Cylindrical battery

Abstract

The cylindrical battery comprises a metal shell, a roll core and a coating structure, and the roll core is provided with a first end, a second end and a side face located between the first end and the second end in the axial direction; the tail end of the negative plate is provided with an outer negative tab, and the outer negative tab protrudes out of the second end; the outermost layer of the roll core is a blank copper foil of the negative plate; the coating structure comprises an expansion adhesive tape arranged outside the side surface, and the expansion adhesive tape is adhered to the blank copper foil; the expansion adhesive tape is in direct contact with the metal shell; the side surface is divided into a wrapping area and an exposure area by an expansion adhesive tape; the exposed area is arranged close to the first end; the ending end of the blank copper foil is positioned in the wrapping area when being overlooked along the central axis of the roll core; the outer negative tab is subjected to centrosymmetric projection around the circle center of the roll core to obtain an outer negative tab projection, and the outer negative tab projection is located in the exposed area. The cylindrical battery can solve the problem of abnormal self-discharge of the battery caused by electrochemical corrosion of the steel shell and dissolution and deposition of metal ions due to the fact that the termination adhesive tape completely covers the side surface of the roll core.

Description

Technical Field

[0001] This specification relates to the field of battery technology, and in particular to a cylindrical battery. Background Technology

[0002] The internal structural design of cylindrical lithium-ion batteries has a critical impact on battery performance and safety. During battery manufacturing, termination tape, as a key component for cell insulation protection, is mainly used for insulating and fixing the end points of the core electrode sheets or separator, preventing core loosening and safety issues during subsequent use. In existing technologies, the termination tape is typically applied for a long length, almost completely covering the outermost surface of the core, to ensure the stability of the core structure and the safety and reliability of the cell during subsequent use.

[0003] Currently, the industry standard for applying termination tape typically uses a long tape to almost completely wrap the negative electrode end foil area or the end separator, aiming for a stronger fixation and ensuring the structural stability of the core. However, this design has a significant drawback: the termination tape almost completely covers the core surface, causing the core to tilt towards the opposite side of the external negative electrode tab. This results in a larger contact area between the top of the core and the steel casing, where electrolyte tends to accumulate. Residual electrolyte cannot effectively diffuse to other areas, and over time, it gradually oxidizes during battery operation, leading to corrosion of the steel casing. The resulting transition metal ions (such as Fe and Ni) diffuse into the core, depositing on the negative electrode surface and forming internal micro-short circuits. This ultimately causes self-discharge, accelerated capacity decay, and severely impacts the battery's calendar life and safety.

[0004] In existing technologies, battery manufacturers have attempted to improve this problem by adjusting the electrolyte formulation or changing the adhesive formulation of the termination tape, but neither approach has fundamentally solved the issue of residual electrolyte acidification. On the one hand, adjusting the electrolyte formulation increases the risk of other performance issues not being met, affecting the overall battery performance; on the other hand, while improving the adhesive formulation can enhance electrolyte resistance, it cannot solve the problem of electrolyte residue at the steel casing location on the side of the core opposite the outer negative electrode tab. Furthermore, in existing processes, the excessively long length of the termination tape reduces the efficiency of automated application, increasing production costs. Therefore, effectively solving the problem of residual electrolyte acidification while ensuring the stability of the core structure has become a pressing technical challenge in the manufacturing of cylindrical lithium-ion batteries. Summary of the Invention

[0005] Through long-term research and practice, the inventors of this application have discovered a hidden but highly detrimental defect in the traditional adhesive application method: it easily induces corrosion of the steel casing and dissolution of transition metals, leading to abnormal self-discharge of the battery and severely affecting its long-term reliability and storage life. Specifically, the root cause and mechanism of this problem are as follows: 1. Electrolyte Residue and Acidification: During the electrolyte filling process, trace amounts of electrolyte may remain in the tiny gaps between the termination tape and the negative electrode sheet, and between the inner wall of the steel casing. During long-term storage or in high-temperature environments, these residual electrolytes may undergo slow hydrolysis or react with trace impurities, causing a localized decrease in pH and creating an acidic microenvironment. 2. Induction of corrosion: The side of the core tip opposite the outer negative electrode tab will form a large contact area with the steel shell, making it more difficult for the electrolyte to diffuse to other areas. The acidified electrolyte directly corrodes the inner wall of the steel shell (usually a pre-nickel-plated steel shell) in contact with it. 3. Dissolution and Deposition of Metal Ions: Metal elements (Fe, Ni, etc.) present in microscopic defects on the surface of the pre-plated nickel steel shell exhibit decreased chemical stability in an acidic environment, leading to metal dissolution and the formation of metal ions. These dissolved metal ions migrate through the separator and undergo reduction reactions on the negative electrode surface, forming elemental metal deposits. These deposits can puncture the separator, causing microscopic short circuits and creating channels for abnormal self-discharge, manifesting as a continuous decrease in battery voltage or capacity decay.

[0006] Previous technicians did not fully recognize the connection between the application method of the termination tape and the aforementioned corrosion-deposition-self-discharge chain reaction. They focused on the adhesive strength and mechanical function of the tape to prevent loosening, neglecting its negative electrochemical effects. Attempts to solve the self-discharge problem typically focused on improving electrolyte purity, the corrosion resistance of the steel shell, or improving diaphragm performance; these solutions were either costly or complex.

[0007] Therefore, there is an urgent need for a simple, efficient solution that can fundamentally block this corrosion path without significantly increasing costs, starting with the core structure design.

[0008] In view of the shortcomings of the prior art, one object of this specification is to provide a cylindrical battery that aims to solve the problem of abnormal self-discharge of the battery caused by the electrochemical corrosion of the steel shell and the dissolution and deposition of metal ions due to the complete coverage of the side of the core by the termination tape.

