Cylindrical battery top assembly and cylindrical battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a cylindrical battery top assembly and a cylindrical battery. The top assembly comprises a semi-enclosed cap assembly and a positive current collector, wherein the semi-enclosed cap assembly comprises a top cover, an explosion-proof valve and a current interrupting device, the edge of the explosion-proof valve is provided with a curled edge, the curled edge covers the outer wall of the top cover, and the curled edge is a semi-enclosed structure; the positive current collector comprises a disc surface part, a folded lug part and a root connecting area, the disc surface part is a complete conductive surface with a continuous structure, and a positive lug is connected with the positive current collector through an annular ring welding mark located in the root connecting area and a plurality of groups of wave-shaped welding marks located in the disc surface part. Through the cooperative design of the semi-enclosed cap and the fuseless current collector, the significant release of the top space and the effective reduction of the contact impedance are realized without sacrificing the safety.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a cylindrical battery top assembly and a cylindrical battery. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage technologies, increasingly higher requirements are being placed on the energy density, charge / discharge rate performance, and safety performance of lithium-ion batteries. The battery cap assembly and current collector are crucial components of the battery's internal conductive network and safety protection; their structural design directly affects the overall space utilization and electrical performance of the battery.

[0003] In traditional cylindrical battery top structures, the cap assembly typically employs a fully enclosed design, where the outer edge of the top cover wraps downwards around the upper surface of the casing opening. This results in a significant axial assembly height for the cap assembly. To address this issue, a semi-enclosed cap design has been proposed. This design not only maintains the top cover's coverage after impact, improving sealing performance, but also features a bottom cover plate welded to a safety plate with grooves, forming a current interruption device (CID). This CID can promptly cut off the current when the internal pressure of the battery abnormally increases, providing a crucial safety protection mechanism. However, simply optimizing the cap structure alone cannot solve the high impedance and heat generation challenges faced by modern large cylindrical batteries under super-fast charging conditions, primarily due to limitations in the design of existing current collectors. Existing positive current collectors generally adopt an integrated or separate structure of "plate surface-folding lug-Fuse (fuse)". Although the fuse area can melt to protect the battery in the event of an extreme short circuit, the sudden change in cross-sectional area at the fuse during normal operation and high-rate charging and discharging will cause a significant increase in local resistance, generate additional Joule heat, and limit the overcurrent capacity.

[0004] Specifically, traditional fully enclosed cap assemblies typically require a height of 4.2–4.8 mm. However, the effective conductive cross-sectional area of ​​positive current collectors with fuses is reduced by 20–40% compared to the main body due to the slotted or narrowed design of the fuse, leading to increased temperature rise and limited rate performance. How to compress the top space and reduce contact resistance through structural innovation while ensuring safety, and then feed the freed-up space back to the core to increase capacity, has become a pressing technical problem in this field. Summary of the Invention

[0005] Based on this, this application provides a top component and a cylindrical battery. Through the collaborative design of a semi-enclosed cap and a fuse-free current collector, significant release of top space and effective reduction of contact resistance are achieved without sacrificing safety. The released space can be converted into an increase in battery capacity, which is suitable for the mass production of high-energy-density 21700 cylindrical batteries.

[0006] To achieve the above objectives, this application adopts the following technical solution: This application provides a top assembly for a cylindrical battery, including a semi-enclosed cap assembly and a positive current collector. The semi-enclosed cap assembly includes a top cover, an explosion-proof valve, and a current interruption device. The edge of the explosion-proof valve has a raised edge that covers the outer wall of the top cover, forming a semi-enclosed structure. The positive current collector includes a disk surface, a folded lug, and a root connection area. The disk surface is a structurally continuous and complete conductive surface. The positive electrode lug is connected to the positive current collector through an annular weld mark located in the root connection area and multiple sets of wavy weld marks located in the disk surface. The folded lug is connected to the conductive end of the semi-enclosed cap assembly.

[0007] In one possible implementation, the height reduction rate of the cap assembly is η, where η = (H0 - H1) / H0 × 100%, and η ranges from 10% to 25%. Here, H0 is the maximum occupied height of the full-coverage cap assembly of the same specification along the axial direction of the cylindrical battery in the assembled state, and H1 is the maximum occupied height of the semi-coverage cap assembly along the axial direction of the cylindrical battery in the assembled state. The maximum occupied height is the distance between the highest and lowest points of the corresponding cap assembly along the axial direction.

