Cordless Tool Battery Pack Structure for Pouch Cell Swelling
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Solution Overview
Problem
Conventional battery packs for cordless power tools using cylindrical 18650 cells face issues with cell swelling, which can lead to pressure buildup and potential rupture, reducing the battery's effective life and requiring mechanisms to accommodate expansion while maintaining dimensional stability and preventing mechanical conflicts with the power tool.
Innovation Solution
The use of non-cylindrical pouch cells with a sealed metal/polymer laminated pouch and a firm internal plate structure to manage swelling, along with features like notches or holes in the pouch seal for controlled venting, and electrical connections in series-parallel configurations, ensures the battery pack can expand without interfering with the power tool and maintains mechanical integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cylindrical 18650 battery cells are used in conventional battery packs, then the battery pack can be manufactured with standard form factors, but cell swelling leads to pressure buildup and potential rupture, reducing battery life and requiring mechanisms to accommodate expansion
Solution Approach 1:
The patent changes the battery cell form from cylindrical 18650 to pouch cells with a flat plate structure. This parameter change allows the cells to be contained within rigid frames that prevent swelling-induced pressure buildup and rupture, thereby extending battery life while eliminating the harmful effects of cell expansion.
Solution Approach 2:
The patent employs a composite structure combining rigid frames (made of rigid plastic or metal) with pouch battery cells. This composite design provides mechanical support and constraint to the pouch cells, preventing them from swelling and causing pressure buildup, thus resolving the reliability issue without requiring additional accommodation mechanisms.
2Object-affected harmful factors
If mechanisms are added to accommodate cell expansion, then cell swelling can be managed, but the device complexity increases and dimensional stability may be compromised
Solution Approach 1:
The patent implements beforehand cushioning by designing rigid frames with predetermined spacing and structural support before cell swelling occurs. The frames are engineered with sufficient internal volume and structural rigidity to accommodate any potential cell expansion without requiring additional dynamic accommodation mechanisms, thus managing cell swelling while maintaining device simplicity.
3Stability of the object's composition
If rigid frames are used to constrain pouch battery cells, then dimensional stability is maintained and mechanical conflicts with power tool are prevented, but the manufacturing process becomes more complex
Solution Approach 1:
The patent divides the battery pack into modular segments, with each pouch cell individually housed within its own rigid frame. This segmentation allows for standardized frame designs that can be manufactured independently and then assembled with the cells and other components, simplifying the overall manufacturing process while maintaining dimensional stability through the rigid frame structure.
Data Source
AI summary
A battery pack comprises a battery pack housing operably connectable to a power tool, at least five battery cells disposed in the housing, and battery pack terminals electrically connectable to power tool terminals of the power tool and electrically connected to the battery cells. An inductance characteristic of the battery pack is greater than 0 and less than 0.20 micro Henries. A ratio of inverse impedance and inductance characteristic of the battery pack is greater than 5×107 Ω−1H−1.