[0009] To achieve the above objectives, this specification provides a cylindrical battery comprising a metal casing, a core, and a covering structure. The core is formed by winding a positive electrode sheet, a separator, and a negative electrode sheet. The core has a first end and a second end along its axial direction, and a side surface located between the first end and the second end. The negative electrode sheet has an external negative electrode tab at its terminal end, and the external negative electrode tab protrudes from the second end. The outermost layer of the core is a blank copper foil of the negative electrode sheet. The covering structure includes an expansion tape disposed outside the side surface, the expansion tape being adhered to the blank copper foil. The expansion tape is in direct contact with the metal casing. The side surface is divided into a wrapped area and an exposed area by the expansion tape. The wrapped area is wrapped by the expansion tape. The exposed area is not wrapped by the expansion tape and is located close to the first end. Viewed from above along the central axis of the core, the terminal end of the blank copper foil is located within the wrapped area. The external negative electrode tab is projected symmetrically about the center of the core, and the projection of the external negative electrode tab is located within the exposed area.

[0010] In a preferred embodiment, the axial length of the exposed area is equal to the axial length of the expansion tape, the expansion tape is C-shaped, and the expansion tape has opposite beginning and end points in the circumferential direction.

[0011] In a preferred embodiment, the central angle corresponding to the line connecting the first end and the tail end is the first included angle, and the range of the first included angle is 30°~120°.

[0012] In a preferred embodiment, the first included angle is in the range of 45° to 100°.

[0013] In a preferred embodiment, the distance between the center point of the projection of the outer negative electrode ear and the first end is greater than 2.5 mm, and the distance between the center point of the projection of the outer negative electrode ear and the tail end is greater than 2.5 mm; Alternatively, the central angle corresponding to the line connecting the center point of the projection of the outer negative electrode ear to the first end is the second included angle, and the central angle corresponding to the line connecting the center point of the projection of the outer negative electrode ear to the tail end is the third included angle, both the second included angle and the third included angle being greater than 15°.

[0014] In a preferred embodiment, the axial length of the exposed area is less than the axial length of the expanding tape, and the exposed area is formed by a notch in the expanding tape.

[0015] In a preferred embodiment, the bottom of the exposed area is adjacent to the concave edge of the expansion tape; the concave edge of the expansion tape does not exceed the upper edge of the blank copper foil after absorbing liquid and expanding.

[0016] In a preferred embodiment, the distance between the concave edge of the expanded tape after absorbing liquid and the first end is at least 2 mm.

[0017] In a preferred embodiment, the side of the exposed area is adjacent to the expanding tape to form opposing beginning and end points, and the central angle corresponding to the line connecting the beginning and end points is a first included angle, which ranges from 30° to 120°; preferably, the first included angle ranges from 45° to 100°.

[0018] In a preferred embodiment, the distance between the center point of the projection of the outer negative electrode ear and the first end is greater than 2.5 mm, and the distance between the center point of the projection of the outer negative electrode ear and the tail end is greater than 2.5 mm; Alternatively, the central angle corresponding to the line connecting the center point of the projection of the outer negative electrode ear to the first end is the second included angle, and the central angle corresponding to the line connecting the center point of the projection of the outer negative electrode ear to the tail end is the third included angle, both the second included angle and the third included angle being greater than 15°. Beneficial effects

[0019] The cylindrical battery provided in this embodiment aims to solve the problem of abnormal self-discharge caused by electrochemical corrosion of the steel casing and leaching and deposition of metal ions due to the complete coverage of the core side by the terminating tape. Compared with the prior art, this application optimizes the placement of the expansion tape, resulting in an exposed area on the core side not covered by the expansion tape, and the projection of the external negative electrode tab is located within the exposed area, achieving the following significant beneficial effects: 1. It fundamentally eliminates key corrosion points, improving the long-term reliability of the battery.

[0020] By precisely controlling the length, width, and position of the expansion tape, an exposed area not covered by the expansion tape is ensured on the side of the core, with the projection of the external negative electrode tab located within this exposed area. This breaks the closed, acidic microenvironment created by complete tape coverage in traditional structures. This improvement effectively prevents the accumulation and acidification of residual electrolyte in this area, thus completely eliminating the root cause of electrochemical corrosion of the steel casing induced by electrolyte acidification. Under long-term storage or high-temperature environments, the battery's internal state is more stable, fundamentally guaranteeing its reliability and lifespan.

[0021] 2. Significantly inhibits the dissolution and deposition of transition metals, greatly reducing the abnormal self-discharge rate of the battery.

[0022] By blocking the corrosion reaction, transition metal ions (such as Fe and Ni) in the steel shell and its coating lose the conditions for dissolution in a localized acidic environment. Therefore, it fundamentally prevents dissolved metal ions from being reduced and deposited on the negative electrode surface, thus avoiding the formation of microscopic internal short circuits. Experimental data show that batteries using the core-wrapped structure provided in this application exhibit significantly improved self-discharge rates after storage at both room and high temperatures, enhanced charge retention, effectively curbed abnormal self-discharge phenomena, and a substantial increase in product consistency and yield.

[0023] 3. Battery performance was optimized without increasing cost or complexity.

[0024] The technical solution presented in this application only requires precise control of the parameters of the existing winding and adhesive application process (such as the adhesive application length and position), without introducing new expensive materials or complex production equipment, nor requiring any modification to the core chemical system of the battery. This is a "low-cost, high-return" solution that is easily scaled up on existing production lines and has extremely high commercial promotion value.

[0025] 4. It perfectly balances structural safety and electrochemical stability.

[0026] This application, while altering the length / width of the expansion tape, ensures through process control that the end of the core remains effectively secured, meeting the mechanical design requirements to prevent core loosening. This application successfully strikes the optimal balance between "mechanical fixation" and "electrochemical inertness," maximizing electrochemical stability without sacrificing battery structural safety.

[0027] In summary, this application solves a long-standing but neglected technical problem in the field of cylindrical batteries with an extremely ingenious design concept. The battery products produced have lower self-discharge rate, longer storage life and higher reliability, and their overall performance is superior to batteries produced by traditional processes.

