cell

Abstract

The application provides an electric core, which comprises a pole piece assembly and a diaphragm, the pole piece assembly comprises a positive pole piece and a negative pole piece, and the diaphragm is located between the positive pole piece and the negative pole piece; the positive pole piece comprises a first protruding area, the first protruding area comprises a plurality of first protrusions, and the first protrusions are formed by protruding a partial area of the positive pole piece to one side; the negative pole piece comprises a second protruding area, the second protruding area comprises a plurality of second protrusions, and the second protrusions are formed by protruding a partial area of the negative pole piece to one side; the first protruding area comprises a first edge, the second protruding area comprises a second edge corresponding to the first edge, and the distance between the first edge and the second edge in the width direction of the pole piece of the electrode assembly is x, and x satisfies: 0≤x≤5mm. The electric core can effectively alleviate the problems of lithium precipitation and current collector fracture caused by the expansion of the pole piece.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a battery cell. Background Technology

[0002] As lithium-ion batteries develop towards higher energy density and faster charging, the internal stress generated by the volume expansion of electrode materials during cycling becomes increasingly significant. Particularly on the negative electrode side, the introduction of high-capacity materials such as silicon further exacerbates the expansion stress. With the continuous contraction and expansion of the electrode sheets during multiple charge-discharge cycles, the interlayer compression within the cell intensifies, leading to insufficient electrolyte and poor wetting. This can easily cause lithium plating due to electrode expansion and current collector breakage in the later stages of cycling. Summary of the Invention

[0003] Based on this, this application provides a battery cell to address the shortcomings of related technologies.

[0004] The battery cell provided in this application embodiment includes an electrode assembly and a separator. The electrode assembly includes a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode coating on the positive current collector. The negative electrode includes a negative current collector and a negative electrode coating on the negative current collector. The separator is located between the positive electrode and the negative electrode. The positive electrode includes a first protrusion region, which includes a plurality of first protrusions. The first protrusions are formed by a portion of the positive electrode protruding to one side. The negative electrode includes a second protrusion region, which includes a plurality of second protrusions. The second protrusions are formed by a portion of the negative electrode protruding to one side. The first protrusion region includes a first side, and the second protrusion region includes a second side corresponding to the first side. In the width direction of the electrode assembly, the distance between the first side and the second side is x, where x satisfies: 0 ≤ x ≤ 5 mm.

[0005] In one possible implementation, the first protrusion region and the second protrusion region have an overlapping area when projected onto the thickness direction of the positive electrode sheet; the area of ​​the second protrusion region is S2, the area of ​​the overlapping area is S3, and S2 and S3 satisfy: S3 / S2×100%≥70%;

[0006] And / or, along the length direction of the positive electrode sheet, the length of the second protrusion region is greater than the length of the first protrusion region.

[0007] In one possible implementation, the distance between two adjacent first protrusions in the first protrusion region is d; and the diameter of the second protrusion in the second protrusion region is D, where d > D.

[0008] Preferably, 1mm≤d≤20mm, and / or 0.5mm≤D≤10mm.

[0009] In one possible implementation, the maximum protrusion height of the first protrusion is H1, and the maximum protrusion height of the second protrusion is H2, wherein H2>H1;

[0010] Preferably, 5μm≤H2≤60μm, and / or 5μm≤H1≤60μm.

[0011] In one possible implementation, the positive electrode sheet further includes a positive electrode tab extending from one side of the positive current collector; the positive electrode coating includes a first thinned region near the positive electrode tab, and the minimum distance between the first protrusion region and the first thinned region in the width direction of the positive electrode sheet is W1, wherein W1 ≥ 5 mm;

[0012] And / or, the negative electrode sheet further includes a negative electrode tab extending from one side of the negative electrode current collector; the negative electrode coating includes a second thinned region near the negative electrode tab; in the width direction of the negative electrode sheet, the minimum distance between the second protrusion region and the second thinned region is W2, wherein W2 ≥ 5 mm.

[0013] In one possible implementation, the battery cell is a wound battery cell having a flat region and arc-angle regions located at opposite ends of the flat region. The negative electrode includes a first surface near the center of the battery cell and a second surface away from the center of the battery cell. The positive electrode includes a third surface near the center of the battery cell and a fourth surface away from the center of the battery cell. In the flat region, a second protrusion protrudes from the second surface toward the first surface, and the first protrusion protrudes from the third surface toward the fourth surface.

[0014] In one possible implementation, along the winding direction of the positive electrode sheet, the positive electrode coating includes a first region located at the tail end of the positive electrode sheet, the first region and the first protrusion region being adjacent to each other along the length direction of the positive electrode sheet, and the dimension of the first region along the winding direction of the positive electrode sheet being K1; along the winding direction of the negative electrode sheet, the negative electrode sheet includes a first bent section, a first straight section, and a second bent section located at the center of the core, wherein the length of the first straight section of the negative electrode sheet is K2; wherein K1 and K2 satisfy: K1≥1.5K2,

[0015] And / or, along the winding direction of the negative electrode sheet, the negative electrode coating includes a second straight section and a third bent section located on the outermost ring of the negative electrode sheet, and along the length direction of the negative electrode sheet, the second protrusion area includes a third side, the third side not extending beyond the third bent section of the negative electrode sheet.

[0016] In one possible implementation, the negative electrode sheet includes a single-sided negative electrode region and a double-sided negative electrode region. The negative electrode current collector in the single-sided negative electrode region has a negative electrode coating on only one surface. The single-sided negative electrode region includes a second protruding region and is located near the winding start end of the negative electrode sheet.

