Multilayer Porous Membrane Structure for Battery Heat Shrinkage Resistance
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Solution Overview
Problem
Conventional multilayer porous membranes used in lithium ion secondary batteries for on-vehicle applications face challenges in ensuring safety and heat shrinkage resistance, particularly when subjected to nail penetration testing, due to their thickness and structure, which can lead to short circuiting.
Innovation Solution
A multilayer porous membrane with specific pore structure and composition, including a polyolefin resin base and porous layers containing inorganic particles and a binder polymer, is developed, with controlled thickness, hole distribution, and air permeability to enhance safety and resistance against heat shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the thickness of the porous layer is reduced to decrease separator thickness, then energy density and battery thickness are improved, but heat shrinkage resistance deteriorates significantly
Solution Approach 1:
The patent uses composite materials by combining inorganic particles (alumina, silica, titania, zirconia, magnesia, or boehmite) with binder polymers to form a porous layer that achieves high heat shrinkage resistance even at reduced thickness. The inorganic particles provide thermal stability while the binder polymer provides structural integrity, creating a composite that maintains strength despite thinning the separator.
Solution Approach 2:
The patent employs porous materials with specific pore structures (porosity of 30-70%, mean pore size of 0.01-1.0 μm) in the porous layer to maintain ion permeability while achieving high heat shrinkage resistance. The porous structure allows ion transport while the inorganic particles and binder polymer framework provide mechanical strength and heat resistance even at thin configurations.
2Reliability
If the porous layer thickness is increased to improve heat shrinkage resistance, then safety is improved, but battery thickness and energy density deteriorate
Solution Approach 1:
The composite of inorganic particles and binder polymer achieves high heat shrinkage resistance (heat shrinkage factor of 5% or less at 150°C) with minimal thickness (0.1-5.0 μm). This composite structure provides exceptional strength-to-thickness ratio, enabling high safety performance without increasing battery thickness.
Solution Approach 2:
The patent optimizes parameters including inorganic particle size (0.1-10.0 μm), porosity (30-70%), and binder polymer content to achieve maximum heat shrinkage resistance at minimum thickness. By controlling these parameters, the porous layer achieves heat shrinkage factors of 5% or less at 150°C while maintaining thickness within 0.1-5.0 μm.
3Reliability
If conventional porous layers are used to maintain current safety levels, then heat shrinkage resistance is maintained, but further safety improvements for on-vehicle applications cannot be achieved
Solution Approach 1:
The patent creates a superior composite material system combining specific inorganic particles (alumina, silica, titania, zirconia, magnesia, or boehmite) with binder polymers that achieves heat shrinkage factors of 5% or less at 150°C. This composite provides a foundation for further safety improvements while maintaining compatibility with battery performance requirements.
Solution Approach 2:
The patent develops porous materials with optimized pore structures (porosity of 30-70%, mean pore size of 0.01-1.0 μm) that maintain excellent ion permeability while achieving exceptional heat shrinkage resistance. This porous composite structure enables continued safety improvements for on-vehicle applications without compromising battery performance.
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 membrane provides improved safety and heat shrinkage resistance, maintaining battery characteristics and preventing short circuiting during nail penetration tests, while allowing for higher energy density and reduced thickness.
Implementation Method 1
the heat shrinkage-inhibiting functions of the conventional multilayer porous membranes described in PTLs 1 and 2 have been insufficient for the demands of high safety and high capacity for on-vehicle purposes
Implementation Method 2
Separators are generally required to have ion permeability and to also exhibit safety, including a shutdown function, and therefore separators comprising microporous membranes with polyolefin resins have been used
Data Source
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Figure 5
AI summary
A multilayer porous membrane comprising: a porous membrane that contains a polyolefin resin as a main component, a first porous layer that contains inorganic particles and a binder polymer, disposed on one side of the porous membrane, and a second porous layer that contains inorganic particles and a binder polymer, disposed on the other side of the porous membrane, wherein in a 400°C solder test in which the multilayer porous membrane is pierced with a soldering iron having a diameter of 1 mm and a temperature of 400°C, and the piercing soldering iron is held for 3 seconds and then removed, an area of a hole formed in the multilayer porous membrane is 10.0 mm2 or smaller whether the soldering iron has been inserted from the first porous layer side or the second porous layer side, and wherein (i) the basis weight-equivalent puncture strength of the porous membrane is 50 gf/(g/m2) or greater or (ii) the heat shrinkage factor of the multilayer porous membrane at 150°C is lower than 10.0%.