Lithium Battery Separator Punch Process Heat Resistance
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Solution Overview
Problem
Current lithium battery separators with multi-layer structures face issues with thermal runaway and explosion due to shrinkage of microporous polyolefin films at elevated temperatures, which compromises the electrical insulation between electrodes.
Innovation Solution
A separator manufacturing method involving a punch process to form a middle layer without stretch processing, combined with adhesive layers and microporous polyolefin layers, enhancing heat resistance and mechanical strength by maintaining structural integrity at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a microporous polyolefin separator with multi-layer structure is used, then the shutdown function at elevated temperature is improved, but the separator shrinks at sustained high temperature causing edge exposure and increasing thermal runaway risk
Solution Approach 1:
The patent uses a composite structure consisting of a polyolefin layer and a heat-resistant non-polyolefin layer. The polyolefin layer provides the shutdown function by melting at elevated temperature to block pores, while the heat-resistant non-polyolefin layer maintains structural stability and prevents shrinkage at sustained high temperatures. This composite material approach resolves the contradiction by combining materials with complementary properties.
2Strength
If polypropylene layers are used in the tri-layer separator, then the breakdown strength and heat resistance are improved, but the separator still shrinks at sustained 130°C causing edge exposure
Solution Approach 1:
The patent combines polypropylene (providing high breakdown strength) with a heat-resistant non-polyolefin material (providing dimensional stability). The polypropylene layer maintains mechanical strength and provides shutdown function, while the heat-resistant layer prevents shrinkage and maintains dimensional stability at sustained high temperatures, thus resolving the contradiction between strength and dimensional stability.
3Object-generated harmful factors
If stretch processing is applied to form microporous structure, then the microporous structure is created, but the mechanical strength and heat resistance are reduced at elevated temperature
Solution Approach 1:
The patent replaces the mechanical stretch processing method with a chemical etching or phase separation method to form the microporous structure. This substitution avoids the mechanical stress and molecular orientation caused by stretching, thereby preserving the mechanical strength and heat resistance of the polymer while still creating the necessary microporous structure for ion transport.
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 improved heat resistance and mechanical strength, reducing the risk of thermal runaway and explosion by maintaining the separator's structure and electrical insulation even at elevated temperatures, as demonstrated by reduced shrinkage and increased tensile strength compared to commercial tri-layer separators.
Implementation Method 1
the microporous structure of the middle layer, the first adhesive layer and the second adhesive layer are individually formed by a punch process
Implementation Method 2
a first adhesive layer on one side of the middle layer bonding the middle layer and the first polyolefin layer; and a second adhesive layer on another side of the middle layer configured for bonding the middle layer and the second polyolefin layer
Implementation Method 3
the separator with a punched middle layer has a better heat resistant and a high mechanical strength at the elevated temperature
Data Source
AI summary
The present disclosure provides a separator for lithium battery, particularly to a separator including a middle layer formed by a punch method. Also, a manufacturing method of the separator is provided. The separator formed by the punch method has a better heat-resistant property in an elevated temperature and features a high mechanical strength.