Composite Battery Separator Coating for Thermal Shrinkage Control
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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
A composite separator with a porous active layer containing a mixture of inorganic particles and binder polymers, ensuring a peeling force of 5 gf/cm or above and thermal shrinkage below 50% at 150°C, using a blend of polymers with different hydrophile properties to enhance adhesion and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the content of inorganic particles in the porous active layer is increased to restrain thermal shrinkage, then thermal stability is improved, but adhesion between the porous active layer and polyolefin porous substrate is weakened
Solution Approach 1:
The patent changes the chemical composition parameters of the binder polymer to achieve optimal adhesion. Specifically, it uses a binder polymer containing carboxyl groups (such as polyacrylic acid, carboxymethyl cellulose, or polyvinyl alcohol) which form strong chemical bonds with both the inorganic particles and the polyolefin substrate, thereby maintaining strong adhesion even with high inorganic particle content (90-99 wt%).
Solution Approach 2:
The patent creates a composite porous active layer by combining inorganic particles with a specifically selected binder polymer that has carboxyl functional groups. This composite structure allows the inorganic particles to provide thermal stability while the carboxyl-containing binder polymer provides strong adhesion, resolving the contradiction between these two properties.
2Strength
If the content of binder polymer is increased to improve adhesion, then adhesion strength is improved, but thermal shrinkage restraint ability is deteriorated
Solution Approach 1:
The patent optimizes the binder polymer content to be within 1-10 wt% of the total separator weight, and specifically requires carboxyl groups in the binder polymer. This parameter optimization ensures that even at low binder polymer content, strong adhesion is achieved through chemical bonding, while the high inorganic particle content (90-99 wt%) maintains thermal stability.
3Ease of manufacture
If inorganic particles are extracted during assembly process, then manufacturing ease is improved, but device reliability is deteriorated
Solution Approach 1:
The patent applies a porous active layer coating to the polyolefin porous substrate before assembly, where the coating process firmly bonds inorganic particles to the substrate through carboxyl-containing binder polymer. This preliminary action prevents particle extraction during subsequent assembly processes, ensuring both ease of manufacture and device 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
Prevents inorganic particle extraction and maintains strong adhesion, effectively restraining thermal shrinkage and preventing short circuits, thereby improving battery stability and performance.
Implementation Method 1
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
Implementation Method 2
a porous active layer which is formed by coating at least one surface of a polyolefin porous substrate having many pores with a mixture of inorganic particles and a binder polymer
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.