Secondary battery and electric device

Abstract

The invention provides a secondary battery and a power utilization device, the secondary battery comprises an electrode assembly of a winding structure, the electrode assembly comprises a positive pole piece, a diaphragm and a negative pole piece, the diaphragm is located between the positive pole piece and the negative pole piece, and the electrode assembly comprises a straight area and a corner area; at least one surface of the diaphragm in the corner region is provided with a plurality of first concave parts, the average depth of the first concave parts is H1 [mu] m along the thickness direction of the diaphragm, the thickness of the diaphragm is H0 [mu] m, and 0.05 < = H1 / H0 < = 0.2. According to the invention, the plurality of first concave parts are arranged on the surface of the corner region of the diaphragm, and H1 / H0 is regulated and controlled within the range, so that the secondary battery has good cycle performance and safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, in particular to a secondary battery and a power utilization device. BACKGROUND

[0002] Secondary batteries, such as lithium ion batteries, are widely used in the fields of smart phones, wearable devices, consumer drones and electric vehicles due to their high energy density, long cycle life and no memory effect. With the wide application of lithium ion batteries in the above fields, the market has higher and higher requirements for the performance of lithium ion batteries. However, the gas generated after the existing lithium ion battery is formed to a high potential will be stored in the corner, resulting in lithium precipitation, which affects the safety performance and cycle performance of the lithium ion battery. SUMMARY

[0003] The purpose of the present application is to provide a secondary battery and a power utilization device to improve the safety performance and cycle performance of the secondary battery. The specific technical solutions are as follows:

[0004] The first aspect of the present application provides a secondary battery, which comprises an electrode assembly in a roll structure, the electrode assembly comprising a positive electrode sheet, a separator and a negative electrode sheet, the separator being located between the positive electrode sheet and the negative electrode sheet, the electrode assembly comprising a flat area and a corner area; a plurality of first recesses are arranged on at least one surface of the separator in the corner area, along the thickness direction of the separator, the average depth of the first recesses is H1 μm, the thickness of the separator is H0 μm, and 0.05≤H1 / H0≤0.2, preferably 0.11≤H1 / H0≤0.16. By arranging a plurality of first recesses on the surface of the separator corner area and adjusting H1 / H0 within the above range, the first recesses can reserve space for electrolyte and store more electrolyte, which is beneficial to improve the problem of insufficient electrolyte immersion in the corner area of the secondary battery. At the same time, the first recesses can absorb and store the gas generated during the formation process of the secondary battery, reduce the influence of the gas on the transmission of lithium ions, thereby reducing the risk of lithium precipitation in the corner caused by the accumulation of gas during the formation process of the secondary battery, and further improving the cycle performance and safety performance of the secondary battery.

[0005] In some embodiments of the present application, 0.35≤H1≤6. By adjusting H1 within the above range, the risk of the first recesses in the corner area of the separator being flattened during the heat pressing process can be reduced, more suitable space for electrolyte can be reserved in the corner area of the separator, which is more beneficial to improve the problem of insufficient electrolyte immersion in the corner area of the secondary battery. At the same time, the influence of the gas generated during the formation process of the secondary battery on the transmission of lithium ions can be further reduced, the problem of lithium precipitation in the corner can be improved, and the secondary battery has better safety performance and cycle performance.

[0006] In some embodiments of the present application, 7≤H0≤30. By regulating H0 in the above range, the first recesses can provide more appropriate space in the corner region of the separator, which can improve the problem of insufficient electrolyte infiltration in the corner region of the secondary battery, and further reduce the influence of gas production on lithium ion transport during the formation process of the secondary battery, thereby improving the problem of lithium precipitation in the corner region, and thus improving the safety performance and cycle performance of the secondary battery.

[0007] In some embodiments of the present application, 0.35≤H1≤6 and 7≤H0≤30. By regulating H1 and H0 in the above range, the safety performance and cycle performance of the secondary battery can be further improved.

[0008] In some embodiments of the present application, along the length direction of the separator after being developed, the corner region comprises a middle section and two edge sections, the middle section is located between the two edge sections, and the length ratio of the middle section to the corner region is L%, 30≤L≤50; a plurality of first recesses are arranged on the surfaces of the middle section and the two edge sections, and along the thickness direction of the separator, the average depth of the first recesses in the middle section is H3μm, the average depth of the first recesses in the two edge sections is H2μm, and H3<H2. By regulating the average depth H2 of the first recesses in the two edge sections to be greater than the average depth H3 of the first recesses in the middle section, the problem of more serious lithium precipitation in the edge sections than in the middle section of the corner region of the secondary battery can be improved, and the problem of insufficient electrolyte infiltration in the corner region of the secondary battery can also be improved, thereby improving the safety performance and cycle performance of the secondary battery.

[0009] In some embodiments of the present application, 1.1≤H2 / H3≤2. By regulating H2 / H3 in the above range, the problem of more serious lithium precipitation in the edge sections than in the middle section of the corner region of the secondary battery can be further improved, and the problem of insufficient electrolyte infiltration in the corner region of the secondary battery can also be further improved, thereby improving the safety performance and cycle performance of the secondary battery.

[0010] In some embodiments of the present application, the plurality of first recesses are distributed in a dot shape, the shape of the orthographic projection of a single first recess along the thickness direction of the separator comprises a circle, an ellipse or a polygon, the diameter of the maximum circumscribed circle of the outer contour of the orthographic projection of a single first recess is D1 mm, and 0.1≤D1≤1. By regulating D1 in the above range, the first recesses can reserve moderate space, which can store more electrolyte, thereby improving the problem of insufficient electrolyte infiltration in the corner region of the secondary battery, and further reducing the influence of gas production on lithium ion transport during the formation process of the secondary battery, thereby improving the problem of lithium precipitation in the corner region, and thus improving the safety performance and cycle performance of the secondary battery.

[0011] In some embodiments of the present application, the distance between two adjacent first recesses along the length direction of the membrane after being developed is A1 mm, and 0.1≤A1≤1. By regulating A1 within the above range, the present application can make the first recesses evenly distributed, thereby improving the problem of insufficient electrolyte infiltration in the corner area of the secondary battery, and better absorbing the gas generated in the formation process of the secondary battery, thereby reducing the risk of corner lithium precipitation caused by the accumulation of generated gas in the formation process of the secondary battery, and further improving the cycle performance and safety performance of the secondary battery.

[0012] In some embodiments of the present application, the plurality of first recesses are distributed in a strip shape, and the plurality of first recesses are arranged at intervals, and the width of the orthographic projection of a single first recess along the direction of the interval arrangement is D2 mm, and 0.5≤D2≤2. By regulating D2 within the above range, the present application can make the reserved space of the first recess moderate, and store more electrolyte, thereby improving the problem of insufficient electrolyte infiltration in the corner area of the secondary battery, and reducing the influence of gas generation on lithium ion transmission in the formation process of the secondary battery, thereby improving the problem of corner lithium precipitation, and further improving the safety performance and cycle performance of the secondary battery.

