Heat-Shrink Sleeve Film for Battery Post-Shrinkage Control
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Solution Overview
Problem
Residual stress in sleeve films of cylindrical battery cells leads to post shrinkage during cycling, exposing bare steel shells and posing a risk of short circuits, affecting safety and reliability.
Innovation Solution
A heat-shrink sleeve film with a framework material and a functional polymer having a controlled glass transition temperature, allowing molecular chain segments to move at low temperatures to release internal stress, ensuring dimensional stability throughout the battery's life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a sleeve film is wrapped and heated to induce shrinkage during battery production, then the sleeve film wraps the steel shell and covers the end, but residual stress is generated in the sleeve film
Solution Approach 1:
The patent changes the glass transition temperature parameter of the polymer material to a specific range (−50°C to 0°C) to enable stress release at battery operating temperatures. This parameter modification allows the material to transition from a rigid state during shrinkage to a more flexible state during cycling, releasing residual stress without compromising the initial wrapping function.
Solution Approach 2:
The patent uses a composite polymer structure consisting of crystalline regions (for structural integrity and shrinkage) and amorphous regions with specific glass transition temperature (for stress release). This composite material design combines the benefits of both crystalline and amorphous phases to simultaneously achieve shape control and stress management.
2Stability of the object's composition
If residual stress is not released during processing or cycling, then post shrinkage occurs in later stages of battery cycling, but releasing stress requires specific material properties
Solution Approach 1:
The patent performs preliminary stress release action during the shrinkage process by designing the material to automatically release residual stress when exposed to battery operating temperatures. This preliminary stress relief prevents future dimensional instability and potential safety issues during long-term cycling without requiring additional processing steps.
Solution Approach 2:
The patent modifies the glass transition temperature parameter to occur within the battery's normal operating temperature range, enabling the material to dynamically adjust its mechanical properties. This parameter change allows the sleeve film to maintain dimensional stability during storage and initial operation while releasing accumulated stress during normal cycling, thereby preventing post-shrinkage and maintaining reliability.
3Stress or pressure
If the glass transition temperature of the functional polymer is controlled to allow molecular chain movement at low temperature, then internal residual stress is released, but the material composition becomes more complex
Solution Approach 1:
The patent employs a composite polymer material with distinct crystalline and amorphous phases, where the amorphous phase has a specifically controlled glass transition temperature. This composite structure enables stress release functionality while maintaining a relatively simple overall material composition that can be processed using conventional extrusion and shrinkage techniques.
Solution Approach 2:
The patent introduces local quality by creating regions with different thermal properties within the polymer structure. The amorphous regions with specific glass transition temperature serve as stress-release zones, while the crystalline regions maintain structural integrity. This local differentiation enables stress release functionality without requiring complex overall material composition.
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 alleviates post shrinkage during cycling, improving high- and low-temperature performance by maintaining dimensional stability and preventing exposure of bare steel shells.
Implementation Method 1
a glass transition temperature of the functional polymer is −80° C. to 50° C., and a glass transition temperature of the heat-shrink sleeve film is less than or equal to 10° C. to 65° C.
Implementation Method 2
molecular chain segments of the functional polymer can move at a relatively low temperature (near the glass transition temperature of the functional polymer), and this property is used to release the internal residual stress of the heat-shrink sleeve film
Implementation Method 3
a sleeve film is typically wrapped outside a steel shell of the battery cell and heated to induce transverse shrinkage to wrap a wall of the steel shell and induce longitudinal shrinkage to cover an end of the steel shell
Data Source
AI summary
A heat-shrink sleeve film includes a framework material and a functional polymer, where a glass transition temperature of the functional polymer is −80° C. to 50° C., and a glass transition temperature of the heat-shrink sleeve film is 10° C. to 65° C. The heat-shrink sleeve film releases its internal residual stress during processing or cycling of a battery, thereby alleviating the post shrinkage of a battery cell in a later stage of cycling, and improving the high- and low-temperature performance of the battery cell.