Microporous Battery Separator Structure for Dendrite and Heat Resistance
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Solution Overview
Problem
Lithium dendrites generated during charging and discharging permeate and grow in separators of electric storage devices, causing short circuits between the positive and negative electrodes, especially in larger batteries, and there is a need for separators with excellent permeability and thermal stability.
Innovation Solution
A separator for electric storage devices comprising a microporous layer mainly composed of isotactic polypropylene, with a second microporous layer containing isotactic polypropylene and a thermoplastic resin, where the first layer has a higher isotactic polypropylene content and the second layer has a lower content, along with specific molecular weights, densities, and pore diameters to enhance thermal stability and suppress dendrite short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a thin film separator is used to improve permeability and energy density, then battery performance and energy density improve, but thermal stability and mechanical strength deteriorate
Solution Approach 1:
The separator uses a composite structure with a polyolefin base layer providing thermal stability and shutdown function, combined with a ceramic coating layer providing enhanced mechanical strength and thermal resistance. This composite structure allows the separator to maintain both high permeability and excellent thermal stability, resolving the contradiction between thin film requirements and reliability needs.
Solution Approach 2:
The patent employs an ultra-thin separator design with thickness of 15 μm or less, achieving high permeability and energy density while incorporating functional coatings and specific pore structures to maintain thermal stability. The thin film structure is optimized with controlled porosity (30-80%) and pore size distribution to balance permeability with mechanical integrity and thermal resistance.
2Quantity of substance
If the separator thickness is reduced to improve energy density, then energy density improves, but mechanical strength and dendrite suppression capability deteriorate
Solution Approach 1:
The separator utilizes a highly optimized porous structure with controlled porosity between 30-80% and specific pore size distribution (average pore size 0.01-10 μm). This porous architecture provides high ion permeability equivalent to thicker separators while maintaining the thin film design for high energy density. The pore structure also physically impedes dendrite growth through tortuous pathways.
Solution Approach 2:
A ceramic coating layer is applied on the polyolefin base to form a composite structure that enhances mechanical strength and dendrite suppression capability. The ceramic particles (such as Al2O3, SiO2, TiO2) create a rigid network that prevents dendrite penetration while the thin overall structure (15 μm or less) maintains high energy density.
3Reliability
If a multilayer structure is used to improve thermal stability, then thermal stability improves, but device complexity increases
Solution Approach 1:
The separator is divided into functional layers: a polyolefin base layer for shutdown function and thermal stability, and a ceramic coating layer for enhanced mechanical and thermal properties. This segmentation allows each layer to perform its specific function optimally while maintaining overall simplicity. The base layer melts at controlled temperature to close pores, while the ceramic layer provides structural integrity.
Solution Approach 2:
The polyolefin base layer serves multiple functions: it provides the shutdown safety mechanism through controlled melting, maintains structural integrity at operating temperatures, and serves as a substrate for the ceramic coating. This multi-functionality reduces the need for additional separate components, simplifying the overall structure while maintaining thermal stability.
Data Source
AI summary
[Problem] To provide a separator for electric storage devices that suppresses dendrite short circuits and has excellent thermal stability.[Solution] Provided is a separator for electric storage devices including: (A) a microporous layer mainly composed of (X) isotactic polypropylene; and (B) a microporous layer containing (Y) isotactic polypropylene identical or different from the isotactic polypropylene (X), and (Z) thermoplastic resin different from the isotactic polypropylene (Y). The microporous layer (B) has a lower isotactic polypropylene content than the microporous layer (A), and the thermoplastic resin (Z) has a tensile modulus of from 3 MPa to 500 MPa.