Method for manufacturing a wound cylindrical battery pole group and a battery pole group

Abstract

This invention discloses a method for preparing a wound cylindrical battery electrode assembly, comprising: Step S1, aligning one end of a first separator and a second separator and attaching them to a cylindrical winding needle, then rotating the needle two turns; Step S2, inserting the starting end of a negative electrode sheet into the gap between the two separators and inserting it to the bottom, then winding the starting end of the outer active material layer of the negative electrode sheet into the space between the first and second separators for a predetermined length in the circumferential direction, and then stopping the winding; Step S3, inserting the starting end of a positive electrode sheet into the radially inner side of the first separator, and then winding until a battery electrode assembly is formed; Step S4, attaching a termination tape to the winding termination end of the battery electrode assembly; Step S5, removing the cylindrical winding needle to obtain a battery electrode assembly with the winding operation completed. This invention also discloses a wound cylindrical battery electrode assembly. This invention can effectively reduce the radial unbalanced stress caused by the expansion or contraction of the electrode sheet, and significantly improve the overall safety performance of the wound cylindrical battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for preparing a wound cylindrical battery electrode assembly and the battery electrode assembly itself. Background Technology

[0002] Currently, lithium-ion batteries have advantages such as high specific energy, high cycle life, and long storage time. They are widely used not only in portable electronic devices (such as mobile phones, digital cameras, and laptops), but also in large and medium-sized electric equipment such as electric vehicles, electric bicycles, and power tools. Therefore, the performance requirements for lithium-ion batteries are becoming increasingly stringent.

[0003] The most important component of a wound cylindrical lithium-ion battery is the electrode assembly, which is encapsulated in a steel casing. The electrode assembly is mainly composed of long, thin strips such as positive electrode sheets, separators, and negative electrode sheets, wound spirally together.

[0004] In this battery system, the main body of the positive and negative electrodes consists of an active material layer coated on both sides of the current collector. The current collector is a thin metal sheet; aluminum foil is commonly used for the positive electrode, and copper foil for the negative electrode. Additionally, metal tabs are soldered onto the positive and negative electrodes to connect to the battery cover and casing, forming an electrical circuit. The volume of the active material on the current collector expands and contracts with the electrochemical reactions that occur during battery charging and discharging. The positive electrode experiences relatively small changes, while the negative electrode experiences significant changes. Testing has shown that the most commonly used graphite negative electrode has an expansion rate exceeding 10%, while the silicon negative electrode has an expansion rate exceeding 300%.

[0005] Given that cylindrical lithium-ion batteries use a rigid casing, the expansion and contraction of the inner electrode plates will generate large radial stress. As the number of charge and discharge cycles increases, the current collector in the uneven thickness area between the electrode layers will break under this stress, causing battery failure. In particular, the current collector is more likely to break at the outermost two rings of the electrode assembly where the accumulated stress is the greatest. Summary of the Invention

[0006] The purpose of this invention is to address the technical deficiencies of existing technologies by providing a method for preparing a wound cylindrical battery electrode assembly and the battery electrode assembly itself.

[0007] Therefore, the present invention provides a method for preparing a wound cylindrical battery electrode assembly, comprising the following steps:

[0008] Step S1: Align one end of the long strip-shaped first separator and the second separator as their common starting end, attach them to the cylindrical winding needle of the battery electrode winding machine, and then rotate them around the cylindrical winding needle twice; wherein, the second separator is located on the radial outer side of the first separator.

[0009] Step S2: Insert the starting end of the long strip negative electrode sheet into the gap between the other end of the first diaphragm and the other end of the second diaphragm, and insert it all the way in. The negative electrode sheet includes a negative electrode current collector, and the inner and outer sides of the negative electrode current collector are coated with a negative inner active material layer and a negative outer active material layer, respectively.

[0010] Then, in the circumferential direction, the starting end of the outer active material layer of the negative electrode on the negative electrode sheet is wound into the predetermined length between the first and second separators, and then the winding is stopped.

[0011] Step S3: Insert the starting end of the positive electrode sheet into the radial inner side of the first separator, and then continue to wind them together until a cylindrical battery electrode assembly is formed.

[0012] Step S4: For the cylindrical battery electrode assembly obtained in step S3, attach termination tape to the winding termination end of the battery electrode assembly to fix the shape of the battery electrode assembly and prevent the battery electrode assembly from unraveling.

[0013] Step S5: Remove the cylindrical winding needle from the battery electrode assembly winding machine, thereby leaving a cylindrical cavity in the core of the battery electrode assembly that matches the shape and size of the cylindrical winding needle, and finally obtain the battery electrode assembly with the winding operation completed.