[0013] In some embodiments of the present application, the distance between two adjacent first recesses is A2 mm, and 0.5≤A2≤2. By regulating A2 within the above range, the present application can make the first recesses evenly distributed, thereby improving the problem of insufficient electrolyte infiltration in the corner area of the secondary battery, and better absorbing the gas generated in the formation process of the secondary battery, thereby reducing the risk of corner lithium precipitation caused by the accumulation of generated gas in the formation process of the secondary battery, and further improving the cycle performance and safety performance of the secondary battery.

[0014] In some embodiments of the present application, the first recess is located on the surface of the membrane facing the negative electrode tab. By regulating the first recess on the surface of the membrane facing the negative electrode tab, the present application can store more electrolyte on the negative side, thereby improving the problem of insufficient infiltration in the corner area of the secondary battery, and better absorbing the gas generated in the formation process of the secondary battery, thereby further reducing the risk of corner lithium precipitation caused by the accumulation of generated gas in the formation process of the secondary battery, and further improving the cycle performance and safety performance of the secondary battery.

[0015] In some embodiments of the present application, the membrane comprises a substrate layer and a coating layer located on at least one surface of the substrate layer, and the coating layer has the plurality of first recesses. By using the membrane comprising a substrate layer and a coating layer, and arranging the first recesses in the coating layer, the present application can improve the cycle performance and safety performance of the secondary battery.

[0016] In some embodiments of the present application, the coating layer comprises at least one of an inorganic coating layer and an organic coating layer; the inorganic coating layer comprises inorganic particles and a binder; and the organic coating layer comprises a polymer. The present application uses a separator comprising the above-mentioned coating layer, and provides a first recess in the coating layer, so that the secondary battery has good cycle performance and safety performance.

[0017] In some embodiments of the present application, a plurality of second recesses are provided on at least one surface of the separator in the flat area, and the average depth of the second recesses in the thickness direction of the separator is H4 μm, 0.1≤H4≤0.3. The present application regulates H4 in the above range, which is conducive to storing more electrolyte in the flat area of the separator, and further reduces the risk of lithium precipitation caused by the accumulation of generated gas in the formation process of the secondary battery, thereby making the secondary battery have good cycle performance and safety performance.

[0018] In some embodiments of the present application, the second recesses are located on the surface of the separator facing the negative electrode tab. The present application regulates the second recesses to be located on the surface of the separator facing the negative electrode tab, so that more electrolyte is stored on the negative electrode side, which is conducive to improving the problem of insufficient electrolyte wetting of the secondary battery, and can better absorb and store the gas generated in the formation process of the secondary battery, thereby reducing the risk of lithium precipitation caused by the accumulation of generated gas in the formation process of the secondary battery, and further making the secondary battery have good cycle performance and safety performance.

[0019] The second aspect of the present application provides a power-using device comprising the secondary battery provided by the first aspect of the present application.

[0020] The present application provides a secondary battery and a power-using device. The secondary battery comprises an electrode assembly in a winding structure, the electrode assembly comprising a positive electrode tab, a separator, and a negative electrode tab, the separator being located between the positive electrode tab and the negative electrode tab, and the electrode assembly comprising a flat area and a corner area; at least one surface of the separator in the corner area is provided with a plurality of first recesses, and the average depth of the first recesses in the thickness direction of the separator is H1 μm, the thickness of the separator is H0 μm, and 0.05≤H1 / H0≤0.2. The present application regulates H1 / H0 in the above range by providing a plurality of first recesses on the surface of the separator in the corner area, so that the first recesses can reserve space for electrolyte and store more electrolyte, which is conducive to improving the problem of insufficient electrolyte wetting in the corner area of the secondary battery, and the first recesses can absorb and store the gas generated in the formation process of the secondary battery, thereby reducing the influence of the generated gas on the transmission of lithium ions, and further reducing the risk of lithium precipitation in the corner area of the secondary battery caused by the accumulation of generated gas in the formation process of the secondary battery, thereby making the secondary battery have good cycle performance and safety performance. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only represent some embodiments of the present application, and other embodiments can be obtained by those skilled in the art based on these drawings.

[0022] Figure 1 A partial structure diagram of an electrode assembly in an embodiment of the present application;

[0023] Figure 2 A structure diagram of a separator in a corner area of an electrode assembly in an embodiment of the present application;

[0024] Figure 3 A structure diagram of a separator in a corner area of an electrode assembly in another embodiment of the present application;

[0025] Figure 4 A structure diagram of a separator in a corner area of an electrode assembly in another embodiment of the present application;

[0026] Figure 5 A structure diagram of a separator in a corner area of an electrode assembly in another embodiment of the present application.

[0027] In the drawings, 100. separator, 200. positive electrode sheet, 300. negative electrode sheet, 101. flat area, 102. corner area, 110. first recess, 1120. middle section, 1130. edge section. DETAILED DESCRIPTION

[0028] The technical solutions in the present application will be described clearly and completely below in combination with the embodiments of the present application and the accompanying drawings. Obviously, the described embodiments only represent some 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 are within the scope of protection of the present application.

[0029] The first aspect of the present application provides a secondary battery, which comprises an electrode assembly in a roll structure, the electrode assembly comprising a positive electrode tab, a separator, and a negative electrode tab, the separator being located between the positive electrode tab and the negative electrode tab, the electrode assembly comprising a flat area and a corner area; at least one surface of the separator in the corner area is provided with a plurality of first recesses, the average depth of the first recesses being H1 μm in the thickness direction of the separator, the thickness of the separator being H0 μm, 0.05≤H1 / H0≤0.2, preferably 0.11≤H1 / H0≤0.16. For example, H1 / H0 can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.15, 0.16, 0.18, 0.19, 0.2, or a range between any two of the above values. The above-mentioned "at least one surface of the separator in the corner area is provided with a plurality of first recesses" means that the plurality of first recesses can be provided on one surface in the thickness direction of the separator in the corner area, or on both surfaces in the thickness direction of the separator in the corner area. For example, as shown in FIG. 1, the secondary battery comprises an electrode assembly in a roll structure, the electrode assembly comprising a positive electrode tab 200, a separator 100, and a negative electrode tab 300, the separator 100 being located between the positive electrode tab 200 and the negative electrode tab 300, the electrode assembly comprising a flat area 101 and a corner area 102; at least one surface of the separator 100 in the corner area 102 is provided with a plurality of first recesses 110. Figure 1

[0030] If H1 / H0 is too small, for example less than 0.05, the average depth of the first recesses is relatively shallow compared to the separator, and the gas generated during the pressurized formation process of the secondary battery will accumulate in the corner area and be difficult to discharge, while the electrolyte will be less retained in the corner area, resulting in lithium precipitation during the formation process of the secondary battery, which is difficult to improve the safety performance and cycle performance of the secondary battery. If H1 / H0 is too large, for example greater than 0.2, the average depth of the first recesses is relatively deep compared to the separator, which will affect the stability of the separator and is not conducive to improving the safety performance and cycle performance of the secondary battery. By providing a plurality of first recesses on the surface of the separator in the corner area and adjusting H1 / H0 within the above range, the first recesses can reserve space for the electrolyte and store more electrolyte, which is beneficial to improve the problem of insufficient electrolyte wetting in the corner area of the secondary battery. At the same time, the first recesses can absorb and store the gas generated during the formation process of the secondary battery, reducing the impact of the gas on the transmission of lithium ions, thereby reducing the risk of lithium precipitation in the corner due to the accumulation of gas during the formation process of the secondary battery, and thus the secondary battery has good cycle performance and safety performance.

