Polyolefin Separator Deformation Control for Battery Cycle Life
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Solution Overview
Problem
Conventional battery separators are insufficient in maintaining battery output characteristics during long-term charge-discharge cycles, as they do not adequately address the deformation and stress applied by repeated electrode expansion and shrinkage.
Innovation Solution
A nonaqueous electrolyte secondary battery separator with a polyolefin porous film, where the displacement ratio at the 10th loading-unloading cycle to the 50th cycle is within a specific range of 100% to 130%, ensuring minimal plastic deformation and maintaining battery capacity during long-term cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional polyolefin porous film separator is used, then the battery can operate with basic separator functions, but the battery output characteristic deteriorates during long-term charge-discharge cycles due to insufficient deformation control
Solution Approach 1:
The invention changes the physical parameters of the polyolefin porous film by controlling its compression characteristics (amount of compression deformation and amount of increase in compression deformation) and pore ratio. These parameter adjustments enable the separator to maintain stable displacement ratios during loading-unloading cycles, resolving the contradiction between reliability and compositional stability.
Solution Approach 2:
The invention makes the separator dynamically adaptive by designing it with specific compression characteristics that allow controlled deformation during charge-discharge cycles. The separator can deform to accommodate electrode expansion and shrinkage while maintaining stable mechanical properties over long-term cycling, thus improving reliability without sacrificing stability.
2Strength
If the separator is made more rigid to prevent deformation, then structural stability improves, but gap formation between separator and electrodes occurs during electrode expansion and shrinkage, reducing battery performance
Solution Approach 1:
The invention uses a flexible polyolefin porous film with controlled compression characteristics instead of a rigid separator. This flexible structure can deform with electrode expansion and shrinkage during charge-discharge cycles, preventing gap formation while maintaining sufficient structural strength. The flexibility allows the separator to adapt to electrode dimensional changes without compromising structural integrity.
3Reliability
If the separator allows more deformation to accommodate electrode expansion, then contact maintenance improves, but excessive plastic deformation occurs, leading to separator failure and reduced cycle life
Solution Approach 1:
The invention provides beforehand cushioning by designing the separator with specific compression characteristics that absorb and distribute mechanical stress from electrode expansion and shrinkage. The controlled amount of compression deformation and its increase rate act as a cushioning mechanism, preventing excessive plastic deformation and separator failure during long-term cycling, thus extending service life while maintaining electrode contact.
Solution Approach 2:
The invention performs preliminary action by pre-configuring the separator's compression characteristics and pore ratio during manufacturing. This preliminary structuring ensures the separator has the appropriate mechanical properties before battery operation, enabling it to maintain stable displacement ratios during loading-unloading cycles and prevent both gap formation and excessive deformation throughout its service life.
Data Source
AI summary
An embodiment of the present invention provides, as a nonaqueous electrolyte secondary battery separator excellent in cycle characteristic, a nonaqueous electrolyte secondary battery separator including a polyolefin porous film, wherein a ratio of a displacement amount of the nonaqueous electrolyte secondary battery separator at a 10th loading-unloading cycle to a displacement amount of the nonaqueous electrolyte secondary battery separator at a 50th loading-unloading cycle is in a range of 100% to 130%.