[0017] In one possible implementation, the negative electrode includes a second region along the winding direction of the negative electrode. The second region and the second protrusion region are arranged adjacent to each other in the length direction of the negative electrode. The second region is close to the winding start end of the negative electrode. The dimension of the second region along the winding direction of the negative electrode is K5, wherein K5 and K2 satisfy: K5≥1.5K2.

[0018] In one possible implementation, the positive electrode includes a third region, and along the winding direction of the positive electrode, the third region and the first protruding region are arranged adjacent to each other in the length direction of the positive electrode; along the winding direction of the negative electrode and along the width direction of the cell, a gap is left between the end of the third region and the intersection point between the first bent section and the first straight section of the negative electrode.

[0019] The battery cell of this application embodiment, by setting a first protrusion area on the positive electrode and a second protrusion area on the negative electrode, can disperse the in-plane compressive stress generated by the volume expansion of the electrode material during charging and discharging to multiple protrusions (the first protrusion and / or the second protrusion). Each protrusion, as an independent buffer area, absorbs part of the expansion stress through its own geometric deformation, thereby blocking stress concentration and crack propagation paths. At the same time, since the protrusion structure is formed by bending the electrode itself, the current collector corresponding to the protrusion can be transformed from a planar tension state to a curved tension state, improving the bending strength of the current collector and thus suppressing fatigue fracture of the current collector.

[0020] Furthermore, the positive electrode is provided with a first raised area, and the negative electrode is provided with a second raised area, which greatly increases the micro-spacing between the positive electrode and the separator, as well as between the negative electrode and the separator. These micro-spacings form a space that can accommodate the electrolyte, so that the electrolyte has sufficient wetting amount on the electrode, avoiding the abnormal situation of insufficient electrolyte between the electrode and the separator, poor wetting, or even lithium plating on the negative electrode caused by interlayer compression of the electrode.

[0021] Secondly, by limiting the distance x between the first and second sides, the first and second protrusions are made to be more aligned in the width direction of the electrode assembly. This is beneficial for the symmetrical distribution of lithium-ion flow in the width direction and avoids abnormal current concentration or deficiency caused by structural abrupt changes on one side of the first or second protrusion area, thereby further improving lithium plating. Moreover, the edge region of the electrode is itself a sensitive area for side reactions. This symmetrical structure can ensure the continuity of mechanical pressure and electrochemical environment of the edge region with the central region, thereby further avoiding problems such as local warping, local overcharging, or lithium plating caused by structural asymmetry in the edge region.

[0022] In addition to the technical problems solved by the embodiments of this application, the technical features constituting the technical solutions, and the beneficial effects brought about by the technical features of these technical solutions described above, other technical problems that the battery provided by this application can solve, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further described in detail in the specific embodiments. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of a battery cell provided in a specific embodiment of this application;

[0025] Figure 2 This is a schematic diagram of the structure of an electrode assembly provided in a specific embodiment of this application;

[0026] Figure 3 This is a schematic diagram of the structure of a positive electrode sheet provided in a specific embodiment of this application;

[0027] Figure 4 This is a schematic diagram of the structure of a negative electrode sheet provided in a specific embodiment of this application;

[0028] Explanation of reference numerals in the attached figures:

[0029] 1-Positive electrode, 2-Negative electrode, 3-Separator, 4-First convex part, 5-Second convex part, 6-First side, 7-Second side, 8-First thinning region, 9-Second thinning region, D-Diameter of the second convex part, d-Spacing of the first convex parts, H1-Height of the first convex part, H2-Height of the second convex part. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0031] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an indirect connection through an intermediate medium, or the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0032] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0033] The terms "first," "second," and "third" (if any) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein.

[0034] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or display that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or display.

[0035] With the continuous growth in demand for high energy density in lithium-ion batteries, silicon-based anode materials have become the core research direction for next-generation lithium-ion batteries due to their high theoretical specific capacity. However, in practical applications, silicon-based anodes undergo severe volume expansion during lithium-ion insertion / extraction, leading to problems such as electrode structure damage, active material shedding, and poor electrolyte wetting. Especially in high-energy-density battery designs, the tiny gaps between electrode layers inside the cell are rapidly consumed during cycling. When the expansion stress of the silicon-based anode cannot be effectively released, local current density anomalies will form in the edge region of the cell, which will then trigger lithium plating. In addition, the continuous expansion of the electrode may also cause the current collector (such as copper foil) to break, ultimately resulting in safety risks such as battery capacity decay, internal short circuit, or even thermal runaway.

[0036] In view of the above problems, embodiments of this application provide a battery cell, such as... Figure 1 As shown, the battery cell includes an electrode assembly and a separator. The electrode assembly includes a positive electrode 1 and a negative electrode 2, and the separator 3 is located between the positive electrode 1 and the negative electrode 2.

[0037] In one possible implementation, the positive electrode sheet includes a positive current collector and a positive electrode coating located on the positive current collector. The positive electrode sheet also includes a positive electrode tab extending from one side of the positive current collector, and the positive electrode tab and the positive current collector are integrally formed.

[0038] In some examples, the positive electrode current collector may comprise aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). The composite current collector can be formed by coating a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) onto a polymer substrate. In some examples, the thickness of the positive electrode current collector is 4μm-12μm, for example, any value or a range of any combination of 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, etc.

[0039] In some examples, the positive electrode coating includes a positive electrode active material, which includes lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, ternary materials, and Li. a1 Co x1 M k1 O2, Li a2 Ni x2 Co y2 D z2 R k2At least one of O2, wherein 0.85≤a1≤1.1, 0.85≤x1≤1.05, 0≤k1≤0.15, 0.85≤a2≤1.1, 0.3≤x2≤0.98, 0≤y2≤0.5, 0≤z2≤0.5, 0≤k2≤0.15; D includes at least one of Mn and Al, M includes at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb, and Mn, and R includes at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb, and Mn.