[0031] ​In some embodiments of the present application, 0.35≤H1≤6. For example, H1 can be 0.35, 0.5, 0.7, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 2.2, 2.3, 2.5, 2.6, 2.8, 3, 3.2, 3.5, 3.6, 3.8, 4, 4.2, 4.3, 4.5, 4.6, 4.8, 5, 5.2, 5.3, 5.5, 5.6, 5.8, 6, or a range defined by any two of the above values. By controlling H1 within the above range, the risk of the first recess in the corner area of the separator being flattened during the heat pressing process can be reduced, more suitable space for the electrolyte in the corner area of the separator can be reserved, which is more conducive to improving the problem of insufficient electrolyte immersion in the corner area of the secondary battery, and further reduces the influence of gas production on lithium ion transport during the formation process of the secondary battery, thereby improving the problem of lithium precipitation in the corner, and thus the secondary battery has better safety performance and cycle performance.

[0032] In some embodiments of the present application, 7≤H0≤30. For example, H0 can be 7, 8, 9, 10, 11, 12, 13, 15, 16, 18, 20, 21, 22, 23, 25, 26, 28, 30, or a range defined by any two of the above values. By controlling H0 within the above range, the first recess in the corner area of the separator can have more suitable space, which is more conducive to improving the problem of insufficient electrolyte immersion in the corner area of the secondary battery, and further reduces the influence of gas production on lithium ion transport during the formation process of the secondary battery, thereby improving the problem of lithium precipitation in the corner, and thus the secondary battery has better safety performance and cycle performance.

[0033] In some embodiments of the present application, 0.35≤H1≤6 and 7≤H0≤30. By controlling H1 and H0 within the above ranges, the safety performance and cycle performance of the secondary battery can be further improved.

[0034] In some embodiments of the present application, along the length direction of the developed separator, the corner area includes a middle section and two edge sections, the middle section is located between the two edge sections, and the length ratio of the middle section to the corner area is L%, 30≤L≤50, for example, L can be 30, 32, 33, 35, 36, 38, 40, 42, 44, 45, 46, 48, 50, or a range defined by any two of the above values. A plurality of first recesses are arranged on the surfaces of the middle section and the two edge sections. Along the thickness direction of the separator, the average depth of the plurality of first recesses in the middle section is H3μm, the average depth of the plurality of first recesses in the two edge sections is H2μm, and H3 Figure 1As shown, the corner region 102 includes a middle section 1120 and two edge sections 1130, the middle section 1120 is located between the two edge sections 1130, and the length of the middle section 1120 accounts for L% of the length of the corner region 102, 30≤L≤50; a plurality of first recesses 110 are arranged on the surfaces of the middle section 1120 and the two edge sections 1130, and the average depth of the plurality of first recesses 110 located in the middle section 1120 is H3μm, the average depth of the plurality of first recesses 110 located in the two edge sections 1130 is H2μm, and H3

[0035] In some embodiments of the present application, 1.1≤H2 / H3≤2. For example, H2 / H3 can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a range formed by any two of the above values. By controlling H2 / H3 within the above range, the present application can further improve the problem that lithium precipitation is more serious in the edge sections than in the middle section of the corner region of the secondary battery, and further improve the problem of insufficient electrolyte infiltration in the corner region of the secondary battery, so that the secondary battery has better safety performance and cycle performance.

[0036] In some embodiments of the present application, 0.35≤H2≤6.6. For example, H2 can be 0.35, 0.5, 0.7, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.3, 4.5, 4.8, 5, 5.3, 5.5, 5.8, 6, 6.2, 6.4, 6.6, or a range formed by any two of the above values. By controlling H2 within the above range, the present application can make the secondary battery have better safety performance and cycle performance.

[0037] In some embodiments of the present application, 0.3≤H3≤6. For example, H3 can be 0.3, 0.32, 0.35, 0.5, 0.7, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.3, 4.5, 4.8, 5, 5.3, 5.5, 5.7, 6, or a range formed by any two of the above values. By controlling H3 within the above range, the present application can make the secondary battery have better safety performance and cycle performance.

[0038] In some embodiments of this application, multiple first recesses are distributed in a dotted pattern along the thickness direction of the separator. The orthographic projection of a single first recess includes a circle, an ellipse, or a polygon. The diameter of the largest circumscribed circle of the orthographic projection of a single first recess is D1 mm, where 0.1 ≤ D1 ≤ 1. For example, D1 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range of any two of these values. By adjusting D1 within the above range, this application allows for a suitable amount of space reserved in the first recesses, enabling the storage of more electrolyte. This helps to improve the problem of insufficient electrolyte wetting in the corner area of ​​the secondary battery. Simultaneously, it reduces the impact of gas generation on lithium-ion transport during the formation process of the secondary battery, improving the problem of lithium plating at the corner, thereby giving the secondary battery better safety and cycle performance.

[0039] In some embodiments of this application, multiple first recesses are distributed in a dotted pattern along the length of the unfolded separator, with the distance between two adjacent first recesses being A1 mm, where 0.1 ≤ A1 ≤ 1. For example, A1 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range of any two values ​​therein. The distance between two adjacent first recesses refers to the minimum distance between the outer contours of the orthographic projections of two adjacent recesses. By adjusting A1 within the above range, this application can ensure a uniform distribution of the first recesses, which helps to improve the problem of insufficient electrolyte wetting in the corner area of ​​the secondary battery. Simultaneously, it can better absorb the gas generated during the formation process of the secondary battery, reducing the risk of lithium plating at the corner due to gas accumulation and difficulty in venting during formation. This, in turn, results in better cycle performance and safety performance of the secondary battery.

[0040] For example, such as Figure 2 As shown, multiple first recesses 110 are distributed in a dot-like array. Along the thickness direction of the diaphragm 100, the orthographic projection of a single first recess 110 is circular, and the diameter of the largest circumscribed circle of the orthographic projection of a single first recess 110 is D1 mm, where 0.1 ≤ D1 ≤ 1. Along the length direction of the unfolded diaphragm 100, the distance between two adjacent first recesses 110 is A1 mm, where 0.1 ≤ A1 ≤ 1. It can be understood that when the multiple first recesses are distributed in a dot-like pattern, they can also be distributed in a scattered pattern, and the diameter D1 of the largest circumscribed circle of the orthographic projection of a single first recess and the distance between two adjacent first recesses both satisfy the above ranges. It can be understood that... Figure 2 The dimensions and the number and shape of the first recess are merely examples and do not limit the scope of protection of this application.

[0041] In some embodiments of this application, multiple first recesses are arranged in a strip shape, with the multiple first recesses spaced apart. Along the direction of the spacing, the width of the orthographic projection of a single first recess is D2 mm, where 0.5 ≤ D2 ≤ 2. For example, D2 can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a range consisting of any two of these values. By adjusting D2 within the above range, this application can ensure that the reserved space of the first recesses is moderate, allowing for the storage of more electrolyte. This helps to improve the problem of insufficient electrolyte wetting in the corner area of ​​the secondary battery. At the same time, it can reduce the impact of gas generation on lithium-ion transport during the formation process of the secondary battery, improve the problem of lithium plating at the corner, and thus enable the secondary battery to have better safety and cycle performance.

