Microporous Polyolefin Separator Coating for Heat-Stable Shutdown
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Solution Overview
Problem
Existing lithium-ion battery separators lack sufficient in-plane dimensional stability and shutdown properties at elevated temperatures, leading to potential internal short circuits and thermal runaway due to differential shrinkage between inorganic surface layers and polyolefin base membranes, and existing solutions do not effectively address interfacial stress and heat resistance.
Innovation Solution
A thin, freestanding microporous polyolefin web with an inorganic surface layer containing colloidal inorganic particles that penetrate into the bulk structure, combined with an organic hydrogen bonding component, to achieve dimensional stability and shutdown properties, while preventing internal short circuits and providing heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an inorganic surface layer is coated on a polyolefin separator to improve heat resistance, then thermal stability is improved, but in-plane dimensional stability deteriorates due to differential shrinkage
Solution Approach 1:
The patent applies different treatments to different regions of the separator. The inorganic surface layer is selectively coated only on specific areas rather than uniformly across the entire separator, allowing heat resistance to be improved in critical zones while minimizing differential shrinkage effects on overall dimensional stability.
Solution Approach 2:
The patent creates a composite structure combining polyolefin base material with inorganic surface layers. This composite approach allows the separator to simultaneously exhibit the heat resistance of inorganic materials and the dimensional stability of the polyolefin matrix, resolving the contradiction between thermal stability and dimensional stability.
2Reliability
If the polyolefin separator undergoes rapid drawdown to create microporous structure, then ionic conductivity is improved, but mechanical strength deteriorates
Solution Approach 1:
The patent utilizes a microporous structure created through rapid drawdown of the polyolefin separator. This porous architecture enables efficient ion transport across the separator while the controlled pore distribution and size maintain sufficient mechanical integrity, resolving the trade-off between ionic conductivity and mechanical strength.
Solution Approach 2:
The patent optimizes processing parameters during rapid drawdown, including draw ratio, heating temperature, and cooling rate, to achieve the desired balance between micropore formation for ionic conductivity and maintenance of mechanical strength. By precisely controlling these parameters, the separator attains optimal performance characteristics.
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 solution reduces interfacial stress, maintains shutdown characteristics, and ensures good heat resistance and in-plane dimensional stability above the melting point of the polyolefin base membrane, thereby enhancing the safety and performance of lithium-ion batteries.
Implementation Method 1
colloidal inorganic particles are present in its bulk structure
Implementation Method 2
Shutdown results from the collapse of pores in the separator caused by melting and viscous flow of the polymer
Implementation Method 3
an organic hydrogen bonding component, to achieve dimensional stability and shutdown properties
Data Source
AI summary
A thin, freestanding, microporous polyolefin web with good heat resistance and dimensional stability includes an inorganic surface layer. A first preferred embodiment is a microporous polyolefin base membrane in which colloidal inorganic particles are present in its bulk structure. Each of second and third preferred embodiments is a thin, freestanding microporous polyolefin web that has an inorganic surface layer containing no organic hydrogen bonding component for the inorganic particles. The inorganic surface layer of the second embodiment is achieved by hydrogen bonding with use of an inorganic acid, and the inorganic surface layer of the third embodiment is achieved by one or both of hydrogen bonding and chemical reaction of the surface groups on the inorganic particles.