Porous Battery Separator Coating for Adhesion and Thermal Stability
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Solution Overview
Problem
Existing separators for electrochemical devices face challenges with adhesion to electrodes, air permeability, and resistance, particularly due to degradation of these properties in lithium ion polymer batteries at low temperatures and the risk of thermal runaway leading to explosions.
Innovation Solution
A separator design featuring a porous polymer substrate with a porous coating layer containing inorganic particles and a binder polymer, and a porous adhesive layer made of polyvinylidene fluoride-co-hexafluoropropylene, which is formed through a dry phase separation process to enhance adhesion, air permeability, and reduce resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous organic/inorganic coating layer is formed by coating a mixture of inorganic particles with a binder polymer to the separator surface, then safety against thermal runaway is improved, but adhesion between electrodes deteriorates
Solution Approach 1:
The coating layer is divided into multiple layers with different functions: a lower layer containing inorganic particles for thermal stability and an upper layer without inorganic particles for electrode adhesion. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
Different regions of the coating layer have different compositions and properties. The lower layer has high inorganic particle content for heat resistance, while the upper layer has low or no inorganic particles for good adhesion. This local quality variation resolves the contradiction between safety and adhesion.
2Reliability
If a porous organic/inorganic coating layer is formed on the separator surface, then thermal stability is improved, but air permeability deteriorates
Solution Approach 1:
The coating layer is designed with a porous structure that maintains air permeability while providing thermal stability. The porous structure allows gas transport through the coating layer, preventing the complete blockage of pores that would occur with dense inorganic particle coatings.
Solution Approach 2:
The coating layer is segmented into regions with different inorganic particle concentrations, allowing areas with sufficient porosity for gas transport while maintaining thermal stability in other regions.
3Reliability
If a porous organic/inorganic coating layer is formed on the separator surface, then thermal resistance is improved, but electrical resistance increases
Solution Approach 1:
The coating layer has spatially varying composition with inorganic particles concentrated in the lower layer for thermal resistance, while the upper layer maintains low resistance properties for efficient electrical conduction.
Solution Approach 2:
The coating layer uses a composite structure combining organic binder polymer and inorganic particles in a specific arrangement that provides thermal resistance from the inorganic phase while maintaining electrical conductivity through the organic phase continuity.
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 achieves improved adhesion with electrodes, enhanced air permeability, and reduced resistance, thereby preventing dendrite formation and ensuring excellent life characteristics for secondary batteries, while also mitigating safety risks such as thermal runaway and explosions.
Implementation Method 1
a porous adhesive layer made of polyvinylidene fluoride-co-hexafluoropropylene, which is formed through a dry phase separation process
Data Source
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AI summary
Provided is a separator which includes: a separator base including a porous polymer substrate having a plurality of pores, and a porous coating layer positioned on at least one surface of the porous polymer substrate and containing a plurality of inorganic particles and a binder polymer positioned on the whole or a part of the surface of the inorganic particles to connect the inorganic particles with one another and fix them; and a porous adhesive layer positioned on at least one surface of the separator base and including polyvinylidene-co-hexafluoropropylene containing vinylidene-derived repeating units and hexafluoropropylene-derived repeating units, wherein the ratio of the number of the hexafluoropropylene (HFP)-derived repeating units (HFP substitution ratio) based on the total number of the vinylidene-derived repeating units and the hexafluoropropylene-derived repeating units is 4.5-9%. An electrochemical device including the separator is also provided.