[0040] In one possible implementation, the negative electrode sheet includes a negative current collector and a negative electrode coating located on the negative current collector. The negative electrode sheet also includes a negative electrode tab extending from one side of the negative current collector, and the negative electrode tab and the negative current collector are integrally formed.

[0041] In some examples, the negative electrode current collector may include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (e.g., carbon-copper composite current collectors, nickel-copper composite current collectors, titanium-copper composite current collectors, etc.). In some embodiments, the thickness of the negative electrode current collector is 3μm-12μm, for example, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, or 12μm.

[0042] In another specific example, the negative electrode coating includes a negative electrode active material, which includes a silicon-based material and / or a graphite material. The silicon-based material may include at least one of silicon, a silicon-carbon composite, and a silicon-oxygen composite. The silicon-carbon composite may include at least one of spherical silicon-carbon and bulk silicon-carbon. The silicon content of the silicon-based material has a mass fraction of 10%-70% (e.g., 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 60%, 65%, 70%, etc.).

[0043] In one specific example, the separator includes a base membrane and adhesive layers on both sides of the base membrane. In a further embodiment, a ceramic layer and an adhesive layer are sequentially formed on a first side of the base membrane, and an adhesive layer is formed on a second side. The first side surface of the base membrane is disposed opposite to the positive electrode, and the second side surface of the base membrane is disposed opposite to the negative electrode. In some embodiments, the thickness of the separator is 5 μm-20 μm (e.g., 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, or 20 μm).

[0044] In one specific example, the battery cell also includes an electrolyte comprising a lithium salt and a solvent, wherein the solvent comprises at least one selected from ethylene carbonate, diethyl carbonate, or fluoroethylene carbonate. In another embodiment, the electrolyte further includes a nitrile additive; the content of the nitrile additive is C3 based on the total mass of the electrolyte. C3 is 0.5%-8%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%. In some embodiments, the nitrile additive includes, for example, at least one selected from butadionitrile, adiponitrile, and 1,3,6-hexanetrionitrile.

[0045] In this embodiment, such as Figure 2 As shown, the positive electrode includes a first protrusion region, which includes multiple first protrusions 4, and the first protrusions 4 are formed by a portion of the positive electrode protruding to one side; the negative electrode includes a second protrusion region, which includes multiple second protrusions 5, and the second protrusions 5 are formed by a portion of the negative electrode protruding to one side.

[0046] In one specific example, the first protrusion includes a raised portion of the positive current collector and a raised portion of the positive electrode coating. The positive electrode sheet also includes a first recess corresponding to the first protrusion. In another specific example, the second protrusion includes a raised portion of the negative current collector and a raised portion of the negative electrode coating. The negative electrode sheet also includes a second recess corresponding to the second protrusion.

[0047] Among them, such as Figure 2 As shown, the first protruding area includes a first side 6, and the second protruding area includes a second side 7 corresponding to the first side. The first side 6 and the second side 7 are correspondingly positioned, specifically meaning that the first side 6 and the second side 7 are the same edge of the first and second protruding areas, respectively. For example, the first side 6 and the second side 7 are the top edges of the first and second protruding areas along the width direction of the electrode sheet, respectively, or the bottom edges of the first and second protruding areas along the width direction of the electrode sheet. The distance between the first side 6 and the second side 7 in the width direction of the electrode sheet is x, where x satisfies: 0 ≤ x ≤ 5 mm. It should be noted that, as... Figure 2 As shown, the first side of the first protrusion region can be, for example, the line connecting the tops of the first protrusions in the uppermost row of the first protrusion region in the width direction of the positive electrode sheet. Similarly, the second side of the second protrusion region can be, for example, the line connecting the tops of the second protrusions in the uppermost row of the second protrusion region in the width direction of the negative electrode sheet.

[0048] The distance x between the first and second sides can be, for example, the distance between the first and second sides along the width direction of the electrode. The distance x between the first and second sides satisfies: 0 ≤ x ≤ 5 mm. For example, x can be any value or a range of any two of the following: 0, 0.1, 0.5, 1, 1.5, 2, 3, 3.5, 4, 4.5, 5. The distance x between the first and second sides can be obtained by conventional testing methods in this field. For example, the following method can be used for testing: After disassembling the battery cell, stack the positive and negative electrode plates. First, measure the distance a1 (overhang) between the edges of the positive and negative electrode plates in the width direction of the electrode plates. Then, measure the distance a2 from the first protrusion area of ​​the positive electrode plate to the edge of the positive electrode plate and the distance a3 from the second protrusion area of ​​the negative electrode plate to the edge of the negative electrode plate in the width direction of the electrode plate. If a3 is less than a1, it means that the second protrusion area is formed on the overhang. The distance between the first and second sides along the width direction of the electrode plate can be directly measured by visual inspection. If a3 is greater than a1, the distance x between the first and second sides can be obtained by calculating the difference between (a3-a1) and a2.

[0049] In this embodiment, the battery cell has a first protrusion area on the positive electrode and a second protrusion area on the negative electrode. This allows the in-plane compressive stress generated by the volume expansion of the electrode material during charging and discharging to be dispersed to multiple protrusions (the first protrusion and / or the second protrusion). Each protrusion acts as an independent buffer area, absorbing part of the expansion stress through its own geometric deformation, thereby blocking stress concentration and crack propagation paths. At the same time, since the protrusion structure is formed by bending the electrode itself, the current collector corresponding to the protrusion can be transformed from a planar tension state to a curved tension state, improving the bending strength of the current collector and thus suppressing fatigue fracture of the current collector.

