Positive electrode sheet, method for manufacturing the same, electrode assembly, and battery cell

Abstract

The application relates to a positive electrode sheet and a preparation method thereof, an electrode assembly and a battery cell. The positive electrode sheet comprises a current collector and an electrode material part. The electrode material part is arranged on both sides of the current collector in the thickness direction of the current collector. The electrode material parts on the two sides are partially laminated in the thickness direction, and each of the electrode material parts on the two sides is beyond the other electrode material part in the longitudinal direction of the current collector to form a staggered section. The edge of the staggered section is to a first thinning area. The technical scheme of the application helps to reduce the risk of lithium precipitation at the edge of the negative electrode sheet.

Description

Technical Field

[0001] This application relates to the field of battery manufacturing technology, and in particular to positive electrode sheets and their preparation methods, electrode assemblies and battery cells. Background Technology

[0002] Stacked cells have a high volume utilization rate, giving them a significant advantage in the application of high-capacity batteries. However, lithium plating is prone to occur at the edges of the electrodes in stacked cells, causing capacity decay, increased internal resistance, and a higher risk of puncturing the separator, leading to internal short circuits and thermal runaway, which greatly reduces battery reliability. Summary of the Invention

[0003] Based on this, in order to improve lithium plating in stacked batteries and enhance battery reliability, a positive electrode sheet, its preparation method, electrode assembly, and battery cell are provided.

[0004] In a first aspect, this application proposes a positive electrode sheet, comprising: Current collector; and Electrode material portions are disposed on both sides of the current collector in its thickness direction, and the electrode material portions on both sides are partially stacked along the thickness direction, with one end of each portion extending beyond the other in the longitudinal direction of the current collector to form a staggered segment. The staggered segment has a first thinning zone at its longitudinal edge.

[0005] In some embodiments, a second thinning region is provided at one end of each electrode material portion away from its own offset segment; the second thinning region is stacked with another electrode material portion.

[0006] In some embodiments, each of the electrode material portions includes a stacked segment that is stacked with another electrode material portion, and the second thinning region is located in the stacked segment; In the same electrode material section, the staggered segment is directly connected to the laminated segment via the first thinning region. The thickness of the first thinning region decreases from the laminated segment toward the edge of the staggered segment. Alternatively, the staggered segment includes a first uniform thickness region with the same thickness as the laminated segment. The thickness of the first thinning region decreases from the first uniform thickness region toward the edge of the staggered segment.

[0007] In some embodiments, in the second thinning region and the first thinning region located at the same end in the longitudinal direction of the current collector, the distance between the end of the thickness reduction of the second thinning region and the beginning of the thickness reduction of the first thinning region along the longitudinal direction is L, where 0≤L≤20mm.

[0008] In some embodiments, the thickness of the second thinning region decreases along a first curve, and the thickness of the first thinning region decreases along a second curve, wherein the first curve and the second curve are arcs that curve away from the current collector.

[0009] In some embodiments, the sum of the maximum thicknesses of the two electrode material portions is d, the dimension of each second thinning region along the longitudinal direction is h1, the dimension of each first thinning region along the longitudinal direction is h2, and the maximum thickness of the stacked segment connected by the first thinning regions is k. In the xy coordinate system formed by the longitudinal direction and the thickness direction, the starting coordinates of the first curve are (0, d), and the first curve is: y = -ax 2 +d, 0≤x≤h1; the starting coordinates of the second curve are (h1+L, -a×h1) 2 +d), the second curve is y=-a(x-(h1+L)) 2 +k,h1+L≤x≤h1+h2+L,k=-a×h1 2 +d; Among them, 6.9×10 -6 ≤a≤1.5, 0≤L≤20mm, 0.05mm≤k≤0.2mm, 0.35mm

[0010] In some embodiments, the current collector is provided with blank sections at both ends in the longitudinal direction, and the blank sections have blank surfaces on both sides in the thickness direction; The electrode material portion is located between the blank sections at both ends.

[0011] In some embodiments, the current collector includes a blank surface, and each electrode material portion has the blank surface arranged at both ends in the longitudinal direction, with an insulating portion provided on the blank surface.

[0012] Secondly, this application proposes a method for preparing a positive electrode sheet, comprising: A current collector is provided, and its two sides in the thickness direction are the current collection surfaces; An electrode material layer comprising a plurality of electrode material portions spaced apart along the longitudinal direction of the current collector is coated on each of the current collector surfaces. Each electrode material portion corresponds to one of the electrode material portions of another electrode material layer and is partially stacked along the thickness direction. The two stacked electrode material portions are staggered along the longitudinal direction, and each one extends beyond the other at one end in the longitudinal direction to form a staggered segment. A first thinning region is provided at the edge of each staggered segment. ​Each region containing two electrode material portions in the phase stack is taken as an electrode unit, and each electrode unit is cut to obtain a plurality of positive electrode sheets as described in the first aspect.

[0013] In some embodiments, an electrode material layer comprising a plurality of electrode material portions spaced apart along the longitudinal direction of the current collector is coated on each of the current collector surfaces, including: An electrode material layer comprising a plurality of electrode material portions evenly spaced along the longitudinal direction of the current collector is coated on each of the current collector surfaces; In some embodiments, the current collector includes a blank section located between every two adjacent electrode units; Cutting each of the electrode units includes: cutting the blank sections between each adjacent electrode unit to obtain the positive electrode sheet with the blank sections provided on both sides of the electrode unit; In some embodiments, after slicing each of the electrode units, the method further includes: An insulating portion is applied to the blank surface of the current collector.

[0014] Thirdly, this application proposes an electrode assembly, including a separator, a negative electrode sheet and the positive electrode sheet described in the first aspect, wherein the positive electrode sheet and the negative electrode sheet are stacked sequentially and separated by the separator; Along the longitudinal direction of the current collector of the positive electrode, the edge of the negative electrode extends beyond or is flush with the edge of the positive electrode.

