Microporous Separator Webs With Shutdown and Dimensional Stability
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Solution Overview
Problem
Lithium-ion battery separators face challenges with residual stress and mechanical property degradation above the polymer melting point, leading to potential internal short circuits and thermal runaway due to shrinkage and pinhole formation, which complicates the guarantee of sufficient and uniform shutdown in large format cells.
Innovation Solution
Development of freestanding microporous polymer webs using ultrahigh molecular weight polyethylene (UHMWPE) as a base membrane, combined with inorganic surface coatings and gel-forming polymer layers, which maintain dimensional stability and ionic conduction while allowing shutdown at elevated temperatures, preventing electrode contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyethylene separator is used to achieve shutdown at low temperature, then shutdown properties are improved, but dimensional stability deteriorates above melting point
Solution Approach 1:
The patent uses a composite structure consisting of a polyethylene base membrane (providing shutdown at 130°C) combined with a heat-resistant porous coating layer containing high melting point polymers (providing dimensional stability above 130°C). This composite structure allows the separator to maintain both shutdown properties and dimensional stability across a wide temperature range.
Solution Approach 2:
The separator is divided into two functional segments: the base membrane layer responsible for low-temperature shutdown and the heat-resistant coating layer responsible for high-temperature dimensional stability. This segmentation allows each layer to independently perform its specific function without interfering with the other.
2Temperature
If heat-resistant coating is applied to maintain dimensional stability, then thermal stability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent modifies the coating layer's porosity parameter (30-70% porosity) and composition to balance thermal stability with manufacturing feasibility. The porous structure allows the coating to be formed through conventional battery manufacturing processes while maintaining the necessary heat-resistant properties.
3Stability of the object's composition
If inorganic filler is added to prevent shrinkage, then dimensional stability is improved, but ionic conduction decreases
Solution Approach 1:
The heat-resistant coating layer is designed with controlled porosity (30-70%) to maintain ion transport channels. This porous structure allows lithium ions to conduct through the coating layer while the inorganic filler particles provide dimensional stability and prevent shrinkage at high temperatures.
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 provides enhanced thermal stability, dimensional stability, and shutdown properties, reducing the risk of internal short circuits and thermal runaway, thereby improving the safety and performance of lithium-ion batteries.
Implementation Method 1
the inorganic material has a coating ratio...sufficient to maintain in-plane dimensional stability above the melting point of the polyolefin membrane
Implementation Method 2
the gel-forming polymer material gels in the presence of electrolyte during manufacture of the energy storage device
Implementation Method 3
permitting ionic conduction by means of the electrolyte
Implementation Method 4
Shutdown results from the collapse of pores in the separator caused by melting and viscous flow of the polymer
Data Source
AI summary
Laminable microporous polymer webs wish good dimensional stability are disclosed herein. Methods of making and using laminable microporous polymer webs with good dimensional stability are also disclosed herein.