[0008] In one possible implementation, the maximum occupied height H1 of the semi-enclosed cap assembly along the axial direction of the cylindrical battery in the assembled state ranges from 3.4 to 3.8 mm.

[0009] In one possible implementation, the outer diameter of the positive current collector is 17.5~18.5 mm, the thickness is 0.18~0.22 mm, and the width of the folded ear is 7.5~8.5 mm.

[0010] In one possible implementation, the outer diameter of the annular weld bead is 4.5~5.5 mm.

[0011] In one possible implementation, the wavy solder mark consists of 3 × 4 sets of wavy solder lines, evenly distributed along the circumference, with the length of the wavy solder line being 5~7mm and the width being 0.25~0.35mm.

[0012] In one possible implementation, the effective current cross-sectional area improvement rate is δ, where δ = (A1 - A0) / A0 × 100%, and the range of δ is 15~40%, where A1 is the effective current cross-sectional area of ​​the positive current collector and A0 is the effective current cross-sectional area of ​​the same size current collector with fuse.

[0013] In one possible implementation, the effective cross-sectional area A1 of the positive current collector (120) ranges from 2.2 to 2.8 mm².

[0014] This application also provides a cylindrical battery, including the aforementioned cylindrical battery top assembly.

[0015] In one possible implementation, the cylindrical battery is a 21700 type cylindrical battery.

[0016] Compared with the prior art, this application has the following advantages: First, this application adopts a semi-enclosed cap, and the released physical space is transformed into usable space for active materials inside the cell, thereby achieving an effective improvement in battery energy density without changing the external specifications of the battery; Second, the fuse-free current collector design effectively optimizes the conductive path, significantly reduces the contact impedance between components, and improves the electrochemical performance of the battery; In summary, the synergistic design of the semi-enclosed cap and the fuse-free current collector achieves a significant release of top space and an effective reduction in contact impedance, which can be transformed into an increase in battery capacity. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a partial cross-sectional view of the semi-enclosed cap assembly provided in an embodiment of this application; Figure 2 This is a partial cross-sectional view of a fully enclosed cap assembly in the prior art; Figure 3 This is a schematic diagram of the positive current collector provided in the embodiments of this application; Figure 4 This is a schematic diagram of the structure of the positive current collector with a fuse in the existing technology; Figure 5 This is a schematic diagram of the current density distribution and overcurrent cross-sectional area of ​​the current collector without a fuse provided in the embodiments of this application and the current collector with a fuse in the prior art; Figure 6 This is a performance comparison chart of the battery using the top component of this application and the comparative example in terms of assembly height, internal resistance, capacity, and rate-induced temperature rise.

[0019] Figure label: 110-Semi-enclosed cap assembly, 111-Top cover, 112-Explosion-proof valve, 1121-Warped edge, 113-Current interruption device CID, 114-Sealing ring, 115-Outer G ring, 116-Insulating ring, 210-Full-enclosed cap assembly, 211-Top cover, 212-Explosion-proof valve, 2121-Full-enclosed warped edge, 213-Current interruption device CID, 214-Sealing ring, 215-Outer G ring, 21 6-Insulating ring, 120-Positive current collector, 121-Disc surface, 122-Folded lug, 123-Root connection area, 124-Wave solder mark, 125-Wave solder wire, 126-Annular solder mark, 127-Gas through hole, 128-Center hole, 129-Disc body, 221-Disc body with Fuse positive current collector, 222-Tail body, 223-Groove, 300-Shell, 400-Positive electrode tab. Detailed Implementation

[0020] The technical solutions of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. It should be understood that the specific embodiments described are merely used to explain this application and are not intended to limit this application.