[0014] As can be seen from the technical solutions provided by the present invention above, compared with the prior art, the present invention provides a method for preparing a wound cylindrical battery electrode assembly and a battery electrode assembly. Its design is scientific and can balance the thickness difference of each component in the same layer of the outer ring of the electrode assembly, avoid the transmission and accumulation of thickness collapse, thereby effectively reducing the radial unbalanced stress caused by the expansion or contraction of the electrode sheet, preventing battery failure caused by the breakage of the current collector of the electrode sheet, significantly improving the overall safety performance of the wound cylindrical lithium-ion battery, which is conducive to improving the market application prospects of the battery manufacturer's products and has significant practical significance for production. Attached Figure Description

[0015] Figure 1 This is a basic flowchart of a method for preparing a wound cylindrical battery electrode assembly provided by the present invention;

[0016] Figure 2 This is a radial cross-sectional schematic diagram of a method for preparing a wound cylindrical battery electrode assembly based on the present invention. For ease of illustration, gaps are left between the layers in the diagram, and the number of winding turns between the starting and ending ends of the winding is only an example. Adjusting the number of winding turns and the size of the gaps between the layers does not depart from the technical solution of the present invention.

[0017] Figure 3This is a magnified view of a partial structure at the starting end of the winding of a battery electrode assembly provided by the present invention, showing the structure of the innermost two turns of the electrode assembly in a parallel unfolding manner.

[0018] Figure 4 This is a magnified view of a portion of the structure of the terminal end of the battery electrode assembly provided by the present invention, showing the structure of the outermost two rings of the electrode assembly in a parallel unfolding manner.

[0019] Figure 5 Taking the setting of a single positive electrode tab at the beginning of the positive electrode plate as an example, other methods, such as setting the positive electrode tab at a position within a preset length range from the beginning of the positive electrode plate (e.g., from one-third to two-thirds of the length of the positive electrode plate), or setting two electrodes within the above range, do not deviate from the scope of the electrode group design described in this invention.

[0020] Figure 6 This is a cross-sectional schematic diagram of a wound cylindrical battery electrode assembly prepared according to the present invention placed in a battery casing, perpendicular to the axis of the battery electrode assembly;

[0021] In the diagram: 1 is the electrode assembly body, 2 is the center hole, 3 is the positive electrode tab, and 4 is the battery steel casing.

[0022] 5 is the first separator, 6 is the inner active material layer of the negative electrode, 7 is the current collector of the negative electrode, 8 is the outer active material layer of the negative electrode, 9 is the second separator, and 10 is the positive electrode.

[0023] 11 is the negative electrode protective tape, 12 is the negative electrode tab, 13 is the termination tape, 14 is the first elastic tape, 15 is the second elastic tape, and 16 is the third elastic tape.

[0024] 71 is the point where the positive electrode termination is located radially inward at the current collector of the negative electrode;

[0025] 72 is the current collector of the negative electrode sheet attached to the termination end of the outer active material layer of the negative electrode;

[0026] 73 is the point where the positive electrode termination point is radially outermost from the current collector of the negative electrode;

[0027] 74 is the current collector of the negative electrode sheet attached to the end of the inner active material layer of the negative electrode.

[0028] 75 is the current collector point of the negative electrode sheet that the beginning end of the negative electrode tab contacts;

[0029] 76 is the current collector of the negative electrode sheet that is in contact with the termination end of the negative electrode tab;

[0030] 77 is the point where the end of the negative electrode protective tape is located radially inward at the current collector closest to the negative electrode sheet;

[0031] 78 is the end of the second elastic tape at the point on the radially inner side closest to the negative electrode current collector;

[0032] 79 is the current collector of the negative electrode sheet attached to the end of the first elastic tape;

[0033] It should be noted that, since the structure of different layers in contact with each other in the spiral winding is displayed in parallel, Figure 3 The components such as the first separator 5, the inner active material layer of the negative electrode 6, the current collector of the negative electrode sheet 7, the outer active material layer of the negative electrode 8, and the second separator 9 appear repeatedly in different winding layers. Figure 4 The situation is the same. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention 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 the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0036] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0038] In this invention, the electrode sheet, diaphragm, tape, and tab are all thin sheet structures. Their dimensions are described as follows: the length is defined along the spiral direction (i.e., the winding direction or the circumferential direction), the width is defined along the axial direction of the cylindrical electrode assembly, and the thickness is defined along the radial direction of the cylindrical electrode assembly.

[0039] It should be noted that, for ease of explanation, the spatial relative positions of the battery electrode assembly provided by the present invention are defined as follows: for a cylindrical electrode assembly, the direction closer to the axis is the inner (closer to the core), and the direction farther from the axis is the outer (closer to the outer surface).

[0040] In this invention, the side of the same component that is near the beginning of winding in the circumferential direction is the starting end, and the side that is near the end of winding is the ending end.

[0041] In this invention, components in the same winding layer are categorized as follows: the direction closer to the starting end of the winding is inward (closer to the core), and the direction closer to the ending end of the winding is outward (closer to the tail).

[0042] In this invention, when comparing the positions of components in different layers in the circumferential direction, if the terminal end of the innermost layer is blocked by the outermost layer, the terminal end of the outermost layer is further outward in the circumferential direction than the terminal end of the innermost layer; conversely, if the terminal end of the innermost layer is not blocked by the outermost layer, the terminal end of the outermost layer is further inward in the circumferential direction than the terminal end of the innermost layer.

[0043] See Figure 1 This invention provides a method for preparing a wound cylindrical battery electrode assembly, comprising the following steps:

[0044] Step S1: Align one end of the long strip-shaped first separator 5 and the second separator 9 as their common starting end, attach them to the cylindrical winding needle of the battery electrode winding machine, and then rotate them around the cylindrical winding needle two times; wherein, the second separator 9 is located on the radial outer side of the first separator 5.