[0015] Fourthly, this application proposes a battery cell including a package and the electrode assembly described in the third aspect, wherein the package covers the electrode assembly.

[0016] Compared with the prior art, this application has the following beneficial effects: In practical applications, the aforementioned positive electrode sheet, its preparation method, electrode assembly, and battery cell have a staggered section that corresponds to the edge region of the negative electrode sheet. A first thinning zone is positioned at the edge of the staggered section, allowing the thickness of the positive electrode sheet's edge to change gradually rather than abruptly. During the compression, bending, and warping of the negative electrode sheet, this provides gradient buffer support to the edge region, significantly reducing local stress at the negative electrode edge, preventing excessive bending, and reducing the risk of powder shedding and delamination at the negative electrode edge. The gradient of the first thinning zone reduces the electrode material loading at the edge of the positive electrode sheet, effectively reducing the current density in the corresponding edge region of the negative electrode sheet. This improves the polarization unevenness and lithium dendrite precipitation problems caused by excessive local current, reducing the risk of lithium plating at the negative electrode. Attached Figure Description

[0017] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 These are schematic diagrams of the positive electrode structure in some embodiments; Figure 2 This is a schematic diagram of the positive electrode structure in some other embodiments; Figure 3 This is a schematic diagram of the first and second curves of the positive electrode sheet in some embodiments in the xy coordinate system; Figure 4 This is a schematic diagram of the line shapes of the first curve, the second curve, and the first straight line of the positive electrode in some other embodiments in the xy coordinate system; Figure 5 This is a schematic diagram of the positive electrode structure in some other embodiments; Figure 6 This is a schematic flowchart illustrating the preparation method of the positive electrode sheet in some embodiments; Figure 7 This is a schematic diagram illustrating the preparation process of the positive electrode sheet in some embodiments; Figure 8 Cross-sectional views of electrode assemblies in some embodiments; Figure 9 Cross-sectional view of the electrode assembly in some other embodiments; Figure 10 This is a cross-sectional view of the electrode assembly in some other embodiments; Figure 11 This is a schematic diagram of the external shape of a battery cell in some embodiments; Figure 12 for Figure 11 An exploded view of the battery cell.

[0018] The reference numerals in the detailed embodiments are as follows: 1000, Battery cell; 100, Electrode assembly; 10, Positive electrode sheet; 11, Current collector; X, Thickness direction; Y, Longitudinal direction; M, Current collector surface; m, Blank surface; 11a, Blank section; 12, Electrode material section; t1, Thickness reduction start end; t2, Thickness reduction end end; 12a, Staggered section; a1, First thinning region; a2, First uniform thickness region; 12b, Lamination section; b1, Second thinning region; b2, Second uniform thickness region; 13, Insulating part; T, Electrode material layer; P, Electrode unit; Q, Slitting device; 20, Negative electrode sheet; 30, Separator; 200, Encapsulation component; 210, Top cover assembly; 220, Housing. Detailed Implementation

[0019] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0020] In the description of this application, it should be understood that, where they appear, the terms “center,” “longitudinal,” “lateral,” “length,” “width,” “thickness,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circumferential” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used 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. Therefore, they should not be construed as limitations on this application.

[0021] Furthermore, where applicable, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0022] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," "fixing," etc., shall be interpreted broadly. For example, they may refer to a fixed connection, a detachable connection, or an integral part; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; they may refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0023] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0024] It should be noted that, if an element is described as "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is described as "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0025] In stacked batteries, positive and negative electrodes are stacked one-to-one and separated by a separator. To reduce lithium plating at the electrode edges, a conventional method is to create an overhang region at the edge of the negative electrode to increase its edge lithium intercalation capability. However, this method is not effective in solving the lithium plating problem of the negative electrode. The applicant's in-depth research revealed that this is mainly because the overhang region of the negative electrode extends beyond the positive electrode and is unsupported. During battery production, the overhang region is easily compressed, bent, and warped, leading to cracking, powder shedding, and even delamination of the electrode material layer. This results in insufficient lithium intercalation space in the area corresponding to the positive electrode, failing to effectively solve the lithium plating problem.

[0026] Based on this discovery, the applicant proposes a positive electrode sheet that improves the edge structure of the positive electrode sheet, effectively supports the edge region of the negative electrode sheet, and improves the problem of powder shedding when bent. At the same time, it reduces the content of electrode material at the edge of the positive electrode sheet, thereby reducing its demand for lithium intercalation at the edge of the negative electrode sheet. The combination of the two can significantly improve the problem of lithium plating at the edge of the negative electrode sheet.

[0027] The positive electrode sheet proposed in this application will be described in detail below based on several embodiments.

[0028] Please refer to Figure 1The positive electrode 10 proposed in this embodiment includes a current collector 11 and an electrode material portion 12. The electrode material portions 12 are disposed on both sides of the current collector 11 in its thickness direction X, and the electrode material portions 12 on both sides are partially stacked along the thickness direction X, and each portion extends beyond the other at one end in the longitudinal direction Y of the current collector 11 to form a staggered section 12a. A first thinning region a1 is provided at the edge of the staggered section 12a in the longitudinal direction Y.

[0029] The current collector 11 is conductive and is responsible for collecting electrodes, conducting current, and carrying electrode material. The current collector 11 can be made of materials such as aluminum, aluminum-magnesium alloy, pure carbon, or carbon composite materials. The width direction, longitudinal direction Y, and thickness direction X of the current collector 11 are approximately perpendicular to each other. The size of the current collector 11 in its longitudinal direction Y is not limited to its size in its width direction.

[0030] The current collector 11 has two side surfaces along its thickness direction X, which are called current collection surfaces M. Each current collection surface M has an electrode material portion 12. The electrode material portion 12 is formed by coating a positive electrode material onto the current collection surface M. The positive electrode material can be, but is not limited to, lithium cobalt oxide, lithium iron phosphate, ternary nickel-cobalt-manganese, ternary nickel-cobalt-aluminum, lithium manganese oxide, lithium-rich manganese-based, etc. It is worth noting that the dimensions of each electrode material portion 12 are generally the same along the width direction of the current collector 11.