[0042] In some embodiments of this application, multiple first recesses are distributed in a strip shape, with the distance between two adjacent first recesses being A2 mm, where 0.5 ≤ A2 ≤ 2. For example, A2 can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a range of any two values ​​therein. The distance between two adjacent first recesses refers to the minimum distance between the orthographic projections of two adjacent recesses. By adjusting A2 within the above range, this application can ensure a uniform distribution of the first recesses, which helps to improve the problem of insufficient electrolyte wetting in the corner area of ​​the secondary battery. Simultaneously, it can better absorb the gas generated during the formation process of the secondary battery, reducing the risk of lithium plating at the corner due to gas accumulation and difficulty in venting during formation. This, in turn, results in better cycle performance and safety performance of the secondary battery.

[0043] In this application, multiple first recesses are arranged in a strip shape. These first recesses can be arranged along the width direction of the diaphragm, along the length direction of the diaphragm, or simultaneously along both the width and length directions of the diaphragm. In this application, the width D2 of the orthographic projection of a single first recess is the maximum value of the orthographic projection width. When multiple first recesses are arranged in a strip shape, the width D2 of the orthographic projection of two adjacent first recesses can be the same or different, and the length of the strips can be the same or different, as long as the purpose of this application is achieved. This application does not have a particular limitation on the length of the strips; it can be designed according to the size of the diaphragm, as long as the purpose of this application is achieved.

[0044] For example, such as Figure 3 As shown, multiple first recesses 110 are distributed in a strip shape, and one side of the orthographic projection of a single first recess 110 is parallel to one side of the diaphragm 100. The orthographic projection of a single first recess 110 is a narrow and long rectangle with a width of D2 and a minimum spacing of A2 between adjacent rectangles.Figure 4 As shown, the plurality of first recesses 110 are distributed in a strip shape, and an included angle exists between one side of the single first recess 110 and one side of the diaphragm 100 (not shown in the figure), the width of the single first recess 110 in the projection is D2, and the minimum distance between the adjacent two recesses is A2. The present application does not have a particular limitation on the size of the above-mentioned included angle, as long as the purpose of the present application can be achieved, and the included angle is exemplarily 25° to 65°. As shown, a plurality of first recesses 110 are arranged along the width direction and the length direction of the diaphragm 100, and the plurality of first recesses 110 are distributed in a strip shape. Along the length direction of the diaphragm 100, the width of the single first recess 110 in the projection is D2, and the distance between the adjacent two first recesses 110 is A2. Along the width direction of the diaphragm 100, the width of the single first recess 110 in the projection is D2, and the distance between the adjacent two first recesses 110 is A2. Figure 5 As shown, the plurality of first recesses 110 are distributed in a strip shape, and an included angle exists between one side of the single first recess 110 and one side of the diaphragm 100 (not shown in the figure), the width of the single first recess 110 in the projection is D2, and the minimum distance between the adjacent two recesses is A2. The present application does not have a particular limitation on the size of the above-mentioned included angle, as long as the purpose of the present application can be achieved, and the included angle is exemplarily 25° to 65°. As shown, a plurality of first recesses 110 are arranged along the width direction and the length direction of the diaphragm 100, and the plurality of first recesses 110 are distributed in a strip shape. Along the length direction of the diaphragm 100, the width of the single first recess 110 in the projection is D2, and the distance between the adjacent two first recesses 110 is A2. Along the width direction of the diaphragm 100, the width of the single first recess 110 in the projection is D2, and the distance between the adjacent two first recesses 110 is A2. Figure 3 、 Figure 4 and Figure 5 The size of the dimensions, the number and shape of the first recesses in the above-mentioned figures are only examples, and do not limit the protection scope of the present application.

[0045] In some embodiments of the present application, the first recess is located on the surface of the diaphragm facing the negative electrode tab. The present application controls the first recess to be located on the surface of the diaphragm facing the negative electrode tab, so that more electrolyte can be stored on the negative side, which is more conducive to improving the problem of insufficient wetting of the corner area of the secondary battery, and can better absorb the gas generated during the formation process of the secondary battery, further reducing the risk of lithium precipitation in the corner of the secondary battery due to the accumulation of gas generated during the formation process and difficult to discharge, thereby making the secondary battery have better cycle performance and safety performance.

[0046] The present application does not have a particular limitation on the material of the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) such as polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of diaphragm can include at least one of woven film, non-woven film, microporous film, composite film, calendered film or spunlaid film.

[0047] In some embodiments of the present application, the diaphragm includes a substrate layer and a coating layer located on at least one surface of the substrate layer, and the coating layer has a plurality of first recesses. The present application adopts a diaphragm including a substrate layer and a coating layer, and sets the first recess in the coating layer, so that the secondary battery has better cycle performance and safety performance.

[0048] In some embodiments of the present application, the substrate layer can be a nonwoven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. The thickness of the substrate layer is not particularly limited in the present application as long as the object of the present application can be achieved, and for example, the thickness of the substrate layer is 5 μm to 20 μm.

[0049] In some embodiments of the present application, the coating layer includes at least one of an inorganic coating layer including inorganic particles and a binder, or an organic coating layer including a polymer. The use of the separator including the above-described coating layer and the first recess provided in the above-described coating layer can provide a secondary battery having improved cycle characteristics and safety.

[0050] In some embodiments of the present application, the inorganic coating layer includes inorganic particles and a binder. The inorganic particles are not particularly limited in the present application, and for example, the inorganic particles can include at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited in the present application, and for example, the binder can include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene butadiene rubber, or polyvinylidene fluoride. The mass ratio of the inorganic particles to the binder is not particularly limited in the present application as long as the object of the present application can be achieved, and for example, the mass ratio of the inorganic particles to the binder is 1:9 to 9:1.

[0051] In some embodiments of the present application, the organic coating layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0052] In some embodiments of the present application, the at least one surface of the flat area of the separator is provided with a plurality of second recesses, and the average depth of the second recesses is H4 μm in the thickness direction of the separator, H1 > H4. The average depth H1 of the first recesses is greater than the average depth H4 of the second recesses, which is conducive to storing more electrolyte in the corner area and improving the problem of insufficient electrolyte immersion in the corner area. Meanwhile, the first recesses can absorb and store more gas generated during the formation process of the secondary battery, thereby reducing the impact of gas generation on lithium ion transmission, and thus reducing the risk of lithium precipitation in the corner due to the accumulation of gas during the formation process of the secondary battery, and further improving the cycle performance and safety performance of the secondary battery.

[0053] In some embodiments of the present application, 0.1 ≤ H4 ≤ 0.3. For example, H4 can be 0.1, 0.12, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, or a range formed by any two of them. The present application controls H4 within the above range, which is conducive to storing more electrolyte in the flat area of the separator, and further reduces the risk of lithium precipitation due to the accumulation of gas during the formation process of the secondary battery, and further improves the cycle performance and safety performance of the secondary battery.

