Staged Heat-Setting for Microporous Battery Separators
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Solution Overview
Problem
Existing microporous membranes used as battery separators lack uniform air permeability and high mechanical strength, leading to inefficiencies in battery performance and safety, particularly in lithium-ion batteries, where high temperature exposure poses risks.
Innovation Solution
A method for producing microporous membranes involving staged heat-setting, where the membrane is stretched in a dry orientation zone at an elevated temperature and then heat-set in multiple stages, with the initial stage operating at least 15°C cooler than the final stage, to achieve uniform air permeability and high puncture strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If single-stage heat-setting is used, then production efficiency is improved, but air permeability uniformity deteriorates
Solution Approach 1:
The heat-setting process is divided into multiple stages with different temperature conditions. The first stage uses a lower temperature (at least 15°C cooler than the final stage) to initially set the membrane structure, while subsequent stages progressively increase temperature to achieve uniform air permeability. This segmentation allows each stage to contribute differently to the final product quality, resolving the contradiction between production efficiency and manufacturing precision.
2Strength
If high stretching temperature is used, then membrane strength is improved, but heat shrinkage increases
Solution Approach 1:
The first heat-setting stage is performed at a lower temperature before the final high-temperature stage. This preliminary action partially sets the membrane structure and reduces residual stresses, allowing the subsequent high-temperature stage to achieve high strength without excessive heat shrinkage. The staged approach prepares the membrane in advance for the final temperature treatment.
3Manufacturing precision
If uniform pore distribution is achieved, then air permeability is improved, but mechanical strength deteriorates
Solution Approach 1:
The heat-setting temperature is changed in stages rather than applied uniformly. The first stage uses lower temperature to establish uniform pore distribution, while subsequent stages progressively increase temperature to strengthen the membrane structure. This parameter change strategy allows the membrane to achieve both uniform porosity and high mechanical strength by optimizing thermal conditions at different processing stages.
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 results in a microporous membrane with a standard deviation of air permeability of 15 seconds or less across the transverse direction, puncture strength of 3,500 mN or more, and low heat shrinkage, enhancing battery safety and performance by maintaining high permeability and mechanical strength.
Implementation Method 1
heat-setting the microporous polymeric membrane in at least a first stage and a final stage, the first stage being upstream of the final stage, the temperature of the first stage being at least 15°C cooler than the temperature of the final stage
Implementation Method 2
stretching the microporous polymeric membrane in at least one planar direction in a dry orientation zone at an elevated temperature
Data Source
AI summary
A microporous polymeric membrane having excellent properties for use as a battery separator is provided. The membrane is produced by stretching and then heat-setting the microporous polymeric membrane in at least an upstream stage and a downstream stage, the temperature of the upstream stage being at least 15°C cooler than the temperature of the downstream stage.