Positive plate, battery cell and lithium ion secondary battery

Abstract

The utility model relates to the technical field of batteries, in particular to a positive plate, a battery cell and a lithium ion secondary battery. The positive plate comprises a positive current collector; the positive tab is electrically connected with the positive current collector; the positive electrode paste is arranged on at least one surface of the positive electrode current collector, an angular position is defined by two adjacent side edges of the positive electrode paste, at least one angular position of the positive electrode paste is provided with a first concave part, and the first concave part is located on one side, deviating from the positive electrode current collector, of the positive electrode paste. The first concave part is used for removing part of the positive active material at the positive paste corner position, and the CB value at the negative paste corner position is increased, so that lithium precipitation is not easy to occur at the corner position of the negative plate, and the safety performance of the battery is improved.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and in particular, to a positive electrode sheet, a battery cell, and a lithium-ion secondary battery. Background Art

[0002] A battery is a widely used energy device, which has the characteristics of simple structure, convenient carrying, and easy charging and discharging operations, and plays a great role in various aspects of modern social life.

[0003] Currently, some battery cells of lithium-ion secondary batteries include a positive electrode sheet and a negative electrode sheet that are alternately stacked. During the charging process of the battery, lithium ions are removed from the positive electrode paste of the positive electrode sheet and embedded in the negative electrode paste of the negative electrode sheet. However, there are edge effects between the positive electrode sheet and the negative electrode sheet, that is, there are fewer lithium ion channels at the paste edges of the electrode sheets compared to the inside of the electrode sheets. There is a high risk of lithium deposition at the edges of the negative electrode sheet during battery charging, and there is a superposition of edge effects at the corner positions of the electrode sheets. Therefore, lithium deposition is more likely to occur at the corner positions of the negative electrode sheet than at other positions during battery charging, reducing the safety performance of the battery. Summary of the Utility Model

[0004] Based on this, this application provides a positive electrode sheet, a battery cell, and a lithium-ion secondary battery to solve the problem in the related art that lithium deposition is more likely to occur at the corner positions of the negative electrode sheet in the battery than at other positions, reducing the safety performance of the battery.

[0005] In a first aspect, this application provides a positive electrode sheet, including:

[0006] A positive electrode current collector;

[0007] A positive electrode tab, electrically connected to the positive electrode current collector;

[0008] A positive electrode paste, disposed on at least one surface of the positive electrode current collector. Two adjacent side edges of the positive electrode paste define a corner position. At least one corner position of the positive electrode paste is provided with a first recess, and the first recess is located on the side of the positive electrode paste facing away from the positive electrode current collector.

[0009] In a possible implementation, the first recess includes a concave hole provided on the positive electrode paste, and the number of the concave holes is multiple;

[0010] The distance between the concave hole closest to the side edge of the positive electrode paste and the adjacent side edge of the positive electrode paste is 50 μm - 2000 μm; and / or, the distance between two adjacent concave holes is 120 μm - 4000 μm.

[0011] In a possible implementation, first recesses are respectively provided at the four corner positions of the positive electrode paste.

[0012] In a possible implementation, on a positive electrode sheet,

[0013] The total volume of all the concave holes accounts for 0.05%-1% of the total volume of the positive electrode paste; and / or, the total area of all the concave holes accounts for 1%-10% of the total area of the positive electrode paste.

[0014] In a possible implementation, the thickness of the positive electrode paste is D1, and D1 satisfies: 30μm ≤ D1 ≤ 60μm;

[0015] The depth H of the concave hole satisfies: 5μm ≤ H ≤ 40μm; and / or, the aperture R of the concave hole satisfies: 50μm ≤ R ≤ 200μm.

[0016] In a possible implementation, the thickness of the positive electrode paste is 9μm - 48μm;

[0017] The depth of the concave hole is 1.5μm - 28μm; and / or, the aperture of the concave hole is 15μm - 160μm.

[0018] In a second aspect, the present application further provides an electric core, including a plurality of the above-mentioned positive electrode sheets, a separator, and a plurality of negative electrode sheets, and the plurality of positive electrode sheets, the separator, and the plurality of negative electrode sheets are stacked;

[0019] The negative electrode sheet includes a negative electrode current collector, a negative electrode tab, and a negative electrode paste, the negative electrode tab is electrically connected to the negative electrode current collector, and the negative electrode paste is disposed on at least one surface of the negative electrode tab.

[0020] In a possible implementation, a second concave portion is provided on the side of the negative electrode paste facing away from the negative electrode current collector.

[0021] In a possible implementation, the second concave portion is a wire groove provided on the negative electrode paste, the extending direction of the wire groove is inclined to the side edge of the negative electrode paste and not perpendicular to the side edge of the negative electrode paste, and the end of the wire groove extends to the side edge of the negative electrode paste.

[0022] In a possible implementation, the number of wire grooves on the negative electrode paste is at least two, two adjacent wire grooves are arranged in parallel, and the distance between two adjacent wire grooves is 100μm - 2500μm.

[0023] In a possible implementation, the thickness of the electric core is 3mm - 6mm, the thickness of the negative electrode paste is D2, and D2 satisfies: 30μm ≤ D2 ≤ 80μm;

[0024] The depth of the wire groove is h, and h satisfies: 5μm ≤ h ≤ 40μm; and / or, the width w of the wire groove satisfies: 50μm ≤ w ≤ 400μm.

[0025] In a possible implementation, the thickness of the battery cell is 3 mm - 6 mm, the thickness of the negative electrode paste is D2, where D2 satisfies 30 μm ≤ D2 ≤ 80 μm. The negative electrode paste includes a normal region and a thinned region. The thinned region is located on one side of the normal region facing the side edge of the negative electrode paste. The end of the wire groove extends to the thinned region. The depth of the wire groove in the normal region is h, where h satisfies: 5 μm ≤ h ≤ 40 μm, and the maximum depth of the wire groove in the thinned region is 1.05h - 1.5h.

[0026] In a possible implementation, the thickness of the battery cell is 0.6 mm - 5.4 mm, and the thickness of the negative electrode paste is 6 μm - 80 μm;

[0027] The depth of the wire groove is 1 μm - 36 μm; and / or, the width of the wire groove is 10 μm - 360 μm.

[0028] In a possible implementation, the thickness of the battery cell is 0.6 mm - 5.4 mm, and the thickness of the negative electrode paste is 6 μm - 80 μm;

[0029] The negative electrode paste includes a normal region and a thinned region. The thinned region is located on one side of the normal region facing the side edge of the negative electrode paste. The end of the wire groove extends to the thinned region. The depth of the wire groove in the normal region is 1 μm - 36 μm, and the maximum depth of the wire groove in the thinned region is 1.05 times - 1.5 times the depth of the wire groove in the normal region.

[0030] In a possible implementation, the outermost layer of the battery cell is a negative electrode sheet. The outermost negative electrode sheet is a single-sided coated negative electrode sheet, and the negative electrode paste of the outermost negative electrode sheet is located on the side of the negative electrode current collector facing the adjacent positive electrode sheet.

[0031] In a third aspect, the present application also provides a lithium-ion secondary battery, including the above-mentioned battery cell.

[0032] For the positive electrode sheet, battery cell, and lithium-ion secondary battery provided by the present application, by providing a first recess at the corner position of the positive electrode paste of the positive electrode sheet, the corner position of the positive electrode paste of the positive electrode sheet corresponds to the corner position of the negative electrode paste of the negative electrode sheet. The first recess is used to remove part of the positive active material at the corner position of the positive electrode paste, increasing the CB value at the corner position of the negative electrode paste, making it not easy for lithium deposition to occur at the corner position of the negative electrode sheet of the battery, and improving the safety performance of the battery. Description of the Drawings

[0033] 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 use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 Schematic diagram of the positive electrode sheet provided by an embodiment of the present application;

[0035] Figure 2 is Figure 1 Partial enlarged schematic diagram at position A in

[0036] Figure 3 Explosion diagram of the battery cell provided by an embodiment of the present application;

[0037] Figure 4 Partial section of the positive electrode paste provided by an embodiment of the present application Figure 1 ;

[0038] Figure 5 Partial section of the positive electrode paste provided by an embodiment of the present application Figure 2 ;

[0039] Figure 6 Partial section of the positive electrode paste provided by an embodiment of the present application Figure 3 ;

[0040] Figure 7 Schematic diagram of the negative electrode sheet provided by an embodiment of the present application Figure 1 ;

[0041] Figure 8 Schematic diagram of the negative electrode sheet provided by an embodiment of the present application Figure 2 ;

[0042] Figure 9 Schematic diagram of the negative electrode sheet provided by an embodiment of the present application Figure 3 ;

[0043] Figure 10 is Figure 9 Partial sectional view of the negative electrode sheet shown;

[0044] Figure 11 is Figure 3 Schematic diagram of the outermost negative electrode sheet of the battery cell in

[0045] Explanation of reference numerals:

[0046] 100 - positive electrode sheet; 110 - positive electrode tab; 120 - positive electrode paste; 121 - concave hole;

[0047] 200 - negative electrode sheet; 210 - negative current collector; 220 - negative electrode tab; 230 - negative electrode paste; 231 - wire groove; 232 - normal area; 233 - thinning area. Detailed implementation manners

[0048] To make the objectives, technical solutions and advantages of this application more clear, the following will describe in more detail the technical solutions in the embodiments of this application with reference to the accompanying drawings in the preferred embodiments of this application. In the accompanying drawings, the same or similar reference numerals represent the same or similar components or components with the same or similar functions from beginning to end. The described embodiments are some, but not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain this application, and should not be construed as a limitation to this application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application. The following will explain in detail the embodiments of this application with reference to the accompanying drawings.