[0054] In some embodiments of the present application, the second recesses are located on the surface of the separator facing the negative electrode tab. The present application controls the second recesses to be located on the surface of the separator facing the negative electrode tab, which can store more electrolyte on the negative side, improve the problem of insufficient electrolyte immersion in the secondary battery, and further absorb and store more gas generated during the formation process of the secondary battery, thereby reducing the risk of lithium precipitation due to the accumulation of gas during the formation process of the secondary battery, and further improving the cycle performance and safety performance of the secondary battery.

[0055] In some embodiments of the present application, the coating layer has a plurality of first recesses and a plurality of second recesses. The present application uses a separator comprising a substrate layer and a coating layer, and provides a plurality of first recesses and a plurality of second recesses on the coating layer, which can improve the cycle performance and safety performance of the secondary battery.

[0056] In some embodiments of the present application, the plurality of second recesses are distributed in a dot shape, the shape of the orthographic projection of a single second recess includes a circle, an ellipse or a polygon in the thickness direction of the separator, the diameter of the maximum circumscribed circle of the outer contour of the orthographic projection of a single second recess is D3 mm, and 0.1 ≤ D3 ≤ 1. The present application controls D3 within the above range, which can improve the safety performance and cycle performance of the secondary battery. In some embodiments of the present application, the distance between adjacent two second recesses is A3 mm in the length direction of the separator after being developed, and 0.1 ≤ A3 ≤ 1. The present application controls A3 within the above range, which can improve the safety performance and cycle performance of the secondary battery.

[0057] In some embodiments of this application, a plurality of second recesses are arranged in a strip shape, with the multiple second recesses spaced apart. Along the direction of the spacing, the width of the orthographic projection of a single second recess is D4 mm, where 0.5 ≤ D4 ≤ 2. Adjusting D4 within the above range allows the secondary battery to have better safety and cycle performance. In some embodiments of this application, the distance between two adjacent second recesses is A4 mm, where 0.5 ≤ A4 ≤ 2. Adjusting A4 within the above range allows the secondary battery to have better safety and cycle performance.

[0058] In this application, the method for preparing the diaphragm includes: along the length direction of the unfolded diaphragm, determining the straight area and corner area of ​​the diaphragm according to the size of a preset electrode assembly, and determining the middle section and two edge sections of the corner area, and setting a plurality of first recesses in the corner area. In some embodiments of this application, the two edge sections are symmetrically designed about the middle section, that is, the midline of the corner area of ​​the electrode assembly coincides with the midline of the middle section of the corner area of ​​the diaphragm. For example, the method for preparing the diaphragm includes: based on the length of the corner area, the length ratio of the middle section is L%, the length ratio of any one edge section is L'%, and L'% = (100% - L%) / 2. The shape of the orthographic projection of a single first recess on the diaphragm is set to be circular, elliptical, or polygonal along the thickness direction of the diaphragm; the diameter of the largest circumscribed circle of the outer contour of the orthographic projection of a single first recess is D1 mm; the average depth of all first recesses located in the middle section is H3 μm; and the average depth of all first recesses located in the edge sections is H2 μm. Along the length of the unfolded diaphragm, the distance between two adjacent first recesses is A1 mm. Using an embossing roller of appropriate specifications and size according to the above parameters, the diaphragm is rolled to obtain a diaphragm with multiple first recesses on one surface. Repeating the above steps on the other surface of the diaphragm yields a diaphragm with multiple first recesses on both sides.

[0059] For example, the method for preparing a diaphragm includes: based on the length of the corner area, the length percentage of the middle section is L%, and the length percentage of any edge section is L'%, where L'% = (100% - L%) / 2. Along the thickness direction of the diaphragm, the shape of the orthographic projection of a single first recess on the diaphragm is set to be a strip, the width of the orthographic projection of a single first recess is D2 mm, the average depth of all first recesses located in the middle section is H3 μm, and the average depth of all first recesses located in the edge sections is H2 μm. Along the length direction of the unfolded diaphragm, the distance between two adjacent first recesses is A2 mm. Using embossing rollers of appropriate specifications and sizes according to the above parameters, the diaphragm is rolled to obtain a diaphragm with multiple first recesses on one surface. Repeating the above steps on another surface of the diaphragm yields a diaphragm with multiple first recesses on both sides.

[0060] It should be noted that the average depth of the plurality of first recesses can be less than or equal to the thickness of the coating layer, and the plurality of first recesses with a preset size can be obtained by rolling on the coating surface of the diaphragm. The average depth of the plurality of first recesses can be greater than the thickness of the coating layer, and the plurality of first recesses with a preset size can be obtained by rolling on the surface of the substrate layer and the coating layer of the diaphragm.

[0061] In some embodiments of the present application, the preparation method of the diaphragm further comprises: arranging a plurality of second recesses on the flat area.

[0062] In the present application, the positive electrode tab comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector. The "positive electrode material layer arranged on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be arranged on one surface of the positive electrode current collector along the thickness direction of the positive electrode current collector, or can be arranged on two surfaces of the positive electrode current collector along the thickness direction of the positive electrode current collector. It should be noted that the "surface" herein can be the entire area of the surface of the positive electrode current collector, or can be part of the area of the surface of the positive electrode current collector, and the present application does not have special restrictions as long as the purpose of the present application can be achieved.

[0063] The positive electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, it can comprise an aluminum foil, an aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector) and the like.

[0064] The positive electrode material layer comprises a positive electrode active material, and the positive electrode active material is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the positive electrode active material can comprise but is not limited to at least one of nickel-cobalt-manganese lithium (such as NCM811, NCM622, NCM523, NCM111), nickel-cobalt-aluminum lithium, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate or lithium titanate.

[0065] The positive electrode material layer can further include a conductive agent and a binder, and the kind of the conductive agent and the binder is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, a metal material, or a conductive polymer, and the conductive carbon black can include, but is not limited to, at least one of acetylene black or Ketjen black. The carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The carbon fibers can include, but are not limited to, vapor grown carbon fibers (VGCF) and / or nanocarbon fibers. The metal material can include, but is not limited to, metal powder and / or metal fibers, and specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The conductive polymer can include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The binder can include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene butadiene rubber, or polyvinylidene fluoride. The mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer is not particularly limited in the present application, and a person skilled in the art can select them according to actual needs as long as the purpose of the present application can be achieved.

[0066] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0067] Optionally, the positive electrode sheet can further include a conductive layer between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application, and for example, can be at least one of the above-mentioned conductive agent and the above-mentioned binder.

[0068] In the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector in the thickness direction of the negative electrode current collector, or can be disposed on both surfaces of the negative electrode current collector in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or can be part of the area of the surface of the negative electrode current collector, and the present application is not particularly limited as long as the purpose of the present application can be achieved.

[0069] The negative electrode current collector is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, it can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector, and exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, and the like.

[0070] The negative electrode material layer includes a negative electrode active material, and the present application does not have a particular limitation on the negative electrode active material, as long as the object of the present application can be achieved, for example, the negative electrode active material can include, but is not limited to, at least one of natural graphite, artificial graphite, meso-carbon microbe, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O12, or Li-Al alloy. 12 Or at least one of Li-Al alloy.

