Cell Pack Expanding Portions Manage Internal Pressure
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Solution Overview
Problem
Cell packs experience internal pressure fluctuations due to temperature and altitude changes, leading to localized stress concentration and bulging, which can cause fatigue and airtightness issues in thin-walled cell cases, especially during high-rate charging and discharging.
Innovation Solution
A cell pack design with expanding portions in the non-pressing regions of the cell case, which reduces the gap between the cell case and spacers, disperses stress, and includes a method for producing unit cells by inserting an electrode body into a cell case, applying pressure to form expanding portions, and injecting electrolytic solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the cell case wall thickness is reduced to decrease weight and cost, then weight and cost are reduced, but the cell case becomes easily deformed by internal pressure fluctuation
Solution Approach 1:
The cell case is designed with non-uniform wall thickness, featuring thicker reinforcing ribs at specific locations (top, bottom, and side surfaces) while maintaining thin walls in other areas. This local quality variation allows the cell case to resist internal pressure fluctuation at critical points without increasing overall weight significantly.
Solution Approach 2:
The reinforcing ribs are designed with curved surfaces rather than flat planes. The curved geometry of the ribs provides better structural reinforcement against internal pressure, as curved surfaces naturally distribute stress more effectively than flat surfaces, thereby improving the cell case's resistance to deformation.
2Productivity
If a spacer presses only part of the cell case to improve high-rate charge/discharge characteristics, then high-rate charge/discharge characteristics are improved, but stress concentrates in the non-pressing portion causing local cell bulging
Solution Approach 1:
The spacer is designed with a non-uniform pressing structure that applies different pressures to different regions of the cell case. Specifically, the spacer has pressing portions that contact the cell case at multiple locations with varying contact areas, creating a localized pressure distribution that prevents stress concentration while maintaining high-rate charge/discharge performance.
Solution Approach 2:
The spacer's pressing surface is divided into multiple separate pressing portions rather than a single continuous pressing area. This segmentation allows the spacer to apply distributed pressure at discrete locations, preventing stress concentration in any single region while still providing sufficient compression for high-rate charge/discharge characteristics.
3Stability of the object's composition
If the spacer presses the entire electrode body to suppress dimensional changes, then dimensional changes are suppressed, but high-rate charge/discharge characteristics deteriorate
Solution Approach 1:
The spacer applies pressure selectively to specific regions of the electrode body rather than uniformly across the entire electrode. The pressing portions are positioned to contact the cell case at locations that provide sufficient dimensional stability for the electrode body while leaving other regions uncompressed, thereby maintaining high-rate charge/discharge characteristics.
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 design significantly suppresses cell bulging and fatigue, maintains airtightness, and enhances high-rate charge/discharge characteristics and overcharge resistance by effectively managing internal pressure fluctuations and electrolyte retention.
Implementation Method 1
An expanding portion bulging in a direction of approaching the spacer is provided in the non-pressing region of the cell case, and a gap between the cell case and the spacer is reduced by the expanding portion
Implementation Method 2
a restraining mechanism that applies a load from the arrangement direction to the plurality of unit cells and the one or plurality of spacers
Data Source
AI summary
A cell pack including: a plurality of unit cells arranged in an arrangement direction, each unit cell including a cell case accommodating an electrode body and an electrolytic solution; and a spacer disposed between two unit cells adjacent to each other in the arrangement direction. The cell case has a side surface facing the spacer. At least one of the side surfaces has a pressing region pressed by the spacer and a non-pressing region not pressed by the spacer. An expanding portion bulging in a direction of approaching the spacer is provided in the non-pressing region of the cell case, and a gap between the cell case and the spacer is reduced by the expanding portion.