[0021] This application provides a top assembly for a cylindrical battery. Figure 1A partial cross-sectional view of the semi-enclosed cap assembly shows that, from top to bottom, a top cover 111, an explosion-proof valve 112, and a current cut-off device CID 113 are stacked on the top of the opening of the battery housing 300, forming a semi-enclosed cap assembly 110. The edge of the explosion-proof valve 112 has a raised edge 1121, which covers the outer wall of the top cover 111. The raised edge 1121 is a semi-enclosed structure. Specifically, the outer peripheral edge of the top cover 111 has a bottom surface, an outer peripheral side surface, and a top surface. The raised edge 1121 includes a first straight portion that extends radially outward and conforms to the bottom surface, and a second bent portion that bends axially upward and conforms to the outer peripheral side surface. Unlike a fully enclosed structure that covers both the upper and lower surfaces of the top cover 111, the top end of the raised edge 1121 terminates at the outer peripheral side of the top cover 111 and does not bend inward to extend to the upper surface of the top cover 111. Therefore, the raised edge 1121 is approximately L-shaped in cross-section, forming a semi-enclosed state that supports and limits only the bottom and outer peripheral sides of the edge of the top cover 111. In this semi-enclosed structure, the periphery of the semi-enclosed cap assembly 110 is sealed by an insulating ring 116. Because the raised edge 1121 of the explosion-proof valve 112 adopts a semi-enclosed structure that does not cover the upper surface of the top cover 111, the inner wall of the insulating ring 116 can smoothly conform to the outer side of the top cover 111 and the raised edge 1121. When the casing 300 is closed and pressed at the opening, the casing applies a compressive force to the insulating ring 116, causing the insulating ring 116 to elastically deform and tightly fill the space between the inner wall of the casing 300 and the cap assembly 110, achieving a reliable radial and axial seal. This design not only effectively reduces the encroachment of the cap assembly on the longitudinal and radial space inside the battery, but also ensures reliable leak-proof and high-pressure resistance performance. Figure 3 As shown, in the internal conductive network, the positive current collector 120 is suspended below the CID 113 and between the core. Its outer edge is formed by molding to form an upwardly extending folded ear 122. This folded ear extends beyond the central region and is directly welded upward to the lower surface of the top cover assembly, thereby creating an extremely short and low impedance current transmission path on the outer side of the battery. Figure 2 The diagram shown is a partial cross-sectional view of a fully enclosed cap assembly in the prior art. The fully enclosed explosion-proof valve 212 has a U-shaped fully enclosed curved edge 2121 that not only covers the lower and outer surfaces of the top cover 211 edge but also bends inward to cover its upper surface. This structure results in a significant increase in the edge layer thickness of the cap assembly 210. In order to effectively seal this fully enclosed thick edge, the housing 300 needs to reserve a longer closing edge height in the axial direction. This inevitably squeezes downward and encroaches on the effective physical space inside the battery, resulting in the compression of the core's accommodating space, thereby reducing the overall capacity and volumetric energy density of the battery.

[0022] like Figure 3The diagram shows the structure of the positive current collector of this application. The main body of the positive current collector 120 is a circular aluminum disk with a central hole 128 in the center of its surface. On one side of the outer edge of the current collector, an upwardly bent rectangular lug 122 is integrally formed. This lug structure is specifically used for side welding to the upper top cover assembly across the central area, thereby creating an extremely short, low-impedance conductive path. Regarding the welding connection structure on the disk surface, the current collector displays a dual solder mark structure specifically designed for fuse-free operation and high current carrying capacity. Specifically, firstly, an annular solder mark 126 is provided in the outer area near the central hole in the center of the disk surface. This annular solder mark corresponds to the central connection area of ​​the positive current collector 120, used to achieve precise positioning with the central terminal and initial large-area current conduction. Secondly, on the disk surface 121 surrounding the annular solder mark, four sets of wavy solder marks 124 are evenly distributed along the circumference. Each set includes three wavy weld lines 125 extending outward in a radial wave pattern. This central annular ring welding positioning and peripheral radial wave welding reinforcement of the disk structure not only ensures a strong surface contact between the positive electrode tab 400 and the positive electrode current collector 120, significantly improving resistance to mechanical deformation, but the dense wave-shaped welding lines also expand the effective current-carrying cross-sectional area. This is key to the battery's ability to safely withstand the high current of super-fast charging and effectively suppress ohmic heating even without a fuse. The disk surface 121 is a structurally continuous and complete conductive surface. Since the fuse structure is eliminated, the disk surface 121 does not need to have a fuse groove or a narrowed bridging area, thus ensuring the integrity of the disk surface. Figure 4 This is a schematic diagram of the existing technology of a positive current collector with fuse, including a fuse-equipped positive current collector body 221 and a tail body 222 connected to each other. In this structure, the fuse is specifically manifested as at least one groove 223 opened on the tail body 222 to provide safety protection for the positive current collector. In the event of battery thermal runaway, the groove will melt first due to local heat concentration, thereby cutting off the current.

