Laminated Microporous Separator for High-Voltage Battery Safety
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Solution Overview
Problem
Lithium ion secondary batteries face increased safety risks when the charge voltage exceeds 4.2V, requiring a separator that enhances safety without deteriorating load characteristics.
Innovation Solution
A battery design utilizing a separator formed by laminated microporous membranes with a film thickness of 10x μm and a piercing strength of 150x gf or more, where one layer's air permeability is equal to or greater than 10% or 35% of the whole separator's, made from polyolefin materials like polyethylene, to prevent abnormal temperature increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the charge voltage is raised to 4.25V or more to realize high energy density, then the energy density is improved, but the safety risk increases due to higher degree of risk from erroneous usage
Solution Approach 1:
The separator is divided into multiple layers with different functions: a first microporous membrane layer for shutdown function and a second microporous membrane layer for mechanical strength. This segmentation allows each layer to specialize in one aspect, enabling the separator to provide both safety shutdown capability and high piercing strength simultaneously
Solution Approach 2:
The separator uses a composite structure combining polyethylene microporous membrane (for shutdown function at low temperature) and polypropylene microporous membrane (for high temperature stability and mechanical strength). This composite material approach allows the separator to exhibit both shutdown behavior at abnormal temperatures and high piercing strength to prevent dendrite penetration
2Reliability
If the separator film thickness is increased to improve piercing strength and safety, then the safety is improved, but the load characteristics deteriorate due to increased resistance
Solution Approach 1:
The separator is segmented into two functional layers: the first microporous membrane layer (thickness 3-10 μm) provides shutdown function and the second microporous membrane layer (thickness 7-20 μm) provides mechanical strength. This segmentation allows the total thickness to be optimized for both safety and performance, preventing the need to increase thickness uniformly which would harm load characteristics
Solution Approach 2:
Different regions of the separator have different thicknesses and properties: the first layer has lower thickness optimized for shutdown function while the second layer has higher thickness optimized for mechanical strength. This local differentiation allows each region to perform its specific function optimally without compromising overall performance
3Reliability
If the separator structure is modified to enhance safety features, then the safety is improved, but the load characteristics deteriorate
Solution Approach 1:
The separator structure is segmented into functional layers with the first microporous membrane layer dedicated to shutdown function and the second layer dedicated to mechanical support. This functional segmentation allows safety features to be enhanced without adding unnecessary mass or resistance that would deteriorate load characteristics
Solution Approach 2:
The separator optimizes parameters including thickness ratio (first layer 3-10 μm, second layer 7-20 μm), porosity (30-80% for first layer, 20-60% for second layer), and air permeability to achieve both enhanced safety and maintained load characteristics through precise parameter control
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 effectively suppresses temperature increases in abnormal states without compromising load characteristics, ensuring both safety and performance of the battery.
Implementation Method 1
a first microporous membrane layer made of polyethylene... to suppress an abnormal temperature increase
Implementation Method 2
a separator formed by a plurality of laminated microporous membranes... arranged so as to face each other with having a separator in between
Data Source
AI summary
A battery in which a cathode and an anode are arranged so as to face each other an having a separator in between is provided. The separator is formed from a plurality of laminated microporous membranes and has a film thickness of 10xμm and a piercing strength of 150x gf or more, where 1≦x≦2. The air permeability of one layer among the plurality of microporous membranes is equal to or larger than 10% of the air permeability of the whole separator.