[0049] In the description of this application, it should be noted that, unless otherwise clearly defined and limited, the terms "install", "connect", and "couple" should be understood in a broad sense. For example, it may be a fixed connection, or an indirect connection through an intermediate medium, or the internal connection or interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0050] In the description of this application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to this application.

[0051] The terms "first", "second", "third" (if any) in the description and claims of this application and the above accompanying drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence.

[0052] In addition, the terms "comprise" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or display that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or displays. The "plurality" mentioned above means at least one.

[0053] In the prior art, the cores of some lithium-ion secondary batteries include a positive electrode sheet and a negative electrode sheet that are alternately stacked. During the charging process of the battery, lithium ions are removed from the positive electrode paste of the positive electrode sheet and embedded in the negative electrode paste of the negative electrode sheet. However, there are edge effects in the positive electrode sheet and the negative electrode sheet, that is, there are fewer lithium-ion channels at the paste edges of the electrode sheets compared to the inside of the electrode sheets. That is to say, some lithium ions located inside the negative electrode paste can be transmitted from all around to the inside, while some lithium ions located at the edge of the negative electrode paste can only be transmitted from the edge to the inside. Compared with the inside of the negative electrode paste, there are fewer lithium-ion transmission channels at the edge of the negative electrode paste. There is a high risk of lithium deposition at the edge of the negative electrode sheet during battery charging, and there is a superposition of edge effects at the corner positions of the electrode sheets. Therefore, lithium deposition is more likely to occur at the corner positions of the negative electrode sheet than at other positions, reducing the safety performance of the battery.

[0054] After repeated thinking and verification, the inventors found that if a recess is provided at the corner position of the positive electrode paste of the positive electrode sheet, since the corner position of the positive electrode paste corresponds to the corner position of the negative electrode paste of the negative electrode sheet, by removing part of the positive active material at the corner position of the positive electrode paste through the recess, the CB value at the corner position of the negative electrode paste is increased, making it difficult for lithium deposition to occur at the corner position of the negative electrode paste and improving the safety of the battery.

[0055] In view of this, the inventors designed a positive electrode sheet, a core, and a lithium-ion secondary battery. By providing a first recess at at least one corner position of the positive electrode paste of the positive electrode sheet, part of the positive active material at the corner position of the positive electrode paste is removed by using the first recess. In this way, the CB value at the corner position of the negative electrode paste corresponding to the first recess is increased, making it difficult for lithium deposition to occur at the corner position of the negative electrode paste and improving the safety of the battery.

[0056] The following describes in detail the technical solutions of the positive electrode sheet, the core, and the lithium-ion secondary battery provided in the embodiments of the present application with reference to the accompanying drawings.

[0057] Refer to Figures 1-3 As shown, the positive electrode sheet 100 provided in the embodiment of the present application includes a positive electrode current collector, a positive electrode tab 110, and a positive electrode paste 120. The positive electrode tab 110 is electrically connected to the positive electrode current collector. The positive electrode paste 120 is provided on at least one surface of the positive electrode current collector. Two adjacent side edges of the positive electrode paste 120 define a corner position. A first recess is provided at at least one corner position of the positive electrode paste 120, and the first recess is located on the side of the positive electrode paste 120 facing away from the positive electrode current collector.

[0058] Schematically, the positive electrode tab 110 can be integrally formed with the positive electrode current collector. For the positive electrode sheet 100 provided in this embodiment, the positive electrode paste 120 can be provided only on one surface of the positive electrode current collector, or the positive electrode paste 120 can be provided on opposite surfaces of the positive electrode current collector respectively, which is not uniquely limited herein.

[0059] Among them, the shape of the positive electrode paste 120 can be rectangular, that is, the positive electrode paste 120 has four corner positions, which are respectively located at the four corners of the positive electrode paste 120. When the positive electrode sheet 100 and the negative electrode sheet 200 are made into an electric core, the corner positions of the positive electrode paste 120 correspond to the corner positions of the negative electrode paste 230 of the negative electrode sheet 200. Here, the number of corner positions of the positive electrode paste 120 having the first concave portion is defined as X, and X satisfies: 1≤X≤4, that is, X can be 1, 2, 3 or 4. That is to say, the number of corner positions of the positive electrode paste 120 having the first concave portion can be 1, 2, 3 or 4. Those skilled in the art can set the first concave portion only at one corner position of the positive electrode paste 120 according to needs, or can also set the first concave portion at multiple corner positions of the positive electrode paste 120 respectively, and no unique limitation is made here. By providing the first concave portion on the positive electrode paste 120, part of the positive active material at the corner position of the positive electrode paste 120 is removed.

[0060] It can be understood that the thickness of the positive electrode paste 120 at the position of the first concave portion is less than the thickness of the positive electrode paste 120 at the remaining positions. The first concave portion is located on the side of the positive electrode paste 120 away from the positive electrode current collector, so that the first concave portion does not affect the electrical connection between the positive electrode paste 120 and the positive electrode current collector. Among them, the opening of the first concave portion faces away from the positive electrode current collector.

[0061] For the positive electrode sheet 100 provided in this embodiment, by providing the first concave portion at the corner position of the positive electrode paste 120 of the positive electrode sheet 100, the corner position of the positive electrode paste 120 of the positive electrode sheet 100 corresponds to the corner position of the negative electrode paste 230 of the negative electrode sheet 200. Using the first concave portion to remove part of the positive active material at the corner of the positive electrode paste 120 increases the CB value at the corner position of the negative electrode paste 230, increases the margin of the negative electrode capacity exceeding the positive electrode capacity in the area corresponding to the corner position of the positive electrode paste 120, so that it is not easy for lithium deposition to occur at the corner position of the negative electrode sheet 200 of the battery, and improves the safety performance of the battery.

[0062] In one embodiment, as Figure 1 shown, first concave portions are respectively provided at the four corner positions of the positive electrode paste 120.

[0063] It can be understood that by respectively providing the first concave portions at the four corner positions of the positive electrode paste 120, the CB values at the respective corner positions of the negative electrode paste 230 of the negative electrode sheet 200 are respectively increased, so that it is not easy for lithium deposition to occur at each corner position of the negative electrode paste 230, and the safety performance of the battery is further improved.

[0064] In one embodiment, as Figure 1 and Figure 2 shown, the first concave portion includes a concave hole 121 provided on the positive electrode paste 120, and the number of the concave holes 121 is multiple.

[0065] Among them, the concave holes 121 can be formed on the positive electrode paste 120 through a laser drilling process, and the axis of the concave holes 121 can extend along the thickness direction of the positive electrode paste 120. Schematically, the concave holes 121 do not penetrate the positive electrode paste 120, that is, the depth of the concave holes 121 is less than the thickness of the positive electrode paste 120. It can be understood that the number of the concave holes 121 is greater than two, such as Figure 1 and Figure 2 As shown, multiple concave holes 121 can be arranged in multiple rows and columns at the corner positions of the positive electrode paste 120. Those skilled in the art can set the number of the concave holes 121 at the corners of the positive electrode paste 120 according to needs, and no unique limitation is made here.

[0066] Setting the first recess as the concave hole 121 can avoid excessive loss of positive active material at the corners of the positive electrode paste 120, which is beneficial to ensuring the capacity of the battery.

[0067] Such as Figures 4-6 As shown, after the positive electrode paste 120 is laser drilled to form the concave holes 121, under the influence of factors such as different laser energies and the compaction density of the positive electrode paste 120, the cross-section of the concave holes 121 can be circular, trapezoidal, polygonal or an irregular concave morphology.

[0068] In a specific embodiment, such as Figure 2 As shown, the distance L1 between the concave hole 121 closest to the side of the positive electrode paste 120 and the adjacent side of the positive electrode paste 120 is 50μm - 2000μm. That is to say, the distance between the outermost concave hole 121 and the adjacent side of the positive electrode paste 120 is 50μm - 2000μm.