[0045] In step S1, specifically, the diameter of the cylindrical winding needle is in the range of 3-5 mm. If the diameter is less than 3 mm, the active material layer will easily peel off due to the large curvature of the electrode at the starting end of the winding; if the diameter is greater than 5 mm, it will significantly increase the space occupied by the central hole 2 and reduce the capacity per unit volume of the battery.

[0046] Step S2: Insert the starting end of the long strip negative electrode sheet into the gap between the other end of the first diaphragm 5 and the other end of the second diaphragm 9, and insert it all the way in (i.e., until it can not be inserted any deeper). The negative electrode sheet includes a negative electrode current collector 7, and the inner and outer sides of the negative electrode current collector 7 are respectively coated with a negative inner active material layer 6 and a negative outer active material layer 8.

[0047] Then, in the circumferential direction, the starting end of the negative electrode outer active material layer 8 on the negative electrode sheet is wound into the space between the first separator 5 and the second separator 9 for more than one turn of a predetermined length (e.g., 12-26 mm), and then the winding is stopped.

[0048] Step S3: Insert the starting end of the positive electrode 10 into the radial inner side of the first separator 5, and then continue to wind them together until a cylindrical battery electrode assembly is formed.

[0049] The overall length of the first diaphragm 5 and the second diaphragm 9 is greater than the overall length of the negative electrode sheet.

[0050] The overall length of the negative electrode sheet is greater than the overall length of the positive electrode sheet 10, so that in the winding and finishing stage, the positive electrode sheet is first completely wound into the battery electrode assembly, then the negative electrode sheet is completely wound into the battery electrode assembly, and then the first separator 5 and the second separator 9 are completely wound into the battery electrode assembly.

[0051] Step S4: For the cylindrical battery electrode assembly obtained in step S3, attach termination tape 13 to the winding termination end (i.e., tail) of the battery electrode assembly to fix the shape of the battery electrode assembly and prevent the battery electrode assembly from unraveling.

[0052] In step S4, for specific implementation details, see [link to implementation details]. Figure 4 As shown, the terminating tape 13 crosses the terminating end of the outermost second separator 9 in the circumferential direction, and simultaneously adheres to the outermost second separator 9 and the next outermost second separator 9 of the battery electrode assembly.

[0053] Step S5: Remove the cylindrical winding needle from the battery electrode assembly winding machine, thereby leaving a cylindrical cavity in the core (i.e., the center part) of the battery electrode assembly that matches the shape and size of the cylindrical winding needle, and finally obtain the battery electrode assembly with the winding operation completed.

[0054] In step S2, specifically, at the starting end of the negative electrode sheet, the starting ends of the inner active material layer 6 and the outer active material layer 8, located on both sides of the current collector 7, are aligned (i.e., at the same position in the circumferential direction). Furthermore, the starting end of the outer active material layer is wound more than one turn. These design elements together ensure that the starting end of the positive electrode sheet has corresponding negative active material layers on both the inner and outer radial sides, preventing lithium plating.

[0055] For the negative electrode, the overall length of the inner active material layer 6 on the negative electrode current collector 7 is greater than the overall length of the outer active material layer 8.

[0056] Therefore, through the above design, the section at the winding termination end (i.e., the tail) of the negative electrode sheet has only a single layer of active material (specifically, the inner active material layer 6 of the negative electrode). Since the outermost negative electrode sheet only has a corresponding positive electrode sheet on its radially inner side, and no corresponding positive electrode sheet on its radially outer side, there is no need to set a corresponding negative electrode active material layer. The above design can reduce the amount of negative electrode active material used, reduce production costs, and improve the space utilization rate inside the battery.

[0057] In step S3, specifically, after the negative electrode sheet completes its final winding operation along with the positive electrode sheet 10, the first separator 5, and the second separator 9, for the cylindrical battery electrode assembly obtained in step S3, the inner active material layer 6 on the negative electrode current collector 7 is required to be wound one more turn than the outer active material layer 8. Furthermore, the termination end (i.e., the tail) of the inner active material layer 6 on the outermost ring of the negative electrode current collector 7 is radially aligned with the termination end (i.e., the tail) of the outermost ring of the negative electrode electrode assembly, and is at the same position in the circumferential direction. (See [reference]). Figure 4 As shown.

[0058] In step S3, specifically, for the cylindrical battery electrode assembly obtained in step S3, the termination ends of the inner negative electrode active material layer 6 located in the outermost ring of the battery electrode assembly and the termination ends of the outer negative electrode active material layer 8 located in the second outermost ring of the battery electrode assembly are both positioned further outward by a predetermined length (e.g., 3-12 mm) in the circumferential direction than the termination end of the positive electrode sheet 10. That is, the inner negative electrode active material layer 6 located in the outermost ring of the battery electrode assembly and the outer negative electrode active material layer 8 located in the second outermost ring of the battery electrode assembly together complete the double-sided coating of the last ring (i.e., the tail ring) of the positive electrode sheet 10. See [link to relevant documentation]. Figure 4 As shown in the diagram, the above design ensures that there are corresponding layers of negative electrode active material on both the inner and outer radial sides of the positive electrode tail, thus preventing lithium plating.

