Dual-Layer Battery Separator Coating for Adhesion and Air Permeability
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Solution Overview
Problem
Secondary battery separators with polyolefin-based porous substrates face challenges in adhesion with electrodes due to thermal shrinkage and insufficient interlayer adhesion, leading to safety issues like internal short circuits, and existing solutions like vapor-induced phase separation methods are difficult to control and environmentally unfriendly.
Innovation Solution
A separator with a porous polymer substrate coated with a first layer of inorganic particles and a nonparticulate acrylic polymer with a glass transition temperature of 15° C. or less, and a second layer of particulate acrylic polymer with a glass transition temperature of 20° C. to 50° C., ensuring strong adhesion with electrodes and preventing pore clogging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If an organic-inorganic composite porous separator comprising a porous polymer substrate coated with a mixture of inorganic particles and a binder polymer is used, then thermal shrinkage behavior is reduced, but interlayer adhesion with the electrode becomes insufficient
Solution Approach 1:
The coating layer is divided into two distinct layers: a first layer containing inorganic particles and binder polymer for thermal stability, and a second layer containing adhesive polymer for electrode adhesion. This segmentation allows each layer to perform its specific function optimally without compromising the other.
Solution Approach 2:
Different regions of the coating layer are assigned different material compositions and properties. The first layer near the porous substrate provides thermal shrinkage resistance, while the second layer at the outer surface provides adhesion to the electrode. This local differentiation resolves the contradiction between thermal stability and adhesion strength.
2Strength
If a vapor-induced phase separation method is used to form an adhesive layer, then binder polymer content near the surface is increased, but process control becomes difficult and environmental issues arise
Solution Approach 1:
The problematic vapor-induced phase separation step is extracted and replaced with a simpler coating process. The binder polymer is directly applied in the coating slurry without requiring vapor-induced phase separation, thereby eliminating process control difficulties and environmental issues while still achieving sufficient adhesive layer formation.
Solution Approach 2:
The coating process parameters are optimized by adjusting the composition and concentration of the coating slurry, particularly the ratio of binder polymer to inorganic particles, to achieve the desired adhesive layer strength without complex phase separation processes.
3Strength
If the binder polymer penetrates into the pores of the porous polymer substrate, then adhesion is improved, but pore clogging occurs and air permeability is reduced
Solution Approach 1:
The coating structure is segmented into two layers with distinct functions. The first layer contains the binder polymer that provides adhesion, while the second layer contains adhesive polymer that bonds to the electrode. This segmentation prevents excessive binder polymer penetration into the substrate pores while maintaining adequate adhesion through the first layer.
Solution Approach 2:
The coating layers are designed as porous structures that maintain the underlying porous polymer substrate's pore structure. The porous coating layers provide adhesion functionality without blocking the substrate pores, preserving air permeability while achieving the desired adhesive strength.
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 proposed separator design achieves robust adhesion with electrodes and maintains air permeability, addressing safety concerns and environmental issues associated with previous methods.
Implementation Method 1
the nonparticulate acrylic polymer connects and fixes the inorganic particles
Implementation Method 2
the second layer includes a particulate acrylic polymer having a glass transition temperature of 20° C. to 50° C.
Data Source
AI summary
A separator for a secondary battery comprising a porous polymer substrate; a first layer on at least one surface of the porous polymer substrate, wherein the first layer includes inorganic particles and a nonparticulate acrylic polymer having a glass transition temperature of 15° C. or less, wherein the nonparticulate acrylic polymer connects and fixes the inorganic particles; and a second layer on an upper surface of the first layer, wherein the second layer includes a particulate acrylic polymer having a glass transition temperature of 20° C. to 50° C. The separator for a secondary battery has good adhesion with the electrode and can solve the resistance problem in the presence of the inorganic particles.