[0050] Furthermore, the positive electrode is provided with a first raised area, and the negative electrode is provided with a second raised area, which greatly increases the micro-spacing between the positive electrode and the separator, as well as between the negative electrode and the separator. These micro-spacings form a space that can accommodate the electrolyte, so that the electrolyte has sufficient wetting amount on the electrode, avoiding the abnormal situation of insufficient electrolyte between the electrode and the separator, poor wetting, or even lithium plating on the negative electrode caused by interlayer compression of the electrode.

[0051] Secondly, by limiting the vertical distance x between the first and second sides, the first and second protrusions are made more aligned in the width direction of the electrode assembly. This is beneficial for the symmetrical distribution of lithium-ion flow in the width direction, avoiding excessive misalignment between the edges of the first or second protrusion area, which could lead to structural abrupt changes (e.g., extreme asymmetry between the positive electrode protrusion and the negative electrode plane, and the negative electrode protrusion and the positive electrode plane on the other side). This would result in uneven current density distribution, causing problems such as excessively high or low local current density, thus further improving lithium plating. Moreover, the edge region of the electrode is itself a sensitive area for side reactions. This symmetrical structure can ensure the continuity of the mechanical pressure and electrochemical environment of the edge region with the central region, thereby further avoiding problems such as local warping, local overcharging, or lithium plating caused by structural asymmetry in the edge region.

[0052] In some examples, the first raised region of the positive electrode and the second raised region of the negative electrode can be formed, for example, by pressing the electrode with an embossing roller.

[0053] In one possible implementation, the difference between the dimensions of the first protrusion and the second protrusion along the length of the electrode assembly is less than 2 mm. This ensures that the cross-sectional areas of the first and second protrusions are similar, preventing excessive dimensional differences that could lead to large fluctuations in the CB values ​​at the corresponding positions of the first and second protrusions, which could easily result in lithium plating or purple spots. The dimensions include any measurable cross-sectional dimensions such as length, width, and diameter. For example, if the cross-section of the first and second protrusions is rectangular, the difference between their lengths is less than 2 mm, and the difference between their widths is also less than 2 mm. Similarly, if the cross-sections of the first and second protrusions are circular, the difference between their diameters is less than 2 mm.

[0054] In one possible implementation, the first protrusion region and the second protrusion region have an overlapping area when projected onto the thickness direction of the positive electrode sheet; the area of ​​the second protrusion region is S2, and the area of ​​the overlapping area is S3, where S2 and S3 satisfy: S3 / S2×100%≥70%.

[0055] Understandably, both the positive and negative electrodes in the overlapping region include a first convex portion and a second convex portion, respectively. The overall bending strength of the positive and negative electrodes in the overlapping region is higher, and the spacing between the positive and negative electrodes in the overlapping region is larger. During the charging and discharging process of the battery cell, the second convex region will be squeezed outward in both width and height directions due to the expansion force of the silicon particles in the negative electrode. The first convex region and the second convex region reduce the spacing between the first convex region and the second convex region to offset the expansion stress of the second convex region, thereby preventing the particles in the second convex region from falling off. At the same time, it prevents the current collector corresponding to the non-first convex region of the positive electrode from breaking when the second convex region collides with the non-first convex region of the positive electrode during expansion. Furthermore, S3 / S2×100%≥70% further ensures the overlap ratio of the first and second raised areas, guaranteeing that the expansion force of the second raised area during charging and discharging is distributed to the first raised area. This avoids unpredictable shear stress and point pressure in mismatched areas (referring to areas where the first and second raised areas do not overlap, such as the area between the first raised portion and the non-second raised area of ​​the negative electrode, or the area between the second raised portion and the non-first raised area of ​​the positive electrode), thereby reducing the risk of local puncture of the separator. For example, S3 / S2×100% can be any value or a range of any two of the following: 70%, 75%, 80%, 85%, 90%, 95%, 100%.

[0056] It should be noted that the overlapping area of ​​the first and second raised regions can be determined as follows: the first raised region has a fourth and a fifth side along the length of the positive electrode sheet, and a sixth side corresponding to the first side along the width of the positive electrode sheet. The area enclosed by the first, fourth, fifth, and sixth sides is the region of the first raised region. Similarly, the second raised region has a third and a seventh side along the length of the electrode sheet, and an eighth side corresponding to the second side along the width of the electrode sheet. The second, eighth, third, and seventh sides enclose the region of the second raised region. The area S2 of the second raised region is the product of the second and third sides; the area of ​​the overlapping region is the area of ​​the overlapping portion of the regions of the first and second raised regions.

[0057] In one possible implementation, see Figures 3-4 In the first raised region, the distance between two adjacent first protrusions is d; in the second raised region, the diameter of the second protrusion is D, where d > D. The distance d between adjacent first protrusions can be measured by observing the electrode sheet with a 2.5D microscope, and the diameter of the second protrusion can be measured by a 3D profilometer.

[0058] In the above embodiments, by setting the distance between two adjacent first protrusions of the positive electrode sheet to be greater than the diameter of the second protrusion of the second protrusion area of ​​the negative electrode sheet, the situation of powder shedding caused by repeated friction between the second protrusion and the first protrusion or the inclined wall of the first protrusion of the expanded negative electrode sheet is avoided during the charging and discharging process of the battery cell.

