A high-rate cylindrical lithium-ion battery cap structure

Abstract

This invention discloses a high-rate cylindrical lithium-ion battery cap structure, including a steel cap, an explosion-proof sheet, and a connecting piece. The steel cap is located at the top layer of the cap, the explosion-proof sheet is located below the steel cap, and the connecting piece is located at the bottom layer. A conductive cotton sheet is disposed between the explosion-proof sheet and the connecting piece. A sealing ring is also included, and the edge of the explosion-proof sheet is fixed by the sealing ring. The explosion-proof sheet is a thin metal sheet with a central concave surface. The central area of ​​the connecting piece and the central concave surface of the explosion-proof sheet are laser-welded to form a weld point. An insulating isolation ring is also included, disposed between the edge of the explosion-proof sheet and the edge of the connecting piece. This invention utilizes a conductive cotton sheet, which combines conductivity and elasticity. Its lower surface is firmly electrically connected to the connecting piece through conductive adhesive, while its upper surface maintains elastic contact with the explosion-proof sheet. During normal operation, current can be diverted from the connecting piece to the explosion-proof sheet through the conductive cotton sheet, effectively increasing the current-conducting area between the connecting piece and the explosion-proof sheet.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a high-rate cylindrical lithium-ion battery cap structure, which is particularly suitable for high-rate charge and discharge scenarios. Background Technology

[0002] Cylindrical lithium-ion batteries (such as 18650, 21700, and 26650 models) are widely used in smart homes, power tools, drones, and other fields due to their high energy density and long cycle life. As application scenarios increasingly demand higher charging speeds and power outputs, batteries need to be charged and discharged at 4C, 6C, or even higher rates.

[0003] Reference Figure 3-5 As shown, the cap structure of a conventional cylindrical lithium-ion battery 7 typically includes components such as a steel cap 1, an explosion-proof sheet 2, a connecting piece 4, an insulating sealing ring 5, and a sealing ring 6. Current 8 is output from the cell tab or the end face 10 of the winding core, flowing sequentially through the connecting piece 4, the explosion-proof sheet 2, and the steel cap 1 before flowing to the external circuit. In this path, the part with the smallest current-conducting area becomes the bottleneck for current 8 transmission, resulting in excessively high local current density, increased ohmic internal resistance, and a significant increase in Joule heat. For example, the current-conducting area of ​​a conventional 21700 cap is only 0.5~1mm², and under 6C discharge conditions, the temperature rise in the cap area can reach over 40°C, severely restricting the battery's continuous high-rate output capability and cycle life.

[0004] To address these issues, existing technologies have attempted to reduce internal resistance by increasing the number of tabs or adopting an all-tab design. However, these solutions often require significant modifications to the cell structure and manufacturing process, resulting in high costs. Therefore, how to increase the current-carrying area and reduce internal resistance by optimizing the cap structure itself without drastically altering existing production lines has become a pressing technical problem in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a high-rate cylindrical lithium-ion battery cap structure.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A high-rate cylindrical lithium-ion battery cap structure includes a steel cap, an explosion-proof sheet, and a connecting piece; the steel cap is located at the top layer of the cap, the explosion-proof sheet is located below the steel cap, and the connecting piece is located at the bottom layer; a conductive cotton sheet is provided between the explosion-proof sheet and the connecting piece. Furthermore, it also includes a sealing ring, which secures the edge of the explosion-proof sheet. Preferably, the explosion-proof sheet is a thin metal sheet with a central concave surface. Furthermore, the central region of the connecting piece and the central concave surface of the explosion-proof piece are laser-welded to form a weld point. Furthermore, it also includes an insulating ring, which is a circular insulating component located between the edge of the explosion-proof sheet and the edge of the connecting sheet, with a through hole in the center of the insulating ring. Furthermore, the compression of the free height of the conductive cotton sheet is controlled between 10% and 20%. Preferably, the conductive cotton sheet is made of a polymer foam substrate combined with a conductive coating. Furthermore, the conductive cotton sheet is in the shape of a ring. Preferably, the polymer foam substrate includes polyurethane (PU), silicone, or EPDM rubber, and the conductive coating includes nickel, copper, or carbon. Preferably, the lower surface of the conductive cotton sheet is uniformly coated with a layer of conductive adhesive, and the conductive cotton sheet is fixed to the upper surface of the connecting piece by the conductive adhesive, with the upper surface of the conductive cotton sheet abutting against the lower surface of the explosion-proof sheet.

