Porous Separator Coating Ratio for Heat Resistance and Electrode Adhesion
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Solution Overview
Problem
Current lithium secondary battery separators face issues with heat resistance and adhesion due to poor substrate materials, leading to safety concerns and degradation in battery performance, especially when thinning is attempted to increase energy density.
Innovation Solution
A separator with a porous coating layer containing a specific ratio of inorganic filler to binder polymer, optimized by the BET surface area of the inorganic filler, is developed to enhance adhesion and heat resistance, ensuring safety and stability even at small thicknesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a porous coating layer including an inorganic filler mixed with a binder polymer is formed on the porous substrate to improve heat resistance, then heat resistance is improved, but resistance increases and adhesion to electrode degrades
Solution Approach 1:
The patent changes the chemical composition parameters of the binder polymer from conventional polyolefin-based resins to carboxymethyl cellulose (CMC) and its derivatives. This parameter change allows the coating layer to maintain heat resistance while improving adhesion to electrodes, as CMC provides better electrochemical stability and bonding characteristics compared to traditional polyolefin binders.
Solution Approach 2:
The patent uses composite materials by combining inorganic fillers (such as alumina, silica, or boehmite) with carboxymethyl cellulose-based binder polymers. This composite approach creates a coating layer that leverages the heat resistance of inorganic fillers while the CMC binder provides excellent adhesion and electrochemical stability, resolving the contradiction between heat resistance and adhesion.
2Quantity of substance
If the separator thickness is reduced to increase energy density and reduce resistance, then energy density increases and resistance decreases, but adhesion between separator and electrode is lowered causing degradation of assemblage processability and battery safety
Solution Approach 1:
The patent changes the material composition of the coating layer to use carboxymethyl cellulose-based binders, which provide superior adhesion strength even at reduced thicknesses. This allows the separator to be thinner for higher energy density while maintaining sufficient adhesion to electrodes and safety characteristics.
Solution Approach 2:
The patent employs a porous coating layer structure with controlled porosity that maintains mechanical integrity and adhesion at reduced thickness. The porous structure of the coating layer, formed by the inorganic filler network bound by CMC, provides both mechanical strength for adhesion and ion transport pathways, enabling thin separator design without compromising safety.
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 optimized separator achieves improved adhesion between the substrate and coating layer, as well as between the separator and electrodes, while maintaining heat resistance and stability, addressing the safety and performance issues in lithium secondary batteries.
Implementation Method 1
as the amount of the binder polymer distributed on the surface of the porous coating layer is increased, adhesion to an electrode may be improved
Data Source
AI summary
A separator for an electrochemical device, including a porous substrate, and a porous coating layer on at least one surface of the porous substrate. The porous coating layer includes a binder polymer and an inorganic filler, and satisfies Formula 1 of 20≤[amount of inorganic filler (wt %)×BET surface area of inorganic filler (m2/g)]/[amount of binder polymer (wt %)]≤30, wherein the amount of binder polymer and the amount of inorganic filler are based on 100 wt % of the total weight of the porous coating layer.) The separator ensures the safety of the electrochemical device, while providing improved adhesion between the porous substrate and the porous coating layer of the separator and improved adhesion to an electrode, thereby achieving improved heat resistance and stability.