[0023] Furthermore, the outer diameter of the positive current collector 120 is 17.5~18.5 mm, the thickness is 0.18~0.22 mm, and the width of the folded ear portion 122 is 7.5~8.5 mm.

[0024] Furthermore, the outer diameter of the annular ring solder mark 126 is 4.5~5.5mm.

[0025] Furthermore, the length of the wavy welding line 125 is 5~7mm, and the width w is 0.25~0.35mm.

[0026] In some embodiments, the height reduction rate of the cap assembly is η, where η = (H0 - H1) / H0 × 100%, and η ranges from 10 to 25%, and can further be from 15 to 25%, for example, any value or any two of 15%, 20%, and 25%. Here, H0 is the maximum occupied height of the full-coverage cap assembly of the same specification along the axial direction of the cylindrical battery in the assembled state, and H1 is the maximum occupied height of the semi-coverage cap assembly along the axial direction of the cylindrical battery in the assembled state. The maximum occupied height is the distance between the highest and lowest points of the corresponding cap assembly along the axial direction.

[0027] Furthermore, such as Figure 1 As shown, the upper measurement reference of H1 is the highest axial point of the semi-enclosed cap assembly 110 after assembly, and the lower measurement reference of H1 is the lowest axial point of each component in the semi-enclosed cap assembly 110 that extends the furthest along the internal direction of the battery; the distance between the two references along the axial direction of the cylindrical battery is H1, and H1 can be 3.4~3.8 mm.

[0028] It should be noted that this application achieves a key balance between high energy density and high safety and reliability by controlling the height reduction rate of the semi-enclosed cap assembly within a specific range. If the reduction is too small, the internal space cannot be effectively freed up to increase the rated capacity; however, if the assembly height is excessively compressed, the gas generation buffer chamber and electrolyte storage space at the top will be severely insufficient, which can easily lead to the failure of the explosion-proof valve or the drying of the electrolyte. At the same time, extreme compression will greatly reduce the internal insulation safety gap, which not only increases the risk of short circuit between the tab and the top cover and reduces the yield of automated welding assembly, but also fails to leave enough margin to absorb the Z-axis volume expansion during the long cycle of the cell. Therefore, reasonably controlling this height reduction rate can maximize the increase in capacity and improve thermal performance while taking into account the manufacturing process window, long-term cycle life, and thermal runaway explosion-proof safety.

[0029] like Figure 5Part a shows a schematic diagram of the current density distribution and overcurrent cross-sectional area of ​​a current collector with a fuse in the prior art. Part b shows a schematic diagram of the current density distribution and overcurrent cross-sectional area of ​​the current collector without a fuse in this application. The current collector with a fuse has a fuse slot, which cuts off part of the metal in the conductive path, forming a distinct narrow waist structure, i.e., a physical conductive bottleneck. When a large current flows through this current collector, as shown in the figure, the current density becomes extremely concentrated in the fuse area. This effect leads to a small local effective conductive cross-sectional area A0. The small conductive cross-sectional area and the highly concentrated current density directly lead to a high DC internal resistance and local ohmic heating in this area, which can easily induce fuse blowing under fast charging conditions. In contrast, this application uses a current collector without a fuse. As shown in the figure, the disk structure is complete and continuous, exhibiting a slotless shape. When a large current passes through, the current density contour lines show an extremely smooth and uniform distribution on the entire disk surface, eliminating the phenomenon of local current concentration. At this time, the effective conductive cross-sectional area A1 corresponding to the current collector is also larger, realizing uniform carrying of large current.

[0030] Furthermore, the effective current cross-sectional area improvement rate is δ, where δ = (A1 - A0) / A0 × 100%, and the range of δ is 15~40%, for example, it can be any value or any two values ​​among 15%, 20%, 25%, 30%, 35% and 40%, where A1 is the effective current cross-sectional area of ​​the positive current collector 120, and A0 is the effective current cross-sectional area of ​​the same size current collector with fuse.

[0031] In some embodiments, the effective cross-sectional area A1 of the positive current collector 120 described in this application can be in the range of 2.2~2.8 mm², for example, it can be any value or any two of 2.35 mm², 2.5 mm² and 2.75 mm².