[0007] Compared to existing technologies, the beneficial effects of the technology are: 1. This invention incorporates a conductive cotton sheet that combines conductivity and elasticity. The lower surface of the conductive cotton sheet is firmly electrically connected to the connecting piece via conductive adhesive, while the upper surface maintains elastic contact with the explosion-proof sheet. This effectively adds a current-conducting step. During normal operation, current can be diverted from the connecting piece to the explosion-proof sheet via the conductive cotton sheet. The conductive cotton sheet effectively increases the current-conducting area between the connecting piece and the explosion-proof sheet, thereby effectively reducing the internal resistance and temperature rise during high-rate charging and discharging, and improving the high-rate charging and discharging performance of the cylindrical lithium-ion battery. 2. The conductive cotton pad has weak elasticity. When CID is not triggered, it maintains contact with the explosion-proof sheet by slight compression. Once CID is triggered and the explosion-proof sheet flips up, the conductive cotton pad cannot provide enough rebound force to compensate for the increased gap between the two. The contact between the conductive cotton pad and the explosion-proof sheet will naturally separate, effectively avoiding interference from additional conductive paths to the CID power-off function. 3. The conductive cotton pad significantly reduces internal resistance. Since resistance is inversely proportional to cross-sectional area, this directly reduces contact resistance, resulting in a more uniform current distribution and avoiding local overheating. This improves the cycle life and safety of the battery under high-rate charge and discharge conditions. The reduced internal resistance also directly reduces Joule heating, effectively suppressing temperature rise and contributing to the thermal stability and safety of the battery under continuous high-rate operation. Attached Figure Description

[0008] Figure 1 This is a cross-sectional schematic diagram of the cylindrical lithium-ion battery cap structure of the present invention. Figure 2 This is an exploded view of the cylindrical lithium-ion battery cap structure of the present invention. Figure 3 This is a schematic diagram of the cross-section of a conventional cap structure. Figure 4 This is an exploded view of a standard cap structure. Figure 5 This is a schematic diagram of the electron flow under normal operating conditions of a standard cap. Figure 6 This is a schematic diagram of the electron flow under normal operating conditions of the cylindrical lithium-ion battery cap structure of the present invention. In the diagram, 1 is a steel cap; 2 is an explosion-proof sheet; 3 is a conductive cotton sheet; 4 is a connecting piece; 5 is an insulating isolation ring; and 6 is a sealing ring. Detailed Implementation

[0009] The present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0010] Reference Figure 1-2 As shown, a cylindrical lithium-ion battery cap structure includes a steel cap 1, an explosion-proof sheet 2, and a connecting piece 4. The steel cap 1 is located at the top of the cap and serves as the positive terminal of the battery. The explosion-proof sheet 2 is located below the steel cap 1 and is a thin metal sheet with a central concave surface. The connecting piece 4 is located at the bottom layer, and a conductive cotton sheet 3 is placed between the explosion-proof sheet 2 and the connecting piece 4. It also includes a sealing ring 6, and the edge of the explosion-proof sheet 2 is fixed by the sealing ring 6. The central area of ​​the connecting piece 4 and the central concave surface of the explosion-proof piece 2 are laser-welded to form a weld point. The thickness of the engraved lines at the edge of the central area is small, which makes it easy for the central concave surface of the explosion-proof piece 2 to pull the weld point and flip it upward. It also includes an insulating ring 5, which is a circular insulating component that is placed between the edge of the explosion-proof sheet 2 and the edge of the connecting piece 4, and serves as a physical support and insulating barrier. The insulating ring 5 has a through hole in the center. The sealing ring 6 has a bowl-shaped structure and covers the outer edge of the cap, achieving electrical insulation and electrolyte sealing. The conductive cotton pad 3 is in the shape of a ring and is made of a polymer foam substrate combined with a conductive coating, which gives it both conductivity and elasticity. Polymer foaming substrates include polyurethane (PU), silicone, or EPDM rubber. Conductive coatings include nickel, copper, and carbon. The lower surface of the conductive cotton pad 3 is uniformly coated with a layer of conductive adhesive 9. The conductive cotton pad 3 is fixed to the upper surface of the connecting piece 4 by the conductive adhesive 9, forming a stable and low-resistance electrical contact. The upper surface of the conductive cotton pad 3 abuts against the lower surface of the explosion-proof piece 2. The conductive cotton pad 3 relies on its own slight elastic deformation to just fill the gap between the explosion-proof piece 2 and the connecting piece 4, ensuring that it maintains a tight mechanical contact with the explosion-proof piece 2.