[0059] In step S3, specifically, for the cylindrical battery electrode assembly obtained in step S3, the winding termination end (i.e., the tail) of the negative electrode sheet leaves a pre-set length (specifically 10-40 mm) of uncoated negative electrode sheet current collector 7 (i.e., blank current collector area) outside the termination end of the inner active material layer 6 of the negative electrode sheet.

[0060] The radial outer side of the uncoated negative electrode current collector 7 (i.e., the blank current collector area) is welded with a negative electrode tab 12.

[0061] On the radial inner side of the uncoated negative electrode current collector 7 (i.e., the blank current collector area), at the position corresponding to the negative electrode tab 12, a negative electrode protective tape 11 is pasted.

[0062] In practice, the starting end of the negative electrode protective tape 11 is further inward in the circumferential direction than the starting end of the negative electrode tab 12.

[0063] The terminating end of the negative electrode protective tape 11 is further outward in the circumferential direction than the terminating end of the negative electrode tab 12. That is, the length of the negative electrode protective tape 11 is greater than the length of the negative electrode tab 12 and completely covers the corresponding area on its reverse side. The above-mentioned negative electrode protective tape design can shield the sharp edges of the negative electrode tab and the solder joint between the negative electrode tab and the current collector, preventing them from cutting or piercing the corresponding components on the radially inner side.

[0064] In practice, the distance between the starting end of the negative electrode protective tape 11 and the ending end of the negative electrode inner active material layer 6 located on the outermost ring of the battery electrode assembly is a preset length (0-1 mm).

[0065] The terminating end of the negative electrode protective tape 11 is further inward in the circumferential direction than the terminating end of the negative electrode current collector 7, that is, the terminating end (tail end) of the negative electrode protective tape does not extend beyond the terminating end (tail end) of the negative electrode.

[0066] In practice, the thickness of the negative electrode protective tape 11 is the same as the thickness of the negative electrode inner active material layer 6 (when not charged or discharged).

[0067] In this invention, specifically, the positive electrode 10 is welded to the positive electrode tab 3;

[0068] The structure of the positive electrode tab 3 is similar to that of the negative electrode tab 12. The difference is that the positive electrode tab 3 is located at the starting end of the winding of the positive electrode sheet 10, or at a position within a preset length range (e.g., from one-third to two-thirds of the length of the positive electrode sheet) from the starting end of the positive electrode sheet. Specifically, one or two positive electrodes tabs can be set.

[0069] In practice, the lengths of both the positive and negative tabs are between 3 and 6 millimeters. A tab length of less than 3 millimeters will limit the current carrying capacity due to high ohmic impedance; while a tab length of more than 6 millimeters will reduce the roundness of the pole assembly. This roundness is measured by the range of the radial radii of the entire cylindrical pole assembly (the difference between the maximum and minimum radii). The smaller the range, the higher the roundness.

[0070] In step S3, specifically, for the cylindrical battery electrode assembly obtained in step S3, the terminating ends of the first separator 5 and the second separator 9 located on the outermost ring of the battery electrode assembly are aligned radially, that is, they are in the same position in the circumferential direction.

[0071] The termination ends of the first separator 5 and the second separator 9, located at the outermost edge of the battery electrode assembly, are positioned further outward by a predetermined length (e.g., 2-10 mm) than the termination end of the negative electrode current collector 7, to prevent radial collapse of the tail of the negative electrode current collector due to incomplete coverage by the separator.

[0072] In step S3, specifically, for the cylindrical battery electrode assembly obtained in step S3, the starting end of the first elastic tape 14 is provided at a distance of 0-1 mm after the termination end of the negative electrode outer active material layer 8 of the negative electrode sheet of the secondary outer ring of the battery electrode assembly.

[0073] The first elastic tape 14 is attached to the radial outer surface of the negative electrode current collector 7 of the secondary outer ring of the battery electrode assembly;

[0074] The thickness of the first elastic tape 14 is the same as the thickness of the outer active material layer 8 of the negative electrode on the negative electrode current collector 7 (when not charged or discharged).

[0075] In step S3, specifically, for the cylindrical battery electrode assembly obtained in step S3, the starting end of the second elastic tape 15 is provided at a predetermined distance (0-1 mm) on the outer side of the circumferential direction of the terminating end of the positive electrode 10.

[0076] The second elastic tape 15 is attached to the radial outer surface of the second separator 9 of the battery electrode assembly.

[0077] The thickness of the second elastic tape 15 is the same as the thickness of the positive electrode 10 (when not charged or discharged).

[0078] In practice, the termination end of the second elastic tape 15 extends outward by 2-6 mm beyond the termination end of the first diaphragm 5 in the circumferential direction (i.e., in the winding direction) to avoid radial collapse at the tail of the current collector of the negative electrode sheet due to incomplete support from the second elastic tape.

