Polyolefin Separator Surface Roughness Control
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Solution Overview
Problem
Conventional nonaqueous electrolyte secondary battery separators lack both high strength and low shutdown temperature (SD temperature) simultaneously.
Innovation Solution
A nonaqueous electrolyte secondary battery separator using a polyolefin porous film with a specific surface roughness ratio and thickness, balanced with a crystalline and non-crystalline fibrous structure, enhancing both piercing strength and shutdown temperature performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the separator uses a polyolefin porous film with conventional structure, then the manufacturing process is simple, but the separator cannot simultaneously achieve high strength and low shutdown temperature
Solution Approach 1:
The patent applies local quality by creating a surface layer with different properties from the base layer. The surface layer has controlled roughness (Ra 0.03-0.15 μm) that provides low shutdown temperature, while the base layer maintains the mechanical strength. This layered approach with differentiated local properties resolves the contradiction between strength and shutdown temperature.
Solution Approach 2:
The patent changes physical parameters of the separator, specifically controlling the surface roughness Ra within 0.03-0.15 μm and the product of roughness differences in MD and TD directions within 0.0020-0.0280 μm². By precisely controlling these surface parameter changes, the separator achieves both high piercing strength and low shutdown temperature simultaneously.
2Productivity
If the separator thickness is reduced to improve battery density, then the energy density increases, but the piercing strength decreases
Solution Approach 1:
The patent uses a thin film structure with controlled surface properties to maintain strength while reducing thickness. The specific surface roughness control (Ra 0.03-0.15 μm) allows the thin separator to achieve both high energy density and sufficient piercing strength, resolving the contradiction between thickness reduction and strength maintenance.
3Temperature
If the surface roughness is increased to improve shutdown temperature performance, then the SD temperature decreases, but the manufacturing precision requirements increase
Solution Approach 1:
The patent defines specific parameter ranges for surface roughness (Ra 0.03-0.15 μm) and the product of roughness differences (0.0020-0.0280 μm²) to achieve the desired shutdown temperature while providing clear manufacturing targets that balance performance improvement with manufacturability.
Data Source
AI summary
The present invention provides, as a separator having both a sufficient level of safety and sufficient strength, a nonaqueous electrolyte secondary battery separator including a polyolefin porous film, the nonaqueous electrolyte secondary battery separator being arranged such that in regard to a surface of the nonaqueous electrolyte secondary battery separator, a product obtained by multiplying (a) a difference between a surface roughness in a machine direction obtained by a contact measurement and a surface roughness in the machine direction obtained by a non-contact measurement by (b) a difference between a surface roughness in a transverse direction obtained by a contact measurement and a surface roughness in the transverse direction obtained by a non-contact measurement is not less than 0.0020 and not more than 0.0280.