Separator Tensile Strength via Intermittent Biaxial Stretching
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Solution Overview
Problem
Current separator manufacturing methods for electrochemical batteries fail to achieve sufficient tensile strength, particularly in the machine and transverse directions, which limits high-rate winding productivity and increases the risk of breakage during the winding process.
Innovation Solution
A method involving temporary stopping during the stretching process of a polyolefin base film, specifically using sequential biaxial stretching and the wet process to enhance tensile strength while maintaining low thermal shrinkage, resulting in a separator with improved winding processability and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous biaxial stretching is performed to improve manufacturing efficiency, then productivity is improved, but tensile strength is insufficient
Solution Approach 1:
The patent applies periodic action by implementing intermittent stretching with stopping periods. The stretching process is divided into multiple stages with temporary stops, where the film is stretched, then stopped for a predetermined period, and then stretched again. This periodic action allows molecular chains to reorient and crystallize during stopping periods, thereby increasing tensile strength while maintaining overall manufacturing efficiency through continuous batch processing.
2Productivity
If stretching rate is increased to improve productivity, then manufacturing speed is improved, but tensile strength development is insufficient
Solution Approach 1:
The patent applies preliminary action by performing initial stretching at a controlled rate to establish a baseline structure, then stopping before completing the full stretching. This preliminary stretching action creates an intermediate state that allows subsequent stretching stages to build upon a more favorable molecular arrangement, ultimately achieving higher tensile strength while maintaining productive manufacturing speeds.
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 method increases tensile strength to 1,900 kgf/cm2 or more in both directions, reduces thermal shrinkage to 1% or less, and enhances puncture strength, preventing breakage during high-rate winding and ensuring excellent thermal stability for secondary batteries.
Implementation Method 1
stretching a polyolefin base film in the machine direction and/or in the transverse direction
Implementation Method 2
a thermal shrinkage of 1% or less both in the machine direction and in the transverse direction, as measured after being left at 105° C. for 1 hour
Data Source
AI summary
The present invention relates to a method for manufacturing a separator for batteries, a separator manufactured by the method, and a secondary battery including the separator. More specifically, the present invention relates to a method for manufacturing a separator having enhanced tensile strength by performing a shutdown process stopping a stretch during a process of stretching a base film of the separator.