[0069] For example, the distance between the outermost concave hole 121 and the adjacent side of the positive electrode paste 120 can be 50μm, 80μm, 100μm, 150μm, 170μm, 200μm, 300μm, 400μm, 500μm, 600μm, 800μm, 1000μm, 1500μm, 2000μm, etc., and no unique limitation is made here. When the distance between the outermost concave hole 121 and the adjacent side of the positive electrode paste 120 is less than 50μm, the concave hole 121 is close to the side of the positive electrode paste 120. During the process of drilling the positive electrode sheet 100, it may hit the edge of the positive electrode sheet 100, causing damage to the stage, or resulting in distortion of the shape of the concave hole 121 at the edge of the positive electrode sheet 100, destroying the consistency of drilling and making it inconvenient to detect the drilled positive electrode sheet 100; when the distance between the outermost concave hole 121 and the adjacent side of the positive electrode paste 120 is greater than 2000μm, the concave hole 121 is far from the side of the positive electrode paste 120, and the concave holes 121 on the positive electrode paste 120 cannot reliably increase the CB value at the corner position of the negative electrode paste 230, and the effect of improving lithium deposition at the corner position of the negative electrode sheet 200 is small.

[0070] By restricting the distance between the side of the outermost concave hole 121 adjacent to the positive electrode paste 120, it is possible to avoid damaging the stage during the drilling process by drilling to the edge of the positive electrode sheet 100, while ensuring the consistency of drilling and the improvement effect of the concave holes 121 on the positive electrode paste 120 on the lithium deposition at the corner position of the negative electrode sheet 200.

[0071] In a specific embodiment, as Figure 2 shown, the distance L2 between two adjacent concave holes 121 is 120 μm - 4000 μm.

[0072] Wherein, the distance L2 between two adjacent concave holes 121 is the distance between the axes of two adjacent concave holes 121. Exemplarily, the distance between two adjacent concave holes 121 can be 120 μm, 210 μm, 250 μm, 300 μm, 350 μm, 400 μm, 600 μm, 800 μm, 1200 μm, 1500 μm, 2000 μm, 3000 μm or 4000 μm, etc., which is not uniquely limited herein. When the distance between two adjacent concave holes 121 is less than 120 μm, the multiple concave holes 121 are too densely arranged at the corner position of the positive electrode paste 120, resulting in a decrease in the battery capacity of the battery using the positive electrode sheet 100; when the distance between two adjacent concave holes 121 is greater than 4000 μm, the multiple concave holes 121 are too sparsely arranged at the corner position of the positive electrode paste 120, and the concave holes 121 on the positive electrode paste 120 cannot reliably increase the CB value at the corner position of the negative electrode paste 230, and the improvement effect on the lithium deposition at the corner position of the negative electrode sheet 200 is small.

[0073] The above setting can ensure the battery capacity, that is, the concave holes 121 do not affect the capacity of the non-lithium-deposited part, and at the same time can ensure the improvement effect of the concave holes 121 on the positive electrode paste 120 on the lithium deposition at the corner position of the negative electrode sheet 200. Within the range of the smallest possible drilling area, the advantages brought by drilling are increased.

[0074] Schematically, on a positive electrode sheet 100, the total volume of all the concave holes 121 accounts for 0.05% - 1% of the total volume of the positive electrode paste 120.

[0075] For example, the total volume of all the concave holes 121 may account for 0.05%, 0.35%, 0.5%, 0.65%, 0.8% or 1% etc. of the total volume of the positive electrode paste 120, and there is no unique limitation here. Among them, when the total volume of all the concave holes 121 is less than 0.05% of the total volume of the positive electrode paste 120, the concave holes 121 on the positive electrode paste 120 cannot reliably increase the CB value at the corner position of the negative electrode paste 230, and the effect of improving lithium deposition at the corner position of the negative electrode sheet 200 is relatively small; when the total volume of all the concave holes 121 is greater than 1% of the total volume of the positive electrode paste 120, a relatively large amount of positive active material is removed at the corner position of the positive electrode paste 120, and the capacity of the battery after the positive electrode sheet 100 is made into a battery is relatively low.

[0076] It is worth mentioning that when the surface density of the positive electrode paste 120 is the same, the total mass removed by the positive electrode paste 120 at all the concave holes 121 accounts for 0.05% - 1% of the total mass of the positive electrode paste 120.

[0077] Schematically, on a positive electrode sheet 100, the total area of all the concave holes 121 accounts for 1% - 10% of the total area of the positive electrode paste 120.

[0078] It is worth mentioning that the area of the concave hole 121 is the area at the end of the concave hole 121 far from the positive electrode current collector, that is, the maximum area of the concave hole 121. For example, the total area of all the concave holes 121 may account for 1%, 4%, 5%, 6%, 8% or 10% etc. of the total area of the positive electrode paste 120, and there is no unique limitation here. When the total area of all the concave holes 121 is less than 1% of the total area of the positive electrode paste 120, the concave holes 121 on the positive electrode paste 120 cannot reliably increase the CB value at the corner position of the negative electrode paste 230, and the effect of improving lithium deposition at the corner position of the negative electrode sheet 200 is relatively small; when the total area of all the concave holes 121 is greater than 10% of the total area of the positive electrode paste 120, the capacity of the battery after the positive electrode sheet 100 is made into a battery is relatively low.

[0079] Through the above settings, while ensuring the capacity of the battery after the positive electrode sheet 100 is made into a battery, it is also possible to ensure that the effect of improving lithium deposition at the corner position of the negative electrode sheet 200 is relatively small.

[0080] In a possible implementation manner, the thickness of the positive electrode paste 120 is D1, and D1 satisfies: 30μm ≤ D1 ≤ 60μm. The depth H of the concave hole 121 satisfies: 5μm ≤ H ≤ 40μm.

[0081] It should be noted that the thickness of the positive electrode paste 120 is the thickness of the positive electrode paste 120 on one side of the positive electrode current collector. For example, the thickness of the positive electrode paste 120 can be 30μm, 35μm, 40μm, 50μm, 60μm, etc., and there is no unique limitation here. The positive electrode sheet 100 with the positive electrode paste 120 having the above thickness can be used to make a conventional battery cell with a thickness of 3mm - 6mm. The depth of the concave hole 121 can be 5μm, 15μm, 25μm, 35μm, 40μm, etc., and can be specifically set according to the thickness of the positive electrode paste 120 and the number of the concave holes 121. When the depth of the concave hole 121 is less than 5μm, the improvement effect of the concave hole 121 on lithium deposition at the corner position of the negative electrode paste 230 is small; when the depth of the concave hole 121 is greater than 40μm, the positive electrode paste 120 loses more positive electrode active substances, resulting in a decrease in the capacity of the battery made from the positive electrode sheet 100.

[0082] When the thickness D1 of the positive electrode paste 120 on one side of the positive electrode current collector satisfies: 30μm ≤ D1 ≤ 60μm, the aperture R of the concave hole 121 satisfies: 50μm ≤ R ≤ 200μm.

[0083] Among them, the aperture of the concave hole 121 is the maximum aperture at the end of the concave hole 121 away from the positive electrode current collector. For example, the aperture of the concave hole 121 can be 50μm, 80μm, 110μm, 150μm, 180μm, 200μm, etc., and can be specifically set according to the thickness of the positive electrode paste 120 and the number of the concave holes 121, and there is no unique limitation here. When the aperture of the concave hole 121 is less than 50μm, the improvement effect of the concave hole 121 on lithium deposition at the corner position of the negative electrode paste 230 is small; when the aperture of the concave hole 121 is greater than 200μm, the positive electrode paste 120 loses more positive electrode active substances, resulting in a decrease in the capacity of the battery made from the positive electrode sheet 100.

[0084] When the thickness of the positive electrode paste 120 on one side of the positive electrode current collector is between 30μm and 60μm, by restricting the depth and / or the aperture of the concave hole 121, it is possible to ensure both the improvement effect of the concave hole 121 on lithium deposition at the corner position of the negative electrode paste 230 and the capacity of the battery made from the positive electrode sheet 100.

[0085] In another possible implementation, the thickness of the positive electrode paste 120 is 9μm - 48μm. The depth of the concave hole 121 is 1.5μm - 28μm.

[0086] That is to say, the thickness of the positive electrode paste 120 on one side of the positive electrode current collector is 9μm - 48μm. Exemplarily, the thickness of the positive electrode paste 120 on one side of the positive electrode current collector can be 9μm, 20μm, 30μm, 40μm, 48μm, etc.

