Secondary battery, battery pack, and electronic device

Abstract

PURPOSE: To provide a secondary battery capable of enhancing energy density of the secondary battery by at least reducing lithium deposition.SOLUTION: Embodiments of the present invention provide a secondary battery, a battery pack, and an electronic device. The secondary battery includes a negative electrode plate including a negative electrode current collector and a negative active material layer, wherein the negative active material layer includes a negative electrode flat region and a negative ultra-thin region located at one end of the negative electrode flat region in a first direction, a positive electrode plate including a positive electrode current collector and a positive active material layer, wherein the positive active material layer includes a positive electrode flat region and a positive electrode thinned region located at one end of the positive electrode flat region away from the first direction, and a separator located between the positive electrode plate and the negative electrode plate. Along a first direction, the positive active material layer includes an extending portion beyond the negative flat region, the extending portion overlaps with an orthographic projection of the negative ultra-thin region along a second direction perpendicular to the first direction, and a thinning depth of a region of the negative ultra-thin region corresponding to the extending portion is less than or equal to 9 μm.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a secondary battery, a battery pack, and an electronic device. [Background technology]

[0002] In the field of new energy power batteries, common power batteries include soft-pack batteries, prismatic batteries, and cylindrical batteries. Cylindrical batteries refer to cylindrically wound core batteries, which include a case and an electrode assembly enclosed within the case. The electrode assembly includes a wound positive electrode sheet, a wound negative electrode sheet, and a separator positioned between the positive and negative electrode sheets to separate the positive and negative electrode sheets. Summary of the Invention [Problem to be solved by the invention]

[0003] In response to the problems present in the related art, an object of the present invention is to provide a secondary battery, a battery pack, and an electronic device that can enhance the capacity of at least the negative electrode sheet and increase the energy density of the secondary battery. [Means for solving the problem]

[0004] To achieve the above object, an embodiment of the present invention provides a secondary battery including: a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer including a negative electrode flat region and a negative electrode thinned region located at one end of the negative electrode flat region along a first direction; a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer including a positive electrode flat region and a positive electrode thinned region located at one end of the positive electrode flat region away from the first direction; and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode active material layer includes an extending portion that exceeds the negative electrode flat region along the first direction, the extending portion overlaps with an orthogonal projection of the negative electrode thinned region along a second direction perpendicular to the first direction, and the thickness reduction depth of the region of the negative electrode thinned region corresponding to the extending portion is 9 μm or less.

[0005] In some embodiments, the thickness reduction depth is the difference between the lowest point of the thickness in the area of ​​the negative electrode thinned region corresponding to the stretched portion and the average thickness of the negative electrode flat region, and the value of the thickness reduction depth of the negative electrode thinned region ranges from 0 μm to 5 μm.

[0006] In some embodiments, the width of the extension along the first direction ranges from 1.0 mm to 2 mm.

[0007] In some embodiments, in the negative electrode thinned region corresponding to the stretched portion, the distance from the lowest point of the thinned region where the thickness is smallest to the boundary between the negative electrode active material layer and the negative electrode current collector ranges from 1 mm to 3 mm.

[0008] In some embodiments, the separator has a consistent thickness along the first direction, the ionic conductivity of corresponding regions along the first direction is consistent, and the maximum range of thickness of the negative electrode thinned region corresponding to the extension is 3.73 μm or less.

[0009] In some embodiments, in the negative electrode thinned region corresponding to the stretched portion, the standard deviation of the thickness of the negative electrode thinned region is 1.24 or less.

[0010] In some embodiments, a positive electrode active material layer is provided on each of opposite sides of the positive electrode current collector in the thickness direction of the positive electrode current collector perpendicular to the first direction.A negative electrode active material layer is provided on each of opposite sides of the negative electrode current collector in the thickness direction of the negative electrode current collector perpendicular to the first direction.In regions of the negative electrode sheet and positive electrode sheet corresponding to the extension portions, the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area is ≧1.

[0011] In some embodiments, the negative electrode current collector includes a negative electrode tab protruding from the negative electrode thinned region along the first direction, and the secondary battery is a cylindrical battery.

[0012] An embodiment of the present invention further provides a battery pack including any of the secondary batteries described above.

[0013] An embodiment of the present invention further provides an electronic device including the battery pack described above. [Effects of the Invention]

[0014] The beneficial technical effects of the present invention are as follows:

[0015] In an embodiment of the present invention, the positive electrode active material layer is arranged to have an extension portion, and the thickness reduction depth of the negative electrode thinned region corresponding to the extension portion is arranged to be 9 μm or less, thereby maximizing the capacity of the negative electrode sheet.Furthermore, the technical issue of lithium precipitation in the negative electrode thinned region can be avoided, improving the safety of the battery and achieving a balance between capacity and safety. [Brief explanation of the drawings]

[0016] In order to more clearly describe the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings necessary for describing the embodiments or the prior art. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without paying creative labor.