[0079] In practice, the terminating end of the first elastic tape 14 extends outward by 2-6 mm beyond the terminating end of the second elastic tape 15 in the circumferential direction to avoid radial collapse at the tail of the current collector of the negative electrode sheet due to incomplete support from the first elastic tape.

[0080] In specific implementation, the negative electrode outer active material layer 8 and the second elastic tape 15 of the battery electrode assembly overlap radially.

[0081] The length of the overlapping portion in the circumferential direction is between 2 and 10 millimeters.

[0082] In practice, the second elastic tape 15 and the negative electrode inner active material layer 6 of the outermost ring of the battery electrode group overlap radially.

[0083] The length of the overlapping portion in the circumferential direction is between 2 and 10 millimeters.

[0084] In other words, the three layers—the outermost layer of the negative electrode active material 8, the second elastic tape 15, and the innermost layer of the negative electrode active material 6—located in the outermost ring of the battery electrode assembly, overlap radially.

[0085] In step S3, specifically, for the cylindrical battery electrode assembly obtained in step S3, a third elastic tape 16 is provided at a predetermined distance (0-1 mm) inside the circumference of the negative electrode tab 12.

[0086] The third elastic tape 16 is attached to the radial outer surface of the negative electrode current collector 7 of the outermost ring of the battery electrode assembly;

[0087] The termination position of the third elastic tape 16 is further outward in the circumferential direction relative to the starting position of the negative electrode protective tape 11.

[0088] In specific implementation, the first elastic tape 14, the second elastic tape 15, the negative electrode protective tape 11, and the third elastic tape 16 are overlapped in the radial direction.

[0089] The length of the overlapping portion is between 2 and 5 millimeters.

[0090] In practice, the thickness of the third elastic tape 16 is the same as the thickness of the negative electrode tab 12.

[0091] In practice, the length of the third elastic tape 16 is greater than one-sixteenth of the circumference and less than one-eighth of the circumference. This circumference is calculated by taking the radial vertical distance from the end of the third elastic tape 16 to the axis of the battery electrode group as the radius (i.e., calculated by the existing formula for calculating the circumference of a circle, 2πr), thereby determining the position of the starting end of the third elastic tape 16.

[0092] In step S4, specifically, the starting end of the terminating tape 13 is further inward in the circumferential direction than the starting end of the third elastic tape 16.

[0093] The terminating end of the terminating tape 13 is located more than 5 millimeters further outward in the circumferential direction than the terminating end of the first elastic tape 14.

[0094] The length of the termination tape 13 is greater than one-quarter of the circumference and less than one full circumference;

[0095] The circumference is calculated using the radial vertical distance r from the starting end of the termination tape 13 to the center of the battery electrode assembly (i.e., calculated using the existing formula for calculating the circumference of a circle, 2πr).

[0096] The width, thickness, and material of the battery electrode assembly prepared by the present invention will be described below.

[0097] I. Width Description (This width is the dimension along the axial direction of the cylindrical battery electrode assembly).

[0098] See Figure 5 In the width direction (i.e., the axial direction), one end of the negative electrode tab 12 extends 8-25 mm beyond the negative electrode current collector 7 welded to it, and is used as a negative electrode terminal.

[0099] The other end of the negative electrode tab 12 is 0-2 mm shorter than the negative electrode current collector 7, meaning it does not extend beyond the edge of the negative electrode current collector 7. If it is more than 2 mm shorter than the current collector, it can easily cause an imbalance in the diameter of the two ends of the electrode assembly along the axial direction; if it extends beyond the current collector, it can easily contact the positive electrode, causing a short circuit. The positive electrode tab 3 is similar, except that its direction of extending beyond the positive electrode current collector in the width direction is opposite to that of the negative electrode tab. The design of placing the positive and negative electrodes at opposite ends of the electrode assembly along the axial direction can avoid direct contact between the two, which could lead to a short circuit.

[0100] The first diaphragm 5 and the second diaphragm 9 have the same width, and are at least 0.5 mm wider than the width of the negative electrode sheet (including the inner active material layer 6, the outer active material layer 8, and the current collector of the negative electrode sheet).

[0101] The width of the negative electrode sheet is equal to the width of the first elastic tape 14, the second elastic tape 15, the negative electrode protective tape 11, and the third elastic tape 16, and is at least 0.5 mm larger than the positive electrode sheet 10 (including the positive electrode active material layer and the positive electrode current collector).

[0102] The width of the termination tape 13 is the same as the width of the positive electrode 10.

[0103] For the battery electrode assembly, observe the perpendicular projection points from the center point in the width direction of the positive electrode sheet, negative electrode sheet, first separator 5, second separator 9, negative electrode protective tape 11, first elastic tape 14, second elastic tape 15, third elastic tape 16, and termination tape 13 onto the axis of the battery electrode assembly using any cross-section parallel to the axis. The distance between any projection point and the projection point of the center point of the positive electrode sheet is less than 0.25 mm. This ensures that the wider components effectively cover the narrower components at both ends of the axial direction. This guarantees the interlayer support and isolation functions while preventing lithium plating at the electrode edges at both ends of the axial direction.

[0104] II. Thickness Description (This thickness is the dimension along the radial direction of the cylindrical battery electrode assembly).