[0031] One of the electrode material portions 12 on both sides is defined as the first electrode material portion 12, and the other is defined as the second electrode material portion 12. Each electrode material portion 12 includes a first end and a second end disposed opposite to each other along the longitudinal direction Y. The first end of the first electrode material portion 12 extends beyond the second electrode material portion 12, and the extended portion forms a staggered segment 12a. The second end of the second electrode material portion 12 extends beyond the first electrode material portion 12, and the extended portion forms a staggered segment 12a.

[0032] A first thinning region a1 is provided at the edge of the staggered segment 12a in the longitudinal direction Y. This "edge" refers to the edge position of the staggered segment 12a in the longitudinal direction Y; that is, the first thinning region a1 is located at one end edge of the staggered segment 12a in the longitudinal direction Y. The thickness of the first thinning region a1 of each staggered segment 12a decreases gradually along the longitudinal direction Y away from the other electrode material portion 12. This gradual decrease includes both continuous decreases and step decreases.

[0033] During battery fabrication, positive electrode 10 and negative electrode 20 are stacked alternately, separated by a separator 30. Since the staggered section 12a of the positive electrode 10 corresponds to the edge region of the negative electrode 20, and a first thinning region a1 is provided at the edge of the staggered section 12a, the thickness of the positive electrode 10 edge changes slowly rather than abruptly. During the compression, bending, and warping of the negative electrode 20, a gradient support is formed on the edge region of the negative electrode 20, significantly reducing local stress at the negative electrode edge, preventing excessive bending, and reducing the risk of powder shedding and delamination at the negative electrode edge. The gradient reduction of the first thinning region a1 decreases the electrode material loading at the edge of the positive electrode 10, effectively reducing the current density in the corresponding edge region of the negative electrode 20, improving polarization unevenness and lithium dendrite precipitation caused by excessive local current, and reducing the risk of lithium plating at the negative electrode.

[0034] Furthermore, staggered sections 12a are provided at opposite ends of the electrode material sections 12 on both sides. This not only reduces the amount of electrode material loaded on both sides of the electrode material section 12, but also makes the amount of electrode material loaded on each side of the electrode material section 12 more uniform. This makes the lithium intercalation requirements of the negative electrode sheet 20 on both sides of the electrode material section 12 more consistent, which helps to reduce lithium plating and improve the performance consistency of each negative electrode sheet 20, thereby improving the overall cycle stability of the battery. At the same time, the staggered sections 12a at different ends of each side of the electrode material section 12 can provide gradient support for the edges of the negative electrode sheets 20 on both sides of the same positive electrode sheet 10, so as to cope with different bending conditions and improve the performance consistency of each negative electrode sheet 20.

[0035] In summary, the positive electrode 10 in this embodiment can effectively improve the powder shedding at the edge of the negative electrode 20 and reduce the risk of lithium plating at the edge of the negative electrode 20.

[0036] It is worth noting that the outline shape and electrode material loading of the staggered segments 12a of the two electrode material portions 12 are usually the same.

[0037] In some embodiments, please refer to Figure 1 and Figure 2 Each electrode material portion 12 has a second thinning region b1 at one end away from its offset section 12a, and the second thinning region b1 is stacked with another electrode material portion 12.

[0038] In other words, each electrode material portion 12 has a first thinning region a1 and a second thinning region b1 at both ends in the longitudinal direction Y. The thickness of the second thinning region b1 decreases gradually from the end where the first thinning region a1 is located in the longitudinal direction Y.

[0039] At this point, a second thinning region b1 is added to the end of each electrode material portion 12 facing away from the first thinning region a1. For the negative electrode sheet 20 located on the same side as each electrode material portion 12, regardless of which end of the negative electrode sheet 20 is subjected to pressure bending in the longitudinal direction Y, it can obtain gradient support through the thinning region at the end of each electrode material portion 12. This eliminates stress concentration caused by abrupt changes in the edge thickness of each electrode material portion 12, reduces the risk of excessive bending and powder shedding at the edge of the negative electrode sheet 20, improves the structural reliability of the negative electrode sheet 20, and structurally reduces the risk of lithium plating at the edge of the negative electrode sheet 20. At the same time, the second thinning region b1 can further reduce the amount of electrode material loaded at the edge of the positive electrode sheet 10, reduce the current density and local polarization in the corresponding area of ​​the negative electrode sheet 20, further improve lithium plating at the edge of the negative electrode sheet 20, and enhance the cycle stability of the battery.

[0040] It is worth noting that the thickness of the first thinning region a1 typically decreases continuously to make the thickness change at the edge of the positive electrode 10 smoother, and to further disperse the stress experienced by the negative electrode 20 when bending and pressing the positive electrode 10, thereby preventing powder shedding from the negative electrode 20 and also reducing powder shedding from the positive electrode 10. Similarly, the thickness of the second thinning region b1 typically decreases continuously. In some embodiments, the thicknesses of the first thinning region a1 and the second thinning region b1 may also decrease in a stepped manner, thus allowing each thinning region to be obtained through a segmented thinning coating process, which is easier to implement.

[0041] It is worth noting that the minimum thickness of the first thinning region a1 and the second thinning region b1 is usually greater than zero. This arrangement can improve the adhesion of the electrode material portion 12 to the current collector 11, enabling each thinning region to provide stronger bending resistance to the negative electrode sheet 20, resulting in a more robust support effect, preventing excessive bending of the negative electrode sheet 20, and further reducing the risk of powder shedding from the negative electrode sheet 20.

