Lithium Battery Separator Coating for Low Shrinkage and Air Permeability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing rechargeable lithium batteries face challenges in achieving high energy density, capacity, stability, and lifetime due to issues with membrane resistance, heat shrinkage, and air permeability in the separator.
Innovation Solution
A separator for rechargeable lithium batteries is designed with a porous substrate coated with a heat-resistant layer containing a (meth)acryl-based binder and filler, and an adhesive layer with a cross-linked (meth)acryl-based adhesive binder, featuring a particle diameter of 250-350 nm, which enhances heat resistance, reduces membrane resistance, and improves air permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a separator with low membrane resistance is used to increase battery capacity, then capacity is improved, but heat resistance and heat shrinkage control may deteriorate
Solution Approach 1:
The separator is constructed as a composite material consisting of a polyolefin base layer combined with a coating layer containing (meth)acryl-based binder, hydroxyalkyl (meth)acrylate units, and inorganic filler particles. This composite structure allows the separator to simultaneously achieve low membrane resistance (improved capacity) while maintaining excellent heat resistance through the thermal stability of the (meth)acryl-based coating system.
Solution Approach 2:
The invention optimizes specific parameters including the glass transition temperature of the (meth)acryl-based binder (controlled through copolymer composition), the particle size distribution of filler materials (D50: 0.1-1.0 μm), and the thickness of the coating layer (1-10 μm). These parameter optimizations enable the separator to achieve low heat shrinkage rate (≤5% at 100°C) while maintaining low membrane resistance for high battery capacity.
2Reliability
If a separator with high heat resistance is used to improve stability, then heat shrinkage is reduced, but membrane resistance may increase reducing capacity
Solution Approach 1:
The separator utilizes a porous structure with controlled porosity (30-70%) and specific pore size distribution (0.01-10 μm). The porous coating layer allows efficient lithium ion transport (maintaining low membrane resistance for high capacity) while the porous network structure of the (meth)acryl-based binder provides thermal stability and low heat shrinkage. The porosity is controlled through the filler content (5-50 wt%) and binder molecular weight (10,000-1,000,000 g/mol).
Solution Approach 2:
The separator employs local quality differentiation through its layered structure: the base layer provides mechanical strength and basic separation function, while the coating layer applied on at least one surface provides enhanced heat resistance and controlled ion transport. The coating layer's composition is locally optimized with (meth)acryl-based binder containing specific functional units (carboxyl, hydroxyl, amine groups) to achieve both thermal stability and ion permeability in the critical interface region with electrodes.
3Temperature
If the coating layer is made thicker to improve heat resistance, then heat shrinkage is reduced, but air permeability deteriorates
Solution Approach 1:
The coating layer is designed with controlled porosity (30-70%) through the selection of filler content (5-50 wt%) and binder properties. The porous structure allows air and lithium ions to permeate efficiently even when the coating layer thickness is increased (1-10 μm) for improved heat resistance. The pore size distribution (0.01-10 μm) is optimized to balance thermal stability with permeability requirements.
Solution Approach 2:
The invention addresses the thickness-permeability trade-off by transitioning from a dense uniform structure to a porous three-dimensional network structure. The (meth)acryl-based binder forms a cross-linked gel network that provides thermal stability in the thickness direction while maintaining open channels for ion and air transport. This dimensional restructuring allows the coating layer to be thicker without sacrificing permeability.
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 increases the capacity, stability, and lifetime of the lithium battery by providing low heat shrinkage, low membrane resistance, and desired air permeability, thereby improving overall battery performance.
Implementation Method 1
The binder includes a (meth)acryl-based binder including a first structural unit derived from (meth)acrylic acid, (meth)acrylate, or a salt thereof, a second structural unit derived from hydroxyalkyl (meth)acrylate, and a third structural unit derived from (meth)acrylamido sulfonic acid or a salt thereof
Implementation Method 2
the separator increases the capacity of a rechargeable lithium battery by having a low membrane resistance
Implementation Method 3
an adhesive layer located on the heat-resistant layer and including an adhesive binder. The adhesive binder includes a cross-linked (meth)acryl-based adhesive binder
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present disclosure relates to a separator for a rechargeable lithium battery, and a rechargeable lithium battery including the separator, and the separata porous substrate and a coating layer located on at least one surface of the porous substrate. The coating layer includes a heat-resistant layer including a binder and a filler, and an adhesive layer located on the heat-resistant layer and including an adhesive binder. The binder includes a (meth)acryl-based binder including a first structural unit derived from (meth)acrylic acid, (meth)acrylate, or a salt thereof, a second structural unit derived from hydroxyalkyl (meth)acrylate, and a third structural unit derived from (meth)acrylamido sulfonic acid or a salt thereof. The filler includes a filler having a particle diameter D50 ranging from 250 nm to 350 nm, and the adhesive binder includes a cross-linked (meth)acryl-based adhesive binder.