[0017] [Figure 1] 1 is a schematic diagram illustrating an electronic device according to an embodiment of the present invention, which is a vehicle. [Figure 2] 1 is a three-dimensional view of a secondary battery according to an embodiment of the present invention; [Figure 3] 1 is a cross-sectional view of a secondary battery according to an embodiment of the present invention. [Figure 4A] 1A to 1C are diagrams illustrating a manufacturing process of a positive electrode sheet according to one embodiment of the present invention. [Figure 4B] 1A to 1C are diagrams illustrating a manufacturing process of a positive electrode sheet according to one embodiment of the present invention. [Figure 5A] 1A to 1C are diagrams illustrating a manufacturing process of a negative electrode sheet according to one embodiment of the present invention. [Figure 5B]1A to 1C are diagrams illustrating a manufacturing process of a negative electrode sheet according to one embodiment of the present invention. [Figure 6A] FIG. 1 is a schematic diagram showing the structure of a positive electrode sheet and a negative electrode sheet in a conventional prismatic battery or soft-pack battery. [Figure 6B] FIG. 1 is a structural schematic diagram of a positive electrode sheet and a negative electrode sheet in another prismatic battery, soft pack battery, or cylindrical battery. [Figure 7] 1 is a structural schematic diagram of a positive electrode sheet and a negative electrode sheet of a cylindrical battery according to an embodiment of the present invention. FIG. [Figure 8A] FIG. 2 is a curve diagram of thickness rate change of an active material layer according to some embodiments of the present invention. [Figure 8B] FIG. 2 is a lateral coating thickness distribution diagram of an active material layer according to some embodiments of the present invention. [Figure 8C] 1 is a graph showing change curves of thickness of one surface of a negative electrode active material layer in the prior art and an embodiment of the present invention. [Figure 9] 1 is a schematic planar structural view of a coating gasket according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] In order to further understand the spirit of the embodiments of the present invention, some preferred embodiments of the present invention are further described in combination below.

[0019] The embodiments of the present invention are described in detail below. Throughout the specification of the present invention, the same or similar components and components having the same or similar functions are indicated by similar drawing symbols. The embodiments related to the drawings described herein are of explanatory and illustrative nature and are used to provide a basic understanding of the present invention. The embodiments of the present invention should not be construed as limiting the present invention.

[0020] As used herein, the terms "nearly," "generally," "substantially," and "about" are used to describe and account for small variations. When used in conjunction with an event or circumstance, the term can refer to instances in which the event or circumstance therein occurs exactly, as well as instances in which the event or circumstance therein occurs very approximately.

[0021] In this specification, unless otherwise specified or limited, relative terms such as "center," "longitudinal," "lateral," "front," "rear," "right-hand," "left-hand," "inner," "outer," "lower," "higher," "horizontal," "vertical," "higher," "lower," "upper," "lower," "top," "bottom," and derivatives thereof (e.g., "horizontally," "downward," "upward," etc.) should be construed as referring to the orientations described in the discussion or shown in the drawings. These relative terms are used for convenience of description only and do not require the invention to be constructed or operated in a particular orientation.

[0022] For ease of description, terms such as "first," "second," "third," etc. may be used in the text to distinguish between different elements in a figure or series of figures. "First," "second," "third," etc. are not intended to describe corresponding elements.

[0023] In the following embodiments, for ease of explanation, a case where the electronic device is a vehicle will be described as an example. Fig. 1 is a schematic diagram showing a case where the electronic device is a vehicle in an embodiment of the present invention.

[0024] 1, a battery pack 1002 is installed inside a vehicle 1000, and the battery pack 1002 may be installed at the bottom (shown in FIG. 1), head, or tail of a vehicle body 1001, or any other suitable location. The battery pack 1002 may be used to supply power to the vehicle 1000; for example, the battery pack 1002 may function as an operating power source or a driving power source for the vehicle 1000. The battery pack 1002 may include a plurality of cylindrical batteries (e.g., cylindrical battery 100 in FIG. 2) and a housing that houses the plurality of cylindrical batteries.

[0025] FIG. 2 shows a three-dimensional view of a cylindrical battery 100 according to an embodiment of the present invention, and FIG. 3 shows a cross-sectional view of the cylindrical battery 100 according to an embodiment of the present invention.

[0026] 2 and 3 , the cylindrical battery 100 includes an electrode assembly 120, a case 200, and a cover plate 202. The case 200 and the cover plate 202 collectively house the electrode assembly 120. The case 200 may be made of any of a variety of available materials, such as copper, iron, aluminum, steel, or an aluminum alloy. The case 200 may be cylindrical and define a housing space within which the electrode assembly 120 is disposed. The diameter of the case 200 can be determined based on the specific dimensions of the electrode assembly 120 and may be, for example, 18 mm, 21 mm, or 46 mm. In some embodiments, the cylindrical battery 100 is a 4680 cylindrical battery.

[0027] The case 200 can be connected to the negative electrode of the electrode assembly 120. The case 200 can have an attachment opening 205 at one end along the height direction H, and a cover plate 202 is provided at the attachment opening 205 to seal the storage space. The cylindrical battery 100 can further have a pole 208 at one end facing the cover plate 202, and the pole 208 can be connected to the positive electrode of the electrode assembly 120. It should be understood that there is an insulating coordination between the pole 208 and the case 200 to avoid short-circuiting the battery.