[0028] Specific embodiments of the present invention are disclosed in detail with reference to the following description and accompanying drawings, indicating how the principles of the invention can be employed. It should be understood that the embodiments of the present invention are not limited in scope as a result.

[0029] Features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0030] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, whole, step, or component, but does not exclude the presence or addition of one or more other features, wholes, steps, or components. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A perspective view of a cylindrical battery in the prior art; Figure 2 for Figure 1 A schematic diagram of the structure of the core in the winding; Figure 3 for Figure 1 A schematic diagram of a local structure in the image; Figure 4 This is a schematic diagram of steel shell corrosion in the prior art; Figure 5 This is a schematic diagram of the structure of a cylindrical battery provided in this embodiment; Figure 6 This is a schematic diagram of the covering structure provided in this embodiment; Figure 7 for Figure 6 A structural diagram from another perspective; Figure 8 for Figure 6 A schematic diagram of the cross-section of the core; Figure 9 for Figure 6 A partial structural diagram of the core after it has been inserted into the steel shell; Figure 10 This is a schematic diagram of another covering structure provided in this embodiment; Figure 11 for Figure 10 A structural diagram from another perspective; Figure 12 for Figure 10 A partial structural diagram of the core after it has been inserted into the steel shell; Figure 13 This is a schematic diagram of the structure of a core after it has been unfolded, as provided in the implementation method.

[0033] Explanation of reference numerals in the attached figures: 1' Core; 11' Positive electrode sheet; 12' Negative electrode sheet; 13' Separator; 14' External negative electrode tab; 2' Adhesive tape; 3' Steel shell; 31' Support surface; 32' Support point; 4' Contact area; 5' Diffusion path; α, Tilt angle; 10. Cylindrical battery; 1. Core; 11. First end; 12. Second end; 13. Expansion tape; 131. Beginning end; 132. Ending end; 14. Positive electrode sheet; 141. Positive current collector; 142. Positive electrode coating; 143. Positive electrode empty foil area; 144. Positive electrode sheet ending end; 15. Negative electrode sheet; 151. Negative current collector; 152. Negative electrode coating; 153. Negative electrode empty foil area; 154. Negative electrode sheet ending end ; 155, blank copper foil; 16, positive electrode tab; 17, negative electrode tab; 18, side; 181, enclosed area; 182, exposed area; 183, side edge; 184, concave edge; 19, diaphragm; 110, outer negative electrode tab; 112, projection of outer negative electrode tab; 111, center point of projection of outer negative electrode tab; 2, steel shell; 3, cap; α1, first included angle; α2, second included angle; α3, third included angle; X, axial direction. Detailed Implementation

[0034] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0035] It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or may be interposed with another element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or may be interposed with another element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementations.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0037] The inventors discovered through research that, for example Figure 1 and Figure 2As shown, after the core 1' is inserted into the steel shell 3', due to the presence of the outer negative electrode tab 14', the bent outer negative electrode tab 14' located at the bottom of the core 1' will abut against the bottom surface of the steel shell 3'. The bottom surface of the steel shell 3' provides a support surface 31' for the bent outer negative electrode tab 14'. Taking the point where the bent outer negative electrode tab 14' contacts the bottom surface of the steel shell 3' as the support point 32', the core 1' will be slightly tilted (forming an inclination angle α) inside the steel shell 3', so that the side of the core 1' that is close to the positive electrode side and opposite to the outer negative electrode tab 14' will contact the inner wall of the steel shell 3', forming a contact area 4'.

[0038] A partial schematic diagram of the tilted core 1' is shown below. Figure 3 As shown. The core 1' is formed by winding a positive electrode sheet 11', a separator 13', and a negative electrode sheet 12', with the outermost layer of the core 1' being the copper foil of the negative electrode sheet 12'. Within the contact area 4', when the positive electrode side of the copper foil-wrapped core 1' is in close contact with the steel shell 3', electrolyte will locally accumulate at the interface of the contact area 4'. This electrolyte will oxidize during battery use, thus corroding the steel shell 3' (the corroded steel shell is shown in the image). Figure 4 (As shown). If the tape 2' attached to the outermost copper foil is longer than the copper foil in the axial direction, it is easy to overlap with the diaphragm 13' to form a diffusion path 5' for corroding metal, which will cause self-discharge inside the core 1'.

[0039] Based on the inventor's research and practice, this application aims to solve the following interrelated technical problems: 1. Eliminate corrosive environment: Solve the problem of localized acidic microenvironment formed at the interface between the termination tape and the negative electrode / foil and the steel shell due to acidification by residual electrolyte, and block the conditions for electrochemical corrosion to occur; 2. Prevent steel shell corrosion: Solves the problem of acidic electrolyte directly contacting and corroding the inner wall of the battery steel shell, fundamentally eliminating the source of corrosion; 3. Suppress metal deposition: Solve the problem of microscopic internal short circuits caused by the dissolution of metal ions from microscopic defects on the inner surface of the steel shell in an acidic environment and their reduction deposition on the negative electrode surface; 4. Reduce self-discharge: Ultimately solve the problems of high abnormal self-discharge rate, rapid capacity decay, and decreased reliability caused by the above-mentioned chain reaction.

[0040] The present invention aims to achieve the above objectives through a simple, low-cost improvement scheme that does not require changes to the core material system, thereby significantly improving the long-term storage reliability and service life of cylindrical lithium-ion batteries without affecting the stability of the core structure and the manufacturing process.