[0059] To further reduce friction between the second convex portion and the first convex portion or the inclined wall of the first convex portion of the expanded negative electrode sheet, in one specific example, 1mm ≤ d ≤ 20mm; for example, d is any value or a range of any two of 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 10mm, 12mm, 15mm, 17mm, 20mm, etc.; in another specific example, 0.5mm ≤ D ≤ 10mm, for example, D is any value or a range of any two of 0.5mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 10mm, etc.

[0060] In one possible implementation, the length of the second protrusion region is greater than the length of the first protrusion region along the length direction of the positive electrode. This greater length of the second protrusion region compared to the first protrusion region can further increase the bending strength of the negative electrode, while simultaneously preventing lithium plating due to excessively low CB values ​​in certain areas between the positive and negative electrodes.

[0061] In one possible implementation, see Figures 3-4 The maximum protrusion height of the first protrusion is H1, and the maximum protrusion height of the second protrusion is H2, where H2>H1.

[0062] In this embodiment, the height of the first protrusion of the positive electrode is lower than the height of the second protrusion of the negative electrode. This is mainly because the expansion stress of the silicon-doped negative electrode is too large during the charging and discharging process of the cell. By increasing the height of the second protrusion of the negative electrode, that is, increasing the depth of the second concave part corresponding to the second protrusion of the negative electrode, the bending ability of the negative electrode is improved. This allows the second protrusion area with a larger protrusion height to release the expansion stress to a greater extent when the silicon-doped negative electrode expands.

[0063] To further ensure that the second protrusion region possesses sufficient structural strength and stress buffering capacity, in one specific example, 5μm ≤ H2 ≤ 60μm. Exemplarily, H2 can be any value or a range between any two of the following: 5μm, 8μm, 15μm, 25μm, 35μm, 45μm, 55μm, 60μm. To further ensure that the first protrusion region possesses sufficient structural strength and stress buffering capacity, in another example, 5μm ≤ H1 ≤ 60μm. Exemplarily, H1 can be any value or a range between any two of the following: 5μm, 8μm, 15μm, 25μm, 35μm, 45μm, 55μm, 60μm.

[0064] In one possible implementation, the positive electrode includes a positive current collector and a positive electrode coating on the current collector, and the positive electrode also includes a positive electrode tab extending from one side of the current collector; such as Figure 2 As shown, the positive electrode coating includes a first thinned region 8 near the positive electrode tab, and the thickness of the first thinned region is less than the thickness of the non-first thinned region of the positive electrode coating.

[0065] In a specific example, the first thinning area is formed by extending the positive electrode coating. In the width direction of the positive electrode sheet, the minimum distance between the first raised area and the first thinning area is W1, where W1 ≥ 5 mm. By maintaining a gap between the first raised area and the first thinning area in the width direction of the positive electrode sheet, it can firstly prevent the first raised area from forming on the thinner first thinning area, which could easily lead to powder shedding from the first thinning area and purple spots on the corresponding negative electrode sheet. Furthermore, during the positive electrode sheet winding process, it can also prevent the formation of wavy or serpentine sheets due to uneven stress between the first and non-first thinning areas, thus avoiding poor coverage of the wound cell and subsequent lithium plating.

[0066] In one possible implementation, the negative electrode includes a negative current collector and a negative electrode coating on the negative current collector; the negative electrode also includes a negative electrode tab extending from one side of the negative current collector; such as Figure 2 As shown, the negative electrode coating includes a second thinned region 9 near the negative electrode tab; in the width direction of the negative electrode sheet, the minimum distance between the second raised region and the second thinned region is W2, where W2 ≥ 5 mm. By leaving a gap between the second raised region and the second thinned region in the width direction of the negative electrode sheet, it is possible to avoid the situation where the second raised region is formed in the thinner second thinned region, which is prone to powder shedding and lithium deposition. It can also prevent the second raised region and the second thinned region from forming wavy or serpentine sheets due to uneven stress during the winding process, which would result in poor coverage of the wound cell and thus lithium deposition.

[0067] In one possible implementation, the battery cell is a wound battery cell, which has a flat region and arc-angle regions located at opposite ends of the flat region. The negative electrode includes a first surface near the center of the battery cell and a second surface away from the center of the battery cell, and the positive electrode includes a third surface near the center of the battery cell and a fourth surface away from the center of the battery cell. In the flat region, a second protrusion protrudes from the second surface toward the first surface, and a first protrusion protrudes from the third surface toward the fourth surface.

[0068] In the arc-angle region, the first convex part of the positive electrode sheet protrudes from the third surface toward the fourth surface, and the second convex part of the negative electrode sheet protrudes from the first surface toward the second surface. That is to say, the first convex part of the positive electrode sheet and the second convex part of the negative electrode sheet protrude in the same direction in the arc-angle region, both forming a protrusion from the center of the cell toward the outside. This ensures that the distance between the positive and negative electrode sheets in the arc-angle region, where the winding stress is greater, is larger, and avoids the positive and negative electrode sheets in the arc-angle region from being squeezed and expanded by each other, resulting in powder shedding.

[0069] In one possible implementation, along the winding direction of the positive electrode sheet, the positive electrode coating includes a first region located at the tail end of the positive electrode sheet, wherein no first protrusion region is formed on the first region, and the first region and the first protrusion region are arranged adjacent to each other along the length direction of the positive electrode sheet. The dimension of the first region along the winding direction of the positive electrode sheet is K1. Along the winding direction of the negative electrode sheet, the negative electrode sheet includes a first bent section, a first straight section, and a second bent section located at the center of the core, wherein the length of the first straight section of the negative electrode sheet is K2. K1 and K2 satisfy: K1≥1.5K2. K1≥1.5K2 can avoid the situation where the stress of the outer ring increases with the number of turns, which can easily lead to poor adhesion between the positive electrode sheet and the separator, resulting in arc-shaped lithium plating. By extending the length of the first region where no first protrusion region is formed, the bonding strength between the positive electrode sheet and the separator at the tail end of the cell can be guaranteed.