[0028] 3, a pressure contact portion 203 protruding inward is further provided adjacent to the mounting opening 205 of the case 200. The electrode assembly 120 is set between the end wall 111 and the pressure contact portion 203 along the height direction H of the cylindrical battery 100, and the pressure contact portion 203 can limit axial movement (movement in the height direction H) of the electrode assembly 120 between the end wall 111 of the case 200 and the pressure contact portion 203. A thinned portion is provided on the cover plate 202, and in the event of thermal runaway of the battery, high-temperature and high-pressure waste from the inside can be discharged from the bottom of the battery after breaking through the thinned portion on the cover plate 202 and being discharged to the outside, thereby enabling the waste to be efficiently discharged.

[0029] The electrode assembly 120 may include a wound positive electrode sheet, a wound negative electrode sheet, and a separator disposed between the positive and negative electrode sheets. The separator may be made of, for example, polypropylene (PP) or polyethylene (PE). To protect and insulate the electrode assembly 120, the outside of the electrode assembly 120 may be further coated with an insulating film. The insulating film may be made of, for example, PP, PE, polyethylene terephthalate (PET), polyvinyl chloride (PVC), or other polymer materials.

[0030] The electrode assembly 120 has a positive electrode tab and a negative electrode tab installed at each end of the cylindrical battery 100 in the height direction H. In some embodiments, the positive electrode tab is disposed opposite the end wall 111 and electrically connected to the electrode post 208, giving the electrode post 208 a positive charge. The negative electrode tab is disposed opposite the mounting hole 205, and the case 200 is electrically connected to the negative electrode tab, giving the case 200 a negative charge. However, in other embodiments, the negative electrode tab may be connected to the electrode post 208, and the positive electrode tab may be connected to the case 200.

[0031] 4A and 4B are diagrams illustrating a manufacturing process of a positive electrode sheet according to one embodiment of the present invention. Here, FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view. In the embodiment shown in FIGS. 4A and 4B, the positive and negative electrode sheets are manufactured by a slitting process in which one electrode sheet is cut into two electrode sheets.

[0032] Specifically, referring to FIGS. 4A and 4B , the method for manufacturing a positive electrode sheet includes applying a positive electrode active material layer 16 to both surfaces of a positive electrode current collector 18, with the peripheral portions of the positive electrode current collector 18 not being coated with the positive electrode active material. The portion of the positive electrode current collector 18 without the positive electrode active material layer 16 forms a positive electrode tab 19. The positive electrode active material layer 16 adjacent to the positive electrode tab 19 forms a thinned positive electrode region 12. The positive electrode current collector 18 and the positive electrode active material layer 16 are then cut along dashed line L1 to obtain two positive electrode sheets 10 as shown in FIG. 4B . The positive electrode active material layer 16 of each positive electrode sheet 10 has a thinned positive electrode region 12 on only one side. The thinned positive electrode region 12 is adjacent to a non-thinned region, i.e., a flat positive electrode region 14. The thickness of the flat positive electrode region 14 may be greater than the thickness of the thinned positive electrode region 12. The thinned positive electrode region 12 is essentially uniform in thickness. In the direction from the cathode flat region 14 to the cathode tab 19, the thickness of the cathode thinned region 12 gradually decreases.

[0033] In the present invention, all thicknesses can be preferably measured using an offline laser thickness gauge, and in some specific embodiments, thicknesses can also be measured using an SEM or other thickness measuring device, as will be appreciated by those skilled in the art.

[0034] 5A and 5B are diagrams illustrating a manufacturing process for a negative electrode sheet according to one embodiment of the present invention. Here, FIG. 5A is a plan view, and FIG. 5B is a cross-sectional view. Referring to FIGS. 5A and 5B, the manufacturing process for a negative electrode sheet is similar to the manufacturing process for a positive electrode sheet described above with reference to FIGS. 4A and 4B. After applying a negative electrode active material layer 26 to both surfaces of a negative electrode current collector 28, the negative electrode current collector 28 and the negative electrode active material layer 26 are cut along dashed line L2 to obtain two negative electrode sheets 20 as shown in FIG. 5B. The negative electrode active material layer 26 of each negative electrode sheet 20 also has a negative electrode thinned region 22 on only one side. The portion of the negative electrode current collector 28 where the negative electrode active material layer 26 is not provided forms a negative electrode tab 29. The negative electrode thinned region 22 is adjacent to a non-thinned region, i.e., a negative electrode flat region 24. The thickness of the negative electrode flat region 24 may be greater than the thickness of the negative electrode thinned region 22. The thickness of the negative electrode thinned region 22 is essentially uniform. In the direction from the negative electrode flat region 24 to the negative electrode tab 29, the thickness of the negative electrode thinned region 22 gradually decreases.

[0035] In some embodiments, taking a lithium-ion battery as an example, the material of the positive electrode current collector 18 may be aluminum, and the positive electrode active material layer 16 may include a positive electrode active material, which may be, for example, lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide. The material of the negative electrode current collector 28 may be, for example, copper, and the negative electrode active material layer 26 may include a negative electrode active material, which may be, for example, carbon or silicon.