[0042] In some embodiments, please combine Figure 1 and Figure 2 Each electrode material portion 12 includes a stacked segment 12b that is stacked with another electrode material portion 12, and a second thinning region b1 is located in the stacked segment 12b. In the same electrode material portion 12, a staggered segment 12a is directly connected to the stacked segment 12b via a first thinning region a1. The thickness of the first thinning region a1 decreases from the stacked segment 12b toward the edge of the staggered segment 12a. Alternatively, the staggered segment 12a includes a first uniform thickness region a2 that is the same thickness as the stacked segment 12b, and the thickness of the first thinning region a1 decreases from the first uniform thickness region a2 toward the edge of the staggered segment 12a.

[0043] It is easy to understand that the projections of the stacked segments 12b of the two electrode material portions 12 along the thickness direction X overlap. When the dimensions of each electrode material portion 12 in the width direction of the current collector 11 are the same, the projections of the two stacked segments 12b along the thickness direction X completely overlap. The thickness of each stacked segment 12b is generally the same at all points, and the thickness of each stacked segment 12b is generally equal to maintain the consistency of electrode performance.

[0044] One solution is, such as Figure 1 As shown, the entire staggered segment 12a is the first thinning region a1, which is directly connected to the corresponding stacked segment 12b, and its thickness begins to decrease from the end connected to the stacked segment 12b. At this time, the thickness of the entire staggered segment 12a decreases from the stacked segment 12b, which helps to reduce the electrode material loading of the staggered segment 12a, reduce the lithium intercalation pressure on the edge of the negative electrode 20, and alleviate lithium plating at the edge of the negative electrode 20.

[0045] Another option is, such as Figure 2 As shown, the staggered segment 12a includes a first uniform thickness region a2 and a first thinning region a1. The first uniform thickness region a2 connects the corresponding laminated segment 12b and the first thinning region a1. It is easy to understand that the thickness of the first uniform thickness region a2 is equal at all points and consistent with the thickness of the connected laminated segment 12b. This allows the staggered segment 12a to provide stronger and more stable support in the region near the laminated segment 12b, preventing insufficient overall support stiffness of the positive electrode 10 for the negative electrode 20 due to an excessively long first thinning region a1. This results in a more uniform stress distribution on the negative electrode 20 in the pressure-bearing region near the laminated segment 12b, reducing the risk of bending and powder shedding at this location. Meanwhile, the setting of the first uniform thickness zone a2 is equivalent to shortening the arrangement length of the first thinning zone a1. This not only ensures the gradient thinning structure of the staggered segment 12a edge and the stress buffering effect on the edge of the negative electrode 20, but also simplifies the coating and rolling process, and avoids the overall rigidity of the positive electrode 10 edge decreasing due to the first thinning zone a1 being too long. It takes into account both the support effect and the feasibility of the process.

[0046] Understandably, the stacked segment 12b where the second thinning region b1 is located includes a second uniform thickness region b2, the thickness of the second uniform thickness region b2 is equal at all points, and it is connected between the staggered segment 12a and the second thinning region b1 along the longitudinal direction Y of the current collector 11.

[0047] In some embodiments, in the second thinning region b1 and the first thinning region a1 located at the same end of the longitudinal direction Y of the current collector 11, the distance between the end of the thickness reduction t2 of the second thinning region b1 and the beginning of the thickness reduction t1 of the first thinning region a1 along the longitudinal direction Y is L, 0≤L≤20mm.

[0048] The two ends of the first thinning region a1 and the second thinning region b1 in the longitudinal direction Y are defined as the starting end t1 and the ending end t2 of the thickness reduction, respectively. The thickness of each thinning region decreases gradually from its starting end t1 to its ending end t2.

[0049] In the first thinning region a1 and the second thinning region b1 located at the same end in the longitudinal direction Y of the current collector 11, the end t2 of the thickness reduction of the second thinning region b1 is flush with the end of the stacked segment 12b of the electrode material part 12 where the first thinning region a1 is located.

[0050] If L=0, it indicates that the starting point t1 of the thickness reduction of the first thinning region a1 is the end of the stacked segment 12b of the electrode material part 12, and the entire staggered segment 12a is the first thinning region a1. If L>0, it indicates that there is a distance between the starting point t1 of the thickness reduction of the first thinning region a1 and the end of the stacked segment 12b of the electrode material part 12, and the staggered segment 12a located between the stacked segment 12b and the first thinning region a1 forms the first uniform thickness region a2, where L represents the dimension of the first uniform thickness region a2 in the longitudinal direction Y. If the first uniform thickness region a2 is too long, it will compress the arrangement length of the first thinning region a1, which is not conducive to achieving a gradual gradient support for the negative electrode sheet 20. When the negative electrode sheet 20 is bent, local stress concentration is likely to occur, resulting in powder shedding. When L≤20mm, that is, the length of the first uniform thickness region a2 does not exceed 20mm, it can improve the overall strength of the positive electrode 10 and reduce the stress concentration problem when the negative electrode 20 is bent, thus improving the problem of powder shedding when the negative electrode 20 is bent.

[0051] In some embodiments, the thickness of the second thinning region b1 decreases along the first curve S1, and the thickness of the first thinning region a1 decreases along the second curve S2. The first curve S1 and the second curve S2 are curved arcs that are away from the current collector 11.

[0052] Among them, the first curve S1 and the second curve S2 can be a segment of an arc bending away from the current collector 11 on a hyperbola, parabola, ellipse, circle or other line shape.

[0053] At this point, the thicknesses of the first thinning region a1 and the second thinning region b1 decrease smoothly along the arc formed by the second curve S2 and the first curve S1, which curves away from the current collector 11. This results in a slow transition in the thickness of the positive electrode 10 edge without any abrupt changes. When the negative electrode 20 is compressed and bent along the edge of the positive electrode 10, it can deform smoothly along the arc of each thinning region. The edge of the positive electrode 10 can effectively support the edge area of ​​the negative electrode 20, reducing the bending amplitude and stress peak of the negative electrode 20, and improving the problem of powder shedding when bending the negative electrode 20. Moreover, because the first thinning region a1 and the second thinning region b1 have smooth contours, during the stacking and assembly process, burrs and sharp corners on the edge of the positive electrode 10 can be avoided from scratching the separator 30, reducing the risk of short circuits inside the battery and improving the long-term reliability of the battery.

