Single-Layer Lithium Ion Battery Separator with Low Shrinkage
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Solution Overview
Problem
Current battery separators fail to simultaneously provide low air resistance, low pore size, high tensile strength, isotropic mechanical properties, chemical stability, and dimensional stability, especially under elevated temperatures, which are crucial for long-term reliable lithium battery performance.
Innovation Solution
A polymeric battery separator comprising a single layer of enmeshed microfibers and nanofibers, manufactured through a wet-laid nonwoven fabrication process, offering isotropic strength, controlled pore size, and high porosity, with nanofibers intermingled within microfiber interstices, allowing for efficient ion transport and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If traditional film structure separators are used, then weight and volume are reduced, but dimensional stability and mechanical strength deteriorate at high temperatures
Solution Approach 1:
The separator combines polypropylene microfibers (providing mechanical strength and heat resistance) with polyester nanofibers (providing porosity control and chemical stability) to create a composite nonwoven fabric that achieves both low weight and high dimensional stability at elevated temperatures
Solution Approach 2:
The separator uses bimodal fiber distribution where nanofibers concentrate in specific regions to control pore sizes locally, while microfibers provide overall structural support, allowing different zones of the separator to optimize for different functions (ion transport vs. mechanical strength)
2Reliability
If pore size is reduced to prevent electrode contact, then safety is improved, but air resistance and ion transport resistance increase
Solution Approach 1:
The separator utilizes a controlled porous nonwoven structure with pore sizes between 0.03-0.08 micrometers that are small enough to prevent electrode contact but large enough to allow efficient ion transport, achieving both safety and low air resistance through optimized pore architecture
Solution Approach 2:
The separator transitions from a two-dimensional film structure to a three-dimensional nonwoven fabric with controlled porosity, creating a hierarchical pore structure that provides multiple pathways for ion transport while maintaining small effective pore sizes for safety
3Strength
If tensile strength is increased to prevent separator failure, then mechanical reliability is improved, but isotropic mechanical properties deteriorate
Solution Approach 1:
The separator employs a random nonwoven fabric structure with uniformly distributed microfibers and nanofibers that creates isotropic mechanical properties in all directions, eliminating the directional strength variations found in traditional extruded film separators
4Productivity
If porosity is increased to improve ion transport, then energy storage capacity is improved, but mechanical strength and pore size control deteriorate
Solution Approach 1:
The separator achieves precise pore size control (0.03-0.08 micrometers) and high porosity (40-60%) by controlling fiber diameter distribution, fiber length, and nonwoven fabrication parameters, allowing optimization of both ion transport efficiency and pore size uniformity
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 separator achieves low air resistance, low pore sizes, high tensile strength, and dimensional stability, enabling long-term battery performance with reduced risk of electrode contact and enhanced energy storage capacity.
Implementation Method 1
a single layer of enmeshed microfibers and nanofibers
Implementation Method 2
permit effective transport of electrolytes within power generating cells
Implementation Method 3
shrinks less than 5% when exposed to a temperature of 200° C. for 1 hour
Data Source
AI summary
An insulating (nonconductive) microporous polymeric battery separator comprised of a single layer of enmeshed microfibers and nanofibers is provided. Such a separator accords the ability to attune the porosity and pore size to any desired level through a single nonwoven fabric. Through a proper selection of materials as well as production processes, the resultant battery separator exhibits isotropic strengths, low shrinkage, high wettability levels, and pore sizes related directly to layer thickness. The overall production method is highly efficient and yields a combination of polymeric nanofibers within a polymeric microfiber matrix and/or onto such a substrate through high shear processing that is cost effective as well. The separator, a battery including such a separator, the method of manufacturing such a separator, and the method of utilizing such a separator within a battery device, are all encompassed within this invention.