Cylindrical Battery Cell Cap Structure for Weld-Safe Tab Connection
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Solution Overview
Problem
Cylindrical battery cells face issues with reduced energy density due to the need for a second current collector plate, increased manufacturing complexity, and potential welding defects between the can sidewall and cap, leading to higher costs and reduced reliability of electrical connections.
Innovation Solution
A battery cell structure that enhances adhesion between the cap and electrode tab by controlling the insertion depth of the cap during press-fitting, ensuring robust electrical connections without a current collector plate, and preventing laser welding from damaging the electrode assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a second current collector plate is added to accommodate both positive and negative terminals on one axial side, then the battery can achieve a larger diameter and increased volume, but the volume of the electrode assembly must be reduced to secure space for the current collector plate, resulting in lower energy density
Solution Approach 1:
The patent removes the second current collector plate from the system. Instead of accommodating both terminals on one axial side with a current collector plate, the invention uses the cap as the negative terminal and the bottom as the positive terminal, eliminating the need for a second current collector plate and maximizing electrode assembly volume
Solution Approach 2:
The cap serves multiple functions: it acts as both the closure for the battery can and the negative terminal (second electrode terminal). This multi-functionality eliminates the need for a separate second current collector plate, increasing the volume available for the electrode assembly and thus improving energy density
2Reliability
If the cap is press-fitted deeply into the can to ensure adhesion, then the electrical connection reliability is improved, but the laser welding process may damage the electrode assembly inside the can
Solution Approach 1:
The patent divides the cap structure into two distinct functional regions: a press-fit portion that extends into the can to ensure adhesion and electrical connection, and a welding portion that remains outside the can for laser welding to the sidewall. This segmentation prevents the welding laser from damaging the electrode assembly while maintaining reliable electrical connection
Solution Approach 2:
The press-fit portion of the cap acts as an intermediary element that provides both mechanical adhesion (through press-fitting into the can) and electrical connection (by contacting the electrode tab). This intermediary structure allows the welding portion to be positioned outside the can, protecting the electrode assembly from laser damage while maintaining connection reliability
3Strength
If butt welding is performed between the sidewall and cap to ensure structural integrity, then the bonding strength is improved, but welding defects may occur due to height differences or gaps between the sidewall and cap
Solution Approach 1:
The patent segments the cap into a press-fit portion (inside the can) and a welding portion (outside the can). The welding portion is designed with a flange-like structure that provides a large, flat surface for butt welding to the sidewall. This segmentation ensures that the welding surface is level with the sidewall opening, eliminating height differences and gaps that cause welding defects while maintaining strong bonding
4Device complexity
If the cap structure is simplified to eliminate the current collector plate, then manufacturing complexity and cost are reduced, but additional processes are required to connect the electrode assembly directly to the can
Solution Approach 1:
The patent merges the functions of the cap (closure) and the negative terminal (second electrode terminal) into a single component. The cap is press-fitted to the sidewall for structural closure and simultaneously contacts the electrode tab for electrical connection. This merging eliminates the need for separate current collector plate and its associated connection processes, reducing manufacturing complexity while maintaining productivity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution increases energy density, reduces manufacturing complexity and costs, and enhances the reliability of electrical connections while maintaining structural integrity and preventing welding defects.
Implementation Method 1
the inner circumferential surface of the contacting wall surface portion (113) and the outer circumferential surface of the contacting surface portion (48) are press-fitted to be strongly abutted
Implementation Method 2
The inner circumferential surface of the contacting wall surface portion (113) and the outer circumferential surface of the contacting surface portion (48) are bonded to be electrically connected
Data Source
AI summary
A battery cell may include a contacting wall surface with an expanded inner diameter at an open end of a sidewall of a battery can of the battery cell. The cap covering the open end includes a press-fitted contacting surface portion in contact with the inner circumferential surface of the contacting wall surface portion, and an electrode connecting part connected to an electrode tab of an electrode assembly accommodated in the battery can. The press-fitting depth of the cap into the battery can is regulated by the electrode connecting part of the cap and the electrode tab of the electrode assembly. The contacting surface portion and the contacting wall surface portion are bonded and electrically connected by welding. A battery pack may include the battery cell, and a vehicle may include the battery pack.