[0036] The examples in Figures 4A to 5B are examples in which positive electrode sheets and negative electrode sheets are formed by slitting, which cuts one electrode sheet into two electrode sheets. In other embodiments, however, positive electrode sheets and negative electrode sheets may be formed by slitting, which cuts two electrode sheets into four electrode sheets, or slitting, which cuts three electrode sheets into six electrode sheets, and in these other embodiments, the formed positive electrode sheets and negative electrode sheets have a thinned region on only one side.

[0037] After forming the positive electrode sheet 10 and the negative electrode sheet 20, one positive electrode sheet 10 and one negative electrode sheet 20 are selected from among them, and the positive electrode sheet / separator / negative electrode sheet laminate is wound or stacked to obtain an electrode assembly (such as the electrode assembly 120 described above).

[0038] 6A is a structural schematic diagram of a positive electrode sheet 10 and a negative electrode sheet 20 in a conventional prismatic or soft-pack battery 60A. In FIG. 6A, a positive electrode tab 19 and a negative electrode tab 29 are located on the same side of the positive electrode sheet 10 and the negative electrode sheet 20. Therefore, a negative electrode thinned region 22 and a positive electrode thinned region 12 are located on the same side of the positive electrode sheet 10 and the negative electrode sheet 20. A tab adhesive 40 may be provided on the surface of the positive electrode tab 19 of the positive electrode sheet 10, or may be adjacent to the positive electrode thinned region 12.

[0039] Both ends of the negative electrode active material layer 26 extend beyond both ends of the positive electrode active material layer 16. Here, the negative electrode thinned region 22 of the negative electrode active material layer 26 of the negative electrode sheet 20 does not overlap with the positive electrode active material layer 16 of the positive electrode sheet 10. In Fig. 6A, H1 represents the distance by which one end of the negative electrode active material layer 26 (its negative electrode flat region 24) extends beyond one end of the positive electrode active material layer 16 (its positive electrode flat region 14), and H2 represents the distance by which the other end of the negative electrode active material layer 26 (its negative electrode thinned region 22) extends beyond the other end of the positive electrode active material layer 16 (its positive electrode thinned region 12).

[0040] For a prismatic or soft-pack battery 60A having the arrangement of the positive electrode sheet 10 and the negative electrode sheet 20 shown in Figure 6A, H2 is typically relatively large, for example, about 3 mm, to ensure safety and reduce the demand for extremely high energy density. If the H2 distance is made large, problems arise in that the battery's space utilization is insufficient.

[0041] FIG. 6B is a structural schematic diagram of the positive electrode sheet 10 and the negative electrode sheet 20 in another prismatic, soft-pack, or cylindrical battery 60B. Referring to FIG. 6B, the positive electrode tab 19 and the negative electrode tab 29 are located on different sides of the positive electrode sheet 10 and the negative electrode sheet 20. Therefore, the negative electrode thinned region 22 of the negative electrode active material layer 26 and the positive electrode thinned region 12 of the positive electrode active material layer 16 are located on the same side of the positive electrode sheet 10 and the negative electrode sheet 20. Both ends of the negative electrode active material layer 26 extend beyond both ends of the positive electrode active material layer 16. Here, the negative electrode thinned region 22 of the negative electrode active material layer 26 of the negative electrode sheet 20 does not overlap with the positive electrode active material layer 16 of the positive electrode sheet 10. In FIG. 6B, H1 represents the distance by which one end of the negative electrode active material layer 26 (its negative electrode flat region 24) extends beyond one end of the positive electrode active material layer 16 (its positive electrode thinned region 12), and H2 represents the distance by which the other end of the negative electrode active material layer 26 (its negative electrode thinned region 22) extends beyond the other end of the positive electrode active material layer 16 (its positive electrode flat region 14).

[0042] 6A, for a prismatic battery, soft pack battery, or cylindrical battery 60B having the arrangement of the positive electrode sheet 10 and the negative electrode sheet 20 shown in FIG. 6B, H2 is typically relatively large, for example, H2 may be about 3 mm, to ensure safety and reduce the demand for extremely high energy density. If the distance H2 is made large, there is a problem of insufficient space utilization in the battery.

[0043] Typically, the full-tab design of large cylindrical batteries aims for high energy density, and the H2 limit requirement is 1 to 1.5 mm. The thinned area of ​​the negative electrode sheet corresponds to the flat area of ​​the positive electrode sheet. Due to the existence of the thinned negative electrode area 22, the negative electrode active material in the area corresponding to H2 has a lower negative electrode capacity than negative electrode active material of the same width. This can easily cause the CB value (Cell Balance, equal to the negative electrode capacity per unit area / positive electrode capacity per unit area) to deviate from the design, resulting in lithium deposition in the negative electrode.

[0044] FIG. 7 is a structural schematic diagram of a positive electrode sheet and a negative electrode sheet of a cylindrical battery according to an embodiment of the present invention. Referring to FIG. 7, an electrode assembly (e.g., the electrode assembly 120 described above) of a cylindrical battery (e.g., the cylindrical battery 100 described above) may include a positive electrode sheet 10, a negative electrode sheet 20, and a separator 122 positioned between the positive electrode sheet 10 and the negative electrode sheet 20. The positive electrode sheet 10, the negative electrode sheet 20, and the separator 122 may be stacked and then wound to form the electrode assembly. The first direction Da in FIG. 7 is parallel to the winding axis of the positive electrode sheet 10, the negative electrode sheet 20, and the separator 122. The first direction Da in FIG. 7 may correspond to the height direction H from top to bottom in FIG. 3.