[0105] For the present invention, the thickness of the positive electrode sheet, the negative electrode sheet (both including two active material layers and a current collector), and the second elastic tape is no greater than 350 micrometers;

[0106] The thickness of the positive electrode tab, negative electrode tab, and third elastic tape shall not exceed 200 micrometers;

[0107] The thickness of the first elastic tape and the negative electrode protective tape shall not exceed 175 micrometers;

[0108] The thickness of the positive electrode current collector (including the positive electrode sheet), the negative electrode current collector (including the negative electrode sheet), the first separator, the second separator, and the termination tape is no greater than 50 micrometers.

[0109] III. Material Description.

[0110] The base material of the first elastic tape 14, the second elastic tape 15, the third elastic tape 16, the negative electrode protective tape 11, and the termination tape 13 is an elastic polymer, preferably polyimide (PI) or polypropylene (PP).

[0111] Based on the above technical solution, compared with the prior art, the present invention has the following beneficial technical effects:

[0112] 1. The present invention designs a first elastic tape 14, the thickness of which is the same as the thickness of the outer active material layer 8 of the negative electrode (when not charged or discharged), which balances the thickness difference of the winding layer where the end of the outer active material layer 8 of the negative electrode is located, and avoids thickness collapse.

[0113] 2. The present invention designs a second elastic tape 15, the thickness of which is the same as the thickness of the positive electrode 10 (when not charged or discharged), which balances the thickness difference of the winding layer where the end of the positive electrode 10 is located, and avoids thickness collapse.

[0114] 3. The present invention designs a third elastic tape 16, the thickness of which is the same as the thickness of the negative electrode tab 12, which balances the thickness difference of the winding layer where the negative electrode tab is located and avoids thickness collapse.

[0115] 4. The thickness of the negative electrode protective tape 11 of the present invention is the same as the thickness of the negative electrode inner active material layer 6 (when not charged or discharged), which balances the thickness difference of the winding layer where the negative electrode protective tape 11 is located and avoids thickness collapse.

[0116] 5. In the radial direction, the three layers of negative electrode outer active material layer, second elastic tape 15, and negative electrode inner active material layer located in the outermost ring of the battery electrode assembly are sequentially overlapped. In the circumferential direction, the termination end of the second elastic tape 15 is further outward than the termination end of the negative electrode outer active material layer 8 and the termination end of the negative electrode inner active material layer 6. This avoids the thickness collapse transmission in the radial direction, which would cause current collector breakage at multiple locations (the multiple locations specifically include: the negative electrode current collector 71 where the termination end of the positive electrode sheet is radially inner; the negative electrode current collector 72 to which the termination end of the negative electrode outer active material layer is attached; the negative electrode current collector 73 where the termination end of the positive electrode sheet is radially outer; and the negative electrode current collector 74 to which the termination end of the negative electrode inner active material layer is attached).

[0117] 6. In the radial direction, the first elastic tape 14, the second elastic tape 15, the negative electrode protective tape 11, and the third elastic tape 16 overlap sequentially. In the circumferential direction, the terminating ends of the first elastic tape 14, the second elastic tape 15, and the negative electrode protective tape 11 are all further outward than the terminating end of the negative electrode tab 12. This prevents the current collector from breaking due to thickness collapse transmission at the current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector current collector 75 contacted by the terminating end of the negative electrode tab 76.

[0118] 7. In the outermost two rings of the electrode assembly, the relative positions of the termination ends of the negative electrode tab 12, the negative electrode protective tape 11, the first diaphragm 5, the second elastic tape 15, and the first elastic tape 14, arranged radially from the outside in, are designed as a transitional structure that tapers sequentially in the circumferential direction. Furthermore, the substrates of the negative electrode protective tape 11, the second elastic tape 15, and the first elastic tape 14 are all elastic polymers. Under the combined effect of the above design, as the negative electrode tab 12, negative electrode protective tape 11, first diaphragm 5, second elastic tape 15, and first elastic tape 14 are successively finished, the stress impact of the five-layer thickness difference on the corresponding negative electrode current collector part on the radial inner side is dispersed and does not accumulate. This can effectively prevent current collector breakage at multiple locations in this area (these multiple locations specifically include: the negative electrode current collector 77 at the radial inner side where the end of the negative electrode protective tape is closest, the negative electrode current collector 78 at the radial inner side where the end of the second elastic tape is closest, and the negative electrode current collector 79 to which the end of the first elastic tape is attached).

[0119] Therefore, in summary, because the thickness of each component in the same layer of the outermost two turns of the battery electrode assembly in the present invention is relatively uniform, and there is internal support in the radial direction, and stress dispersion measures at the end are also provided, the thickness collapse transmission and accumulation will not occur, resulting in less unbalanced stress generated during battery charging and discharging, thereby avoiding the problem of current collector breakage at multiple preset positions of the negative electrode current collector and preventing further battery failure.