[0041] Please see Figures 5 to 13This application provides a cylindrical battery 10, including a metal casing, a winding core 1, and a covering structure. The metal casing is preferably a steel casing 2. The winding core 1 is disposed within the steel casing 2. The winding core 1 has a first end 11 and a second end 12 along the axial direction X, and a side surface 18 located between the first end 11 and the second end 12. Figure 5 As shown, the cylindrical battery 10 may further include a cap 3, which is located at the first end 11 of the winding core 1. It should be noted that the steel casing 2 and cap 3 of the cylindrical battery provided in this embodiment can be any suitable existing structure. To clearly and concisely illustrate the technical solution provided in this embodiment, the above-mentioned parts will not be repeated here, and the accompanying drawings have also been simplified accordingly. However, it should be understood that this embodiment is not limited in scope as a result.

[0042] This application does not limit the size of the winding core 1. Preferably, the winding core 1 of an 18650 or 21700 type cylindrical battery 10 can be used, and the axial length (i.e., height) of the winding core 1 can be 61mm (taking an 18650 type battery as an example). Figure 13 As shown, the core 1 is formed by winding a positive electrode sheet 14, a separator 19, and a negative electrode sheet 15. The positive electrode sheet 14 includes a positive current collector 141 (e.g., aluminum foil), a positive electrode coating 142, and a positive electrode empty foil area 143. The positive electrode coating 142 is coated on the surface of the positive current collector 141 (including...). Figure 13 The upper and lower surfaces of the positive current collector 141. The positive electrode empty foil region 143 is the area on the surface of the positive current collector 141 that is not coated with the positive electrode coating 142. A separate positive electrode tab 16 is provided on the positive electrode empty foil region 143. The separate positive electrode tab 16 extends from the first end 11 of the positive electrode sheet 14. The negative electrode sheet 15 includes a negative electrode current collector 151 (e.g., copper foil), a negative electrode coating 152, and a negative electrode empty foil region 153. The negative electrode coating 152 is coated on the surface of the negative electrode current collector 151 (including...). Figure 13 The upper and lower surfaces of the negative electrode current collector 151. The negative electrode empty foil area 153 is the area on the surface of the negative electrode current collector 151 that is not coated with the negative electrode coating 152. Two separate negative electrode tabs 17 are provided on the negative electrode empty foil area 153 (of which the negative electrode tab 17 near the end is the outer negative electrode tab 110, that is, the end of the negative electrode sheet 15 is provided with the outer negative electrode tab 110, and the outer negative electrode tab 110 protrudes from the second end 12). The separate negative electrode tabs 17 extend from the second end 12 of the negative electrode sheet 15. The outermost layer of the core 1 is the blank copper foil 155 of the negative electrode sheet 15.

[0043] like Figure 6 , Figure 7 , Figure 10 and Figure 11As shown, the covering structure includes an expansion tape 13 disposed on the outside of the side 18. The expansion tape 13 adheres to the blank copper foil 155 and can fix and insulate the core 1. The expansion tape 13 is in direct contact with the metal casing. The side 18 is divided into a wrapped area 181 and an exposed area 182 by the expansion tape 13. The wrapped area 181 is wrapped by the expansion tape 13. The exposed area 182 is not wrapped by the expansion tape 13 and is located near the first end 11. Figure 8 As shown, viewed from above along the central axis of the core 1, the end 154 of the blank copper foil 155 is located within the wrapping area 181; the outer negative electrode tab 110 is projected symmetrically with the center of the core 1 to obtain the outer negative electrode tab projection 112, which is located within the exposed area 182.

[0044] The structure described in this application is universally applicable to 18650 and 21700 type cylindrical batteries, such as Figure 8 and Figure 9 As shown, since the expansion tape 13 attached to the outermost blank copper foil 155 forms an exposed area 182 on the side, and the projection 112 of the outer negative electrode is located within the exposed area 182, the exposed area 182 is isolated from the inner wall of the steel shell 2, so the diffusion path 5' of the electrolyte no longer exists. Therefore, it can effectively block the diffusion path 5' of corroded metal and reduce the probability of self-discharge.

[0045] The cylindrical battery 10 provided in this embodiment aims to solve the problem of electrochemical corrosion and metal ion dissolution and deposition in the steel shell 2 caused by the complete coverage of the core side by the termination tape, ultimately leading to abnormal self-discharge of the battery. Compared with the prior art, this application optimizes the placement of the expansion tape 13, so that there is an exposed area 182 on the side 18 of the core 1 that is not covered by the expansion tape 13, and the projection 112 of the outer negative electrode is located within the exposed area 182. This invention creatively constructs an "isolation area" (i.e., exposed area 182) on the side opposite to the outer negative electrode 110. This area, through physical isolation, isolates the contact between the expansion tape 13 and the negative electrode sheet 15 / foil and the steel shell 2, making it difficult for any trace electrolyte that may remain here to accumulate over a long period of time and form a high-concentration acidic microenvironment. Even with trace amounts of electrolyte present, it can diffuse within the isolation area, preventing a sharp drop in local pH and fundamentally breaking the chain reaction path of "electrolyte acidification → steel shell corrosion → metal dissolution → negative electrode deposition → internal short circuit". This invention significantly improves the long-term storage reliability and electrochemical stability of batteries in an extremely simple and low-cost manner, effectively reducing the abnormal self-discharge rate.

[0046] In this embodiment, the expansion tape 13 expands after absorbing the electrolyte, filling the residual space between the core 1 and the steel shell 2. Under vibration, it provides an effective buffer for the internal core 1, thereby protecting the internal structure of the cylindrical battery 10 from damage. Ordinary termination tape does not have this function.

[0047] In one embodiment, the expansion rate of the expanding tape 13 is 10% to 25%. As a preferred embodiment, the expansion rate of the expanding tape 13 is 13%. In this application, we consider the length / width of the expanded tape 13 after expansion (where length refers to the circumferential length of the expanding tape 13, and width refers to the axial length of the expanding tape 13 in the X direction). Because the expansion rate can have different ranges depending on the material of the expanding tape 13, this application selects 13% as an example.

