Polyolefin Separator Gloss Ratio Crease Recovery
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Solution Overview
Problem
Nonaqueous electrolyte secondary battery separators are prone to deformation, such as creasing or bending, due to anisotropy in crease recovery angles during storage, transport, and production, making them difficult to handle effectively.
Innovation Solution
A nonaqueous electrolyte secondary battery separator featuring a polyolefin porous film with a controlled 60-degree gloss ratio in the machine direction (MD) to transverse direction (TD) of at least 1.00, potentially combined with an insulating porous layer, to reduce anisotropy and enhance crease recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional nonaqueous electrolyte secondary battery separator is used, then the separator can be manufactured with standard properties, but the separator becomes easily deformed (creased or bent) during storage, transport, and production due to large anisotropy in crease recovery angles
Solution Approach 1:
The invention changes the physical parameter of surface gloss anisotropy by controlling the MD/TD gloss ratio to be 1.00 or more. This parameter change directly addresses the crease recovery angle anisotropy problem, as the surface gloss ratio correlates with the anisotropy in mechanical recovery properties. By adjusting this optical parameter, the invention achieves isotropic crease recovery behavior, improving handleability during storage and transport.
Solution Approach 2:
The invention applies asymmetry principle in reverse by eliminating directional asymmetry. Conventional separators exhibit asymmetric behavior between MD and TD directions in terms of crease recovery. The invention makes the separator symmetric in its recovery properties by ensuring the MD/TD gloss ratio is 1.00 or more, thereby achieving uniform crease recovery angles in both directions and eliminating the deformation issues caused by directional asymmetry.
2Reliability
If the polyolefin porous film has high ion permeability and mechanical strength, then the battery performance is improved, but the separator becomes more prone to folding and deformation under stress
Solution Approach 1:
The invention changes the surface optical parameter (gloss ratio) to control the mechanical behavior under stress. By setting the MD/TD gloss ratio to 1.00 or more, the invention modifies how the porous film responds to folding stresses, reducing anisotropic deformation while maintaining the inherent ion permeability and mechanical strength properties of the polyolefin material.
Solution Approach 2:
The invention applies homogeneity by making the mechanical recovery properties uniform across different directions. The controlled gloss ratio ensures that the separator exhibits homogeneous behavior in both MD and TD directions, preventing preferential folding along specific axes and thereby improving overall shape stability while maintaining high reliability properties.
Data Source
AI summary
As a nonaqueous electrolyte secondary battery separator having a transverse direction/machine direction crease recovery angle ratio of close to 1, a nonaqueous electrolyte secondary battery separator is provided that includes a polyolefin porous film having a ratio of a 60-degree gloss in an machine direction to a 60-degree gloss in a transverse direction which ratio is not less than 1.00.