[0032] It should be noted that, compared to traditional structures with fuses, this application employs a fuse-free current collector design, resulting in a significant increase in the effective current-carrying cross-sectional area. This substantial increase in effective current-carrying cross-sectional area not only physically eliminates current congestion during high-current transmission, making the current density distribution nearly uniform, but also directly leads to a significant reduction in contact impedance and AC internal resistance. Most importantly, the significant increase in cross-sectional area eliminates localized hot spots during high-rate charging and discharging. Therefore, this significant increase in effective current-carrying cross-sectional area resulting from the fuse-free design is a key structural parameter for achieving reduced contact impedance and improved high-power fast charging performance without sacrificing safety. While increasing the effective current-carrying cross-sectional area A in a fuse-free design can significantly reduce internal resistance and temperature rise, the increase must be strictly controlled within a reasonable range. This is because once the cross-sectional area increases to a certain threshold, the decrease in contact resistance exhibits a significant diminishing marginal effect. The battery's internal resistance and heat generation bottleneck shift to the electrochemical system. If the cross-sectional area continues to increase without restriction, it will inevitably lead to an increase in the thickness or volume of the current collector. This not only encroaches on the effective internal space, thus weakening the battery's energy density, but also significantly increases the difficulty of laser welding and the risk of thermal damage. Furthermore, excessive structural rigidity can easily cause stress tearing of the tabs under vibration conditions. Therefore, controlling the increase of the effective current-carrying cross-sectional area within a specific range is a balance between low resistance and temperature rise, high energy density, and assembly yield.

[0033] This application also provides a cylindrical battery, including the aforementioned cylindrical battery top assembly.

[0034] In some embodiments, the cylindrical battery may be a 21700 type cylindrical battery.

[0035] The following examples will further illustrate this application.

[0036] Example 1 This embodiment 1 provides a top assembly for a cylindrical battery and a 21700 cylindrical battery. The top assembly includes a semi-enclosed cap assembly 110 and a positive current collector 120. The semi-enclosed cap assembly 110, from top to bottom along the axial direction, includes: a top cover 111, an explosion-proof valve 112, a current interruption device (CID) 113, a sealing ring 114, an outer G-ring 115, and an insulating ring 116. The outer edge of the top cover 111 forms a radial sealing fit with the inner wall of the opening through the outer peripheral surface of the sealing ring 114. Therefore, the axial projection boundary of the top cover 111 does not exceed the radial wall thickness area of ​​the opening, and the assembly height H1 occupied by the semi-enclosed structure along the battery axial direction can be compressed to 3.6 mm.

[0037] The positive current collector 120 is a fuse-free disc integrally stamped from aluminum (such as 1060-O state aluminum), with an outer diameter of 18.0 mm and a thickness of 0.20 mm. The current collector 120 includes a disc surface 121, a folded lug 122, and a root connection area 123. The folded lug 122 is bent upwards at approximately 90° relative to the disc surface 121, with a width of 8.0 mm, for direct welding to the conductive terminals of the top cover 111 or CID 113. Because the fuse structure is eliminated, the disc surface 121 does not need to have a fuse groove or a narrowed bridging area, thus ensuring the integrity of the disc surface.

[0038] The disk surface 121 has a wavy solder mark 124, which consists of 3 × 4 groups of wavy solder lines 125, evenly distributed along the circumference. Each group of wavy solder lines 125 extends radially, with a length of 6.0 mm and a width of 0.30 mm. The central angle between two adjacent groups of wavy solder lines 125 is approximately 90°, and the spacing between adjacent wavy solder lines within the same group is 0.5 ~ 1.0 mm.

[0039] At the root connection area 123, an annular solder mark 126 is provided between the positive electrode tab 400 and the current collector 120. The outer diameter of the annular solder mark 126 is 5.0 mm. First, the root of the tab 400 is circumferentially fixed, and then a wavy solder mark 124 is welded on the outer disk surface 121 to form a double parallel conductive structure. The end of the tab 400 is attached to the upper surface of the disk surface 121. The wavy solder mark 124 formed by laser welding penetrates the tab 400 and is metallurgically bonded to the disk surface 121. The solder mark depth h is controlled at 0.12 mm (approximately 60% of the current collector thickness) to ensure welding strength and prevent penetration of the disk surface 121.

[0040] This embodiment also provides a 21700 cylindrical battery. First, the positive and negative electrode sheets and the separator are wound into a core. After flattening the electrode tabs, positive current collectors and negative current collectors are welded to both ends. Then, the core is installed into a steel shell, and the bottom is welded to the shell body for conductivity. Next, the top insulating component is placed in and grooved. Then, a semi-enclosed cap assembly is installed and welded to the positive current collector for connection. At the same time, the sealing is completed. Afterwards, post-processing processes such as vacuum baking, liquid injection, formation, aging, and capacity testing are carried out to finally obtain the finished battery cell.