[0054] Specifically, in this embodiment, the sum of the maximum thicknesses of the two electrode material portions 12 is d, and the dimension of each second thinning region b1 along the longitudinal direction Y is h1. The dimension of each first thinning region a1 along the longitudinal direction Y is h2, and the maximum thickness of the stacked segment 12b connected to the first thinning region a1 is k. In the xy coordinate system formed by the longitudinal direction Y and the thickness direction X, the starting coordinates of the first curve S1 are (0, d), and the first curve S1 is: y = -ax 2 +d, 0≤x≤h1; the initial coordinates of the second curve S2 are (h1+L, -a×h1) 2 +d), the second curve S2 is y=-a(x-(h1+L)) 2 +k,h1+L≤x≤h1+h2+L,k=-a×h1 2 +d. Where, 6.9 × 10 -6 ≤a≤1.5, 0≤L≤20mm, 0.05mm≤k≤0.2mm, 0.35mm

[0055] It is worth noting that the curve in the xy coordinate system is formed by the thickness variation curves of the second thinning zone b1 located at the same end and the staggered segment 12a. Figure 1 and Figure 2 In this context, s represents the thickness of the current collector.

[0056] Specifically, when L=0, combined with Figure 1 and Figure 3 Understanding this means that the entire staggered segment 12a constitutes the first thinning zone a1. At this point, in the xy coordinate system, the thinning endpoint of the first curve S1 is directly connected to the thinning starting endpoint of the second curve. When L > 0, combined with... Figure 2 and Figure 4 It is understood that the staggered segment 12a also includes the first uniform thickness region a2. At this time, in the xy coordinate system, the thinning end of the first curve S1 and the thinning start of the second curve are connected by the first straight line S3.

[0057] y=-ax 2 ​+d is a parabola opening downward, and the part thereof located in the first quadrant and within the range of [0,h1] is taken as the first curve S1 forming the second thinned region b1. h1 represents the length of the second thinned region b1. If h1 is too small, the support distance provided by the second thinned region b1 when the negative electrode sheet 20 is bent is too short, and the negative electrode sheet 20 is prone to excessive bending. If h1 is too large, the load of electrode material on the positive electrode sheet 10 is severely lost, which is not conducive to the capacity of the entire electrode. When 0.35mm < h1 ≤ 170mm, the second thinned region b1 can provide effective support for the bending of the negative electrode sheet 20, and it also helps to ensure the load of electrode material on the positive electrode sheet 10 and contributes to improving the battery capacity. Specifically, h1 can take values of 0.36mm, 0.5mm, 1mm, 10mm, 20mm, 50mm, 80mm, 100mm, 120mm, 150mm, 170mm and any value between any adjacent values.

[0058] y=-a(x-(h1+L)) 2 +k, which is a parabola opening downward, and the vertex coordinate of the parabola is (h1+L,k). The part in the range of h1+L ≤ x ≤ h1+h2+L is taken as the second curve S2 of the first thinned region a1. h2 represents the length of the first thinned region a1. If h2 is too small, the support distance provided by the first thinned region a1 when the negative electrode sheet 20 is bent is too short, and the negative electrode sheet 20 is prone to excessive bending. If h2 is too large, the load of electrode material on the positive electrode sheet 10 is severely lost, which is not conducive to the capacity of the entire electrode. When 0.35mm < h2 ≤ 170mm, the first thinned region a1 can provide effective support for the bending of the negative electrode sheet 20, and it also helps to ensure the load of electrode material on the positive electrode sheet 10 and contributes to improving the battery capacity. Specifically, h2 can take values of 0.36mm, 0.5mm, 1mm, 10mm, 20mm, 50mm, 80mm, 100mm, 120mm, 150mm, 170mm and any value between any adjacent values.

[0059] a determines the steepness of the parabola. The larger a is, the steeper the parabola is, and the faster the thickness of each thinned region changes. It is easy to form a thickness protruding edge like a step within a short distance, which cannot provide gentle support for the negative electrode sheet 20. When the negative electrode sheet 20 is bent, a stress cusp will still be formed at the mutation position, and the bending amplitude cannot be effectively controlled, resulting in powder shedding. The smaller a is, the gentler the parabola is, the slower the thickness of each thinned region changes, and the thinning effect is insufficient. Reasonable bending and deformation space cannot be reserved for the edge of the negative electrode sheet 20, and the coating at the edge of the negative electrode sheet 20 will be excessively squeezed by the positive electrode sheet 10, which also causes problems such as coating cracking and powder shedding. When 6.9×10 -6With a value ≤ a ≤ 1.5, the thinning speed of each thinning zone is reasonable, providing strong support for the bending of the negative electrode sheet 20, reasonably controlling the degree of bending, reducing powder shedding, and lowering the risk of lithium plating at the edge of the negative electrode sheet 20. Specifically, a can take values ​​of 0.1, 0.5, 1, 1.5, and any values ​​between adjacent values.

[0060] pass Figure 3 and Figure 4 It can be seen that the thickness of the laminated segment 12b is k = -a × h1 2 +d, combined with the range of 0.05mm≤k≤0.2mm, constrains a to ensure that the value of k falls within the allowable range, thereby improving the structural reliability of the positive electrode 10. Specifically, k can take values ​​of 0.05mm, 0.1mm, 0.2mm, and any values ​​between adjacent values.

[0061] In practical applications, given d, h1, h2, k, and L, a second thinning region b1 and a1 are obtained by coating using a coating device based on the first curve S1 and the second curve S2 located on a parabola. Since the first curve S1 and the second curve S2 are continuous and differentiable parabolas, the coating thickness can be directly derived, eliminating the need for complex multi-segment curve splicing or surface fitting, thus greatly simplifying the curve design and process development process.

