PET Nonwoven Separator for Battery Thermal Stability
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Solution Overview
Problem
Conventional lithium ion secondary batteries and lithium ion polymer batteries have inadequate heat resistance, leading to short-circuit issues due to low thermal stability and reduced ionic conductivity, which limits their use in high-energy density and large-capacity applications such as vehicle power sources.
Innovation Solution
A PET nonwoven fabric separator is developed, comprising two types of PET fibers with different melting temperatures and a nanofiber layer, providing high heat resistance, mechanical strength, and ionic conductivity, while maintaining porosity and electrolyte wettability without the need for a binder resin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a polyolefin separator is coated with a heat-resistant resin to improve heat resistance, then the short-circuit temperature increases, but the pores are closed and ionic conductivity deteriorates
Solution Approach 1:
The patent uses a porous heat-resistant resin coating layer that maintains porosity to allow lithium ion transport. The coating layer has controlled pore structure with porosity of 30-80% and average pore diameter of 0.1-1.0 μm, ensuring both heat resistance and ionic conductivity are achieved simultaneously.
Solution Approach 2:
The patent creates a composite separator structure consisting of a polyolefin base layer combined with a porous heat-resistant resin coating layer. This composite structure integrates the advantages of both materials: the polyolefin provides mechanical strength and shutdown function, while the porous heat-resistant resin coating provides thermal stability without blocking ion transport.
2Stability of the object's composition
If the amount of heat-resistant resin coating is increased to improve heat resistance, then thermal stability improves, but pore closure increases and charge-discharge properties deteriorate
Solution Approach 1:
The patent optimizes the parameters of the heat-resistant resin coating, specifically controlling the coating amount to 0.5-6.0 g/m², porosity to 30-80%, and average pore diameter to 0.1-1.0 μm. These parameter optimizations ensure sufficient thermal stability while maintaining adequate porosity for lithium ion transport and charge-discharge performance.
3Reliability
If a polyolefin separator is used to achieve low shutdown temperature, then safety shutdown function is achieved, but heat resistance is inadequate for high energy density batteries
Solution Approach 1:
The patent divides the separator into two functional segments: a polyolefin base layer that provides the shutdown function at low temperature (melting point 160-180°C), and a porous heat-resistant resin coating layer that provides high-temperature stability (short-circuit temperature 200-300°C). This segmentation allows both safety shutdown and heat resistance requirements to be satisfied.
Solution Approach 2:
The patent creates a composite separator structure consisting of a polyolefin base layer combined with a porous heat-resistant resin coating layer. This composite structure integrates the advantages of both materials: the polyolefin provides mechanical strength and shutdown function, while the porous heat-resistant resin coating provides thermal stability without blocking 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 PET nonwoven fabric separator effectively prevents short-circuiting at high temperatures, ensuring superior thermal stability and charge-discharge performance for high-energy density batteries, particularly in severe conditions like rapid charge-discharge and high heat scenarios.
Implementation Method 1
first fibers comprising PET having a melting temperature of 240° C. or more
Implementation Method 2
second fibers comprising PET having a melting temperature of 180 ̃220° C.
Implementation Method 3
maintaining porosity and pore size adapted for use in a separator for a secondary battery to thereby manifest superior ionic conductivity
Data Source
AI summary
A PET nonwoven fabric for a separator for a secondary battery includes first fibers composed of PET having a melting temperature of 240° C. or more and second fibers composed of PET having a melting temperature of 180˜220° C., respective fibers having two types of fibers having different diameters, and has a fine pore size and uniform pore distribution and exhibits superior surface properties, low surface defects, high mechanical strength and excellent mass production. Even when the temperature of a battery is increased to 200° C. or more, the PET nonwoven fabric has heat resistance which prevents thermal runaway and does not generate melting and shrinking.