[0087] When the thickness of the positive electrode paste 120 on one side of the positive electrode current collector of the positive electrode sheet 100 is 9 μm - 48 μm, the positive electrode sheet 100 can be used to fabricate a thin battery cell with a thickness of 0.9 mm - 4.8 mm. Compared with a conventional battery cell, the thin battery cell is suitable for a battery with a smaller reserved space. The depth of the concave holes 121 can be 1.5 μm - 28 μm, such as 1.5 μm, 9.5 μm, 15 μm, 20 μm, 25 μm, or 28 μm, etc. Specifically, it can be set according to the thickness of the positive electrode paste 120 and the number of the concave holes 121. Among them, the depth of the concave holes 121 is less than the thickness of the positive electrode paste 120 on one side of the positive electrode current collector. The above depth of the concave holes 121 can not only ensure the improvement effect of the concave holes 121 on lithium deposition at the angular position of the negative electrode paste 230 but also ensure the capacity of the battery after the positive electrode sheet 100 is made into a battery.

[0088] When the thickness of the positive electrode paste 120 on one side of the positive electrode current collector is 9 μm - 48 μm, the aperture of the concave holes 121 is 15 μm - 160 μm.

[0089] For example, the aperture of the concave holes 121 can be 15 μm, 50 μm, 85 μm, 120 μm, 150 μm, or 160 μm, etc. The aperture of the concave holes 121 is also set according to the specific thickness of the positive electrode paste 120 and the number of the concave holes 121. The above aperture of the concave holes 121 can not only ensure the improvement effect of the concave holes 121 on lithium deposition at the angular position of the negative electrode paste 230 but also ensure the capacity of the battery after the positive electrode sheet 100 is made into a battery.

[0090] Such as Figure 3 and Figures 7-10 As shown in the figure, the present application also provides a battery cell, including the above-mentioned positive electrode sheet 100, a separator, and a plurality of negative electrode sheets 200. The plurality of positive electrode sheets 100, the separator, and the plurality of negative electrode sheets 200 are stacked alternately. The negative electrode sheet 200 includes a negative electrode current collector 210, a negative electrode tab 220, and a negative electrode paste 230. The negative electrode tab 220 is electrically connected to the negative electrode current collector 210, and the negative electrode paste 230 is disposed on at least one side of the negative electrode tab 220.

[0091] Among them, the battery cell provided by the present application is a stacked battery cell. Those skilled in the art can set the number of the positive electrode sheets 100 and the negative electrode sheets 200 according to needs, and there is no unique limitation here. The separator is not shown in the drawings. The number of the separators can be one or more. The adjacent positive electrode sheets 100 and negative electrode sheets 200 are isolated by the separator to prevent contact short circuit between the positive electrode sheet 100 and the negative electrode sheet 200.

[0092] Schematically, the negative tab 220 can be integrally formed with the negative current collector 210. The negative electrode sheet 200 can be provided with the negative electrode paste 230 on only one side of the negative current collector 210, or the negative electrode paste 230 can be provided on the opposite two sides of the negative current collector 210 respectively. Among them, the negative electrode paste 230 of the negative electrode sheet 200 faces the positive electrode paste 120 of the positive electrode sheet 100.

[0093] For the battery cell provided by this application, due to the adoption of the above-mentioned positive electrode sheet 100, lithium deposition is not likely to occur at the corner of the negative electrode paste 230, and the safety performance of the battery cell is improved.

[0094] As Figure 3 and Figure 11 shown, the outermost layer of the battery cell is the negative electrode sheet 200, the outermost negative electrode sheet 200 is a single-sided coated negative electrode sheet, and the negative electrode paste 230 of the outermost negative electrode sheet 200 is located on the side of the negative current collector 210 facing the adjacent positive electrode sheet 100.

[0095] It can be understood that the outermost layer of the battery cell is the uppermost layer and the lowermost layer in the stacking direction of the battery cell. Figure 3 and Figure 11 show that both the uppermost layer and the lowermost layer of the battery cell are single-sided coated negative electrode sheets, that is, the outermost negative electrode sheet is provided with the negative electrode paste 230 on only one side of the negative current collector 210.

[0096] Optionally, the negative electrode sheets 200 located in the middle of the battery cell are all double-sided coated negative electrode sheets, that is, the negative electrode sheets 200 located in the middle of the battery cell are provided with the negative electrode paste 230 on the two opposite sides of the negative current collector 210 respectively, and the positive electrode sheets 100 of the battery cell are all double-sided coated positive electrode sheets, that is, the positive electrode paste 120 is provided on both sides of the positive current collector.

[0097] The outermost layer of the battery cell is set as the negative electrode sheet 200. Since the performance of the negative electrode paste 230 is relatively more stable than that of the positive electrode paste 120, when the battery undergoes external short circuit or mechanical damage, the outermost negative electrode sheet 200 of the battery cell can reduce the risk of thermal runaway of the battery. In addition, the outermost negative electrode sheet 200 is a single-sided coated negative electrode sheet and the negative electrode paste 230 of this negative electrode sheet 200 faces the adjacent positive electrode sheet 100, so that the negative electrode paste 230 of the negative electrode sheet 200 is opposite to the positive electrode paste 120 of the positive electrode sheet 100, ensuring the energy density of the battery.

[0098] Schematically, as Figures 7-10 shown, a second recess is provided on the side of the negative electrode paste 230 facing away from the negative current collector 210.

[0099] It can be understood that the thickness of the negative electrode paste 230 at the second recess position is less than that at the remaining positions. During the production of the negative electrode sheet 200, after the negative electrode paste 230 is disposed on the negative electrode current collector 210, a portion of the negative electrode active material on the side of the negative electrode paste 230 facing away from the negative electrode current collector 210 is removed to form a second recess on the negative electrode paste 230. Wherein, the opening of the second recess is disposed facing away from the negative electrode current collector 210.

[0100] Exemplarily, after the negative electrode paste 230 is disposed on the negative electrode current collector 210, a second recess can be formed on the negative electrode paste 230 by laser drilling or scribing the negative electrode paste 230. That is, the second recess can be a hole or a line disposed on the negative electrode paste 230.

[0101] It should be noted that during the production of the negative electrode sheet 200, the negative electrode sheet 200 needs to be roll-pressed. However, after roll-pressing, the negative electrode paste 230 is relatively dense on the side facing away from the negative electrode current collector 210, which is equivalent to generating a dense film on the side of the negative electrode paste 230 facing away from the negative electrode current collector 210. In this embodiment, by providing a second recess on the negative electrode paste 230, the second recess can break the dense film generated after roll-pressing of the negative electrode paste 230, and can improve the wetting speed of the electrolyte on the negative electrode paste 230. In addition, the second recess can be used to store the electrolyte, increasing the liquid retention amount of the negative electrode sheet 200, which is beneficial to improving the capacity retention rate of the battery made of the negative electrode sheet 200.

[0102] As Figure 8 shown, the second recess is a wire groove 231 disposed on the negative electrode paste 230. The extending direction of the wire groove 231 is inclined to the side of the negative electrode paste 230 and is not perpendicular to the side of the negative electrode paste 230, and the end of the wire groove 231 extends to the side of the negative electrode paste 230.

[0103] Specifically, the wire groove 231 can be formed on the negative electrode paste 230 by laser scribing. Wherein, during the scribing process of the negative electrode paste 230, under the influence of factors such as different laser energies and the compaction density of the negative electrode paste 230, the cross-section of the wire groove 231 can be circular, trapezoidal, polygonal or an irregular concave morphology. The extending direction of the wire groove 231 is the length direction of the wire groove 231. Here, the included angle between the extending direction of the wire groove 231 and the side of the negative electrode paste 230 is defined as θ1, and θ1 satisfies 0 < θ1 < 90° or 90° < θ1 < 180°. The specific size of θ1 in this embodiment is not limited, and those skilled in the art can set it according to actual needs.

[0104] It is worth mentioning that during the production of the negative electrode sheet 200, after the negative electrode paste 230 is set, it needs to be die-cut. After die-cutting, powder shedding is likely to occur on the side of the negative electrode paste 230. In this embodiment, the extending direction of the wire groove 231 is inclined to the side of the negative electrode paste 230 and the end of the wire groove 231 extends to the side of the negative electrode paste 230. After wire laying on the negative electrode paste 230, the wire groove 231 will reinforce the side of the negative electrode paste 230, and then nail the side of the negative electrode paste 230 to the negative electrode current collector 210, reducing the powder shedding on the side of the negative electrode paste 230 caused by die-cutting.

[0105] As Figures 7-9 shown, the number of wire grooves 231 on the negative electrode paste 230 is at least two, and two adjacent wire grooves 231 are arranged in parallel with each other, and the distance between two adjacent wire grooves 231 is 100μm - 2500μm.