[0120] Among them, the aforementioned negative electrode current collector has multiple preset locations, see [reference needed]. Figure 4 As shown, specifically including: 71, where the termination end of the positive electrode sheet is radially inward and closest to the negative electrode sheet current collector; 72, where the termination end of the outer active material layer of the negative electrode sheet is attached to the negative electrode sheet current collector; 73, where the termination end of the positive electrode sheet is radially outward and closest to the negative electrode sheet current collector; 74, where the termination end of the inner active material layer of the negative electrode sheet is attached to the negative electrode sheet current collector; 75, where the starting end of the negative electrode tab contacts the negative electrode sheet current collector; 76, where the termination end of the negative electrode tab contacts the negative electrode sheet current collector; 77, where the termination end of the negative electrode protective tape is radially inward and closest to the negative electrode sheet current collector; 78, where the termination end of the second elastic tape is radially inward and closest to the negative electrode sheet current collector; and 79, where the termination end of the first elastic tape is attached to the negative electrode sheet current collector.

[0121] See Figures 2 to 6 The present invention provides a wound cylindrical battery electrode assembly, which includes an electrode assembly body 1;

[0122] The electrode assembly body 1 is prepared by the battery electrode assembly preparation method described above;

[0123] The main body 1 of the electrode assembly is housed in a cylindrical, hollow battery casing 4 (specifically a steel casing);

[0124] The center of the electrode assembly body 1 is provided with a vertically penetrating central hole 2.

[0125] In summary, compared with the prior art, the method for preparing a wound cylindrical battery electrode assembly and the battery electrode assembly provided by this invention are scientifically designed. They can balance the thickness differences of various components within the same layer of the outer ring of the electrode assembly, avoid the transmission and accumulation of thickness collapse, thereby effectively reducing the radial unbalanced stress caused by the expansion or contraction of the electrode sheet, preventing battery failure caused by the breakage of the current collector of the electrode sheet, significantly improving the overall safety performance of the wound cylindrical lithium-ion battery, and helping to improve the market application prospects of battery manufacturers' products. It has significant practical significance for production.

[0126] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a wound cylindrical battery electrode assembly, characterized in that, Includes the following steps: Step S1: Align one end of the long strip first diaphragm (5) and the second diaphragm (9) as their common starting end, attach them to the cylindrical winding needle of the battery electrode winding machine, and then rotate them around the cylindrical winding needle twice; wherein, the second diaphragm (9) is located on the radial outer side of the first diaphragm (5). Step S2, insert the starting end of the long strip negative electrode into the gap between the other end of the first diaphragm (5) and the other end of the second diaphragm (9), and insert it to the bottom. The negative electrode includes a negative electrode current collector (7), and the inner and outer sides of the negative electrode current collector (7) are coated with a negative inner active material layer (6) and a negative outer active material layer (8), respectively. Then, in the circumferential direction, the starting end of the negative electrode outer active material layer (8) on the negative electrode sheet is wound into the space between the first diaphragm (5) and the second diaphragm (9) for a predetermined length, and then the winding is stopped; Step S3: Insert the starting end of the positive electrode sheet (10) into the radial inner side of the first separator 5, and then continue to wind them together until a cylindrical battery electrode assembly is formed. Step S4: For the cylindrical battery electrode assembly obtained in step S3, attach termination tape (13) to the winding termination end of the battery electrode assembly to fix the shape of the battery electrode assembly and prevent the battery electrode assembly from spreading out. Step S5: Remove the cylindrical winding needle from the battery electrode winding machine, thereby leaving a cylindrical cavity in the core of the battery electrode that matches the shape and size of the cylindrical winding needle, and finally obtain the battery electrode after the winding operation is completed. In step S4, the terminating tape (13) crosses the terminating end of the outermost second separator (9) in the circumferential direction, and simultaneously adheres to the outermost second separator (9) and the second separator (9) of the battery electrode assembly; The starting end of the termination tape (13) is more inward in the circumferential direction than the starting end of the third elastic tape (16); The terminating end of the terminating tape (13) is more than 5 mm further outward in the circumferential direction than the terminating end of the first elastic tape (14). The length of the termination tape (13) is greater than one-quarter of the circumference and less than one full circumference; The perimeter is calculated by taking the radial vertical distance from the starting end of the terminating tape (13) to the center of the battery electrode assembly as the radius; For the cylindrical battery electrode assembly obtained in step S3, the starting end of the first elastic tape (14) is provided at a distance of 0-1 mm from the end of the negative electrode outer active material layer (8) of the negative electrode sheet of the secondary outer ring of the battery electrode assembly. The first elastic tape (14) is attached to the radial outer surface of the negative electrode current collector (7) of the secondary outer ring of the battery electrode assembly; The thickness of the first elastic tape (14) is the same as the thickness of the outer active material layer (8) of the negative electrode current collector (7); For the cylindrical battery electrode assembly obtained in step S (3), the starting end of the second elastic tape (15) is provided at a predetermined distance on the outer side of the circumferential direction of the terminating end of the positive electrode sheet (10). The second elastic tape (15) is attached to the radial outer surface of the second separator (9) of the battery electrode assembly; The thickness of the second elastic tape (15) is the same as the thickness of the positive electrode sheet (10); The three layers—the outermost layer of the negative electrode active material (8), the second elastic tape (15), and the innermost layer of the negative electrode active material (6) located in the outermost ring of the battery electrode assembly—are sequentially overlapped in the radial direction. For the cylindrical battery electrode assembly obtained in step S3, a third elastic tape (16) is provided at a predetermined distance inside the circumference of the negative electrode tab (12). The third elastic tape (16) is attached to the radial outer surface of the negative electrode current collector (7) of the outermost ring of the battery electrode assembly; The termination position of the third elastic tape (16) is further outward in the circumferential direction relative to the starting position of the negative electrode protective tape (11). The thickness of the third elastic tape (16) is the same as the thickness of the negative electrode tab (12); The thickness of the negative electrode protective tape (11) is the same as the thickness of the negative electrode inner active material layer (6); The length of the third elastic tape (16) is greater than one-sixteenth of the circumference and less than one-eighth of the circumference, which is calculated by taking the radial vertical distance from the end of the third elastic tape (16) to the center of the battery electrode assembly as the radius.

