Separator With Conductive PTC Coating Layer
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Solution Overview
Problem
Lithium ion batteries face safety issues due to thermal shrinkage of porous polyolefin substrates leading to potential short circuits and increased risk of explosion, and existing solutions that add insulating porous coating layers increase battery thickness, making it difficult to achieve high-capacity batteries.
Innovation Solution
A separator with a porous coating layer composed of conductive positive temperature coefficient (PTC) particles and inorganic particles on a non-woven fabric substrate, where the PTC particles have a low melting point resin that expands to reduce conductivity and close pores during overheating, preventing further electrochemical reactions and inhibiting short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an insulating porous coating layer is formed on the porous substrate to improve stability, then safety is improved, but the thickness of the separator increases
Solution Approach 1:
The coating layer uses a composite material system consisting of inorganic filler particles (such as alumina, silica, or boehmite) dispersed in a binder polymer matrix. This composite structure provides both the safety function through thermal shutdown capability and maintains thin profile by optimizing the balance between filler content and binder polymer selection, preventing excessive thickness while ensuring stability.
Solution Approach 2:
The patent optimizes parameters including the weight ratio of filler particles to binder polymer (typically 90:10 to 99:1), particle size distribution (0.1-10 micrometers), and coating layer thickness (1-20 micrometers) to achieve the desired safety performance without excessive separator thickness. The binder polymer's glass transition temperature and melting point are also carefully selected to enable shutdown function at appropriate temperatures.
2Reliability
If a porous coating layer is formed to prevent thermal shrinkage and improve safety, then reliability is improved, but the complexity of fabrication increases
Solution Approach 1:
The binder polymer and inorganic filler particles are pre-mixed to form a homogeneous slurry with appropriate viscosity and solid content (5-50 wt%) before coating. This preliminary preparation ensures uniform distribution of filler particles and consistent coating quality, simplifying the subsequent coating and drying processes while maintaining safety performance.
Solution Approach 2:
The coating layer is designed with controlled porosity (30-80%) matching the underlying porous substrate, allowing electrolyte penetration and maintaining ion transport pathways. The porous structure is achieved through controlled drying conditions and filler particle packing, enabling safety function without requiring complex multi-step fabrication processes.
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 provides appropriate electrical conductivity, enhances stability, and improves safety by suppressing electrochemical reactions and preventing short circuits, making it suitable for high-capacity electrochemical devices while maintaining a suitable thickness for efficient battery fabrication.
Implementation Method 1
the PTC particles have a low melting point resin that expands to reduce conductivity and close pores during overheating
Implementation Method 2
the low melting point resin having a melting point lower than that of the non-woven fabric substrate
Implementation Method 3
conductive positive temperature coefficient (PTC) particles
Data Source
Figure 1~2
Figure 3~4
AI summary
Disclosed is a separator. The separator includes a planar non-woven fabric substrate having a plurality of pores, and a porous coating layer formed on at least one surface of the non-woven fabric substrate. The porous coating layer is composed of a mixture of filler particles and a binder polymer. The filler particles include conductive positive temperature coefficient (PTC) particles composed of a mixture of conductive particles and a low melting point resin having a melting point lower than that of the non-woven fabric substrate. Due to the presence of the conductive PTC particles, the porous coating layer can be imparted with a shutdown function against thermal runaway. In addition, the porous coating layer exhibits appropriate electrical conductivity. Therefore, the separator is suitable for use in a high-capacity electrochemical device.