[0011] Reference Figure 6 As shown, under normal operating conditions, the battery current path is divided into two parallel branches. The main path of the conductive cotton pad 3 is: connecting piece 4 → laser welding point → concave surface of the center of the explosion-proof sheet 2 → steel cap 1; the auxiliary path is: connecting piece 4 → conductive adhesive 9 → conductive cotton pad 3 → edge of the explosion-proof sheet 2 → steel cap 1. The auxiliary path provided by the conductive cotton pad 3 can effectively reduce the overall contact resistance of the cap and reduce heat generation. In abnormal operating conditions, when CID is triggered, if the internal pressure of the battery abnormally increases due to short circuits, overcharging, or other reasons, the central concave surface of the explosion-proof sheet 2 will flip upwards and deform. At this time: the laser weld point between the central concave surface of the explosion-proof sheet 2 and the connecting piece 4 is forcibly broken, and the main circuit is cut off. At the same time, the edge of the explosion-proof sheet 2 moves upwards with the central concave surface, and the gap between it and the conductive cotton sheet 3 below rapidly increases. Because the conductive cotton sheet 3 itself has low elasticity and weak rebound force, its height cannot follow the displacement of the explosion-proof sheet 2 and extend in real time. Therefore, the upper surface of the conductive cotton sheet 3 will automatically detach from the contact with the explosion-proof sheet 2, the auxiliary conductive path is cut off, and the current will not bypass through the conductive cotton sheet 3. To ensure the reliable implementation of the above functions, the elastic modulus of the conductive cotton pad 3 should be significantly less than the driving force required for the explosion-proof sheet to flip, ensuring that it cannot resist the mechanical action of CID. The compression of the conductive cotton pad 3 at its free height is controlled between 10% and 20% to ensure reliable initial contact. At the same time, the compression should not be too large to avoid contact with the explosion-proof pad 2 due to excessive rebound force after CID triggering. The conductive adhesive 9 is selected to be resistant to electrolyte corrosion and has a certain degree of flexibility after curing, so as to buffer vibration and maintain connection stability. In the traditional cap structure, the current is conducted only through the narrow path of the connecting piece 4, resulting in high current density and concentrated ohmic heat in this area. However, the present invention provides an auxiliary conductive path by introducing a conductive cotton sheet 3, which forms a surface contact with the explosion-proof sheet 2 and the connecting piece 4, greatly increasing the current conduction area.

[0012] The improvements of this invention are mainly focused on the design of the cap itself, without changing the internal structure of the battery cell, resulting in limited cost increase, good compatibility, and high industrial application value.

[0013] This invention is applicable to various battery models and can be flexibly applied to cylindrical batteries of different sizes, such as 18650, 21700, and 26650. Simply adjust the size parameters of the conductive cotton sheet proportionally.

Claims

1. A high-rate cylindrical lithium-ion battery cap structure, characterized in that, It includes a steel cap, an explosion-proof plate, and a connecting plate; the steel cap is located at the top of the cap, the explosion-proof plate is located below the steel cap, and the connecting plate is located at the bottom. A conductive cotton sheet is placed between the explosion-proof plate and the connecting plate.

2. The high-rate cylindrical lithium-ion battery cap structure according to claim 1, characterized in that, It also includes a sealing ring, and the edge of the explosion-proof sheet is fixed by the sealing ring.

3. The high-rate cylindrical lithium-ion battery cap structure according to claim 1, characterized in that, The explosion-proof sheet is a thin metal sheet with a central concave surface.

4. The high-rate cylindrical lithium-ion battery cap structure according to claim 1, characterized in that, The central area of ​​the connecting piece and the central concave surface of the explosion-proof piece are laser-welded to form a weld point.

5. The high-rate cylindrical lithium-ion battery cap structure according to claim 1, characterized in that, It also includes an insulating ring, which is a circular insulating component located between the edge of the explosion-proof sheet and the edge of the connecting sheet. The insulating ring has a through hole in its center.

6. The high-rate cylindrical lithium-ion battery cap structure according to claim 1, characterized in that, The compression of the free height of the conductive cotton sheet is controlled between 10% and 20%.

7. The high-rate cylindrical lithium-ion battery cap structure according to claim 1, characterized in that, The conductive cotton sheet is made of a polymer foam substrate combined with a conductive coating.

8. The high-rate cylindrical lithium-ion battery cap structure according to claim 7, characterized in that, The conductive cotton sheet is in the shape of a ring.

9. The high-rate cylindrical lithium-ion battery cap structure according to claim 7, characterized in that, The polymer foam substrate includes polyurethane (PU), silicone, or EPDM rubber, and the conductive coating includes nickel, copper, or carbon.

10. The high-rate cylindrical lithium-ion battery cap structure according to claim 1, characterized in that, The lower surface of the conductive cotton pad is uniformly coated with a layer of conductive adhesive. The conductive cotton pad is fixed to the upper surface of the connecting piece by the conductive adhesive, and the upper surface of the conductive cotton pad abuts against the lower surface of the explosion-proof piece.

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