[0071] In some embodiments of the present application, the negative electrode material layer can further include a conductive agent and a binder, and the present application does not have a particular limitation on the types of the conductive agent and the binder, as long as the object of the present application can be achieved, for example, it can be at least one of the above-mentioned conductive agent and the above-mentioned binder. The present application does not have a particular limitation on the mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode material layer, and a person skilled in the art can select according to actual needs, as long as the object of the present application can be achieved.

[0072] In some embodiments of the present application, the negative electrode material layer can further include a conductive agent, a binder, and a thickening agent, and the present application does not have a particular limitation on the types of the conductive agent, the binder, and the thickening agent, as long as the object of the present application can be achieved, for example, the conductive agent and the binder can be at least one of the above-mentioned conductive agent and the above-mentioned binder. The thickening agent can include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The present application does not have a particular limitation on the mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickening agent in the negative electrode material layer, and a person skilled in the art can select according to actual needs, as long as the object of the present application can be achieved.

[0073] The present application does not have a particular limitation on the thickness of the negative electrode material layer, as long as the object of the present application can be achieved, for example, the thickness of the negative electrode material layer is 30 μm to 120 μm.

[0074] The present application does not have a particular limitation on the thickness of the negative electrode current collector, as long as the object of the present application can be achieved, for example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0075] Optionally, the negative electrode sheet can further include a conductive layer between the negative current collector and the negative material layer. The composition of the conductive layer is not particularly limited in the present application, and can be a conductive layer commonly used in the art. For example, the conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application, and can be, for example, at least one of the above-mentioned conductive agent and the above-mentioned binder.

[0076] In the present application, the secondary battery further includes an electrolyte including a lithium salt and a non-aqueous solvent.

[0077] The lithium salt is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the lithium salt can include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate.

[0078] The non-aqueous solvent is not particularly limited in the present application, as long as the object of the present application can be achieved, and for example, the non-aqueous solvent can include, but is not limited to, at least one of a carbonate compound, a carboxylate compound, an ether compound, or other organic solvents.

[0079] The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro-carbonate compound. The chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The cyclic carbonate can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluoro-carbonate compound can include, but is not limited to, at least one of fluoro-ethylene carbonate (FEC), 1,2-difluoro-ethylene carbonate, 1,1-difluoro-ethylene carbonate, 1,1,2-trifluoro-ethylene carbonate, 1,1,2,2-tetrafluoro-ethylene carbonate, 1-fluoro-2-methyl-ethylene carbonate, 1-fluoro-1-methyl-ethylene carbonate, 1,2-difluoro-1-methyl-ethylene carbonate, 1,1,2-trifluoro-2-methyl-ethylene carbonate, or trifluoromethyl-ethylene carbonate. The carboxylic acid ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or caprolactone. The ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvent can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the non-aqueous solvent in the electrolyte is not particularly limited in the present application, as long as the object of the present application is achieved.

[0080] The secondary battery further includes a case for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art of secondary batteries, which are not limited in the present application. The case is not particularly limited in the present application, and can be a case known in the art, as long as the object of the present application is achieved. For example, the case can be a hard case or a flexible case. The material of the hard case can be a metal, and the kind of the metal is not limited in the present application, and a metal hard case known in the art can be used, as long as the object of the present application is achieved. The flexible case can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, or the like.

[0081] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, the preparation process of the secondary battery can include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding, etc. as needed to obtain an electrode assembly of a wound structure, placing the electrode assembly into the shell, injecting the electrolyte into the shell and sealing to obtain the secondary battery. Alternatively, the positive electrode sheet, the separator and the negative electrode sheet are stacked in order, and then the four corners of the entire stack structure are fixed with adhesive tape to obtain an electrode assembly of a stack structure, the electrode assembly is placed into the shell, the electrolyte is injected into the shell and sealed to obtain the secondary battery. In addition, the overcurrent prevention element, the guide plate, etc. can also be placed in the shell as needed, thereby preventing the pressure rise inside the secondary battery, overcharging and discharging.

[0082] The second aspect of the present application provides a power consuming device comprising the secondary battery of any of the preceding embodiments. Thus, the power consuming device provided by the present application has good use performance.

[0083] The present application does not particularly limit the type of the power consuming device, which can be any power consuming device known in the art. In some embodiments of the present application, the power consuming device can include but is not limited to a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flash, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0084] Examples

[0085] Hereinafter, examples and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis. It should be noted that in the examples of the present application, the lithium ion battery is explained as an example of the secondary battery, but the secondary battery of the present application is not limited to the lithium ion battery.

[0086] Test methods and apparatus:

[0087] Measurement of size:

[0088] 25℃ ambient temperature, lithium ion battery is discharged to 2.5V at 0.5C, then disassembled, the separator is taken out, soaked in N-methyl pyrrolidone (NMP) for 30 minutes, then naturally air dried, along the length direction and thickness direction of the separator after unfolding, the separator with recess is treated by ion polishing.

[0089] Along the thickness direction of the separator, the cross section of the separator is measured by scanning electron microscope (SEM) to obtain the thickness H0 of the separator. Along the thickness direction of the separator, according to the depth change of the recess, along the length direction of the separator after unfolding, the flat area of the separator, and the middle section of the corner area of the separator and the two edge sections connected with the middle section are determined, and the length of the corner area, the length of the middle section and the length of the two edge sections are measured. The recess arranged in the corner area of the separator is the first recess, and the recess arranged in the flat area of the separator is the second recess. The length ratio L of the middle section is calculated by the formula L%=length of middle section / length of corner area×100%. Optionally, 10 first recesses in the middle section are measured along the thickness direction of the separator to obtain the average depth H3 of the multiple first recesses in the middle section. Optionally, 10 first recesses in the two edge sections are measured along the thickness direction of the separator to obtain the average depth H2 of the multiple first recesses in the two edge sections. The average depth H1 of the first recess is calculated according to the formula H1=H3×L%+H2×(100%-L%). Optionally, 10 second recesses in the flat area are measured along the thickness direction of the separator to obtain the average depth H4 of the second recess.

[0090] The separator is placed under the VHX5000 microscope, the magnification is set to 50-200 times, the photo of the surface of the separator with recess is taken, and the diameter D1 of the maximum circumscribed circle of the outer contour of the orthographic projection of a single recess, the spacing A1 of two adjacent recesses, or the width D2 of the orthographic projection of a single recess, the spacing A2 of two adjacent recesses are measured by microscope software. The measurement of each size is measured at 10 points to obtain the average value as the final result.

