Multi-layer Microporous Battery Separator for Pin Puncture Strength
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Solution Overview
Problem
Microporous polyolefin membranes used as battery separators face challenges in achieving optimal permeability, pin puncture strength, shutdown speed, and thickness uniformity, which affect battery safety and performance, particularly in lithium-ion batteries.
Innovation Solution
A multi-layer microporous membrane is developed, comprising layers with specific polyethylene and polypropylene compositions, including a first layer with high molecular weight polyethylene and a second layer with polypropylene having a weight-average molecular weight of 6×105 or more and a heat of fusion of 90 J/g or more, to enhance mechanical properties and permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If separator thickness is reduced to improve permeability, then storage capacity improves, but pin puncture strength decreases
Solution Approach 1:
The multi-layer composite structure provides enhanced mechanical strength through the combination of different polymer layers, allowing the use of thinner overall separator thickness while maintaining adequate pin puncture strength. The composite architecture distributes stress and prevents single-point failure.
Solution Approach 2:
Different layers of the separator have optimized local properties: some layers are designed with higher mechanical strength characteristics to provide pin puncture resistance, while other layers are optimized for permeability. This local optimization allows thin overall thickness while maintaining strength where needed.
2Quantity of substance
If separator thickness is reduced to improve permeability, then permeability improves, but thickness uniformity becomes difficult to control
Solution Approach 1:
The separator is manufactured as multiple discrete layers that are subsequently bonded together. This segmentation allows each layer to be produced with controlled thickness and uniformity, and the layer assembly process maintains overall thickness consistency while achieving high permeability through optimized pore structure in each layer.
Solution Approach 2:
The multi-layer composite structure enables better control of overall thickness uniformity because each layer can be independently manufactured and controlled. The cumulative effect of multiple uniformly-thin layers achieves the desired thinness and permeability while maintaining manufacturing precision through modular construction.
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 multi-layer membrane improves pin puncture strength, shutdown speed, and thickness uniformity, leading to enhanced battery safety and performance by maintaining high meltdown temperatures and reducing the likelihood of short-circuiting.
Implementation Method 1
microporous polyolefin membranes can be used as battery separators
Implementation Method 2
desirable for the batteries to have a relatively low shutdown temperature
Implementation Method 3
microporous membranes containing polypropylene only have high shutdown temperatures
Data Source
AI summary
The invention relates to a multi-layer, microporous polyolefin membrane having appropriate permeability, pin puncture strength, shutdown temperature, shutdown speed, meltdown temperature, and thickness uniformity. The invention also relates to a battery separator formed by such multi-layer, microporous membrane, and a battery comprising such a separator. Another aspect of the invention relates to a method for making the multi-layer, microporous polyolefin membrane, a method for making a battery using such a membrane as a separator, and a method for using such a battery.