Microporous Polyolefin Separator for Thin Li-Ion Cell Safety
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge is to develop a thin-film electricity storage device separator with high strength, high safety, and high dimensional stability at high temperatures, while maintaining high output and preventing clogging, as polyolefins with high molecular weight hinder film thinning due to increased melt tension and viscosity.
Innovation Solution
A microporous layer composed of polyolefin with a specific melt flow rate, average long pore diameter, and melt tension, combined with a polypropylene or polyethylene component, is used to create a separator with enhanced strength, safety, and dimensional stability, allowing for film thinning and improved air permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyolefins with high molecular weight are used to increase strength, then puncture strength is improved, but film thinning becomes difficult due to increased melt tension and viscosity
Solution Approach 1:
The patent applies parameter changes by precisely controlling the melt flow rate (MFR) of the polyolefin within 0.01 to 1.0 mL/10 min and the molecular weight distribution (Mw/Mn) within 3.0 to 10.0. This optimization allows the resin to have sufficiently high molecular weight for strength while maintaining adequate processability for film thinning, resolving the contradiction between strength and thinness.
Solution Approach 2:
The patent uses composite materials by combining polyolefin with specific additives including inorganic fillers (such as alumina, silica), lubricants, and nucleating agents. This composite approach enhances the mechanical strength and thermal stability of thin films without requiring excessively high molecular weights, thereby enabling both thinness and strength.
2Reliability
If polyolefins with high molecular weight are used to improve strength, then safety is improved, but air permeability decreases due to reduced porosity
Solution Approach 1:
The patent employs porous materials by incorporating inorganic fillers (alumina, silica, titania) with specific surface areas and pore structures into the polyolefin matrix. These fillers create controlled porosity that maintains air permeability while the polyolefin matrix provides the safety function through its melt closure characteristics at elevated temperatures.
Solution Approach 2:
The composite structure of polyolefin combined with inorganic fillers and lubricants creates a material system where the inorganic phase maintains porosity for air permeability while the polyolefin phase provides safety through thermal response, resolving the contradiction between safety and air permeability.
3Stability of the object's composition
If polyolefins with high molecular weight are used to increase strength, then dimensional stability at high temperatures is improved, but heat shrinkage increases
Solution Approach 1:
The patent applies parameter changes by optimizing the melt flow rate to 0.01-1.0 mL/10 min and incorporating nucleating agents that promote crystallization. This controlled crystallization structure provides dimensional stability at high temperatures while minimizing anisotropic shrinkage, resolving the contradiction between dimensional stability and heat shrinkage.
Solution Approach 2:
The composite material system includes nucleating agents and lubricants that control the crystallization behavior and molecular orientation of the polyolefin. This results in a more isotropic crystal structure that reduces directional heat shrinkage while maintaining high-temperature dimensional stability.
Data Source
AI summary
Provided are a thin-film separator for a power storage device, the separator having high strength and reduced clogging, and a power storage device separator that provides high strength, high level of safety, and high dimensional stability at high temperature, and that can be formed in a thin film. One aspect provides a power storage device separator comprising a fine-porous layer (X) consisting mainly of polyolefin (A), the fine-porous layer (X) having a melt flow rate of less than or equal to 0.9 g/10 min, and having an average long-hole diameter of more than or equal to 100 nm according to MD-TD surface observation or ND-MD cross-sectional observation with a scanning electron microscope.