Cylindrical Battery Cap Assembly Solder Control
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Solution Overview
Problem
Cylindrical lithium ion secondary batteries face issues with solder distribution and sealing efficiency due to temperature and pressure variations, leading to potential short-circuits and increased resistance, which can result in component cracks and sealing failures during the crimping process.
Innovation Solution
Incorporating a cap assembly with a positive temperature coefficient (PTC) device connected to a cap-up via solder, and an exterior and interior space without solder on the external and internal circumferences, along with an exterior stepped portion to prevent solder flow and maintain planarity, thereby optimizing solder distribution and enhancing sealing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder is applied between the PTC device and cap-up, then electrical connection is achieved, but solder may flow to external circumferences causing short-circuits
Solution Approach 1:
The cap-up incorporates an exterior stepped portion that creates a localized solder containment structure. This stepped portion forms a physical barrier at the external circumference, confining solder to specific areas during the reflow process. The local geometric modification ensures solder remains in designated connection zones without flowing to external circumferences, thereby preventing short-circuits while maintaining reliable electrical connections between the PTC device and cap-up.
2Reliability
If temperature and pressure variations occur during crimping, then sealing is achieved, but solder distribution becomes uneven leading to component cracks
Solution Approach 1:
The exterior stepped portion is pre-formed on the cap-up structure before the crimping and reflow processes. This preliminary geometric feature acts as a proactive constraint that guides solder flow during subsequent temperature and pressure variations. By establishing the solder containment structure in advance, the design prevents uneven solder distribution and component cracks that would otherwise result from uncontrolled solder movement during crimping operations.
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 effectively prevents short-circuits and maintains sealing integrity by controlling solder flow and distribution, reducing component resistance and failure rates, and ensuring stable battery operation under varying conditions.
Implementation Method 1
a positive temperature coefficient (PTC) device connected to the electrode assembly
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A cylindrical lithium ion secondary battery, including a cylindrical can; an electrode assembly in the cylindrical can with an electrolyte solution; and a cap assembly sealing the cylindrical can, the cap assembly including a positive temperature coefficient (PTC) device connected to the electrode assembly, a cap-up connected to the PTC device, solder between the PTC device and the cap-up, and an exterior space without the solder on external circumferences of the PTC device and the cap-up.