[0041] Example 2 This embodiment 2 provides a cylindrical battery top assembly and a 21700 cylindrical battery. The difference between this embodiment and embodiment 1 is that the values ​​of the structural parameters are different. The assembly height H1 occupied by the semi-enclosed structure along the battery axis can be compressed to 3.5mm, further freeing up the top space. The positive current collector 120 has an outer diameter of 18.5 mm, a thickness of 0.22 mm, and a flap width of 8.5 mm. Because the fuse structure is eliminated, the disk surface 121 maintains a continuous and intact conductive surface. Each set of wavy weld lines 125 extends radially, with a length of 6.5 mm and a width of 0.35 mm; the outer diameter of the annular weld mark 126 is 5.5 mm; the end of the tab 400 is attached to the upper surface of the disk surface 121, and the wavy weld mark 124 formed by laser welding penetrates the tab 400 and is metallurgically bonded to the disk surface 121. The weld mark depth h is controlled at 0.14 mm (approximately 64% of the thickness of the manifold) to ensure welding strength and prevent penetration of the disk surface 121.

[0042] Example 3 This embodiment 3 provides a cylindrical battery top assembly and a 21700 cylindrical battery. The only difference between this embodiment and embodiment 1 is the value of the structural parameters. The assembly height H1 occupied by the semi-enclosed structure along the battery axis is 3.8 mm. The positive current collector 120 has an outer diameter of 17.5 mm, a thickness of 0.18 mm, and a folded lug width of 7.5 mm. The surface area 121 is a continuous and complete conductive surface without fuse grooves or narrowed bridging areas.

[0043] Each set of wavy weld lines 125 extends radially, with a length of 5.0 mm and a width of 0.25 mm; the outer diameter of the annular weld mark 126 is 4.5 mm; the end of the tab 400 is attached to the upper surface of the disk surface 121, and the wavy weld mark 124 formed by laser welding penetrates the tab 400 and is metallurgically bonded to the disk surface 121. The weld mark depth h is controlled at 0.10 mm (approximately 56% of the thickness of the manifold) to ensure welding strength and prevent penetration of the disk surface 121.

[0044] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses a fully enclosed cap assembly and a positive electrode current collector with a fuse. The assembly height H0 occupied by the fully enclosed cap assembly structure along the battery axis is 4.5 mm. The positive electrode current collector has a fuse structure and a radial fusion groove (narrow waist structure) on the surface. The current density contour lines are concentrated at the fuse. Other dimensional parameters (outer diameter 18.0 mm, thickness 0.20 mm) are different. The surface of the disk does not have the annular ring solder mark and wavy solder mark structure of Example 1.

[0045] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses a semi-enclosed cap assembly, but the positive current collector retains the fuse structure. Specifically, the cap end uses the same semi-enclosed structure as Example 1, with an assembly height H1 of 3.6 mm; the positive current collector has a fuse structure, and the surface has radial fusing grooves (narrow waist structure), concentrating the current density at the fuse. Other dimensional parameters (outer diameter 18.0 mm, thickness 0.20 mm) are different. The surface of the current collector lacks the annular and wavy solder marks found in Example 1. This comparative example is used to independently verify the contribution of the fuse-free current collector to electrochemical performance.

[0046] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses a fully enclosed cap assembly, but the positive current collector has the same fuse-free structure as Example 1. That is, the cap end adopts a fully enclosed structure with an assembly height H0 of 4.5 mm; the positive current collector is an integrated aluminum disc without a fuse (outer diameter 18.0 mm, thickness 0.20 mm), and the disc surface has the same annular and wavy solder marks as Example 1. This comparative example is used to separately verify the contribution of the semi-enclosed cap to space release and capacity improvement.

[0047] Effect Example Performance testing methods Cross-sectional area of ​​flow A three-dimensional laser scanning profilometer was used to scan point by point along the radial main current path, and the minimum conductive cross-sectional area during the current collection process was taken as the effective overcurrent cross-sectional area; the average value was taken from ≥5 parallel samples in each group. Clear distinctions were made: With a fuse, the value is A0 at the narrowest point of the fuse slot / waist; without a fuse, the value is A1 over the continuous, intact area of ​​the disc surface.