[0045] Specifically, the positive electrode sheet 10 may include a positive electrode current collector 18 and a positive electrode active material layer 16. The positive electrode active material layer 16 includes a positive electrode flat region 14 and a positive electrode thinned region 12 located at one end of the positive electrode flat region 14 away from the first direction Da. The thickness of the positive electrode thinned region 12 may be smaller than the thickness of the positive electrode flat region 14. The negative electrode sheet 20 may include a negative electrode current collector 28 and a negative electrode active material layer 26. The negative electrode active material layer 26 includes a negative electrode flat region 24 and a negative electrode thinned region 22 located at one end of the negative electrode flat region 24 along the first direction Da (the right end in FIG. 7 ). The thickness of the negative electrode thinned region 22 may be smaller than the thickness of the negative electrode flat region 24.

[0046] A second direction Db perpendicular to the first direction Da may be the thickness direction of the positive electrode current collector 18 and the negative electrode current collector 28, and positive electrode active material layers 16 may be provided on opposite sides of the positive electrode current collector 18 in the second direction Db. Negative electrode active material layers 26 may be provided on opposite sides of the negative electrode current collector 28 in the second direction Db. The positive electrode active material layers 16 and the negative electrode active material layers 26 can be formed by applying them onto the positive electrode current collector 18 and the negative electrode current collector 28 using a coating device.

[0047] Along the first direction Da, the positive electrode active material layer 16 may include an extension portion 162 that extends beyond the negative electrode flat region 24. The width of the extension portion 162 along the first direction Da is defined as H3. The extension portion 162 overlaps with an orthogonal projection of the negative electrode thinned region 22 of the negative electrode active material layer 26 along a second direction Db perpendicular to the first direction Da.

[0048] FIG. 8A is a curve diagram of the change in thickness ratio of an active material layer according to some embodiments of the present invention. The meaning of the thinned region of the present invention can be further understood by referring to FIG. 8A. In FIG. 8A, the horizontal axis represents the distance from the edge of the active material layer, which may correspond to the first direction Da in FIG. 7. The vertical axis represents the thickness ratio of the active material layer on one side of the current collector. As shown in FIG. 8A, the thinned region refers to a region where the thickness fluctuates near the edge of the width of the flat region (e.g., corresponding to the edge of the negative electrode flat region in the first direction Da in FIG. 7), and where the thickness of the flat region (e.g., the 100% thickness ratio in FIG. 8A) begins to decrease by more than 1%, and then the thickness gradually decreases.

[0049] Referring to FIG. 7, the region of the negative electrode thinned region 22 corresponding to the extension 162 of the positive electrode active material layer 16 has a thinned depth. That is, the negative electrode thinned region 22 in the region of width H3 has a thinned depth. Referring to FIG. 8A, thinned depth D2 is shown. It should be understood that thinned depth D2 is the difference between the minimum thickness of the thinned region and the average thickness of the flat region of the active material layer of the electrode sheet (which can be expressed as a 100% thickness ratio in FIG. 8A). Referring to FIG. 8B, the average thickness of the flat region refers to the average value of the thickness of the active material layer in a 50 mm long flat region (also called a stable region) 20 mm from the edge of the thinned region.

[0050] In some embodiments, the thickness reduction depth of the negative electrode thinned region 22 is 9 μm or less. In some prior art, the thickness reduction depth is typically about 10 μm. According to an embodiment of the present invention, by arranging the thickness reduction depth of the negative electrode thinned region 22 to be 9 μm or less, the amount of negative electrode active material in the area where the projection of the negative electrode thinned region 22 and the positive electrode active material layer 16 overlap can be increased. This allows the capacity to be maximized within the same active material area, avoiding the technical issue of lithium precipitation in the negative electrode thinned region, improving battery safety, and achieving a balance between capacity and safety.

[0051] In an embodiment in which the secondary battery is a cylindrical battery, the negative electrode current collector 28 may include a negative electrode tab 29 protruding from the negative electrode thinned region 22 along the first direction Da. The positive electrode current collector 18 may include a positive electrode tab 19 protruding from the positive electrode thinned region 12 along a direction away from the first direction Da. In some embodiments, a tab adhesive 40 is applied to the surface of the positive electrode tab 19 of the positive electrode sheet 10. The tab adhesive 40 may be adjacent to the positive electrode thinned region 12. Cylindrical batteries are designed to achieve high energy density. By arranging the negative electrode thinned region 22 of the negative electrode sheet 20 of a cylindrical battery so that the thickness reduction depth is 9 μm or less, capacity can be maximized within the same active material area. This avoids the technical issue of lithium precipitation in the negative electrode thinned region, improves the safety of the cylindrical battery, and achieves a balance between capacity and safety.