[0091] Cycle performance test:

[0092] In a 25℃±2℃ constant temperature box, the lithium ion battery is charged to 4.2V at 1.5C current, then charged to 0.05C at 4.2V, and stopped, then rested for 15 minutes, then discharged to 2.5V at 4C, and rested for 30 minutes. The above charging and discharging process is repeated for 800 cycles, and the discharge capacity of the first cycle is Q0, and the discharge capacity of the 800th cycle is Q800. The cycle capacity retention rate of the 800th cycle of the lithium ion battery is calculated as Q800 / Q0×100%. 800 800

[0093] Lithium precipitation degree test:​​

[0094] The lithium ion battery was placed in a thermostat at 10°C, and after 60 minutes, it was charged at 2C constant current to 4.2V, and then charged at 4.2V constant voltage until the current was 0.05C. After 5 minutes, it was discharged at 0.5C constant current to 2.5V. This was one cycle. After 10 cycles according to the above charging and discharging process, the lithium ion battery was charged at 2C constant current to 4.2V, and then charged at 4.2V constant voltage until the current was 0.05C. After 5 minutes, the lithium ion battery was disassembled, and the lithium deposition state on the surface of the negative electrode sheet was observed. The area without lithium deposition was golden yellow, and the area with lithium deposition was grayish white.

[0095] The judgment standard for the degree of lithium deposition of the lithium ion battery is as follows: lithium deposition area ≤ 5%, no lithium deposition; 5% < lithium deposition area ≤ 8%, basically no lithium deposition; 8% < lithium deposition area ≤ 11%, slight lithium deposition; 11% < lithium deposition area ≤ 13%, lithium deposition; 13% < lithium deposition area ≤ 30%, severe lithium deposition; 30% < lithium deposition area ≤ 40%, heavy lithium deposition; wherein the percentage of lithium deposition area is calculated based on the sum of the areas of the two sides of the negative electrode sheet.

[0096] In the present application, the person skilled in the art can understand that "C" refers to the rated capacity of the finished lithium ion battery when it leaves the factory. "1C" is the current value that completely discharges the capacity of the lithium ion battery within 1 hour, "0.1C" is the current value that completely discharges the capacity of the lithium ion battery within 10 hours, and other rates are calculated in the same way.

[0097] Example 1-1

[0098] <Preparation of the positive electrode sheet>

[0099] The positive electrode active material lithium cobaltate (LiCoO2), the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97.9:0.9:1.2, and N-methyl pyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. After uniform stirring under vacuum, a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and dried at 120°C to obtain a positive electrode sheet with a single-sided positive electrode material layer. The coating weight of the positive electrode material layer was 267.8mg / 1540mm 2 . Then the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer. After drying at 120°C and cold pressing, the positive electrode sheet was cut and the tabs were welded to obtain a positive electrode sheet with a size of 74mm×867mm. The thickness of the single-sided positive electrode material layer was 42μm.

[0100] <Preparation of the negative electrode sheet>

[0101] The negative active material artificial graphite, the binder styrene-butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 97.4:1.4:1.2, deionized water is added as a solvent, and a slurry with a solid content of 45 wt% is prepared. After uniform stirring in a vacuum stirrer, a negative electrode slurry is obtained. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and dried at 120°C to obtain a negative electrode sheet with a single-side coated negative electrode material layer. The coating weight of the negative electrode material layer is 142 mg / 1540 mm 2 Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-side coated negative electrode material layer. After drying at 120°C and cold pressing, the negative electrode sheet is cut and the tabs are welded to obtain a negative electrode sheet with a size of 78 mm x 875 mm for use. The thickness of the single-side negative electrode material layer is 54.5 μm.

[0102] <Preparation of electrolyte>

[0103] In an environment with a water content of less than 10 ppm, dimethyl carbonate, diethyl carbonate, and ethylene carbonate are mixed in a mass ratio of 1:1:1 to obtain a non-aqueous solvent. Then, lithium salt LiPF6 is added to the non-aqueous solvent, and mixed uniformly to obtain an electrolyte. The mass percentage of lithium salt in the electrolyte is 12.5%, and the balance is the non-aqueous solvent.

[0104] <Preparation of separator>

[0105] A polyethylene (PE) film with a thickness of 15 μm is taken as a base layer, and an inorganic coating layer with a thickness of 2.5 μm is coated on both surfaces of the base layer to obtain a separator with a thickness H0 μm of 20 μm. The inorganic coating layer comprises aluminum oxide and polyvinylidene fluoride in a mass ratio of 70:30.

[0106] Along the length direction of the expanded separator, the flat area and the corner area of the separator are determined according to the size of the preset electrode assembly, and the middle section and the two edge sections of the corner area are determined. A first recess is arranged in the corner area. Specifically, based on the length of the corner area, the length ratio L% of the middle section is 36%, and the length ratio L' % of any one edge section is 32%. Along the thickness direction of the separator, the shape of the orthographic projection of a single first recess on the separator is a circle, the diameter D1 mm of the maximum circumscribed circle of the outer contour of the orthographic projection of a single first recess is 0.5 mm, the average depth H3 μm of all first recesses located in the middle section is 2.0 μm, and the average depth H2 μm of all first recesses located in the edge section is 2.6 μm. Along the length direction of the expanded separator, the distance A1 mm between adjacent two first recesses is 0.5 mm. Along the width direction of the expanded separator, the distance between adjacent two first recesses is equal to A1 mm. The separator is cold-pressed by using an embossing roller with the above parameters to obtain a separator with a first recess arranged on one surface.

[0107] Preparation of lithium ion battery

[0108] The positive electrode sheet, the separator, and the negative electrode sheet prepared above are stacked in order, with the separator with the first recessed part facing the negative electrode sheet. The electrode assembly is obtained by winding the core. The electrode assembly is loaded into an outer packaging aluminum plastic film, and the moisture is removed at 80°C, and the electrolyte prepared above is injected. After vacuum packaging, standing, formation, degassing, and edge cutting processes, the lithium ion battery is obtained. The upper limit voltage of the formation is 4.15V, the formation temperature is 70°C, and the standing time of the formation is 2h.

[0109] Examples 1-2 to 1-25

[0110] Except that the related preparation parameters are adjusted according to Table 1, the thickness of the separator is adjusted by adjusting the thickness of the substrate layer and the thickness of the inorganic coating layer as shown in Table 1, and the rest is the same as Example 1-1.

[0111] Example 1-26

[0112] Except that the related preparation parameters are adjusted according to Table 1, and the first recessed part is also provided on the other surface of the separator by using the embossing roller of the corresponding specification according to the parameters in Table 1, and the rest is the same as Example 1-1.

[0113] Example 1-27

[0114] Except that the related preparation parameters are adjusted according to Table 1, and the second recessed part is provided on the flat area of the separator, and the rest is the same as Example 1-1, wherein the second recessed part is provided on the flat area of the separator, specifically: the shape of the orthographic projection of a single second recessed part on the separator along the thickness direction of the separator is circular, the diameter of the maximum circumscribed circle of the outer contour of the orthographic projection of a single second recessed part is equal to D1 mm, and the average depth H4 of a single second recessed part is 0.1 μm; the distance between adjacent two second recessed parts along the length direction of the separator after being developed is equal to A1 mm; and the distance between adjacent two second recessed parts along the width direction of the separator after being developed is equal to A1 mm. The separator is cold-pressed by using the embossing roller of the corresponding specification according to the above parameters to obtain a separator with the first recessed part and the second recessed part on one surface.

[0115] Examples 1-28 to 1-30

[0116] Except that the related preparation parameters are adjusted according to Table 1, and the rest is the same as Example 1-27.

