Porous Separator Coating for Wet-State Thermal Shrinkage Control
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Solution Overview
Problem
Lithium secondary battery separators face challenges in maintaining dimensional stability under high temperature and wet conditions, particularly due to the swelling of polymer binders and reduced adhesive force, which leads to significant shrinkage and potential electrode exposure.
Innovation Solution
A separator design that includes a porous polymer substrate with a porous coating layer containing a polymer binder, inorganic particles with a packing density of 2 g/cm3 or more to 2.5 g/cm3 or less, and an organic filler, optimized with a polymer binder to organic filler weight ratio of 5:1 to 1:5, to enhance heat resistance and reduce shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polymer binder content is increased to improve adhesive force, then dimensional stability is improved, but heat resistance deteriorates due to polymer binder swelling at high temperature
Solution Approach 1:
The patent optimizes the polymer binder content to a specific range (1-10 parts by weight based on total coating layer weight) and controls the pore volume and surface area parameters of the inorganic particles. This parameter optimization ensures sufficient adhesive force while limiting polymer binder swelling at high temperatures, thereby maintaining heat resistance.
Solution Approach 2:
The patent uses a composite system where inorganic particles provide thermal stability and structural support, while the polymer binder provides adhesive force. The synergistic combination allows the coating layer to maintain both strong adhesion and heat resistance, as the inorganic framework prevents excessive polymer expansion at high temperatures.
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 proposed separator achieves improved dimensional stability in wet states at high temperatures, with a heat shrinkage rate of 10% or less at 130°C or higher, thereby preventing electrode exposure and ensuring the integrity of the battery.
Implementation Method 1
The inorganic particles may be connected to other inorganic particles by a polymer binder to form an interstitial volume, and lithium ions may move by passing through the interstitial volume
Implementation Method 2
the polymer binder may swell by the electrolyte solution, or the adhesive force of the polymer binder may deteriorate
Implementation Method 3
In this high-temperature wet state, the separator shrinks significantly as the adhesive force of the porous coating layer decreases
Data Source
AI summary
Disclosed is a separator for an electrochemical device, the separator including a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate. The porous coating layer contains a polymer binder, inorganic particles, and an organic filler, the polymer binder being contained in an amount of 1 to 10 parts by weight based on the total weight of the porous coating layer, and the inorganic particles have a packing density of 2 g/cm3 or more to 2.5 g/cm3 or less.