[0048] Since the end 144 of the positive electrode 14 and the outer negative electrode tab 110 are roughly opposite to each other about the center of the core 1, the end 144 of the positive electrode 14 is located in the exposed area 182 at the corresponding position on the side 18. In this embodiment, the side 18 of the core 1 is the outermost negative electrode 15. The end 154 of the outermost negative electrode 15 is provided with a blank copper foil 155, and the expansion tape 13 covers the end 154 of the blank copper foil 155 (that is, the end 154 of the negative electrode 15), thereby ensuring that the core 1 has sufficient structural strength so that the core 1 can pass the roller test.

[0049] In one embodiment, such as Figures 6 to 9 As shown, the axial X-length of the exposed area 182 is equal to the axial X-length of the expansion tape 13, and the overall shape of the expansion tape 13 is C-shaped. The opening of the C-shaped expansion tape 13 is the exposed area 182, and the expansion tape 13 has a head end 131 and a tail end 132 in the circumferential direction. The head end 131 and the tail end 132 are separate.

[0050] like Figure 8 As shown, the central angle corresponding to the line connecting the first end 131 and the last end 132 is the first included angle α1, which ranges from 30° to 120° (inclusive). The expansion tape 13 only partially wraps around the outer periphery of the core 1, creating an opening in the area of ​​the core 1 not covered by the expansion tape 13 (i.e., the exposed area 182). This opening corresponds to the location of the projection 112 of the outer negative electrode tab, and the central angle corresponding to this opening is the first included angle α1. By reasonably controlling the range of the first included angle α1, the internal chemical stability of the cell can be improved while ensuring that the expansion tape 13 effectively fixes the last end 154 of the negative electrode sheet 15, thereby improving the battery's self-discharge rate and storage life.

[0051] If the first included angle α1 is too large (greater than 120°), the core 1 structure will easily become loose, resulting in the failure of the roller test; if the first included angle α1 is too small (less than 30°), the exposed area 182 (isolation area) formed cannot effectively provide physical isolation, and corrosion of the steel shell 2 will still easily occur. Preferably, the range of the first included angle α1 is 45°~100°.

[0052] Specifically, the circumferential length of the expanding tape 13 is less than the circumferential length of the blank copper foil 155. That is, a portion of the outer blank copper foil 155 is exposed outside the coverage area of ​​the expanding tape 13 (located in the exposed area 182), thus ensuring that the exposed area 182 has sufficient circumferential length for effective physical isolation and to prevent corrosion of the steel shell 2. Preferably, the circumferential length of the expanding tape 13 is less than 54 mm. To ensure the stability of the manufacturing process and the core 1 structure, the adhesive length of the expanding tape 13 is designed to exceed manufacturing capacity and meet mechanical performance requirements.

[0053] like Figure 8 As shown, the outermost negative electrode sheet 15 is provided with an outer negative electrode tab 110, and the expansion tape 13 covers the outer negative electrode tab 110, thereby ensuring that the core 1 has sufficient structural strength. The projection 112 of the outer negative electrode tab on the side 18, which is symmetrical to the center of the outer negative electrode tab 110, is located within the exposed area 182, which can make the exposed area 182 have sufficient circumferential length to avoid corrosion of the steel shell 2.

[0054] Specifically, the distance between the center point 111 of the projection 112 of the outer negative electrode and the first end 131 is greater than 2.5 mm, and the distance between the center point 111 of the projection 112 of the outer negative electrode and the last end 132 is greater than 2.5 mm, to ensure that the exposed area 182 has sufficient circumferential length and to prevent corrosion of the steel shell 2. Alternatively, the central angle corresponding to the line connecting the center point 111 of the projection 112 of the outer negative electrode and the first end 131 is the second included angle α2, and the central angle corresponding to the line connecting the center point 111 of the projection 112 of the outer negative electrode and the last end 132 is the third included angle α3. Both the second included angle α2 and the third included angle α3 are greater than 15°, which is also used to ensure that the exposed area 182 has sufficient circumferential length and to prevent corrosion of the steel shell 2.

[0055] In one embodiment, the distance from the tail end 132 to the outer negative electrode tab 110 (center) is 8.75mm to 16.75mm, and the distance from the head end 131 to the tail end 154 of the blank copper foil 155 is 1mm to 9mm, in order to ensure that the circumferential length of the expansion tape 13 is sufficient to give the core 1 sufficient structural strength.

[0056] Preferably, the circumferential distance between the first end 131 and the last end 132 is 13mm to 15mm, so that the exposed area 182 has sufficient circumferential length to effectively provide physical isolation and prevent corrosion of the steel shell 2. More preferably, the circumferential length of the expansion tape 13 is 39mm to 41mm.

[0057] In another embodiment, such as Figures 10 to 12As shown, the axial X length of the exposed area 182 is less than the axial X length of the expansion tape 13, and the exposed area 182 is formed by a notch in the expansion tape 13. The bottom of the exposed area 182 is adjacent to the concave edge 184 of the expansion tape 13. After the expansion tape 13 absorbs liquid and expands, the concave edge 184 does not exceed the upper edge of the blank copper foil 155.

[0058] Preferably, the distance between the concave edge 184 of the expanded adhesive tape 13 after liquid absorption and the first end 11 is at least 2 mm, which can ensure that the concave edge 184 of the expanded adhesive tape 13 after liquid absorption and expansion does not contact the outermost diaphragm 19. Thus, the expanded adhesive tape 13 attached to the outermost blank copper foil 155 does not exceed the upper edge of the blank copper foil 155 after expansion due to the concave edge 184, thereby blocking the diffusion path 5' of corroded metal and reducing the probability of self-discharge.

