Separator Coating for Thermal Stability in Lithium Batteries
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Solution Overview
Problem
Existing separators for lithium secondary batteries face challenges in achieving high packing density and bindability to both the porous substrate and electrodes, which affects the safety and capacity of the batteries due to thermal shrinkage and mechanical stress, and the production of thin separators is hindered by low packing density.
Innovation Solution
A separator with a porous organic-inorganic coating layer formed by a mixture of inorganic particles and a first binder polymer containing a specific copolymer, along with an organic coating layer, providing improved binding properties and high packing density, and a method for producing this separator involving specific monomer units and binder polymers to enhance stability and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous polyolefin substrate is used as a separator, then it provides basic separation function, but it undergoes extreme thermal shrinkage at 100°C or higher causing short circuits
Solution Approach 1:
The patent applies composite materials by combining organic binder polymers with inorganic particles (such as metal oxides or ceramic particles) to create a coating layer on the porous substrate. This composite structure provides thermal stability while maintaining mechanical integrity, preventing the thermal shrinkage that occurs with pure polyolefin substrates at high temperatures.
2Reliability
If inorganic particles are added to the coating layer to prevent thermal shrinkage, then thermal stability improves, but the bindability to electrodes deteriorates
Solution Approach 1:
The patent applies local quality by creating a coating layer with spatially distributed inorganic particles embedded in an organic binder matrix. The binder polymer provides local adhesive properties for electrode binding, while the inorganic particles provide localized thermal stability. This spatial distribution allows both functions to coexist without compromising overall performance.
3Productivity
If the separator thickness is reduced to increase capacity, then energy density improves, but manufacturing precision becomes difficult to achieve
Solution Approach 1:
The patent applies parameter changes by modifying the coating layer composition and structure to achieve uniform thin film formation. By adjusting the binder polymer molecular weight, crosslinking density, and inorganic particle size distribution, the coating process can produce consistent ultra-thin separators with controlled thickness, enabling high capacity density while maintaining manufacturing precision.
4Reliability
If a porous organic-inorganic coating layer is formed to inhibit thermal shrinkage, then thermal stability improves, but packing density remains low hindering thin separator production
Solution Approach 1:
The patent applies porous materials by designing a coating layer with controlled porosity that balances thermal stability and packing density. The porous structure allows inorganic particles to be densely packed while maintaining pathways for ion transport. The binder polymer fills the interstices between particles, creating a compact yet porous structure that achieves both high packing density and thermal shrinkage resistance.
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 solution enables the fabrication of thin, stable electrochemical devices with enhanced capacity and resistance to thermal and mechanical impacts, preventing inorganic particle separation and ensuring safety by maintaining the structural integrity of the separator.
Implementation Method 1
a first binder polymer containing a copolymer including (a) a first monomer unit including either at least one amine group or at least one amide group
Implementation Method 2
The inorganic particles present in the porous organic-inorganic coating layer coated on the porous substrate serve as spacers that can maintain a physical shape of the porous organic-inorganic coating layer to inhibit the porous substrate from thermal shrinkage when an electrochemical device overheats
Implementation Method 3
a (b) a (meth)acrylate having a C1-C14 alkyl group as a second monomer unit
Data Source
AI summary
A separator includes a porous substrate, a porous organic-inorganic coating layer formed on at least one surface of the porous substrate, and an organic coating layer formed on the surface of the organic-inorganic coating layer. The porous organic-inorganic coating layer includes a mixture of inorganic particles and a first binder polymer. The first binder polymer contains a copolymer including (a) a first monomer unit including either at least one amine group or at least one amide group or both in the side chain thereof and (b) a (meth)acrylate having a C1-C14 alkyl group as a second monomer unit. The organic coating layer is formed by dispersing a second binder polymer on the surface of the organic-inorganic coating layer, leaving scattered uncoated areas. The porous organic-inorganic coating layer of the separator has a high packing density, enabling the fabrication of a thin battery in an easy manner without losing stability. The porous organic-inorganic coating layer has good ability to bind to the porous substrate, which prevents the inorganic particles from separating from the porous organic-inorganic coating layer. In addition, the organic coating layer enhances the bindability of the separator to an electrode without a substantial increase in resistance.