[0052] In some embodiments, the ratio of the height (the distance from the end wall 111 to the cover plate 202 as shown in FIG. 3) to the diameter (outer diameter) of the cylindrical battery is in the range of 1.7 to 3.3, for example, the height is 80 mm and the diameter is 46 mm. Also, for example, the height is 15 mm and the diameter is 46 mm. In some embodiments, the cylindrical battery may be a 4680 cylindrical battery.

[0053] In some embodiments, the thickness reduction depth of the negative electrode thinned region 22 ranges from 0 μm to 5 μm. FIG. 8C shows the thickness reduction curves of the negative electrode active material layer on one side of the conventional technology and an embodiment of the present invention. Here, curve S1 represents the thickness reduction curve of the negative electrode active material layer on one side of the conventional technology, and curve S2 represents the thickness reduction curve of the negative electrode active material layer on one side of the conventional technology. In this embodiment, the average thickness of the flat region of the negative electrode active material layer is approximately 115 μm. As can be seen from curve S1, the thickness reduction depth D1 of the negative electrode thinned region in the conventional technology reaches approximately 10 μm. This is because the conventional coating equipment design can only achieve a thickness reduction depth D1 of 10 μm. As can be seen from curve S2, the thickness reduction depth D2 of the negative electrode thinned region of the negative electrode active material layer in an embodiment of the present invention is improved to 5 μm or less. The range of values ​​in which the thickness reduction depth is 0 μm or more and 5 μm or less is feasible in the manufacturing process, and can suitably increase the amount of negative electrode active material in the area where the projections of the negative electrode thinned region 22 and the positive electrode active material layer 16 overlap, thereby maximizing the capacity.

[0054] 7 and 8C , in negative electrode thinned region 22 corresponding to extension 162 (negative electrode thinned region 22 corresponding to width H3), distance L1 from lowest point D2 where the thickness of the negative electrode thinned region is at its smallest to position P1 of the boundary between negative electrode active material layer 22 and negative electrode current collector 28 is within a range of 1 mm to 3 mm. This makes it possible to reduce the film region of negative electrode active material layer 26 from occupying too much of the negative electrode current collector area, thereby preventing material waste.

[0055] Continuing to show in FIG. 7 , the extension 162 of the positive electrode active material layer 16 is a part of the positive electrode flat region 14. That is, the positive electrode flat region 14 corresponds to the negative electrode thinned region 22. The positive electrode thinned region 12 corresponds to the negative electrode flat region 24. The negative electrode flat region 24 extends beyond the positive electrode thinned region 12 in the direction away from the first direction Da. Arranging a part of the positive electrode flat region 14 as the extension 162 overlapping with the negative electrode thinned region 22 is more advantageous in maximizing capacity development. Furthermore, in an embodiment in which the secondary battery is a cylindrical battery, in order to increase the energy density of the battery, the gap between the rolled positive electrode sheet 10 and negative electrode sheet 20 is very small, and when the cylindrical battery is used, the negative electrode sheet 20 expands. Therefore, by arranging the extension portion 162 of the positive electrode sheet 10 so that it enters the negative electrode thinned region 22 and making the extension portion 162 overlap with the orthogonal projection of the negative electrode thinned region 22 along the second direction Db, it is possible to prevent the sharp portion of the positive electrode flat region 14 from facing directly toward the negative electrode flat region 24, thereby alleviating stress in the cylindrical battery.

[0056] In some embodiments, the width H3 of the extension 162 is in the range of 1.0 mm to 2 mm. This range of the width H3 can increase the energy density of the secondary battery at the edge limit where lithium deposition is not expected to occur.

[0057] In some embodiments, the maximum thickness range of the negative electrode thinned region 22 corresponding to the extension 162 is 3.73 μm or less. In contrast, in some prior art, the maximum thickness range of the negative electrode thinned region 22 is 12 μm. By reducing the maximum thickness range of the negative electrode thinned region 22, the amount of negative electrode active material in the overlapping portion of the negative electrode thinned region 22 and the extension 162 can be increased, further maximizing capacity and preventing lithium deposition in the negative electrode thinned region.

[0058] In some embodiments, the standard deviation of the thickness of the negative electrode thinned region 22 corresponding to the extension 162 is 1.24 or less. In contrast, in some prior art, the standard deviation of the thickness of the negative electrode thinned region is 2.23. As can be seen from this, the thickness uniformity of the negative electrode thinned region 22 is improved compared to the prior art. By improving the thickness uniformity of the negative electrode thinned region 22, it is possible to further stabilize capacity delivery up to the limit and avoid lithium deposition in the negative electrode thinned region.

[0059] The standard deviation of the thickness can be tested by the following method: Select several test points within the negative electrode thinned region 22 corresponding to the extension portion 162, measure the thickness of these test points, and then calculate the standard deviation based on the formula:

[0060]

number

[0061] JPEG2026012085000003.jpg13160

[0062] In some embodiments, in the region of the negative electrode sheet 20 and the positive electrode sheet 10 corresponding to the extension 162 (i.e., the region corresponding to H3), the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area is ≧1. That is, N / P≧1. In contrast, in some prior art, the N / P corresponding to the negative electrode thin region 22 is <1, but the N / P of typical negative electrode sheets and positive electrode sheets is >1. That is, the present invention enhances capacity development within the same active material area.

