Porous Active Separator Coating for Adhesion and Thermal Stability
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Solution Overview
Problem
Existing organic/inorganic composite separators face issues with inorganic particle extraction during assembly and weakened adhesion leading to thermal shrinkage and electric short circuits between cathode and anode, compromising battery stability.
Innovation Solution
An organic/inorganic composite separator with a porous active layer coated on a polyolefin substrate, using a blend of binder polymers with different hydrophile properties and sufficient inorganic particles to enhance adhesion and thermal stability, preventing particle extraction and short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If inorganic particles are increased in the porous active layer to restrain thermal shrinkage, then thermal stability is improved, but adhesion between the porous active layer and substrate deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the binder polymer to achieve optimal balance. Specifically, it uses a binder polymer containing carboxyl groups with a content of 0.1-5 mmol/g, which creates strong chemical bonding with both the inorganic particles and the substrate, thereby maintaining both thermal stability and adhesion strength.
Solution Approach 2:
The patent creates a composite porous active layer combining inorganic particles (such as Al2O3, SiO2, TiO2) with a specifically designed binder polymer containing carboxyl groups. This composite structure allows the inorganic particles to provide thermal stability while the carboxyl-containing binder ensures strong adhesion, resolving the contradiction between these two properties.
2Strength
If binder polymer content is increased to improve adhesion, then adhesion is improved, but thermal shrinkage restraint capability deteriorates
Solution Approach 1:
Instead of simply increasing binder polymer content, the patent changes the quality parameter by introducing carboxyl groups with specific content (0.1-5 mmol/g). This functional group provides strong chemical bonding capability, allowing effective adhesion with lower polymer content, thereby preserving thermal shrinkage restraint capability while maintaining strong adhesion.
3Ease of manufacture
If inorganic particles are extracted during assembly process, then manufacturing ease is improved, but reliability deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-treating the substrate surface and using a binder polymer with carboxyl groups that create strong chemical bonding before the assembly process. This preliminary strong adhesion prevents inorganic particle extraction during subsequent assembly operations, ensuring both ease of manufacture and reliability.
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 composite separator maintains strong adhesion and limits thermal shrinkage, preventing short circuits and improving battery stability by ensuring peeling resistance and controlled thermal shrinkage.
Implementation Method 1
a porous active layer which is coated with a mixture of inorganic particles and a binder polymer
Implementation Method 2
the inorganic particles in the porous active layer formed on the polyolefin porous substrate act as a kind of spacer that keeps a physical shape of the porous active layer, so the inorganic particles restrain thermal shrinkage of the polyolefin porous substrate when the electrochemical device is overheated
Data Source
Figure 1(a)~1(e)
Figure 2
AI summary
An organic/inorganic composite separator includes (a) a polyolefin porous substrate having pores; and (b) a porous active layer containing a mixture of inorganic particles and a binder polymer, with which at least one surface of the polyolefin porous substrate is coated, wherein the porous active layer has a peeling force of 5 gf/cm or above, and a thermal shrinkage of the separator after being left alone at 150°C for 1 hour is 50% or below in a machine direction (MD) or in a transverse direction (TD). This organic/inorganic composite separator solves the problem that inorganic particles in the porous active layer formed on the porous substrate are extracted during an assembly process of an electrochemical device, and also it may prevent an electric short circuit between cathode and anode even when the electrochemical device is overheated.