Dual-Layer Coated Separator for Heat-Resistant Li-Ion Transport
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Solution Overview
Problem
Lithium battery separators face issues with ceramic layer peeling off at high temperatures, reduced heat resistance, and decreased lithium ion conductivity due to large size differences between nanofibers, leading to agglomeration and poor performance.
Innovation Solution
A coated separator design with a dual-layer structure, where the first coating layer consists of longer nanofibers and larger ceramic particles, and the second coating layer consists of shorter nanofibers and smaller ceramic particles, with a thickness ratio greater than 2, to create uniform pore sizes and improve heat resistance and lithium ion conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a single-layer coating with mixed nanofibers of large size difference is used, then ceramic layer heat resistance is improved, but nanofibers agglomerate due to surface energy differences, reducing lithium ion conductivity and causing poor uniformity
Solution Approach 1:
The coating layer is divided into two separate layers: a first coating layer containing longer nanofibers (500-1000 nm) and larger ceramic particles, and a second coating layer containing shorter nanofibers (100-300 nm) and smaller ceramic particles. This segmentation prevents agglomeration by keeping nanofibers of similar sizes together in each layer, while still achieving heat resistance through the ceramic content in both layers.
Solution Approach 2:
Different regions of the coating have different properties tailored to specific functions. The first coating layer (thicker, closer to base film) provides structural support and heat resistance with longer nanofibers and larger ceramic particles, while the second coating layer (thinner, outer layer) enhances lithium ion conductivity and surface uniformity with shorter nanofibers and smaller ceramic particles. The thickness ratio of first to second coating layer is greater than 2.
2Temperature
If ceramic particles are added to improve heat resistance, then thermal stability is enhanced, but the two-phase interface between ceramic layer and separator becomes weak, causing separation and peeling at high temperature
Solution Approach 1:
The coating layers are formed as composite materials combining nanofibers and ceramic particles in specific ratios (mass ratio of nanofiber material to ceramic particles is 5:1 to 1:5). This composite structure creates strong interfacial bonding between the coating layers and the base film, preventing separation and peeling at high temperatures while maintaining thermal stability from the ceramic content.
3Temperature
If a thick ceramic coating is applied to improve heat resistance, then thermal performance is enhanced, but lithium ion transmission distance increases, reducing conductivity and preventing large pores from retaining liquid electrolyte
Solution Approach 1:
The patent optimizes the thickness parameters of the coating layers, with the thickness ratio of the first coating layer to the second coating layer being greater than 2. The first coating layer provides necessary heat resistance with moderate thickness, while the second coating layer is thinner to minimize lithium ion transmission distance. This parameter optimization ensures large pores can still retain liquid electrolyte effectively while providing adequate thermal protection.
Data Source
AI summary
Provided are a coated separator, a preparation method of a coated separator, and a battery, which relates to mixing first nanofibers having similar sizes in a first coating layer and mixing second nanofibers having similar sizes in a second coating layer and setting the first coating layer to be a mixture of large-size first nanofibers and large-particle-diameter first ceramic particles and setting the second coating layer to be a mixture of small-size second nanofibers and small-particle-diameter second ceramic particles.