[0059] For an expansion rate of 13%, this application selects that the distance between the concave edge 184 of the expanded adhesive tape 13 and the first end 11 is 2 mm or more. For example, using a core 1 with an axial X length of 61 mm, the axial X length from the concave edge 184 to the bottom of the expanded adhesive tape 13 is 50 mm. Here, 50 mm is the length of the expanded adhesive tape 13 before absorbing the electrolyte, i.e., its original width. After the expanded adhesive tape 13 expands by 13% after absorbing the electrolyte, the total axial X length from its concave edge 184 to the bottom of the expanded adhesive tape 13 is 56.5 mm. Furthermore, the distance between the concave edge 184 of the expanded adhesive tape 13 and the first end 11 is 4 mm, and the distance between the bottom of the expanded adhesive tape 13 and the second end 12 is 0.5 mm. As an example, this design can achieve the purpose of this application.

[0060] In this embodiment, the distance between the concave edge 184 of the expanded tape 13 and the first end 11 is at least 2 mm. If the distance is less than 2 mm, it will be difficult to effectively avoid the problem of electrolyte residue, which will weaken the anti-corrosion effect.

[0061] Preferably, the distance between the concave edge 184 of the expanded adhesive tape 13 after absorbing liquid and the first end 11 is at least 3 mm. More preferably, the distance between the concave edge 184 of the expanded adhesive tape 13 after absorbing liquid and the first end 11 is at least 5 mm.

[0062] In a preferred embodiment, the distance between the concave edge 184 of the expanded adhesive tape 13 after liquid absorption and expansion and the first end 11 is at least 10 mm. The greater the distance between the concave edge 184 of the expanded adhesive tape 13 and the first end 11, the smaller the electrolyte residue area formed, providing more space and significantly reducing electrolyte accumulation in the end face area, preventing the formation of electrolyte pathways, and effectively inhibiting corrosion of the steel shell 2. Simultaneously, considering manufacturability, to achieve stable fixation of the expanded adhesive tape 13 to the core 1, a distance of at least 10 mm is preferred.

[0063] In one embodiment, the axial X length from the concave edge 184 of the expanded adhesive tape 13 to the bottom of the expanded adhesive tape 13 after liquid absorption and expansion needs to be greater than the axial X length of the core 1. If this condition is not met, the bonding area between the expanded adhesive tape 13 and the surface of the core 1 may be too small, resulting in insufficient fixing strength of the expanded adhesive tape 13 to the core 1, posing a risk of the core 1 unraveling. At the same time, lithium plating may occur on the surface of the negative electrode sheet 15 after formation without adhesive (without expanded adhesive tape 13). Preferably, the axial X length from the concave edge 184 of the expanded adhesive tape 13 to the bottom of the expanded adhesive tape 13 after liquid absorption and expansion is greater than or equal to 35 mm, or the distance between the concave edge 184 of the expanded adhesive tape 13 and the first end 11 is less than or equal to 35 mm. By reasonably setting the axial X length of the expanded adhesive tape 13 and the distance between the concave edge 184 and the first end 11, the three major requirements of "corrosion prevention", "structural stability" and "performance preservation" can be perfectly balanced.

[0064] This embodiment controls the axial X length of the expanded tape 13 after liquid absorption and the distance between the concave edge 184 and the first end 11 within the aforementioned range. This effectively maintains the structural stability of the core 1, avoiding the risk of lithium plating and failure of roller testing caused by the loose core 1. Simultaneously, it eliminates the main residual area of ​​electrolyte on the end face of the core 1, fundamentally suppressing corrosion of the steel shell 2 caused by electrolyte acidification. This structural design significantly improves the overall safety performance and long-term reliability of the battery.

[0065] In one embodiment, for a core 1 with an axial X length of 61 mm, the distance between the bottom end of the expanded tape 13 after absorbing liquid and the second end 12 is generally 0.5 mm to 3 mm, so that the expanded tape 13 will not interfere or curl when inserted into the shell due to being too close to the edge.

[0066] like Figure 10 and Figure 11 As shown, the side 183 of the exposed area 182 is adjacent to the expanding tape, forming opposing beginning 131 and end 132. (As...) Figure 8 As shown, the central angle corresponding to the line connecting the first end 131 and the last end 132 is the first included angle α1, which ranges from 30° to 120°. Preferably, the first included angle α1 ranges from 45° to 100°.

[0067] Specifically, the distance between the center point 111 of the projection 112 of the outer negative electrode and the first end 131 is greater than 2.5 mm, and the distance between the center point 111 of the projection 112 of the outer negative electrode and the last end 132 is greater than 2.5 mm, to ensure that the exposed area 182 has sufficient circumferential length and to prevent corrosion of the steel shell 2. Alternatively, the central angle corresponding to the line connecting the center point 111 of the projection 112 of the outer negative electrode and the first end 131 is the second included angle α2, and the central angle corresponding to the line connecting the center point 111 of the projection 112 of the outer negative electrode and the last end 132 is the third included angle α3. Both the second included angle α2 and the third included angle α3 are greater than 15°, which is also used to ensure that the exposed area 182 has sufficient circumferential length and to prevent corrosion of the steel shell 2.

[0068] In a specific application scenario, the preparation method of the above-mentioned cylindrical battery 10 includes the following steps: Step S1: Provide a positive electrode 14, a separator 19 and a negative electrode 15, and wind them to form a core 1; Step S2: Apply expansion tape 13 to the outer periphery of core 1; Step S3: Insert the fixed core 1 into the steel shell 2; Step S4: Perform subsequent processes such as liquid injection, sealing, and chemical formation.

[0069] In step 2, the expansion tape 13 applied to the outermost blank copper foil 155 forms an exposed area 182 on the side 18, and the projection 112 of the outer negative electrode tab is located within the exposed area 182, thereby forming an area inside the battery that is isolated from the inner wall of the steel casing 2. The tape application step (i.e., step S2 above) can be completed by a high-precision CCD positioning and application device to ensure the accuracy and consistency of the application position of the expansion tape 13.