[0070] In one possible implementation, along the winding direction of the negative electrode sheet, the negative electrode coating includes a second straight section and a third bent section located at the tail end of the negative electrode sheet. Along the length direction of the negative electrode sheet, the second protrusion area includes a third side, which does not extend beyond the third bent section of the negative electrode sheet. That is, the tail end of the second protrusion area will not extend beyond the third bent section, thus forming on the second straight section. This prevents the gap between the outermost second straight section of the cell and the positive electrode sheet or separator from being too large, which could easily lead to initial purple spots or later lithium plating. At the same time, it avoids the occurrence of arc-shaped lithium plating at the end of the cell as the number of turns increases.

[0071] In one possible implementation, the negative electrode sheet includes a single-sided negative electrode region and a double-sided negative electrode region. The negative electrode current collector in the single-sided region has a negative electrode coating on only one surface, while the negative electrode current collector in the double-sided region has a negative electrode coating on both surfaces. The single-sided negative electrode region includes a second raised region located near the winding start end of the negative electrode sheet. By forming the second raised region in the single-sided negative electrode region at the winding start end, the spacing between the innermost positive and negative electrode sheets can be effectively increased, thereby releasing the expansion stress of the innermost ring of the cell during cell cycling and preventing lithium plating or cell deformation.

[0072] In one possible implementation, the negative electrode includes a second region along the winding direction of the negative electrode. The second region and the second protruding region are arranged adjacent to each other along the length of the negative electrode. The second region is located near the winding start end of the negative electrode. The dimension of the second region along the winding direction of the negative electrode is K5, where K5 and K2 satisfy: K5 ≥ 1.5K2. The length of the second region satisfying the above condition can effectively buffer the initial stress at the winding start end of the negative electrode and suppress the risk of lithium plating caused by local stress concentration in this region.

[0073] In one possible implementation, the positive electrode includes a third region. Along the winding direction of the positive electrode, the third region and the first protruding region are arranged adjacent to each other along the length direction of the positive electrode. Along the winding direction of the negative electrode, the negative electrode includes a first bent section, a first straight section, and a second bent section located at the center of the core. Along the width direction of the cell, a gap is left between the end of the third region and the intersection point between the first bent section and the first straight section of the negative electrode. This gap between the intersection points of the first bent section and the first straight section allows the weak areas of the positive electrode (such as the edge of the third region) to avoid the bending initiation point where the stress is most concentrated at the winding center of the negative electrode. This prevents excessive compression or friction between the positive electrode and the negative electrode in this stress concentration area, which could lead to cracking, powder shedding, or breakage of the current collector in the negative electrode coating.

[0074] The specific implementation of the battery according to the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0075] The negative electrode can be any negative electrode in the related technology, and the separator can be any separator in the related technology. This embodiment does not impose any specific limitations.

[0076] The following is a brief description of the preparation process of the battery cell in Example 1.

[0077] 1. Preparation of positive electrode sheet

[0078] Lithium cobalt oxide, a positive electrode conductive agent (conductive carbon black and carbon nanotubes mixed at a mass ratio of 2:1), and a positive electrode binder (polyvinylidene fluoride) were mixed at a mass ratio of 97:1.5:1.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred until homogeneous to prepare a positive electrode slurry. An aluminum foil with a thickness of 10 micrometers, a width of 60 millimeters, and a length of 1180 millimeters was used as the positive electrode current collector. The positive electrode slurry was coated on two opposite surfaces of the positive electrode current collector. After drying and rolling, the foil was slit and die-cut, leaving multiple positive electrode tabs and a first thinning zone near the positive electrode tabs on one edge of the positive electrode current collector to obtain the positive electrode sheet. The thickness of the positive electrode sheet was 0.096 mm.

[0079] In the following embodiments and comparative examples, multiple first protrusions are rolled onto the surface of the positive electrode sheet using a rolling method to form a first raised area. In this example, the maximum protrusion height of the first protrusion is 40µm, the minimum distance between the first raised area and the first thinned area is W1=7mm, and the spacing between the first protrusions is d=5mm.

[0080] 2. Preparation of negative electrode sheet

[0081] Artificial graphite, silicon-carbon material (including a porous carbon matrix and silicon material located in the pores of the porous carbon matrix, the sphericity of the silicon-carbon material being 0.93), carbon nanotubes, lithium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid were mixed in a mass ratio of 54.9:42:0.5:0.8:0.5:1.3, and deionized water was added to prepare a negative electrode slurry. A copper foil with a thickness of 6 micrometers, a width of 63 millimeters, and a length of 1240 millimeters was used as the negative electrode current collector. The above negative electrode slurry was coated on both sides of the negative electrode current collector, and then dried and rolled. After slitting and die-cutting, multiple negative electrode tabs and a second thinning zone near the negative electrode tabs were left on one side edge of the positive electrode current collector to obtain the negative electrode sheet. The thickness of the negative electrode sheet was 0.101 mm, and the mass content of elemental silicon in the negative electrode active coating was 30%.

[0082] In the following embodiments and comparative examples, multiple second protrusions are rolled onto the surface of the negative electrode sheet using a rolling process to form a second raised area. In this example, the maximum protrusion height of the second protrusion is 50µm, the minimum distance between the second raised area and the second thinned area is W1=7mm, and the diameter of the second protrusion is D=3mm.