[0106] Schematically, multiple wire grooves 231 can be evenly arranged on the negative electrode paste 230. Those skilled in the art can determine the distance between two adjacent wire grooves 231 according to the thickness of the negative electrode paste 230, and then determine the number of wire grooves 231 according to the area of the negative electrode paste 230 and the distance between two adjacent wire grooves 231. Exemplarily, the distance between two adjacent wire grooves 231 can be 100μm, 500μm, 1000μm, 1500μm, 2000μm or 2500μm, etc., and it is not uniquely limited here.

[0107] It is worth mentioning that after laser wire laying on the negative electrode paste 230 to form the wire groove 231, under the action of the heat of the laser, the negative electrode of the negative electrode paste 230 located in the wire groove 231 has a heat affected zone. When the distance between two adjacent wire grooves 231 is less than 100μm, the distance between the wire grooves 231 on the negative electrode paste 230 is too close, which is likely to cause the heat affected zones near the two wire grooves 231 to overlap. On the one hand, it is likely to cause powder shedding of the negative electrode paste 230. On the other hand, after the heat affected zones overlap, it is likely to cause the negative electrode paste 230 to lose its activity, and then the battery capacity made from the negative electrode sheet 200 decreases. When the distance between two adjacent wire grooves 231 is greater than 2500μm, the distance between the wire grooves 231 on the negative electrode paste 230 is too far, and the improvement effect on the infiltration speed of the electrolyte into the negative electrode paste 230 and the liquid retention amount of the negative electrode sheet 200 is small.

[0108] Through the above settings, while fully ensuring the battery capacity of the negative electrode sheet 200, it can also ensure the infiltration speed of the electrolyte into the negative electrode paste 230 and the improvement effect of the liquid retention amount of the negative electrode sheet 200.

[0109] Schematically, the thickness of the battery cell is 3 mm - 6 mm, and the thickness of the negative electrode paste 230 is D2, where D2 satisfies: 30 μm ≤ D2 ≤ 80 μm. That is to say, the thickness of the negative electrode paste 230 on one side of the negative electrode current collector is 30 μm - 80 μm. For example, the thickness of the negative electrode paste 230 can be 30 μm, 40 μm, 47 μm, 55 μm, 60 μm, 70 μm, 80 μm, etc. When the thickness of the negative electrode paste 230 is between 30 μm and 80 μm, the negative electrode sheet 200 can be used to make a conventional battery cell with a thickness of 3 mm - 6 mm.

[0110] The depth of the wire groove 231 is h, and h satisfies: 5 μm ≤ h ≤ 40 μm. For example, the depth of the wire groove 231 can be 5 μm, 10 μm, 18 μm, 25 μm, 30 μm, 40 μm, etc., and the depth of the wire groove 231 is less than the thickness of the negative electrode paste 230. When the depth of the wire groove 231 is less than 5 μm, the improvement effect of the wire groove 231 on the infiltration rate of the electrolyte in the negative electrode paste 230 and the liquid retention amount of the negative electrode sheet 200 is small; when the depth of the wire groove 231 is greater than 40 μm, the negative electrode paste 230 loses more negative electrode active substances at the position of the wire groove 231, and the capacity of the battery after the negative electrode sheet 200 is made into a battery is low.

[0111] When the thickness of the battery cell is 3 mm - 6 mm and the thickness of the negative electrode paste 230 is between 30 μm and 80 μm, the width w of the wire groove 231 satisfies: 50 μm ≤ w ≤ 400 μm.

[0112] Exemplarily, the width of the wire groove 231 can be 50 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, etc., and there is no unique limitation here. When the width of the wire groove 231 is less than 50 μm, the improvement effect of the wire groove 231 on the infiltration rate of the electrolyte in the negative electrode paste 230 and the liquid retention amount of the negative electrode sheet 200 is small; when the width of the wire groove 231 is greater than 400 μm, the negative electrode paste 230 loses more negative electrode active substances at the position of the wire groove 231, and the capacity of the battery after the negative electrode sheet 200 is made into a battery is low.

[0113] Through the above settings, while ensuring the battery capacity, it is also possible to effectively improve the infiltration rate of the electrolyte in the negative electrode paste 230 and the liquid retention amount of the negative electrode sheet 200.

[0114] In a possible implementation, such as Figure 9 and Figure 10As shown, the thickness of the battery cell is 3 mm - 6 mm, and the thickness of the negative electrode paste 230 is D2, where D2 satisfies: 30 μm ≤ D2 ≤ 80 μm. The negative electrode paste 230 includes a normal region 232 and a thinning region 233. The thinning region 233 is located on one side of the normal region 232 facing the side of the negative electrode paste 230. The end of the wire groove 231 extends to the thinning region 233. The depth of the wire groove 231 in the normal region 232 is h, where h satisfies: 5 μm ≤ h ≤ 40 μm, and the maximum depth of the wire groove 231 in the thinning region 233 is 1.05h - 1.5h.

[0115] Among them, after the negative electrode slurry is coated on the negative electrode current collector 210, under the action of the fluidity of the slurry and the surface tension of the slurry, a thinning region 233 is formed at the edge of the negative electrode paste 230. The width L3 of the thinning region 233 can satisfy: 1 mm ≤ L3 ≤ 5 mm. The region where the thickness of the negative electrode paste 230 is uniform except for the thinning region 233 is the normal region 232. It is worth mentioning that the thickness of the negative electrode paste 230 is the thickness of the normal region 232 of the negative electrode paste 230 on one side of the negative electrode current collector. For example, the thickness of the negative electrode paste 230 can be 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, etc.

[0116] Exemplarily, the depth of the wire groove 231 in the normal region 232 can be 5 μm, 10 μm, 15 μm, 25 μm, 30 μm, 40 μm, etc., which is not uniquely limited here. It can be understood that the depth of the wire groove 231 in the normal region 232 can ensure the infiltration speed of the electrolyte in the normal region 232 and the capacity of the battery.

[0117] It is worth mentioning that the thickness of the thinning region 233 gradually thins from the center of the negative electrode sheet 200 towards the edge of the negative electrode sheet 200. During the laser scribing process, the distance between the side of the wire groove 231 in the thinning region 233 facing the negative electrode current collector 210 and the negative electrode current collector 210 can be made consistent by controlling the power of the laser. Among them, the maximum depth of the wire groove 231 in the thinning region 233 is the depth of the wire groove 231 in the thinning region 233 away from the side of the negative electrode paste 230. Exemplarily, the maximum depth of the wire groove 231 in the thinning region 233 can be 1.05h, 1.1h, 1.2h, 1.3h, 1.4h, or 1.5h, which is not uniquely limited here. Schematically, the width of the wire groove 231 in the thinning region 233 can be the same as the width of the wire groove 231 in the normal region 232, and the distance between two adjacent wire grooves 231 in the thinning region 233 can be the same as the distance between two adjacent wire grooves 231 in the normal region 232.

[0118] When the maximum depth of the wire groove 231 in the thinning area 233 is less than 1.05h, less electrolyte is stored in the wire groove 231 in the thinning area 233, which is not conducive to the flow of the electrolyte from the wire groove 231 in the thinning area 233 to the wire groove 231 in the normal area 232, and the effect of improving the wetting speed of the electrolyte by the wire groove 231 is small; when the maximum depth of the wire groove 231 in the thinning area 233 is greater than 1.5h, more active substances are lost in the thinning area 233 of the negative electrode paste 230, reducing the capacity of the battery.

[0119] Through the above settings, the wire groove 231 in the thinning area 233 can store more electrolyte, so that the electrolyte flows from the wire groove 231 in the thinning area 233 to the wire groove 231 in the normal area 232, providing space for the electrolyte to flow in from the side, improving the wetting speed of the electrolyte, and the above settings can also ensure the capacity of the battery.

[0120] In a possible implementation, the thickness of the battery cell is 0.6 mm - 5.4 mm, the thickness of the negative electrode paste is 6 μm - 80 μm, and the depth of the wire groove is 1 μm - 36 μm.

[0121] Specifically, the thickness of the negative electrode current collector single-sided negative electrode paste 230 is 6 μm - 80 μm, such as 6 μm, 10 μm, 25 μm, 40 μm, 50 μm, 65 μm, 72 μm or 80 μm, etc. When the thickness of the negative electrode current collector single-sided negative electrode paste 230 is 6 μm - 80 μm, the negative electrode sheet 200 can be used to make a thin battery cell with a thickness of 0.6 mm - 5.4 mm. Exemplarily, the depth of the wire groove can be 1 μm, 5 μm, 10 μm, 20 μm, 25 μm, 30 μm or 36 μm, etc., and can be specifically set according to the thickness of the negative electrode paste 230, and the depth of the wire groove is less than the thickness of the negative electrode paste 230. The depth of the above wire groove 231 can ensure the capacity of the battery while effectively improving the wetting speed of the electrolyte in the negative electrode paste 230 and the liquid retention amount of the negative electrode sheet 200.