[0062] It is worth noting that the y values ​​of the first curve S1 and the second curve S2 in the xy coordinate system do not directly represent the actual thickness values ​​of each thinning zone, but are only used to guide the coating device to process the thinning contours of each thinning zone.

[0063] In some embodiments, combined with Figure 1 and Figure 2 Understandably, the current collector 11 has blank sections 11a at both ends in the longitudinal direction Y, and the two sides of the blank sections 11a in the thickness direction X are blank surfaces m. The electrode material part 12 is located between the two blank sections 11a.

[0064] The blank section 11a refers to a region on the current collector 11 where neither side is coated with electrode material. Taking the electrode material sections 12 on both sides of the current collector 11 as a whole, blank sections 11a are provided at both ends of the electrode material section 12. That is to say, each electrode material section 12 has a blank section 11a adjacent to the staggered section 12a.

[0065] In actual coating, multiple electrode units P are sequentially coated along the longitudinal direction Y of the current collector 11. Each electrode unit P includes two electrode material portions 12 that are staggered vertically. Subsequently, each electrode unit P is cut to obtain a single positive electrode sheet 10. Blank sections 11a are provided on both sides of each electrode material portion 12, that is, blank sections 11a are provided between each electrode unit P. When cutting the electrode unit P, the cutter destroys the edge coating of the electrode material portion 12, improving the success rate of cutting each electrode unit P and increasing the yield of the single positive electrode sheet 10.

[0066] Of course, in other embodiments, for a single positive electrode 10, the edges of the staggered segments 12a of each electrode material portion 12 can be set so that the edges of the current collector 11 are aligned, that is, no blank segments 11a are provided at both ends of the current collector 11.

[0067] In some embodiments, refer to Figure 5 The current collector 11 includes a blank surface m, and each electrode material part 12 has a blank surface m at both ends in the longitudinal direction Y. The blank surface m is provided with an insulating part 13.

[0068] The blank surface m is not coated. Understandably, the surface of the current collector 11 opposite to the staggered section 12a is the blank surface m, and the blank surface m is covered with the insulating part 13. If blank sections 11a are provided at both ends of the current collector 11, the insulating part 13 can also be covered on the blank surface m on both sides of the blank section 11a.

[0069] The insulating part 13 has an insulating effect, and it can be an insulating tape adhered to the blank surface m, an insulating layer coated on the blank surface m, etc.

[0070] At this point, the insulating part 13 is provided on the blank surface m of the current collector 11, which can effectively prevent the blank surface m from directly contacting the negative electrode 20, the battery casing or other conductive parts, thus avoiding internal short circuits in the battery and improving battery reliability. At the same time, the insulating part 13 effectively covers the edge of the current collector 11, preventing burrs, metal shavings or other debris from the current collector 11 from puncturing the separator 30, further reducing the risk of short circuits.

[0071] In one specific embodiment of this application, the positive electrode 10 includes a current collector 11 and an electrode material portion 12. Electrode material portions 12 are disposed on both sides of the current collector 11 in the thickness direction X, and the electrode material portions 12 on both sides are staggered from each other in the longitudinal direction Y. A staggered segment 12a is disposed on each opposite end of the electrode material portions 12 in the longitudinal direction Y, and the staggered segment 12a of each electrode material portion 12 is not stacked with the other electrode material portion 12. Each electrode material portion 12 includes a stacked segment 12b that is stacked with the other electrode material portion 12. Each staggered segment 12a includes a first thinning region a1 and a first uniform thickness region a2. The first uniform thickness region a2 connects the corresponding stacked segment 12b and the first thinning region a1, and has the same thickness as the connected stacked segment 12b. A second thinning region b1 is disposed on one end of each electrode material portion 12 away from its staggered segment 12a. The thickness of the first thinning region a1 and the thickness of the second thinning region b1 are both gradually reduced along an arc away from the current collector 11. The two ends of the current collector 11 are blank sections 11a, and each electrode material part 12 is located between the two blank sections 11a.

[0072] Additionally, refer to Figure 6 and Figure 7 It is understood that this application also provides a method for preparing a positive electrode 10, comprising: S1. A current collector 11 is provided, and its two sides in the thickness direction X are current collector surfaces M; S2. An electrode material layer T is formed on each current collecting surface M, comprising a plurality of electrode material portions 12 spaced apart along the longitudinal direction Y of the current collecting fluid 11. Each electrode material portion 12 corresponds to one of the electrode material portions 12 of another electrode material layer T and is partially stacked along the thickness direction X. The two stacked electrode material portions 12 are staggered along the longitudinal direction Y, and each one extends beyond the other in one part of the longitudinal direction Y to form a staggered segment 12a. A first thinning region a1 is provided at the edge of each staggered segment 12a. S3. Each region containing two electrode material portions 12 in the phase stack is taken as an electrode unit P. Each electrode unit P is cut to obtain the positive electrode sheet 10 in the above embodiment.

[0073] The current collector 11 provided in step S1 is a structure with a relatively long length extending along the longitudinal direction Y. The current collector 11 is generally fed in a roll and carried by a conveyor belt. During the conveyor belt process, a coating device is used to coat the current collector surface M to obtain the electrode material layer T. Specifically, the coating device can perform coating operations on each current collector surface M simultaneously or sequentially.

[0074] Specifically, multiple electrode material portions 12 are coated at intervals on each current collecting surface M along the longitudinal direction Y of the current collector 11 to form an electrode material layer T. In step S2, an electrode material layer T is formed on each side of the current collector 11. In the electrode material layers T on both sides, each electrode material portion 12 is sequentially stacked one-to-one, and together with the current collector 11 region, they form an electrode unit P.

