Cross-Linked Battery Separator Coating for Thermal Shrinkage Control
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in maintaining their shape and safety due to thermal shrinkage in the electrolyte phase, which can compromise their performance and stability.
Innovation Solution
A separator for lithium batteries is developed with a porous substrate and a coating layer containing a cross-linked product of a (meth)acryl-based binder, a carbodiimide-based cross-linking agent, and a filler with a particle diameter of 1.0 μm or less, which reduces both dry and electrolyte-induced shrinkage rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional separator is used in rechargeable lithium batteries, then the battery can operate, but the separator undergoes thermal shrinkage in the electrolyte phase causing safety issues
Solution Approach 1:
The patent applies composite materials by combining a polyolefin-based porous substrate with a coating layer containing inorganic particles (such as alumina, silica, or boehmite) dispersed in a binder resin. This composite structure prevents thermal shrinkage while maintaining the separator's porosity and ion conductivity, directly resolving the contradiction between shape stability and operational functionality.
Solution Approach 2:
The patent changes the thermal and mechanical parameters of the separator by introducing a coating layer with specific properties: inorganic particles with average diameter of 0.1-10 μm, binder resin content of 1-20 wt%, and coating layer thickness of 1-20 μm. These parameter modifications enable the separator to maintain its shape at elevated temperatures while preserving electrolyte wettability and ion transport.
2Temperature
If the separator structure is modified to prevent shrinkage, then heat resistance improves, but manufacturing complexity increases
Solution Approach 1:
The patent maintains the porous structure of the polyolefin-based substrate, which is essential for ion conductivity, while adding a coating layer that does not block the pores. The porous substrate provides the base heat resistance and structural integrity, while the coating layer enhances thermal stability without compromising the porous architecture needed for battery operation.
Solution Approach 2:
The patent applies local quality by concentrating the heat resistance enhancement in a thin coating layer (1-20 μm) on the surface of the porous substrate, rather than modifying the entire bulk structure. This allows the majority of the separator to remain simple and porous for optimal ion transport, while only the surface region is modified to provide enhanced thermal stability.
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 maintains its shape and stability by ensuring low shrinkage rates, enhancing heat resistance and mechanical properties, thereby improving the safety and performance of rechargeable lithium batteries.
Implementation Method 1
the coating layer includes a cross-linked product of a binder and a cross-linking agent; and a filler. The binder includes a (meth)acryl-based binder... The cross-linking agent includes a carbodiimide-based cross-linking agent
Data Source
AI summary
Examples of the present disclosure relate to a separator for a lithium secondary battery, and a lithium secondary battery including the separator, and include a separator for a lithium secondary battery, the separator including a porous substrate and a coating layer located on at least one surface of the porous substrate. The coating layer includes a cross-linked product of a binder and a cross-linking agent and a filler, the binder includes a (meth)acryl-based binder including a structural unit derived from (meth)acrylate or (meth)acrylic acid, a cyano group-containing structural unit, and a sulfonate group-containing structural unit, the cross-linking agent includes a carbodiimide-based cross-linking agent, and the filler includes a filler having a particle diameter D100 of about 1.0 μm or less.