[0122] When the thickness of the battery cell is 0.6 mm - 5.4 mm and the thickness of the negative electrode paste 230 is 6 μm - 80 μm, the width of the wire groove 231 is 10 μm - 360 μm.

[0123] Specifically, the width of the wire groove 231 can be 10 μm, 50 μm, 100 μm, 150 μm, 250 μm or 360 μm, etc., and can be specifically set according to the specific thickness of the negative electrode paste 230. The width of the above wire groove 231 can ensure the capacity of the battery while effectively improving the wetting speed of the electrolyte in the negative electrode paste 230 and the liquid retention amount of the negative electrode sheet 200.

[0124] In a specific embodiment, the thickness of the battery cell is 0.6 mm - 5.4 mm, and the thickness of the negative electrode coating paste 230 is 6 μm - 80 μm. The negative electrode coating paste 230 includes a normal region 232 and a thinning region 233. The thinning region 233 is located on one side of the normal region 232 facing the side edge of the negative electrode coating paste 230, and the end of the wire groove 231 extends to the thinning region 233. The depth of the wire groove 231 in the normal region 232 is 1 μm - 36 μm, and the maximum depth of the wire groove 231 in the thinning region 233 is 1.05 times - 1.5 times the depth of the wire groove 231 in the normal region 232.

[0125] Wherein, when the thickness of the negative electrode current collector with single-sided negative electrode coating paste 230 is 6 μm - 80 μm, the negative electrode sheet 200 can be used to make a thin battery cell with a thickness of 0.6 mm - 5.4 mm. After the negative electrode slurry is coated, under the action of the fluidity and surface tension of the slurry, the negative electrode coating paste 230 formed by the negative electrode slurry has a normal region 232 and a thinning region 233 located on the side of the normal region 232 facing the edge of the negative electrode coating paste 230. The thickness of the thinning region 233 gradually decreases from the center of the negative electrode coating paste 230 towards the edge.

[0126] Exemplarily, the depth of the wire groove 231 in the normal region 232 can be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, 36 μm, etc., and the depth of the wire groove 231 in the normal region 232 is less than the thickness of the negative electrode coating paste 230 in the normal region 232. The depth of the wire groove 231 in the normal region 232 can not only ensure the infiltration speed of the electrolyte in the normal region 232 but also ensure the capacity of the battery.

[0127] The maximum depth of the wire groove 231 in the thinning region 233 is the depth of the wire groove 231 in the thinning region 233 far from the side edge of the negative electrode coating paste 230. For example, the maximum depth of the wire groove 231 in the thinning region 233 can be 1.05 times, 1.1 times, 1.2 times, 1.35 times, 1.5 times, etc. of the depth of the wire groove 231 in the normal region 232.

[0128] The above depth of the wire groove 231 in the thinning region 233 enables the wire groove 231 in the thinning region 233 to store more electrolyte, so that the electrolyte can flow from the wire groove 231 in the thinning region 233 to the wire groove 231 in the normal region 232, providing space for the electrolyte to flow in from the side, improving the electrolyte infiltration speed, and the above setting can also ensure the capacity of the battery.

[0129] The present application also provides a lithium-ion secondary battery, including the above battery cell.

[0130] For the lithium-ion secondary battery provided by the present application, due to the adoption of the above battery cell, lithium deposition is not likely to occur at the corner position of the negative electrode sheet, and the safety performance and cycle service life of the lithium-ion secondary battery are relatively high.

[0131] The following provides a detailed introduction to the battery of the present application through specific embodiments. The battery parameters of the following embodiments and comparative examples are recorded in Table 1.

[0132] Example 1

[0133] 1. Preparation of the positive electrode sheet 100

[0134] Lithium cobalt oxide, carbon black, and polyvinylidene fluoride were mixed with NMP solvent according to the mass percentage contents of 97%, 1%, and 2% respectively to obtain a positive electrode slurry. The above positive electrode slurry was coated on the surface of an aluminum foil current collector with a thickness of 6 μm. After drying, rolling, and slitting, the positive electrode sheet 100 was obtained. The positive electrode slurry formed a positive electrode paste 120, and the thickness H1 of the positive electrode paste 120 was 50 μm;

[0135] A plurality of concave holes 121 were formed at one corner of the positive electrode paste 120 by laser drilling. Each concave hole 121 was located on the side of the positive electrode paste 120 facing away from the aluminum foil current collector. The distance L1 between the outermost concave hole 121 and the adjacent side wall of the positive electrode paste 120 was 1000 μm, and the distance L2 between adjacent two concave holes 121 was 2000 μm. The depth of each concave hole 121 was 20 μm, and the aperture of each concave hole 121 was 100 μm.

[0136] 2. Preparation of the negative electrode sheet 200

[0137] Artificial graphite, conductive carbon black, binder, and thickener were mixed with deionized water according to the mass percentage contents of 97%, 1.0%, 1.0%, and 1.0% respectively to obtain a negative electrode slurry. The negative electrode slurry was coated on the surface of a copper foil current collector with a thickness of 8 μm. After drying, rolling, and slitting, the negative electrode slurry formed a negative electrode paste 230, and the thickness H2 of the negative electrode paste 230 was 70 μm.

[0138] A plurality of parallel wire grooves 231 were formed on the side of the negative electrode paste 230 facing away from the copper foil current collector by laser scribing technology. The depth of each wire groove 231 was 20 μm, the width of each wire groove 231 was 200 μm, and the distance L4 between adjacent two wire grooves 231 was 1500 μm.

[0139] 3. Preparation of the separator

[0140] A polyethylene separator prepared by conventional technical means with a thickness of 10 μm.

[0141] 4. Assembly

[0142] The positive electrode sheet 100, the separator, and the negative electrode sheet 200 are stacked in a stacked manner, and a separator is provided between each adjacent positive electrode sheet 100 and negative electrode sheet 200. The stacked positive electrode sheet 100, separator, and negative electrode sheet 200 are hot-pressed using a hot-pressing device to fix the positive electrode sheet 100 and the negative electrode sheet 200 to the separator respectively. The thickness of the assembled battery cell is 6 mm.

[0143] The battery cell is encapsulated in an aluminum-plastic film bag, and processes such as injecting electrolyte, vacuum encapsulation, aging, formation, secondary encapsulation, and capacity sorting are performed to obtain the corresponding battery. The electrolyte includes an organic solvent and a lithium salt. The organic solvent is propylene carbonate, ethylene carbonate, dimethyl carbonate, or a mixture of the three organic solvents, and the volume ratio of the three solvents is 1:1:1. The lithium salt is LiPF6 with a concentration of 1 M.

[0144] Example 2

[0145] Example 2 is carried out with reference to Example 1. The difference is that a plurality of concave holes 121 are respectively provided at the four corner positions of the positive electrode paste 120 of the positive electrode sheet 100. The arrangement of the plurality of concave holes 121 at each corner position is the same as the arrangement of the plurality of concave holes 121 at the corner position of the positive electrode paste 120 in Example 1, and the size of each concave hole 121 is the same as the size of the concave hole 121 in Example 1.

[0146] Example 3

[0147] Example 3 is carried out with reference to Example 2. The difference is that the distance L1 between the outermost concave hole 121 on the positive electrode paste 120 and the adjacent side wall of the positive electrode paste 120 is 40 μm.

[0148] Example 4

[0149] Example 4 is carried out with reference to Example 2. The difference is that the distance L1 between the outermost concave hole 121 on the positive electrode paste 120 and the adjacent side wall of the positive electrode paste 120 is 50 μm.

[0150] Example 5

[0151] Example 5 is carried out with reference to Example 2. The difference is that the distance L1 between the outermost concave hole 121 on the positive electrode paste 120 and the adjacent side wall of the positive electrode paste 120 is 2000 μm.

[0152] Example 6

[0153] Example 6 is carried out with reference to Example 2. The difference is that the distance L1 between the outermost concave hole 121 on the positive electrode paste 120 and the adjacent side wall of the positive electrode paste 120 is 2100 μm.

[0154] Example 7

[0155] Example 7 was carried out with reference to Example 2, except that the distance L2 between two adjacent recessed holes 121 at the same angular position on the positive electrode paste 120 was 100 μm.

[0156] Example 8

[0157] Example 8 was carried out with reference to Example 2, except that the distance L2 between two adjacent recessed holes 121 at the same angular position on the positive electrode paste 120 was 120 μm.

