Urethane-Coated Battery Separator for Heat Shrinkage Resistance
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Solution Overview
Problem
Secondary batteries, particularly lithium-ion batteries, face challenges with safety due to heat shrinkage of polyolefin-based separators causing short-circuits and reduced adhesion to electrodes, leading to potential explosions and insufficient discharge capacity at low temperatures.
Innovation Solution
A separator for secondary batteries featuring a porous polymer substrate with a porous coating layer containing inorganic particles and a urethane bond-containing crosslinked polymer, which is crosslinked during the battery activation process, providing improved adhesion and heat resistance without the need for additional crosslinking steps or binder polymers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a porous organic-inorganic coating layer is formed by applying a mixture of inorganic particles with a binder polymer onto a porous polymer substrate, then heat resistance is improved, but adhesion to electrode is reduced and resistance increases
Solution Approach 1:
The patent changes the chemical structure parameters of the binder polymer by introducing urethane bonds and controlling the glass transition temperature (Tg) to be below 30°C (preferably 20°C or below). This parameter change allows the binder to maintain flexibility and adhesion at low temperatures while providing sufficient heat resistance, resolving the contradiction between heat resistance and electrode adhesion.
Solution Approach 2:
The patent creates a composite coating layer combining inorganic particles (such as alumina, silica, or boehmite) with a specifically designed urethane bond-containing polymer matrix. This composite structure provides both the heat resistance from the inorganic particles and the adhesion properties from the engineered polymer matrix, simultaneously addressing both requirements.
2Ease of manufacture
If polyolefin-based porous substrate is used as separator, then manufacturing is simplified, but heat shrinkage occurs at 100°C or higher causing short-circuit
Solution Approach 1:
The patent applies a coating layer containing heat-resistant inorganic particles and a polymer with low glass transition temperature onto the polyolefin substrate before battery assembly. This preliminary protective layer counteracts the inherent heat shrinkage tendency of the polyolefin substrate when exposed to high temperatures, preventing short-circuits while maintaining the manufacturing simplicity of using polyolefin base material.
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 enhances adhesion to electrodes and ensures heat resistance, preventing short-circuits and maintaining mechanical properties, while eliminating the need for additional crosslinking processes and binder polymers, thus improving safety and performance.
Implementation Method 1
a porous coating layer disposed on at least one surface of the porous polymer substrate and comprising a plurality of inorganic particles and a urethane bond-containing crosslinked polymer, wherein the urethane bond-containing crosslinked polymer is disposed partially or totally on the surfaces of the inorganic particles so that the inorganic particles may be interconnected and fixed
Implementation Method 2
the separator shows improved adhesion to an electrode and has excellent heat resistance... shows the problems of increased resistance, reduced adhesion to an electrode, or the like... a polyolefin-based porous substrate used conventionally as a separator for an electrochemical device shows a severe heat shrinking behavior at a temperature of 100° C. or higher
Data Source
AI summary
A separator for a secondary battery, including: a porous polymer substrate having a plurality of pores; and a porous coating layer on at least one surface of the porous polymer substrate. The porous coating layer includes a plurality of inorganic particles and a urethane bond-containing crosslinked polymer. The urethane bond-containing crosslinked polymer is present partially or totally on surfaces of the inorganic particles wherein the inorganic particles are interconnected and fixed. The urethane bond-containing crosslinked polymer has a glass transition temperature (Tg) of −15 to 32° C. A secondary battery including the separator is also disclosed.