[0063] In some embodiments, the separator 122 has a consistent thickness along the first direction Da. It should be understood that a consistent thickness means that the separator 122 does not have a specific region (e.g., the region between the negative electrode thinned region 22 and the extension portion 162) where a coating (e.g., a barrier layer) has been newly added along the first direction Da, and the separator 122 is the same in each region of the separator 122. It should be further understood that a consistent thickness does not exclude exceptional circumstances such as microscopic manufacturing errors in the thickness of the separator 122 itself. In this embodiment, the separator 122 has a consistent ionic conductivity in corresponding regions along the first direction Da. That is, each region of the separator 122 has a consistent ionic conductivity. It should be understood that a consistent ionic conductivity may include process errors caused by the manufacturing of the separator 122.

[0064] In the manufacturing process of a cylindrical battery, a coating device is typically used to apply a negative electrode slurry onto a current collector (e.g., negative electrode current collector 28) to form an active material layer (e.g., negative electrode active material layer 26). The coating device includes a coating gasket, and the structural design of the coating gasket allows the formed negative electrode active material layer 26 to meet the parameter requirements described above in FIG. 7.

[0065] FIG. 9 is a schematic planar view of a coated gasket according to some embodiments of the present invention. Referring to FIG. 9, the coated gasket includes a gasket body 1, a first baffle plate 2, and a second baffle plate 3. Specifically, the first baffle plate 2 and the second baffle plate 3 are connected to opposite ends of the gasket body 1. The first baffle plate 2 and the second baffle plate 3 each have a chamfered area 4 at one end facing each other, which together form a bearing-type outlet 6. The first baffle plate 2, the second baffle plate 3, and the gasket body 1 surround an area through which the slurry of the silicon-containing negative electrode system flows. The slurry of the silicon-containing negative electrode system flows out of the gasket body 1 through the outlet 6 formed at the ends of the first baffle plate 2 and the second baffle plate 3.

[0066] If the point A is the point where the vertical distance of the projection of the chamfered region 4 in the thickness direction of the gasket body 1 is closest to the gasket body 1, and the point B is the point where the vertical distance of the projection is farthest from the gasket body 1, the vertical distance from A to B parallel to the length direction of the gasket body 1 is a, and the vertical distance from B to A parallel to the width direction of the gasket body 1 is b, where a>b.

[0067] The gasket body 1 may be a rectangular plate having opposite ends in its length direction, and the first baffle plate 2, the second baffle plate 3, and the gasket body 1 surround an area through which the slurry of the silicon-containing negative electrode system flows, and the slurry of the silicon-containing negative electrode system flows away from the gasket body 1 and exits through outlets 6 formed at the ends of the first baffle plate 2 and the second baffle plate 3.

[0068] Due to the existence of the chamfer region 4, when the slurry of the silicon-containing negative electrode system passes through the chamfer region 4, a thinning region occurs at the edge of the negative electrode sheet film. b determines the lateral distribution of the slurry, a determines the longitudinal distribution of the slurry, and b < a. Therefore, since the slurry has a small lateral distribution and at the same time a small lateral flow velocity, at least in the coating process of the silicon-containing negative electrode sheet, when the silicon-containing negative electrode sheet is coated, the slurry can be prevented from bulging laterally at the edge of the electrode sheet. When a > b as described above is satisfied, the thickness of the thinning region formed at the edge of the film sheet of the negative electrode sheet when the silicon-containing negative electrode sheet is coated is too small, and the thinning region of the negative electrode sheet exceeds the design value, thereby solving the problem of lithium precipitation during full charge of the battery, and furthermore, lithium precipitation can be prevented.

[0069] In contrast, when b > a, when the slurry of the silicon-containing negative electrode system passes through the chamfer region 4, a part of the slurry of a small amount of the silicon-containing negative electrode system extends outward, so that the thickness of the thinning region formed at the edge of the film sheet of the negative electrode sheet is too small, and the thinning region of the negative electrode sheet exceeds the design value, thereby causing lithium precipitation during full charge of the battery.

[0070] In some embodiments, the chamfer region 4 may be a circular chamfer, and the circular chamfer may be a part of an arc. In the embodiment where the chamfer region 4 is a circular chamfer, the radius of the chamfer region 4 is R. In some embodiments, R 2 -a 2 =(R - b) 29, the formed negative electrode active material layer can satisfy the requirements for each parameter described in FIG. 7, such as the requirements that, in negative electrode thinned region 22 corresponding to extension portion 162, the thickness reduction depth is 9 μm or less, the thickness reduction depth is 0 μm or more and 5 μm or less, the distance L1 from the lowest point of the thickness to position P1 is within a range of 1 mm to 3 mm, the maximum range of the thickness of negative electrode thinned region 22 is 3.73 μm or less, and the standard deviation of the thickness of negative electrode thinned region 22 is 1.24 or less.