[0158] Example 9

[0159] Example 9 was carried out with reference to Example 2, except that the distance L2 between two adjacent recessed holes 121 at the same angular position on the positive electrode paste 120 was 4000 μm.

[0160] Example 10

[0161] Example 10 was carried out with reference to Example 2, except that the distance L2 between two adjacent recessed holes 121 at the same angular position on the positive electrode paste 120 was 4100 μm.

[0162] Example 11

[0163] Example 11 was carried out with reference to Example 2, except that the depth of each recessed hole 121 on the positive electrode paste 120 was 3 μm.

[0164] Example 12

[0165] Example 12 was carried out with reference to Example 2, except that the depth of each recessed hole 121 on the positive electrode paste 120 was 5 μm.

[0166] Example 13

[0167] Example 13 was carried out with reference to Example 2, except that the depth of each recessed hole 121 on the positive electrode paste 120 was 40 μm.

[0168] Example 14

[0169] Example 14 was carried out with reference to Example 2, except that the depth of each recessed hole 121 on the positive electrode paste 120 was 45 μm.

[0170] Example 15

[0171] Example 15 was carried out with reference to Example 2, except that the aperture of each recessed hole 121 on the positive electrode paste 120 was 40 μm.

[0172] Example 16

[0173] Example 16 was carried out with reference to Example 2, except that the aperture of each recessed hole 121 on the positive electrode paste 120 was 50 μm.

[0174] Example 17

[0175] Example 17 was carried out with reference to Example 2, except that the aperture diameter of each concave hole 121 on the positive electrode paste 120 was 200 μm.

[0176] Example 18

[0177] Example 18 was carried out with reference to Example 2, except that the aperture diameter of each concave hole 121 on the positive electrode paste 120 was 210 μm.

[0178] Example 19

[0179] Example 19 was carried out with reference to Example 2, except that the depth of each wire groove 231 on the negative electrode paste 230 of the negative electrode sheet 200 was 3 μm.

[0180] Example 20

[0181] Example 20 was carried out with reference to Example 2, except that the depth of each wire groove 231 on the negative electrode paste 230 of the negative electrode sheet 200 was 5 μm.

[0182] Example 21

[0183] Example 21 was carried out with reference to Example 2, except that the depth of each wire groove 231 on the negative electrode paste 230 of the negative electrode sheet 200 was 40 μm.

[0184] Example 22

[0185] Example 22 was carried out with reference to Example 2, except that the depth of each wire groove 231 on the negative electrode paste 230 of the negative electrode sheet 200 was 45 μm.

[0186] Example 23

[0187] Example 23 was carried out with reference to Example 2, except that the width of each wire groove 231 on the negative electrode paste 230 of the negative electrode sheet 200 was 45 μm.

[0188] Example 24

[0189] Example 24 was carried out with reference to Example 2, except that the width of each wire groove 231 on the negative electrode paste 230 of the negative electrode sheet 200 was 50 μm.

[0190] Example 25

[0191] Example 25 was carried out with reference to Example 2, except that the width of each wire groove 231 on the negative electrode paste 230 of the negative electrode sheet 200 was 400 μm.

[0192] Example 26

[0193] Example 26 was carried out with reference to Example 2, except that on the negative electrode paste 230 of the negative electrode sheet 200, the width of each groove 231 was 450 μm.

[0194] Example 27

[0195] Example 27 was carried out with reference to Example 2, except that on the negative electrode paste 230 of the negative electrode sheet 200, the distance L4 between two adjacent grooves 231 was 80 μm.

[0196] Example 28

[0197] Example 28 was carried out with reference to Example 2, except that on the negative electrode paste 230 of the negative electrode sheet 200, the distance L4 between two adjacent grooves 231 was 100 μm.

[0198] Example 29

[0199] Example 29 was carried out with reference to Example 2, except that on the negative electrode paste 230 of the negative electrode sheet 200, the distance L4 between two adjacent grooves 231 was 2500 μm.

[0200] Example 30

[0201] Example 30 was carried out with reference to Example 2, except that on the negative electrode paste 230 of the negative electrode sheet 200, the distance L4 between two adjacent grooves 231 was 2700 μm.

[0202] Example 31

[0203] Example 31 was carried out with reference to Example 2, except that the thickness H1 of the positive electrode paste 120 of the positive electrode sheet 100 was 30 μm, the depth of each concave hole 121 on the positive electrode paste 120 was 10 μm, and the aperture of each concave hole 121 was 100 μm.

[0204] The thickness H2 of the negative electrode paste 230 of the negative electrode sheet 200 was 45 μm, the depth of each groove 231 on the negative electrode paste 230 was 10 μm, and the width of each groove 231 was 200 μm.

[0205] The thickness of the battery cell formed by assembling the positive electrode sheet 100, the separator and the negative electrode sheet 200 was 2 mm.

[0206] Example 32

[0207] Example 32 was carried out with reference to Example 31, except that the depth of each concave hole 121 on the positive electrode paste 120 was 1 μm.

[0208] Example 33

[0209] Example 33 was carried out with reference to Example 31, except that the depth of each recess 121 on the positive electrode paste 120 was 1.5 μm.

[0210] Example 34

[0211] Example 34 was carried out with reference to Example 31, except that the depth of each recess 121 on the positive electrode paste 120 was 28 μm.

[0212] Example 35

[0213] Example 35 was carried out with reference to Example 31, except that the depth of each recess 121 on the positive electrode paste 120 was 30 μm.

[0214] Example 36

[0215] Example 36 was carried out with reference to Example 31, except that the diameter of each recess 121 on the positive electrode paste 120 was 10 μm.

[0216] Example 37

[0217] Example 37 was carried out with reference to Example 31, except that the diameter of each recess 121 on the positive electrode paste 120 was 15 μm.

[0218] Example 38

[0219] Example 38 was carried out with reference to Example 31, except that the diameter of each recess 121 on the positive electrode paste 120 was 160 μm.

[0220] Example 39

[0221] Example 39 was carried out with reference to Example 31, except that the diameter of each recess 121 on the positive electrode paste 120 was 170 μm.

[0222] Example 40

[0223] Example 40 was carried out with reference to Example 31, except that the depth of each groove 231 on the negative electrode paste 230 was 0.8 μm.

[0224] Example 41

[0225] Example 41 was carried out with reference to Example 31, except that the depth of each groove 231 on the negative electrode paste 230 was 1 μm.

[0226] Example 42

[0227] Example 42 was carried out with reference to Example 31, except that the depth of each groove 231 on the negative electrode paste 230 was 36 μm.

[0228] Example 43

[0229] Example 43 was carried out with reference to Example 31, except that the depth of each groove 231 on the negative electrode paste 230 was 40 μm.

[0230] Example 44

[0231] Example 44 was carried out with reference to Example 31, except that the width of each groove 231 on the negative electrode paste 230 was 8 μm.

[0232] Example 45

[0233] Example 45 was carried out with reference to Example 31, except that the width of each groove 231 on the negative electrode paste 230 was 10 μm.

[0234] Example 46

[0235] Example 46 was carried out with reference to Example 31, except that the width of each groove 231 on the negative electrode paste 230 was 360 μm.

[0236] Example 47

[0237] Example 47 was carried out with reference to Example 31, except that the width of each groove 231 on the negative electrode paste 230 was 400 μm.

[0238] Comparative Example 1

[0239] Comparative Example 1 was carried out with reference to Example 1, except that the concave holes 121 were not provided at the corner positions of the positive electrode paste 120 of the positive electrode sheet 100, and the grooves 231 were not provided on the negative electrode paste 230 of the negative electrode sheet 200.

[0240] Comparative Example 2

[0241] Comparative Example 2 was carried out with reference to Example 1, except that the grooves 231 were not provided on the negative electrode paste 230 of the negative electrode sheet 200.

[0242] Table 1

[0243]

[0244]

[0245]

[0246]

[0247]

[0248]

[0249]

[0250]

[0251] The relevant performances of the batteries in the above-mentioned examples and comparative examples were tested, and the test results were recorded in Table 2. The test methods are as follows:

[0252] 1. Capacity and capacity retention rate

[0253] The batteries obtained in the above-mentioned examples and comparative examples were respectively charged at a constant current of 1C and a constant voltage of 4.48V at 25°C until the cut-off current was 0.05C, and discharged at 0.5C to 3V, and cycled 800 times. The initial capacity at the first cycle and the capacity after cycling at the 800th cycle were measured.

[0254] Capacity retention rate = initial capacity / capacity after cycling * 100%.

[0255] 2. Lithium deposition situation

[0256] After the capacity retention rate tests were respectively carried out on the batteries obtained in the above-mentioned examples and comparative examples, the batteries obtained in the above-mentioned examples and comparative examples were fully charged, and the batteries were disassembled in the environment of a drying room, and the lithium deposition situation at the 200 corner position of the negative electrode paste was observed. The degrees of lithium deposition were no lithium deposition, slight lithium deposition, lithium deposition, and severe lithium deposition respectively.