[0075] Each electrode unit P includes two electrode material portions 12 that are staggered along the longitudinal direction Y and partially stacked. Each of the two electrode material portions 12 has a staggered segment 12a. The staggered segments 12a of the two electrode material portions 12 are located at opposite ends of the electrode unit P. The edges of the staggered segments 12a form a first thinning region a1.

[0076] It is worth noting that the coating apparatus typically includes a coating module and a drying module. After the coating module applies the coating layer to the current collector surface M, it is dried by the drying module. Typically, after at least one drying cycle, the electrode unit P is slit by the slitting device Q to obtain a single positive electrode sheet 10.

[0077] The positive electrode 10 prepared by the above preparation method can effectively improve the problem of lithium deposition at the edge of the negative electrode 20 in the electrode assembly 100 and improve the reliability of the battery.

[0078] In some embodiments, an electrode material layer T comprising a plurality of electrode material portions 12 spaced at intervals along the longitudinal direction Y of the current collector 11 is coated on each current collector surface M, including: An electrode material layer T is formed on each current collecting surface M, comprising a plurality of electrode material portions 12 arranged at equal intervals along the longitudinal direction Y of the current collecting fluid 11.

[0079] Typically, the total length of each electrode material portion 12 is consistent. Coating each electrode material portion 12 at equal intervals helps to simplify the coating process, simplify process parameters, and improve the fabrication efficiency of the positive electrode 10.

[0080] In some embodiments, combined with Figure 7 Understanding, the current collector 11 includes a blank section 11a located between every two adjacent electrode units P. The individual electrode units P are slit, including: The blank section 11a between each adjacent electrode unit P is cut to obtain a positive electrode plate 10 with blank sections 11a on both sides of the electrode unit P.

[0081] At this point, during the coating stage, a certain distance of blank space 11a (i.e., no coating on both sides) is reserved between each electrode unit P. Subsequently, each electrode unit P needs to be cut. The cutting position can be at a safe distance from the edge of the cut electrode unit P to avoid the stress generated during cutting causing the coating on the edge of the electrode unit P (specifically the staggered section 12a) to fall off, thereby improving the yield of the positive electrode sheet 10.

[0082] Specifically, it can be divided at the middle position of the blank segment 11a.

[0083] In some embodiments, combined with Figure 7 Understanding that after dividing the individual electrode units P, the process also includes: An insulating part 13 is applied to the blank surface m of the current collector 11.

[0084] The insulating part 13 can be insulating tape or an insulating coating. The blank surface m is the surface of the current collector 11 without a coating. After cutting, the insulating part 13 can be applied by adhering insulating tape or by spraying insulating coating onto the blank surface m to form the insulating part 13. To simplify the process, the insulating part 13 is usually applied to the blank surface m by adhesive tape.

[0085] The insulating part 13 not only insulates and isolates the blank surface m, preventing the positive electrode 10 from contacting other structures and causing a short circuit, but also covers and encapsulates the burrs generated during slitting, reducing the risk of the positive electrode 10 edge puncturing the separator 30.

[0086] Specifically, the insulation part 13 can be made of materials such as polypropylene (PP), polyethylene (PE), or polyethylene terephthalate (PET).

[0087] It is worth noting that in other embodiments, the positive electrode 10 prepared by the preparation method of this application may also include other technical features in the above embodiments, such as the second thinning region b1 and the uniform thickness region. The coating process can refer to the first curve S1 and the second curve S2 mentioned above to construct the first thinning region a1 and the second thinning region b1 respectively. Please refer to the above for details, and it will not be repeated here.

[0088] In addition, this application also proposes an electrode assembly 100, referring to... Figure 8 and Figure 9 The assembly includes a separator 30, a negative electrode 20, and a positive electrode 10 as described in any of the above embodiments. The positive electrode 10 and the negative electrode 20 are stacked sequentially and separated by the separator 30. Along the longitudinal direction Y of the current collector 11 of the positive electrode 10, the edge of the negative electrode 20 extends beyond or is flush with the edge of the positive electrode 10.

[0089] Among them, such as Figure 10As shown, the number of separators 30 can be one. The negative electrode 20 and the positive electrode 10 are placed sequentially within the space formed by the folding of the separators 30, following a Z-shaped stacking direction. Figure 8 and Figure 9 As shown, the separator 30 can also exist as a single piece, stacked together with the negative electrode 20 and the positive electrode 10.

[0090] When the edge of the negative electrode 20 extends beyond the edge of the positive electrode 10, an overhang area is reserved at the edge of the negative electrode 20 to reduce lithium deposition at its edge. When the edge of the negative electrode 20 aligns with the edge of the positive electrode 10, the amount of electrode material loaded at the edge of the positive electrode 10 is reduced due to the thinning area and blank surface m at the edge, which can reduce lithium deposition at the edge of the negative electrode 20.

[0091] Since the electrode assembly 100 includes the aforementioned positive electrode 10, it possesses all the beneficial effects described in the above embodiments, which will not be elaborated upon here.

[0092] In addition, this application also proposes a battery cell 1000, including a package 200 and an electrode assembly 100 as described in the above embodiments, wherein the package 200 covers the electrode assembly 100.

[0093] The package 200 can be a flexible package (such as aluminum foil) that covers the electrode assembly 100 to form a pouch battery. The package 200 can also be a rigid package, for example, as described in some embodiments, referencing... Figure 1 The package 200 includes a housing 220 and a top cover assembly 210. The housing 220 encloses a cavity with one open end, and the top cover assembly 210 covers the cavity. The electrode assembly 100 is disposed within the cavity. The housing 220 can be made of aluminum or steel. A terminal post is typically mounted on the top cover assembly 210, and the terminal post is electrically connected to the tabs of the electrode assembly 100. An electrolyte can be injected into the housing 220, which wets the interior of the electrode assembly 100, providing an ion migration pathway for the electrochemical reaction and also serving a conductive function.