[0070] In summary, given the problems of electrolyte residue, acidification, and subsequent corrosion of the inner surface of the steel shell 2 caused by the use of wide termination tape at the end / outer ring of the cylindrical lithium-ion battery core 1 in the prior art, this application provides a novel battery design solution. This solution aims to fundamentally eliminate the residual electrolyte space through a simple, reliable, and low-cost structural optimization, while ensuring that the original structural fixing strength of the core 1 is not affected, thereby significantly improving the long-term reliability and service life of the battery.

[0071] To verify the technical effect of the cylindrical battery 10 provided in this application, this application provides the following four embodiments and four comparative examples. All the following embodiments and comparative examples use 18650 type cells for demonstration, and the height of the core 1 (i.e., the axial length of the core 1) is 61 mm. Example

[0072] The positive electrode 14, the separator 19, and the negative electrode 15 are wound in a preset order to form a core 1 with a blank copper foil 155 at the end. At the end position of the core 1, an expansion tape 13 is attached along the winding direction, and its attachment area is set to cover the end 154 of the blank copper foil 155, while not covering the projection 112 of the outer negative electrode (i.e., the projection 112 of the outer negative electrode is located in the exposed area 182). The central angle corresponding to the line connecting the first end 131 and the last end 132 of the expansion tape 13 is the first included angle α1, which is 30°. Example

[0073] The difference from Example 1 is that the first included angle α1 is 90°. Example

[0074] The difference from Example 1 is that the first included angle α1 is 100°. Example

[0075] The difference from Example 1 is that the first included angle α1 is 120°.

[0076] Comparative Example 1: Compared to Example 3, the only difference is that the expanding tape 13 is replaced with ordinary tape. Ordinary tape in this application refers to tape that does not expand significantly upon contact with the electrolyte, or has an expansion rate of less than 5%.

[0077] Comparative Example 2: The only difference compared to Example 3 is that the expansion tape 13 does not cover the end 154 of the negative electrode 15.

[0078] Comparative Example 3: The only difference compared to Example 3 is that the first included angle α1 is 200°.

[0079] Comparative Example 4: Compared with Example 3, the difference is that the first included angle α1 is 0° and the position of the expansion tape 13 covers the projection 112 of the outer negative electrode ear.

[0080] To more clearly illustrate the advantages of this application, some key experimental data from Examples 1-4 and Comparative Examples 1-4 are summarized in Table 1 below: Table 1 Is it expansion tape? The first included angle α1 in degrees (°) Is the end of the negative electrode covered? Is core 1 stable? Did the drum test pass? Is there any corrosion on the steel shell 2? Example 1 yes 30 yes yes yes none Example 2 yes 90 yes yes yes none Example 3 yes 100 yes yes yes none Example 4 yes 120 yes yes yes none Comparative Example 1 no 100 yes yes no none Comparative Example 2 yes 100 no no / / Comparative Example 3 yes 200 yes no no none Comparative Example 4 yes 0 (Full Post) yes yes yes have In Table 1, for each battery of Examples 1-4 and Comparative Examples 1-4, a drum test was conducted under the following conditions: the batteries were fully charged in the standard manner, the fully charged cells were placed in the drum, the rotation speed was 66±2 RPM, 6 cells were placed at a time, the test duration was 100 minutes, and the voltage, internal resistance, weight, and cell appearance were recorded at fixed time intervals. The drum test was considered passed if the change in internal resistance was ≤ 1.25 times the internal resistance before the test and the capacity retention rate was ≥ 95% of the initial calibrated capacity; otherwise, it was considered a failure.

[0081] In Table 1, " / " indicates that core 1 of this scheme was not made into a finished battery cell due to considerations such as the stability and safety of core 1.

[0082] As shown in Table 1, the test results show that in Examples 1 to 4, which use expansion tape 13 to partially cover the core 1, covering the end 154 of the negative electrode sheet 15 but not the projection 112 of the outer negative electrode ear, the roller test can be passed smoothly, and no corrosion is observed in the steel shell 2.

[0083] Comparing Example 3 with Comparative Example 1, it can be seen that after replacing the expansion tape 13 with ordinary tape (which has no expansion effect), the battery failed the roller test. This is because the expansion tape 13 expands after absorbing the electrolyte, filling the residual space between the core 1 and the steel shell 2, and providing effective cushioning for the internal core 1 under vibration, thereby protecting the internal structure of the battery cell from damage. Ordinary termination tape does not have this function.

[0084] Comparing Example 3 with Comparative Example 2, it can be seen that if the expansion tape 13 does not cover the end 154 of the negative electrode sheet 15, the core 1 structure will not be firmly fixed, the core 1 will be loose, and the manufacturability of the battery cell cannot be achieved.

[0085] Further comparison of Examples 1-4 with Comparative Examples 3-4 reveals that if the first included angle α1 is too large (Comparative Example 3), it will lead to structural instability and failure of the roller test; if the first included angle α1 is too small (Comparative Example 4), it will easily cause corrosion of the steel shell 2. Therefore, controlling the first included angle α1 within the range of 30° to 120° helps to simultaneously meet the requirements of structural stability and corrosion resistance, and 30° to 120° is the preferred range for the first included angle α1.

[0086] Regarding Comparative Example 4, it represents the existing technology of applying expansion tape entirely, i.e., the traditional adhesive application method, on the attached... Figures 1-4 As demonstrated in the previous paper, the full application of expansion tape will cause the electrolyte to accumulate at the point where the expansion tape 2' contacts the steel shell 3', corroding the steel shell 3'. Furthermore, through the diffusion path 5' formed by the expansion tape 2' and the battery separator 13', metal particles such as Ni ions and Fe ions will diffuse into the interior of the core 1', thereby damaging the positive and negative electrode materials and affecting the lifespan of the battery cell.

[0087] Further comparison of Examples 1-4 with Comparative Example 4 reveals that if the expansion tape 13 completely covers the side 18 of the core 1, it will cause corrosion of the steel shell 2. Therefore, it is preferable to set the attachment area of ​​the expansion tape 13 to cover the end 154 of the negative electrode sheet 15, and not to cover the projection 112 of the outer negative electrode tab (i.e., the projection 112 of the outer negative electrode tab is located within the exposed area 182), so as to balance the structural stability of the core 1 and the safety and reliability of the battery cell.

