Multi-layer Composite Separator for Lithium-ion Battery Heat Resistance
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Solution Overview
Problem
Lithium-ion battery separators face issues with heat shrinkage, poor liquid absorption, and wettability, leading to potential short circuits and explosions during abnormal charging and discharging, which are not adequately addressed by current polyolefin-based separators.
Innovation Solution
A multi-layer composite functional separator is developed, comprising a base layer and additional layers of insulating inorganic compounds or high-temperature resistant polymers, temperature-induced expansion polymer microspheres, and thermoplastic resins, which are sequentially attached to enhance heat resistance and safety features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyolefin-based separators are used, then the separator provides basic isolation function, but the separator shrinks or deforms due to temperature rise causing short circuit
Solution Approach 1:
The patent employs a multi-layer composite structure combining polyolefin base layer with heat-resistant polymer layers (polyimide, polyester, or aramid). This composite approach allows the separator to maintain dimensional stability at high temperatures while preserving the base isolation function, directly resolving the contradiction between basic functionality and heat resistance.
Solution Approach 2:
The separator is divided into functionally distinct layers: a base layer for isolation and coating layers for heat resistance. Each layer performs its specific function independently, allowing the heat-resistant coating to prevent shrinkage without compromising the base layer's isolation capability, thus resolving the dimensional stability issue.
2Reliability
If separator thickness is reduced, then the ionic conductivity is improved, but the mechanical strength decreases
Solution Approach 1:
The multi-layer composite structure provides enhanced mechanical strength through the combination of base layer and heat-resistant polymer layers. This allows the use of thinner overall separator design while maintaining sufficient mechanical strength, as the composite structure distributes stress across multiple layers rather than requiring a single thick layer.
Solution Approach 2:
The patent utilizes thin film technology with the heat-resistant polymer coating applied as a thin layer (0.5-5 μm) on the base layer. This thin film approach maintains ionic conductivity by preserving pore structure while providing the necessary mechanical reinforcement for heat resistance without requiring excessive thickness.
3Reliability
If heat-resistant materials are added to improve thermal stability, then the thermal shrinkage is reduced, but the liquid absorption ability deteriorates
Solution Approach 1:
The heat-resistant polymer is applied as a coating layer on the base layer rather than making the entire separator from heat-resistant material. This localized approach ensures that the base layer's excellent liquid absorption properties are preserved while the coating layer provides the necessary thermal stability and shrinkage resistance.
Solution Approach 2:
The composite structure combines materials with complementary properties: the polyolefin base layer provides liquid absorption and wettability, while the heat-resistant polymer coating provides thermal stability. Together they resolve the contradiction between thermal stability and liquid absorption by assigning each function to the appropriate material layer.
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 composite separator exhibits excellent heat resistance, reduced thermal shrinkage, and improved safety by maintaining mechanical isolation and preventing short circuits, thereby enhancing the reliability of lithium-ion batteries, especially power batteries.
Implementation Method 1
Layer C is a porous layer composed of polymer microspheres with temperature-induced expansion characteristics
Data Source
AI summary
A multi-layer composite functional separator for lithium ion battery includes four layers. Layer A is a base separator. Layer B is a porous structural layer composed of insulating inorganic compounds or high temperature resistant polymers. Layer C is a porous layer composed of polymer microspheres with temperature-induced expansion characteristics. Layer D is a thermoplastic resin with a melting point of 80-110° C. and a crystallinity of <50%. Layer B, Layer C and Layer D are sequentially attached on either or both sides of Layer A. Compared with the existing lithium-ion battery separator, the multi-Layer Composite functional separator has excellent heat resistance. The thermal shrinkage rate is less than 1% when heated for less than one hour at 200° C. Inclusion of organic polymer microspheres produces thermal closure of the batteries, which improves the safety of the batteries.