[0048] AC internal resistance Using an AC internal resistance tester (usually with an AC frequency of 1kHz), a fixed small current AC signal (such as 1A~5A) is applied to the battery cell in a fully charged or half-charged state. By measuring the AC voltage drop across the battery cell, the internal resistance value (unit: mΩ) is calculated using Ohm's law.

[0049] Temperature rise during high-rate discharge After fully charging the battery cell using constant current constant voltage (CCCV), place it in a constant temperature chamber at approximately 25°C. Perform continuous constant current discharge at a 1C rate until the voltage drops to the specified discharge cutoff voltage. During this process, use thermocouples attached to the surface of the battery cell casing or the terminals to record the temperature rise curve throughout the discharge process.

[0050] Rated capacity The process is typically conducted at an ambient temperature of 25℃±2℃. First, the cell is fully charged using a constant current-constant voltage (CCCV) method at 0.5C (or 1C). After a period of rest, it is discharged using a constant current of 0.2C (or 1C) until the voltage reaches the discharge termination voltage. The total amount of electricity discharged during the process is recorded (unit: Ah or Wh).

[0051] Short circuit test The battery cell is fully charged under standard conditions. A purely resistive load with a resistance of 50mΩ is connected to the positive and negative terminals to form an external short-circuit loop with a fixed impedance. During this process, the changes in the battery cell voltage, current, and surface temperature are monitored simultaneously, and the battery cell is continuously observed for any leakage, fire, or explosion.

[0052] The main parameters and test results of Examples 1-3 and Comparative Examples 1-3 are shown in Tables 1 and 2, respectively: Table 1 Table 2 Based on the data in Table 2, it can be seen that the larger the effective current-carrying cross-sectional area A, the lower the contact resistance of the current collector according to the formula R=ρ×l / A, and the more uniform the current density distribution, resulting in lower AC internal resistance and lower temperature rise during rate discharge. Referring to Table 2, Example 2 has the largest A1 (2.75 mm²), corresponding to the lowest AC internal resistance (14.8 mΩ) and the lowest 1C temperature rise (32℃); Example 3 has the smallest A1 (2.35 mm²), corresponding to a slightly higher AC internal resistance (15.8 mΩ) and the highest 1C temperature rise (35℃); Example 1 (A1=2.5 mm²) falls between the two (AC internal resistance 15.2 mΩ, 1C temperature rise 34℃). Comparative Examples 1 and 2, due to the inclusion of a fuse, have the smallest effective current-carrying cross-sectional area A0 (2.0 mm²) and the highest AC internal resistance (18.5 mΩ and 17.2 mΩ, respectively). It can be seen that the increase of the A value is positively correlated with the reduction of impedance, the improvement of temperature rise and the improvement of rate performance. It is a key structural parameter to reduce contact impedance and improve high-power fast charging performance without sacrificing safety.

[0053] Combination Figure 6 It can be seen that, as Figure 6Part a shows a bar chart comparing the assembly height of the embodiments and comparative examples. The test results show that the caps of Comparative Examples 1 and 3 are both full-coverage, with a top component assembly height of 4.5 mm. However, the embodiment using the co-design of this application can significantly reduce its assembly height to 3.5~3.8 mm, a reduction of up to 20% compared to Comparative Examples 1 and 3. This indicates that the structural design of this application can significantly compress the volume of inactive components and effectively release the top space inside the battery; combined with... Figure 6 As can be seen from part d, the reduced assembly height allows the cell to hold more active material. The rated capacities of Comparative Example 1 and Comparative Example 3 are only 4980mAh and 5010mAh respectively, while the capacity of the semi-enclosed type compared to Comparative Example 2 and Examples 1-3 is increased to over 5025mAh, with Example 2 reaching 5080mAh, thus improving the battery's energy density. Figure 6 Part b shows a bar chart comparing the AC internal resistance of the embodiments and comparative examples. The AC internal resistance data shows that the internal resistance of Comparative Examples 1 and 2 with fuse current collectors is relatively high, indicating that the fuse itself and its connection structure introduce a large impedance. Comparative Example 3 without a fuse structure and Examples 1-3 show an overall decrease in AC internal resistance, especially the combination of a semi-enclosed design and a fuse-free design, where the internal resistance is reduced to between 14.8 and 15.8 mΩ. Example 2 reaches a minimum of 14.8 mΩ. This indicates that the synergistic design, including the fuse-free current collector, effectively optimizes the conductive path, significantly reduces the contact impedance between components, and improves the electrochemical performance of the battery. Figure 6 As shown in section c, the surface temperature rise of the batteries in the embodiments and comparative examples at different discharge rates from 0.5C to 4.0C is illustrated. The curves show that as the discharge rate increases, the temperature rise of the embodiments is consistently significantly lower than that of the comparative examples. At high discharge rates (e.g., 4.0C), the temperature rise advantage of the embodiments is particularly pronounced, with Embodiment 2 exhibiting the lowest temperature rise. This is mainly due to the reduced internal resistance of the embodiments, which significantly reduces the Joule heat generated by the battery during high power output, improving the battery's thermal stability without sacrificing safety.