[0088] It should be noted that in the description of this specification, the terms "first," "second," etc., are used only for descriptive purposes and to distinguish similar objects; there is no order between them, nor should they be construed as indicating or implying relative importance. Furthermore, in the description of this specification, unless otherwise stated, "a plurality of" means two or more.

[0089] Any numerical values ​​cited herein include all values ​​ranging from a lower limit to an upper limit, increasing by one unit, with at least two units between any lower and any higher value. For example, if the quantity of a component or the value of a process variable (e.g., temperature, pressure, time, etc.) is described as being from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, the purpose is to illustrate that values ​​such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 are also explicitly listed in this specification. For values ​​less than 1, a unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1, etc. These are merely examples intended for explicit expression, and it can be assumed that all possible combinations of values ​​listed between the minimum and maximum values ​​are explicitly described in this specification in a similar manner.

[0090] Unless otherwise stated, all ranges include the endpoints and all numbers between them. The terms "approximately" or "about" used with ranges apply to both endpoints of the range. Thus, "approximately 20 to 30" is intended to cover "approximately 20 to approximately 30," including at least the specified endpoints.

[0091] All articles and references disclosed herein, including patent applications and publications, are incorporated herein by reference for various purposes. The term “substantially constitutes…” used to describe a combination should include the identified elements, components, parts, or steps, as well as other elements, components, parts, or steps that do not substantially affect the essential novelty of the combination. The use of the terms “comprising” or “including” to describe combinations of elements, components, parts, or steps herein also contemplates embodiments substantially constituted by such elements, components, parts, or steps. The use of the term “may” herein is intended to indicate that any described attribute included by “may” is optional.

[0092] Multiple elements, components, parts, or steps can be provided by a single integrated element, component, part, or step. Alternatively, a single integrated element, component, part, or step can be divided into multiple separate elements, components, parts, or steps. The use of "a" or "an" to describe an element, component, part, or step does not imply the exclusion of other elements, components, parts, or steps.

[0093] It should be understood that the above description is for illustrative purposes and not for limitation. Many embodiments and applications beyond the provided examples will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of this teaching should not be determined by reference to the above description, but rather by reference to the appended claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the inventors have not considered that subject matter as part of the disclosed inventive subject matter.

Claims

1. A cylindrical battery, comprising a metal casing, a core, and a covering structure, wherein the core is formed by winding a positive electrode sheet, a separator, and a negative electrode sheet, and the core has a first end and a second end along an axial direction, and a side surface located between the first end and the second end; characterized in that: The negative electrode sheet has an external negative electrode tab at its end, and the external negative electrode tab protrudes from the second end; The outermost layer of the winding core is the blank copper foil of the negative electrode sheet; The covering structure includes an expansion tape disposed on the outside of the side, the expansion tape being adhered to the blank copper foil; the expansion tape is in direct contact with the metal casing; The side is divided into a wrapped area and an exposed area by the expanding tape; the wrapped area is wrapped by the expanding tape; the exposed area is not wrapped by the expanding tape, and the exposed area is located close to the first end; Viewed from above along the central axis of the roll core, the end of the blank copper foil is located within the wrapping area; the outer negative electrode tab is projected symmetrically with respect to the center of the roll core to obtain the projection of the outer negative electrode tab, and the projection of the outer negative electrode tab is located within the exposed area.

2. The cylindrical battery according to claim 1, characterized in that, The axial length of the exposed area is equal to the axial length of the expansion tape. The expansion tape is C-shaped and has opposite beginning and end points in the circumferential direction.

3. The cylindrical battery according to claim 2, characterized in that, The central angle corresponding to the line connecting the first end and the last end is the first included angle, and the range of the first included angle is 30°~120°.

4. The cylindrical battery according to claim 3, characterized in that, The first included angle ranges from 45° to 100°.

5. The cylindrical battery according to claim 2, characterized in that, The distance between the center point of the projection of the outer negative electrode ear and the first end is greater than 2.5mm, and the distance between the center point of the projection of the outer negative electrode ear and the tail end is greater than 2.5mm; Alternatively, the central angle corresponding to the line connecting the center point of the projection of the outer negative electrode ear to the first end is the second included angle, and the central angle corresponding to the line connecting the center point of the projection of the outer negative electrode ear to the tail end is the third included angle, both the second included angle and the third included angle being greater than 15°.

6. The cylindrical battery according to claim 1, characterized in that, The axial length of the exposed area is less than the axial length of the expanding tape, and the exposed area is formed by a notch in the expanding tape.

7. The cylindrical battery according to claim 6, characterized in that, The bottom of the exposed area is adjacent to the concave edge of the expansion tape; the concave edge of the expansion tape does not exceed the upper edge of the blank copper foil after absorbing liquid and expanding.

8. The cylindrical battery according to claim 7, characterized in that, The distance between the concave edge of the expanded tape after absorbing liquid and the first end is at least 2 mm.

9. The cylindrical battery according to claim 6, characterized in that, The side of the exposed area is adjacent to the expanding tape to form opposite beginning and end points. The central angle corresponding to the line connecting the beginning and end points is the first included angle, which ranges from 30° to 120°. Preferably, the first included angle ranges from 45° to 100°.

10. The cylindrical battery according to claim 9, characterized in that, The distance between the center point of the projection of the outer negative electrode ear and the first end is greater than 2.5mm, and the distance between the center point of the projection of the outer negative electrode ear and the tail end is greater than 2.5mm; Alternatively, the central angle corresponding to the line connecting the center point of the projection of the outer negative electrode ear to the first end is the second included angle, and the central angle corresponding to the line connecting the center point of the projection of the outer negative electrode ear to the tail end is the third included angle, both the second included angle and the third included angle being greater than 15°.

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