2. The method for preparing the wound cylindrical battery electrode assembly as described in claim 1, characterized in that, In step S3, the overall length of both the first diaphragm (5) and the second diaphragm (9) is greater than the overall length of the negative electrode sheet; The overall length of the negative electrode is greater than that of the positive electrode (10), so that in the winding end stage, the positive electrode is first completely wound into the battery electrode assembly, then the negative electrode is completely wound into the battery electrode assembly, and then the first separator (5) and the second separator (9) are completely wound into the battery electrode assembly.

3. The method for preparing the wound cylindrical battery electrode assembly as described in claim 1, characterized in that, In step S2, for the negative electrode, the overall length of the inner active material layer (6) on the negative electrode current collector (7) is greater than the overall length of the outer active material layer (8). At the starting end of the negative electrode, the starting ends of the inner active material layer (6) of the negative electrode and the starting ends of the outer active material layer (8) of the negative electrode are aligned.

4. The method for preparing the wound cylindrical battery electrode assembly as described in claim 1, characterized in that, After the negative electrode sheet completes the last turn of winding along with the positive electrode sheet (10), the first separator (5), and the second separator (9), for the cylindrical battery electrode assembly obtained in step S3, the inner active material layer (6) on the negative electrode sheet current collector (7) is required to be wound one more turn than the outer active material layer (8), and the termination end of the inner active material layer (6) on the negative electrode sheet current collector (7) located on the outermost ring of the battery electrode assembly is aligned radially with the termination end of the outer active material layer (8) on the second outermost ring of the battery electrode assembly, that is, they are in the same position in the circumferential direction.

5. The method for preparing the wound cylindrical battery electrode assembly as described in claim 1, characterized in that, In step S3, for the cylindrical battery electrode assembly obtained in step S3, the termination end of the inner active material layer (6) of the outermost ring of the battery electrode assembly and the termination end of the outer active material layer (8) of the negative electrode assembly are both further outward by a predetermined length in the circumferential direction than the termination end of the positive electrode sheet (10). That is, the inner active material layer (6) of the outermost ring of the battery electrode assembly and the outer active material layer (8) of the negative electrode assembly together complete the double coating of the last ring of the positive electrode sheet (10).

6. The method for preparing the wound cylindrical battery electrode assembly as described in claim 1, characterized in that, In step S3, for the cylindrical battery electrode assembly obtained in step S3, the winding termination end of the negative electrode sheet is outside the termination end of the inner active material layer (6) of the negative electrode sheet, leaving a predetermined length of uncoated negative electrode sheet current collector (7). The radial outer side of the uncoated negative electrode current collector (7) is welded with a negative electrode tab (12). On the radial inner side of the uncoated negative electrode current collector (7), at the position corresponding to the negative electrode tab (12), a negative electrode protective tape (11) is pasted. The starting end of the negative electrode protective tape (11) is further inward in the circumferential direction than the starting end of the negative electrode tab (12); The terminating end of the negative electrode protective tape (11) is further outward in the circumferential direction than the terminating end of the negative electrode lug (12); The distance between the starting end of the negative electrode protective tape (11) and the ending end of the negative electrode inner active material layer (6) located on the outermost ring of the battery electrode assembly is a preset length. The termination end of the negative electrode protective tape (11) is further inward in the circumferential direction than the termination end of the negative electrode current collector (7).

7. The method for preparing a wound cylindrical battery electrode assembly as described in claim 1, characterized in that, The positive electrode plate (10) is welded to one or two positive electrode tabs (3); The positive electrode tab (3) is located at the starting end of the winding of the positive electrode sheet (10), or at a position within a preset length distance from the starting end of the positive electrode sheet; In step S(3), for the cylindrical battery electrode assembly obtained in step S(3), the terminating ends of the first separator (5) and the second separator (9) located on the outermost ring of the battery electrode assembly are aligned radially, that is, they are in the same position in the circumferential direction. The termination ends of the first separator (5) and the second separator (9) located on the outermost ring of the battery electrode assembly are further outward by a predetermined length than the termination end of the negative electrode current collector (7).

8. A wound cylindrical battery electrode assembly, characterized in that, Including the main body of the pole group (1); The electrode assembly body (1) is prepared by the battery electrode assembly preparation method as described in any one of claims 1 to 7; The main body of the electrode assembly (1) is housed in a cylindrical, hollow battery casing (4).

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