[0083] 3. Preparation of diaphragm

[0084] The diaphragm substrate is made of 5μm thick polyethylene (PE). A 2μm thick boehmite ceramic layer is coated on one side of the diaphragm substrate. Finally, polyvinylidene fluoride (PVDF) is coated on both sides of the diaphragm substrate with the single ceramic layer. After drying, a porous layer is formed, and the diaphragm is obtained for use. The porosity of the porous layer of the diaphragm is 45%.

[0085] 4. Preparation of electrolyte

[0086] In an argon-filled glove box (moisture <1 ppm, oxygen <1 ppm), organic solvents (ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate in a mass ratio of 15:15:50:20, totaling 71.5 parts by weight) were mixed to form a homogeneous solvent. Then, 15.5 parts by weight of lithium salt (LiPF6), 2 parts by weight of 1,3-propanesulfonyl lactone, 3 parts by weight of 1,3,6-hexanetrionitrile, and 8 parts by weight of fluoroethylene carbonate were slowly added. After thorough stirring, a lithium-ion battery electrolyte was obtained.

[0087] 5. Manufacturing battery cells

[0088] The positive electrode, separator, and negative electrode are stacked sequentially, ensuring the separator remains between the positive and negative electrodes, and then wound to form a battery cell. The cell is placed inside an outer aluminum-plastic film packaging, and after dehydration at 80°C, the electrolyte is injected and the cell is sealed. It then undergoes formation, degassing, and edge trimming processes. The area S3 of the second protrusion region and the area S2 of the overlapping region satisfy: S3 / S2×100%=100%.

[0089] Example 2

[0090] The difference from Example 1 is that the area S3 of the second protrusion and the area S2 of the overlapping region satisfy: S3 / S2×100%=85%.

[0091] Example 3

[0092] The difference from Example 1 is that the area S3 of the second protrusion and the area S2 of the overlapping area satisfy: S3 / S2×100%=70%.

[0093] Example 4

[0094] The difference from Example 2 is that the distance between the first side and the second side is x=2mm.

[0095] Example 5

[0096] The difference from Example 2 is that the distance between the first side and the second side is x=5mm.

[0097] Example 6

[0098] The difference from Embodiment 2 is that the distance between the first side and the second side is x=4.5mm, the spacing of the first protrusions is d=1mm, the diameter of the second protrusion is D=0.5mm, the maximum protrusion height of the first protrusion is H1=10mm, the maximum protrusion height of the second protrusion is H2=20mm, the minimum distance between the first protrusion area and the first thinning area is W1=8mm, and the minimum distance between the second protrusion area and the second thinning area is W2=5mm.

[0099] Example 7

[0100] The difference from Embodiment 2 is that the distance between the first side and the second side is x=4.5mm, the spacing of the first protrusions is d=20mm, the diameter of the second protrusion is D=10mm, the maximum protrusion height of the first protrusion is H1=75mm, the maximum protrusion height of the second protrusion is H2=80mm, the minimum distance between the first protrusion area and the first thinning area is W1=5mm, and the minimum distance between the second protrusion area and the second thinning area is W2=8mm.

[0101] Example 8

[0102] The difference from Example 2 is that the distance between the first side and the second side is x=5mm, and the area S3 of the second protrusion area and the area S2 of the overlapping area satisfy: S3 / S2×100%=60%.

[0103] Comparative Example 1

[0104] The difference from Example 3 is that the distance between the first side and the second side is x=6mm.

[0105] Comparative Example 2

[0106] The difference from Example 1 is that the positive electrode does not have a first protrusion area and the negative electrode does not have a second protrusion area.

[0107] Test case

[0108] 1. Lithium plating test:

[0109] 1) At a test temperature of 35℃, the initial SOC of the secondary battery is adjusted to 50%. Referring to GB / T31485, the cell is charged at a constant current of 1C to 4.50V, then charged at a constant voltage until the current is less than or equal to 0.05C, and then discharged at a constant current of 2C to 3.0V. This is one charge-discharge cycle. 2) Repeat the above charge-discharge cycle 300 times. Then disassemble the cell, remove the negative electrode, observe the lithium plating on the negative electrode, and judge the degree of lithium plating by comparing the lithium plating area.

[0110] 2) At a test temperature of 35℃, the initial SOC of the secondary battery is adjusted to 50%. Referring to GB / T 31485, the cell is charged at a constant current of 1C to 4.50V, then charged at a constant voltage until the current is less than or equal to 0.05C, and then discharged at a constant current of 2C to 3.0V. This is one charge-discharge cycle. 2) Repeat the above charge-discharge cycle 500 times. Then disassemble the cell and take out the negative electrode. Observe the lithium plating on the negative electrode and judge the degree of lithium plating by comparing the lithium plating area.

[0111] 2. Current collector fracture test:

[0112] At 25℃, the battery cell is charged at a constant current of 1C to 4.5V, then charged at a constant voltage to 0.02C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 3.0V. This charge-discharge process constitutes one cycle. This charge-discharge cycle is repeated 600 times. After each cycle, the battery cell is disassembled, and the positive and negative electrode plates are separated. The current collectors on both the positive and negative electrodes are visually inspected for breakage.

[0113] The cell parameters of Examples 1-8 and Comparative Examples 1-2 are summarized in Table 1, and the performance test results are summarized in Table 2.