[0071] The chamfered region 4 may also be stepped. That is, the chamfered region 4 includes multiple steps from point A to point B, where a > b. This prevents the slurry from swelling at the edge of the electrode sheet when the silicon-containing negative electrode sheet is applied during the coating process of the silicon-containing negative electrode sheet. This allows the thinned region of the negative electrode sheet to be thinned so that it does not exceed the design value, thereby preventing lithium deposition when the battery is fully charged. In the embodiment in which the chamfered region 4 is arc-shaped as shown in FIG. 9, the arc-shaped chamfered region 4 further optimizes the flow of the slurry as a fluid, and the thinned region formed is also more gentle.

[0072] Therefore, by forming the negative electrode active material layer using the coating device having the above-mentioned coating gasket, the formed negative electrode active material layer can have an improved negative electrode thinned region, and the effective area of ​​the negative electrode thinned region can be increased, thereby substantially increasing the width of the positive electrode, improving the energy density of the entire battery, increasing safety, and preventing lithium deposition.

[0073] In an embodiment of the present invention, by changing the thickness reduction depth of the negative electrode thinned region (to 9 μm or less), the capacity can be further improved and maximized for the same area. This region does not affect the transport of lithium ions, so lithium deposition can be avoided.

[0074] The embodiment of the present invention further provides a battery pack 1002 (see FIG. 1) including any of the secondary batteries 100 (see FIG. 2) described above.

[0075] An embodiment of the present invention further provides an electronic device 1000 (see FIG. 1) including the battery pack 1002 (see FIG. 1) described above.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can be subject to various modifications and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention. [Industrial Applicability]

[0077] The present invention provides a secondary battery, a battery pack, and an electronic device that can enhance the capacity of at least the negative electrode sheet and increase the energy density of the secondary battery. [Explanation of symbols]

[0078] 10 Positive electrode sheet 12 Positive electrode thinning region 14 Positive flat region 16 Cathode active material layer 162 Stretching section 18 Positive electrode current collector 19 Positive electrode tab 20 Negative electrode sheet 22 Negative electrode thinning area 24 Negative electrode flat area 26 Negative electrode active material layer 28 Negative electrode current collector 29 Negative electrode tab 40 tab adhesive 60A rectangular or soft pack battery 60B Prismatic or Soft Pack or Cylindrical Battery 100 cylindrical batteries 111 End Wall 120 Electrode Assembly 122 Separator 200 cases 202 Cover Plate 203 Pressure welding part 205 Mounting port 208 Pole Pillar 1000 vehicles 1001 Body 1002 Battery pack 1 Gasket body 2. First baffle plate 3 Second baffle plate 4 Chamfer area 6 Outlet Da 1st direction Db 2nd direction H Height direction H1, H2, L1 distance H3 width P1 position D1, D2 Thinning depth S1, S2 curve

Claims

1. a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer including a negative electrode flat region and a negative electrode thinned region located at one end of the negative electrode flat region along a first direction; a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer including a positive electrode flat region and a positive electrode thinned region located at one end of the positive electrode flat region away from the first direction; a separator located between the positive electrode sheet and the negative electrode sheet; the positive electrode active material layer includes an extending portion that exceeds the negative electrode flat region along the first direction, the extending portion overlaps with an orthogonal projection of the negative electrode thinned region along a second direction perpendicular to the first direction, and a thickness reduction depth of a region of the negative electrode thinned region corresponding to the extending portion is 9 μm or less.

2. the reduced-wall depth of the negative electrode thinned region is the difference between the lowest thickness point in the region of the negative electrode thinned region corresponding to the extension portion and the average thickness of the negative electrode flat region, The secondary battery according to claim 1 , wherein the thickness-reduced depth of the negative electrode thinned region is in the range of 0 μm or more and 5 μm or less.

3. 2. The secondary battery according to claim 1, wherein the width of the extension portion along the first direction is in the range of 1.0 mm to 2 mm.

4. 2. The secondary battery according to claim 1, wherein in the negative electrode thinned region corresponding to the extended portion, a distance from a lowest point of the thinned region having the smallest thickness to a boundary position between the negative electrode active material layer and the negative electrode current collector ranges from 1 mm to 3 mm.

5. the separator has a uniform thickness along the first direction, the separator has corresponding regions in the first direction having the same ionic conductivity; The secondary battery according to claim 1 , wherein the maximum range of the thickness of the negative electrode thinned region corresponding to the extension portion is 3.73 μm or less.

6. The secondary battery according to claim 1 , wherein the standard deviation of the thickness of the negative electrode thinned region corresponding to the stretched portion is 1.24 or less.

7. the positive electrode active material layers are disposed on both opposing sides of the positive electrode current collector in a thickness direction of the positive electrode current collector perpendicular to the first direction; the negative electrode active material layers are disposed on both opposing sides of the negative electrode current collector in a thickness direction of the negative electrode current collector perpendicular to the first direction; 2. The secondary battery according to claim 1, wherein in the regions of the negative electrode sheet and the positive electrode sheet corresponding to the stretched portions, the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area is ≧1.

8. The secondary battery according to claim 1 , wherein the negative electrode current collector includes a negative electrode tab protruding from the negative electrode thinned region along the first direction, and the secondary battery is a cylindrical battery.

9. A battery pack comprising the secondary battery according to any one of claims 1 to 8.

10. An electronic device comprising the battery pack of claim 9.

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