[0094] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A positive electrode (10), characterized in that, include: Current collector(11); and Electrode material portions (12) are provided on both sides of the current collector (11) in its thickness direction (X). The electrode material portions (12) on both sides are partially stacked along the thickness direction (X), and one end of each of them extends beyond the other in the longitudinal direction (Y) of the current collector (11) to form a staggered segment (12a). The staggered segment (12a) has a first thinning zone (a1) at its edge in the longitudinal direction (Y).

2. The positive electrode (10) according to claim 1, characterized in that, Each electrode material portion (12) has a second thinning region (b1) at one end away from its own staggered segment (12a); the second thinning region (b1) is stacked with another electrode material portion (12).

3. The positive electrode (10) according to claim 2, characterized in that, Each of the electrode material portions (12) includes a stacked segment (12b) stacked with another electrode material portion (12), and the second thinning region (b1) is located in the stacked segment (12b); In the same electrode material section (12), the staggered segment (12a) is directly connected to the laminated segment (12b) via the first thinning region (a1). The thickness of the first thinning region (a1) decreases from the laminated segment (12b) toward the edge of the staggered segment (12a). Alternatively, the staggered segment (12a) includes a first uniform thickness region (a2) with the same thickness as the laminated segment (12b). The thickness of the first thinning region (a1) decreases from the first uniform thickness region (a2) toward the edge of the staggered segment (12a).

4. The positive electrode (10) according to claim 3, characterized in that, In the second thinning region (b1) and the first thinning region (a1) located at the same end of the longitudinal direction (Y) of the current collector (11), the distance between the end of the thickness reduction of the second thinning region (b1) (t2) and the beginning of the thickness reduction of the first thinning region (a1) (t1) along the longitudinal direction (Y) is L, 0≤L≤20mm.

5. The positive electrode (10) according to claim 4, characterized in that, The thickness of the second thinning region (b1) decreases along the first curve (S1), and the thickness of the first thinning region (a1) decreases along the second curve (S2). The first curve (S1) and the second curve (S2) are curved arcs that are away from the current collector (11).

6. The positive electrode (10) according to claim 5, characterized in that, The sum of the maximum thicknesses of the two electrode material portions (12) is d, the dimension of each second thinning region (b1) along the longitudinal direction (Y) is h1, the dimension of each first thinning region (a1) along the longitudinal direction (Y) is h2, and the maximum thickness of the stacked segment (12b) connected by the first thinning region (a1) is k; In the xy coordinate system formed by the longitudinal direction (Y) and the thickness direction (X), the starting coordinates of the first curve (S1) are (0, d), and the first curve (S1) is: y = -ax 2 +d, 0≤x≤h1; the starting coordinates of the second curve (S2) are (h1+L, -a×h1) 2 +d), the second curve (S2) is y=-a(x-(h1+L)) 2 +k,h1+L≤x≤h1+h2+L,k=-a×h1 2 +d; Among them, 6.9×10 -6 ≤a≤1.5, 0≤L≤20mm, 0.05mm≤k≤0.2mm, 0.35mm<h1≤170mm, 0.1mm≤d≤0.4mm, 0.35mm<h2≤170mm.

7. The positive electrode (10) according to claim 1, characterized in that, The current collector (11) has blank sections (11a) at both ends in the longitudinal direction (Y), and the blank sections (11a) have blank surfaces (m) on both sides in the thickness direction (X); The electrode material section (12) is located between the blank sections (11a) at both ends.

8. The positive electrode (10) according to claim 1, characterized in that, The current collector (11) includes a blank surface (m) with a blank space. Each electrode material part (12) has the blank surface (m) arranged at both ends in the longitudinal direction (Y). An insulating part (13) is provided on the blank surface (m).

9. A method for preparing a positive electrode sheet, characterized in that, include: A current collector (11) is provided, and its two sides in the thickness direction (X) are current collector surfaces (M); An electrode material layer (T) comprising a plurality of electrode material portions (12) spaced apart along the longitudinal direction (Y) of the current collector (11) is coated on each of the current collector surfaces (M). Each electrode material portion (12) is stacked one-to-one with one of the electrode material portions (12) of another electrode material layer (T) along the thickness direction (X). The two stacked electrode material portions (12) are staggered along the longitudinal direction (Y), and each one extends beyond the other at one end in the longitudinal direction (Y) to form a staggered segment (12a). A first thinning region (a1) is provided at the edge of each staggered segment (12a). Each region containing two of the electrode material portions (12) in the phase stack is taken as an electrode unit (P), and each electrode unit (P) is cut to obtain a plurality of positive electrode sheets (10) as described in any one of claims 1 to 8.

10. The method for preparing the positive electrode sheet according to claim 9, characterized in that, An electrode material layer (T) comprising a plurality of electrode material portions (12) spaced apart along the longitudinal direction (Y) of the current collector (11) is coated on each of the current collector surfaces (M), including: An electrode material layer (T) comprising a plurality of electrode material portions (12) equally spaced along the longitudinal direction (Y) of the current collector (11) is coated on each of the current collector surfaces (M); And / or, the current collector (11) includes a blank section (11a) located between each two adjacent electrode units (P); Cutting each of the electrode units (P) includes cutting the blank section (11a) between each adjacent electrode unit (P) to obtain the positive electrode sheet (10) with the blank section (11a) provided on both sides of the electrode unit (P). And / or, after splitting each of the electrode units (P), the method further includes: An insulating part (13) is provided on the blank surface (M) of the current collector (11).

11. An electrode assembly (100), characterized in that, It includes a separator (30), a negative electrode (20), and a positive electrode (10) as described in any one of claims 1-8, wherein the positive electrode (10) and the negative electrode (20) are stacked sequentially and separated by the separator (30); Along the longitudinal direction (Y) of the current collector (11) of the positive electrode (10), the edge of the negative electrode (20) extends beyond or is flush with the edge of the positive electrode (10).

12. A single battery cell (1000), characterized in that, It includes a package (200) and an electrode assembly (100) as claimed in claim 11, wherein the package (200) covers the electrode assembly (100).

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