[0114] Table 1:

[0115]

[0116] Table 2

[0117]

[0118] As can be seen from Tables 1 and 2, compared with Comparative Example 1, Examples 1-8 can significantly alleviate the lithium plating problem of the battery cell because the distance x between the first side of the first protrusion area and the second side of the second protrusion area satisfies: 0≤x≤5mm. Compared with Comparative Example 2, Examples 1-8 have a first protrusion area and a second protrusion area, which can significantly alleviate the current collector breakage problem of the battery cell.

[0119] Furthermore, compared to Example 8, Examples 1-7 can further alleviate the lithium plating problem of the battery cell because the area S3 of the second protrusion region and the area S2 of the overlapping region satisfy: S3 / S2×100%≥70%.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A battery cell, characterized in that, The battery cell includes an electrode assembly and a separator. The electrode assembly includes a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode coating on the positive current collector. The negative electrode includes a negative current collector and a negative electrode coating on the negative current collector. The separator is located between the positive electrode and the negative electrode. The positive electrode sheet includes a first protrusion area, which includes a plurality of first protrusions, wherein each first protrusion is formed by a portion of the positive electrode sheet protruding to one side. The negative electrode sheet includes a second protruding area, which includes a plurality of second protrusions, the second protrusions being formed by a portion of the negative electrode sheet protruding to one side; The first protrusion area includes a first side, and the second protrusion area includes a second side corresponding to the first side. In the width direction of the electrode assembly, the distance between the first side and the second side is x, where x satisfies: 0≤x≤5mm.

2. The battery cell according to claim 1, characterized in that, The first protrusion region and the second protrusion region have an overlapping area when projected onto the thickness direction of the positive electrode sheet; the area of ​​the second protrusion region is S2, and the area of ​​the overlapping area is S3, wherein S2 and S3 satisfy: S3 / S2×100%≥70%; And / or, along the length direction of the positive electrode sheet, the length of the second protrusion region is greater than the length of the first protrusion region.

3. The battery cell according to claim 1 or 2, characterized in that, In the first raised area, the distance between two adjacent first protrusions is d; in the second raised area, the diameter of the second protrusion is D, where d > D; Preferably, 1mm≤d≤20mm, and / or 0.5mm≤D≤10mm.

4. The battery cell according to any one of claims 1-3, characterized in that, The maximum protrusion height of the first protrusion is H1, and the maximum protrusion height of the second protrusion is H2, wherein H2>H1; Preferably, 5μm≤H2≤60μm, and / or 5μm≤H1≤60μm.

5. The battery cell according to any one of claims 1-4, characterized in that, The positive electrode sheet also includes a positive electrode tab extending from one side of the positive electrode current collector; the positive electrode coating includes a first thinned area near the positive electrode tab, and the minimum distance between the first protrusion area and the first thinned area in the width direction of the positive electrode sheet is W1, wherein W1≥5mm; And / or, the negative electrode sheet further includes a negative electrode tab extending from one side of the negative electrode current collector; the negative electrode coating includes a second thinned region near the negative electrode tab; In the width direction of the negative electrode sheet, the minimum distance between the second protruding area and the second thinned area is W2, where W2 ≥ 5 mm.

6. The battery cell according to any one of claims 1-5, characterized in that, The battery cell is a wound battery cell, which has a flat area and arc-angle areas located at opposite ends of the flat area. The negative electrode includes a first surface near the center of the battery cell and a second surface away from the center of the battery cell. The positive electrode includes a third surface near the center of the battery cell and a fourth surface away from the center of the battery cell. In the flat region, the second convex portion protrudes from the second surface toward the first surface, and the first convex portion protrudes from the third surface toward the fourth surface.

7. The battery cell according to claim 6, characterized in that, Along the winding direction of the positive electrode sheet, the positive electrode coating includes a first region located at the tail end of the positive electrode sheet. The first region and the first protrusion region are arranged adjacent to each other along the length direction of the positive electrode sheet. The dimension of the first region along the winding direction of the positive electrode sheet is K1. Along the winding direction of the negative electrode sheet, the negative electrode sheet includes a first bent section, a first straight section, and a second bent section located at the center of the core, wherein the length of the first straight section of the negative electrode sheet is K2; wherein K1 and K2 satisfy K1≥1.5K2; And / or, along the winding direction of the negative electrode sheet, the negative electrode coating includes a second straight section and a third bent section located on the outermost ring of the negative electrode sheet, and along the length direction of the negative electrode sheet, the second protrusion area includes a third side, the third side not extending beyond the third bent section of the negative electrode sheet.

8. The battery cell according to claim 6 or 7, characterized in that, The negative electrode sheet includes a single-sided negative electrode region and a double-sided negative electrode region. The negative electrode current collector in the single-sided negative electrode region has a negative electrode coating on only one surface. The single-sided negative electrode region includes a second protruding region. The single-sided negative electrode region is located near the winding start end of the negative electrode sheet.

9. The battery cell according to claim 6 or 7, characterized in that, The negative electrode sheet includes a second region. Along the winding direction of the negative electrode sheet, the second region and the second protrusion region are arranged adjacent to each other along the length direction of the negative electrode sheet. The second region is close to the winding start end of the negative electrode sheet, and the dimension of the second region along the winding direction of the negative electrode sheet is K5. Among them, K5 and K2 satisfy: K5≥1.5K2.

10. The battery cell according to any one of claims 6-9, characterized in that, The positive electrode sheet includes a third region, and along the winding direction of the positive electrode sheet, the third region and the first protrusion region are arranged adjacent to each other in the length direction of the positive electrode sheet; Along the width direction of the battery cell, there is a gap between the end of the third region and the intersection of the first bent section and the first straight section of the negative electrode sheet.

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