electrode current collector generally also affects the rate performance and safety performance of the secondary battery. As can be seen from Examples 1-3 and Examples 2-22, for the secondary battery with the groove setting position within the position scope of this application, the negative electrode plate has a high adhesive force, and the secondary battery has high rate performance and impact passing rate, indicating that the secondary battery has good rate performance and safety performance.

[0133] Table 4

[0134]

[0135] The angle θ between the center line of the groove and the length direction of the negative electrode current collector itself generally affects the rate performance and safety performance of the secondary battery. As can be seen from Examples 1-3, Examples 3-1 to Examples 3-3, for the secondary battery with the angle θ between the center line of the groove and the length direction of the negative electrode current collector itself within the scope of this application, the negative electrode plate has a high adhesive force, and the secondary battery has high rate performance and impact passing rate, indicating that the secondary battery has good rate performance and safety performance.

[0136] 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 variation 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 also includes elements inherent to such process, method, article or device.

[0137] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments.

[0138] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. A secondary battery, comprising a positive electrode plate, a negative electrode plate and a separator, wherein the negative electrode plate comprises 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 comprises a negative electrode active material, and the particle size Dv99 of the negative electrode active material is 20 μm to 80 μm; The negative electrode current collector comprises 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 of the negative electrode current collector where the negative electrode active material layer is provided, and the width of the groove is d, 1.5×Dv99 ≤ d ≤ 5 mm.

2. The secondary battery according to claim 1, wherein, The depth h of the groove satisfies: w / 100 ≤ h ≤ 0.8ε with respect to the thickness w of the negative electrode active material layer and the original thickness ε of the negative electrode current collector, where 10 μm ≤ w ≤ 300 μm and 4 μm ≤ ε ≤ 40 μm.

3. The secondary battery according to claim 1, wherein, The total volume V1 of the groove and the total volume V2 of the part of the negative current collector provided with the negative active material layer satisfy: 0.01% ≤ V1 / V2 × 100% ≤ 60%, 1.5×10 -9 m 3 ≤ V2 ≤ 9×10 -4 m 3 .

4. The secondary battery according to claim 1, wherein, The distance between two adjacent grooves is 0.1 mm to 50 mm.

5. The secondary battery according to claim 1, wherein, The angle θ between the center line of the groove and the longitudinal direction of the negative electrode current collector itself is 0° to 90°.

6. The secondary battery according to claim 1, wherein The secondary battery satisfies at least one of the following characteristics: (1) 1.5×Dv99 ≤ d ≤ 2 mm; (2) The depth h of the groove satisfies: w / 80 ≤ h ≤ 0.5ε with respect to the thickness w of the negative electrode active material layer and the original thickness ε of the negative electrode current collector, where 30 μm ≤ w ≤ 200 μm and 6 μm ≤ ε ≤ 40 μm; (3) The total volume V1 of the grooves and the total volume V2 of the part of the negative electrode current collector where the negative electrode active material layer is provided satisfy: 0.2% ≤ V1 / V2×100% ≤ 40%; (4) The distance between two adjacent grooves is 0.5 mm to 30 mm.

7. The secondary battery according to claim 2, wherein, The thickness ε1 of the thinnest region in the negative electrode current collector satisfies: ε1 ≥ 0.2ε with respect to the original thickness ε of the negative electrode current collector.

8. The secondary battery according to any one of claims 1 to 7, wherein, In a direction from the second surface to the first surface, at least one such groove is provided in a region of the negative electrode current collector where the negative electrode active material layer is provided.

9. The secondary battery according to claim 8, wherein, At least two of the grooves located on the first surface and the second surface are parallel or intersect with each other.

10. An electronic device, wherein, The electronic device comprises the secondary battery according to any one of claims 1 to 9.

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