[0117] Example 1-31

[0118] Except that the shape of the orthographic projection of the first recessed part on the separator is adjusted as shown in Table 1, and the rest is the same as Example 1-27. Figure 3The strip-shaped first recesses are arranged in the corner region, and the rest is the same as Example 1-1 except that the related preparation parameters are adjusted according to Table 1. Specifically, the length of the middle section accounts for 36% of the length of the corner region based on the length of the corner region, and the length of any one edge section accounts for 32% of the length of the corner region. The shape of the projection of a single first recess on the diaphragm in the thickness direction of the diaphragm is a strip, the two long edges of the projection of a single first recess are parallel to the width direction of the diaphragm, the width D2 of the projection of a single first recess is 1.0 mm, the average depth H3 of all first recesses in the middle section is 2.0 μm, and the average depth H2 of all first recesses in the edge section is 2.6 μm. The distance A2 between two adjacent first recesses in the length direction of the diaphragm after being developed along the diaphragm is 1.0 mm. The diaphragm is cold-pressed by using a corresponding embossing roller according to the above parameters to obtain a diaphragm with first recesses arranged on the surface.

[0119] Examples 1-32 to 1-35

[0120] The rest is the same as Example 1-31 except that the related preparation parameters are adjusted according to Table 1.

[0121] Example 1-36

[0122] The rest is the same as Example 1-1 except that a polyethylene (PE) film with a thickness H0 of 20 μm is used as the diaphragm, and the related preparation parameters are adjusted according to Table 1.

[0123] Comparative Example 1-1

[0124] The rest is the same as Example 1-1 except that no first recess is arranged on the surface of the diaphragm.

[0125] Comparative Examples 1-2 to 1-3

[0126] The rest is the same as Example 1-1 except that the related preparation parameters are adjusted according to Table 1.

[0127]

[0128]

[0129] From Examples 1-1 to 1-36 and Comparative Examples 1-1 to 1-3, it can be seen that the diaphragm with the first recess in the corner region of the application is used, and H1 / H0 is controlled within the range of the application. The lithium ion battery has a higher 800-cycle capacity retention rate and a lighter lithium precipitation degree, indicating that the lithium ion battery has good cycle performance and safety performance.

[0130] As can be seen from Examples 1-1 to 1-24, 1-27 to 1-35, when the values of H1, H0, H2 / H3, L, D1, A1, H4, D2, A2 are regulated within the ranges of the present application, the lithium ion battery has a higher 800-cycle capacity retention rate and a lighter lithium precipitation degree, indicating that the lithium ion battery has better cycle performance and safety performance.

[0131] As can be seen from Examples 1-1, 1-25 to 1-26, when the first recess is arranged on at least one surface of the separator facing the negative electrode sheet, the lithium ion battery has a higher 800-cycle capacity retention rate and a lighter lithium precipitation degree, indicating that the lithium ion battery has better cycle performance and safety performance.

[0132] As can be seen from Examples 1-1, 1-36, when the separator comprising a substrate layer and a coating layer is used, the lithium ion battery has a higher 800-cycle capacity retention rate and a lighter lithium precipitation degree, indicating that the lithium ion battery has better cycle performance and safety performance.

[0133] It should be noted that the relational terms herein such as first and second and the like are used only to differentiate one entity or operation from another, and do not necessarily require or imply that any such actual relationship or order exists between or among the entities or operations. Also, the terms "comprises", "comprising", or any other variations thereof are intended to cover non-exclusive inclusions, so that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0134] The term "one of", "one", "a kind of" or other similar terms connected to the elements means any one of the listed elements. For example, "one of A or B" means only A or only B; for another example, "one of A, B and C" means only A, only B or only C. The term "at least one of", "at least one", "at least one kind of" or other similar terms connected to the elements means any combination of the listed elements. For example, "at least one of A or B" means only A, only B, A and B. For another example, "at least one of A, B or C" means only A, only B, only C, only A and B, only A and C, only B and C, A and B and C.

[0135] Each embodiment in the specification is described in a relevant manner, and the same and similar parts between each embodiment can be referred to each other, and each embodiment focuses on the difference from other embodiments.

[0136] The above description is only the preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising a wound electrode assembly, the electrode assembly including a positive electrode, a separator and a negative electrode, the separator being located between the positive electrode and the negative electrode, the electrode assembly including a straight region and a corner region; At least one surface of the diaphragm in the corner region is provided with a plurality of first recesses, the average depth of the first recesses along the thickness direction of the diaphragm is H1 μm, the thickness of the diaphragm is H0 μm, and 0.05≤H1 / H0≤0.

2.

2. The secondary battery according to claim 1, wherein, 0.11≤H1 / H0≤0.

16.

3. The secondary battery according to claim 1, wherein, 0.35≤H1≤6, and / or, 7≤H0≤30.

4. The secondary battery according to claim 1, wherein, Along the length of the unfolded diaphragm, the corner area includes a middle section and two edge sections. The middle section is located between the two edge sections. Based on the length of the corner area, the length of the middle section accounts for L%, and 30≤L≤50. The middle section and the two edge sections are each provided with a plurality of first recesses. Along the thickness direction of the diaphragm, the average depth of the plurality of first recesses in the middle section is H3μm, and the average depth of the plurality of first recesses in the two edge sections is H2μm, where H3 < H2.

5. The secondary battery according to claim 4, wherein, 1.1≤H2 / H3≤2.

6. The secondary battery according to any one of claims 1 to 5, wherein, The plurality of first recesses are distributed in a dot-like manner. Along the thickness direction of the diaphragm, the orthographic projection of a single first recess includes a circle, an ellipse, or a polygon. The diameter of the largest circumcircle of the orthographic projection of a single first recess is D1 mm, where 0.1 ≤ D1 ≤ 1.

7. The secondary battery according to claim 6, wherein, Along the length of the unfolded diaphragm, the distance between two adjacent first recesses is A1 mm, where 0.1 ≤ A1 ≤ 1.

8. The secondary battery according to any one of claims 1 to 5, wherein, The plurality of first recesses are arranged in a strip shape and are spaced apart. Along the direction of the spacing, the width of the orthographic projection of a single first recess is D2 mm, where 0.5 ≤ D2 ≤ 2.

9. The secondary battery according to claim 8, wherein, The distance between two adjacent first recesses is A2 mm, where 0.5 ≤ A2 ≤ 2.

10. The secondary battery according to any one of claims 1 to 5, wherein, The first recess is located on the surface of the diaphragm facing the negative electrode sheet.

11. The secondary battery according to any one of claims 1 to 5, wherein, The diaphragm includes a substrate layer and a coating located on at least one surface of the substrate layer, the coating having the plurality of first recesses.

12. The secondary battery according to claim 11, wherein, The coating includes at least one of inorganic coating and organic coating; the inorganic coating includes inorganic particles and a binder; the organic coating includes a polymer.

13. The secondary battery according to any one of claims 1 to 5, wherein, At least one surface of the diaphragm in the flat region is provided with a plurality of second recesses, and the average depth of the second recesses along the thickness direction of the diaphragm is H4μm, 0.1≤H4≤0.

3.

14. The secondary battery according to claim 13, wherein, The second recess is located on the surface of the diaphragm facing the negative electrode sheet.

15. An electrical device comprising a secondary battery as described in any one of claims 1 to 14.

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