[0257] Table 2:

[0258]

[0259]

[0260]

[0261]

[0262]

[0263] According to Table 2, for the batteries provided in Examples 1 - 47, compared with the battery provided in Comparative Example 1, the concave holes 121 at the 120 corner position of the positive electrode paste can effectively improve the lithium deposition at the 230 corner position of the negative electrode paste.

[0264] According to Table 2, for the batteries provided in Examples 1 - 47, compared with Comparative Example 2, the batteries have a higher capacity retention rate.

[0265] As can be seen from Examples 2 - 6 in Table 2, when the distance between the outermost concave hole 121 and the adjacent side wall of the positive electrode paste 120 is greater than 2000 μm, the improvement effect of the concave hole 121 at the corner position of the positive electrode paste 120 on lithium deposition at the corner position of the negative electrode paste 230 is relatively small; however, when the distance between the outermost concave hole 121 and the adjacent side wall of the positive electrode paste 120 is too small, punching holes in the positive electrode sheet 100 is likely to damage the stage.

[0266] As can be seen from Examples 2 and 7 - 10 in Table 2, when the distance L2 between two adjacent concave holes 121 is too small, the battery capacity is low; when the distance L2 between two adjacent concave holes 121 is too large, the improvement effect of the concave hole 121 at the corner position of the positive electrode paste 120 on lithium deposition at the corner position of the negative electrode paste 230 is relatively small.

[0267] As can be seen from Examples 2, 11 - 14 and 31 - 35 in Table 2, when the depth of the concave hole 121 is too large, the battery capacity is low; when the depth of the concave hole 121 is too small, the improvement effect of the concave hole 121 at the corner position of the positive electrode paste 120 on lithium deposition at the corner position of the negative electrode paste 230 is relatively small.

[0268] As can be seen from Table 2, when the aperture of the concave hole 121 is too large, the battery capacity is low; when the aperture of the concave hole 121 is too small, the improvement effect of the concave hole 121 at the corner position of the positive electrode paste 120 on lithium deposition at the corner position of the negative electrode paste 230 is relatively small.

[0269] As can be seen from Table 2, as the depth and / or width of the upper wire groove 231 of the negative electrode paste 230 increases, the battery capacity gradually decreases, but the battery capacity retention rate gradually increases, indicating that the wire groove 231 has an increasingly enhanced effect on improving the infiltration rate of the electrolyte in the negative electrode paste 230 and the liquid retention amount of the negative electrode sheet 200.

[0270] As can be seen from Table 2, when the distance L4 between two adjacent wire grooves 231 on the negative electrode paste 230 is less than 100 μm, the battery capacity is low; when the distance L4 between two adjacent wire grooves 231 on the negative electrode paste 230 is greater than 2500 μm, the battery capacity retention rate is low, indicating that the wire groove 231 has a relatively small effect on improving the infiltration rate of the electrolyte in the negative electrode paste 230 and the liquid retention amount of the negative electrode sheet 200.

[0271] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode sheet (100), characterized in that, Comprising: A positive current collector; A positive tab (110) electrically connected to the positive current collector; A positive paste (120) disposed on at least one side of the positive current collector. Two adjacent side edges of the positive paste (120) define an angular position. At least one of the angular positions of the positive paste (120) is provided with a first recess, and the first recess is located on a side of the positive paste (120) facing away from the positive current collector.

2. The positive electrode sheet (100) according to claim 1, characterized in that, The first recesses are respectively provided at four angular positions of the positive paste (120).

3. The positive electrode sheet (100) according to claim 1, characterized in that, The first recess includes a concave hole (121) provided on the positive paste (120), and the number of the concave holes (121) is multiple; The distance between the concave hole (121) closest to the side edge of the positive paste (120) and the adjacent side edge of the positive paste (120) is 50 μm - 2000 μm; and / or, the distance between two adjacent concave holes (121) is 120 μm - 4000 μm.

4. The positive electrode sheet (100) according to claim 3, characterized in that, On one positive electrode sheet (100), The total volume of all the concave holes (121) accounts for 0.05% - 1% of the total volume of the positive paste (120); and / or, the total area of all the concave holes (121) accounts for 1% - 10% of the total area of the positive paste (120).

5. The positive electrode sheet (100) according to claim 3, characterized in that, The thickness of the positive paste (120) is D1, and D1 satisfies: 30 μm ≤ D1 ≤ 60 μm; The depth H of the concave hole (121) satisfies: 5 μm ≤ H ≤ 40 μm; and / or, the aperture R of the concave hole (121) satisfies: 50 μm ≤ R ≤ 200 μm.

6. The positive electrode sheet (100) according to claim 3, characterized in that, The thickness of the positive paste (120) is 9 μm - 48 μm; The depth of the concave hole (121) is 1.5 μm - 28 μm; and / or, the aperture of the concave hole (121) is 15 μm - 160 μm.

7. A battery cell, characterized in that, Comprising a plurality of positive electrode sheets (100) according to any one of claims 1 - 6, a separator, and a plurality of negative electrode sheets (200), and the plurality of positive electrode sheets (100), the separator, and the plurality of negative electrode sheets (200) are stacked; The negative electrode sheet (200) includes a negative current collector (210), a negative tab (220), and a negative paste (230), the negative tab (220) is electrically connected to the negative current collector (210), and the negative paste (230) is disposed on at least one side of the negative tab (220).

8. The battery cell according to claim 7, characterized in that, A second recess is provided on a side of the negative paste (230) facing away from the negative current collector (210).

9. The battery cell according to claim 8, wherein, The second recess is a wire groove (231) provided on the negative paste (230), and the extending direction of the wire groove (231) is inclined to the side edge of the negative paste (230) and not perpendicular to the side edge of the negative paste (230), and the end of the wire groove (231) extends to the side edge of the negative paste (230).

10. The battery cell according to claim 9, wherein, The number of the wire grooves (231) on the negative paste (230) is at least two, and two adjacent wire grooves (231) are arranged in parallel, and the distance between two adjacent wire grooves (231) is 100 μm - 2500 μm.

11. The battery cell according to claim 9, characterized in that, The thickness of the battery cell is 3 mm - 6 mm, the thickness of the negative electrode paste (230) is D2, and D2 satisfies: 30 μm ≤ D2 ≤ 80 μm; The depth of the wire groove (231) is h, and h satisfies: 5 μm ≤ h ≤ 40 μm; and / or, the width w of the wire groove (231) satisfies: 50 μm ≤ w ≤ 400 μm.

12. The battery cell according to claim 9, wherein, The thickness of the battery cell is 3 mm - 6 mm, the thickness of the negative electrode paste (230) is D2, D2 satisfies 30 μm ≤ D2 ≤ 80 μm, the negative electrode paste (230) includes a normal area (232) and a thinning area (233), the thinning area (233) is located on one side of the normal area (232) facing the side of the negative electrode paste (230), the end of the wire groove (231) extends to the thinning area (233), the depth of the wire groove (231) on the normal area (232) is h, and h satisfies: 5 μm ≤ h ≤ 40 μm, and the maximum depth of the wire groove (231) on the thinning area (233) is 1.05h - 1.5h.

13. The battery cell according to claim 9, wherein, The thickness of the battery cell is 0.6 mm - 5.4 mm, and the thickness of the negative electrode paste (230) is 6 μm - 80 μm; The depth of the wire groove (231) is 1 μm - 36 μm; and / or, the width of the wire groove (231) is 10 μm - 360 μm.

14. The battery cell according to claim 9, wherein, The thickness of the battery cell is 0.6 mm - 5.4 mm, and the thickness of the negative electrode paste (230) is 6 μm - 80 μm; The negative electrode paste (230) includes a normal area (232) and a thinning area (233), the thinning area (233) is located on one side of the normal area (232) facing the side of the negative electrode paste (230), the end of the wire groove (231) extends to the thinning area (233), the depth of the wire groove (231) on the normal area (232) is 1 μm - 36 μm, and the maximum depth of the wire groove (231) on the thinning area (233) is 1.05 times - 1.5 times the depth of the wire groove (231) on the normal area (232).

15. The battery cell according to claim 8, wherein, The outermost layer of the battery cell is a negative electrode sheet (200), the outermost negative electrode sheet (200) is a single-sided coated negative electrode sheet, and the negative electrode paste (230) of the outermost negative electrode sheet (200) is located on the side of the negative electrode current collector (210) facing the adjacent positive electrode sheet (100).

16. A lithium ion secondary battery, characterized in that, A battery cell including any one of claims 7 - 15.

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