[0054] In summary, this application achieves significant release of top space and effective reduction of contact resistance without sacrificing safety through the synergistic design of a semi-enclosed cap and a fuse-free current collector. This release of space can be converted into an increase in battery capacity, making it suitable for the large-scale production of high-energy-density 21700 cylindrical batteries.

[0055] Although embodiments of this implementation have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this implementation, the scope of which is defined by the claims and their equivalents.

Claims

1. A cylindrical battery top assembly, characterized in that, The device includes a semi-enclosed cap assembly (110) and a positive current collector (120). The semi-enclosed cap assembly (110) includes a top cover (111), an explosion-proof valve (112), and a current interruption device (113). The explosion-proof valve (112) has a raised edge (1121) that covers the outer wall of the top cover (111), and the raised edge (1121) is a semi-enclosed structure. The positive current collector (120) includes a disk surface (12... 1) The folded ear (122) and the root connection area (123) are connected. The disk surface (121) is a complete conductive surface with a continuous structure. The positive electrode tab (400) is connected to the positive current collector (120) through the annular ring solder mark (126) located in the root connection area (123) and multiple sets of wavy solder marks (124) located in the disk surface (121). The folded ear (122) is connected to the conductive end of the semi-enclosed cap assembly (110).

2. The cylindrical battery top assembly according to claim 1, characterized in that, The height reduction rate of the cap assembly is η, where η = (H0 - H1) / H0 × 100%, and η ranges from 10% to 25%. Here, H0 is the maximum occupied height of the full-coverage cap assembly of the same specification along the axial direction of the cylindrical battery in the assembled state, and H1 is the maximum occupied height of the semi-coverage cap assembly along the axial direction of the cylindrical battery in the assembled state. The maximum occupied height is the distance between the highest and lowest points of the corresponding cap assembly along the axial direction.

3. The cylindrical battery top assembly according to claim 2, characterized in that, The maximum occupied height H1 of the semi-enclosed cap assembly along the axial direction of the cylindrical battery in the assembled state ranges from 3.4 to 3.8 mm.

4. The cylindrical battery top assembly according to claim 1, characterized in that, The outer diameter of the positive current collector (120) is 17.5~18.5 mm, the thickness is 0.18~0.22 mm, and the width of the folded ear (122) is 7.5~8.5 mm.

5. The cylindrical battery top assembly according to claim 4, characterized in that, The outer diameter of the annular ring solder mark (126) is 4.5~5.5mm.

6. The cylindrical battery top assembly according to claim 5, characterized in that, The wavy solder mark (124) consists of 3 × 4 sets of wavy solder lines (125) evenly distributed along the circumference. The length of the wavy solder line (125) is 5~7mm and the width is 0.25~0.35mm.

7. The cylindrical battery top assembly according to claim 1, characterized in that, The effective current cross-sectional area improvement rate is δ, where δ = (A1 - A0) / A0 × 100%, and the range of δ is 15~40%, where A1 is the effective current cross-sectional area of ​​the positive current collector (120), and A0 is the effective current cross-sectional area of ​​the same size current collector with fuse.

8. The cylindrical battery top assembly according to claim 7, characterized in that, The effective cross-sectional area A1 of the positive current collector (120) ranges from 2.2 to 2.8 mm².

9. A cylindrical battery, characterized in that, Includes the cylindrical battery top assembly as described in any one of claims 1 to 8.

10. The cylindrical battery according to claim 9, characterized in that, The cylindrical battery is a 21700 type cylindrical battery.

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