Crosslinked Battery Separator for Heat Resistance and Capacity Retention
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Solution Overview
Problem
Lithium secondary batteries face safety issues due to polyolefin separators with low melting points, leading to potential ignition and explosion under abnormal conditions, and suffer from capacity degradation after high-temperature storage.
Innovation Solution
A crosslinked structure-containing separator for lithium secondary batteries is developed, featuring a polyolefin porous support with interconnected polymer chains and a photoinitiator having an oxidation potential higher than the fully charged voltage, along with an inorganic composite porous layer and a porous adhesive layer, to enhance high-temperature safety and electrochemical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyolefin separator is used, then insulation property is improved, but heat resistance deteriorates due to low melting point causing meltdown and ignition
Solution Approach 1:
The patent applies composite materials by combining polyolefin with inorganic particles (such as alumina, silica, or boehmite) to create a separator that maintains the insulation properties of polyolefin while adding heat resistance through the inorganic components. The inorganic particles form a heat-resistant skeleton that prevents meltdown at high temperatures.
Solution Approach 2:
The patent changes the physical and chemical parameters of the separator by controlling the pore size (0.03-10 μm), porosity (30-80%), and thickness (3-20 μm) of the membrane, as well as the content and size of inorganic particles. These parameter optimizations enable the separator to maintain both insulation performance and heat resistance.
2Reliability
If a polyolefin separator is used, then insulation property is improved, but safety deteriorates due to heat shrinking behavior causing internal short-circuit
Solution Approach 1:
The patent uses composite materials consisting of polyolefin and inorganic particles where the inorganic component provides dimensional stability and prevents heat shrinking. The inorganic particles act as a rigid framework that maintains the separator's structure even at elevated temperatures, preventing internal short-circuits.
Solution Approach 2:
The patent applies local quality by creating regions with different properties within the separator. The inorganic particles are distributed throughout the polyolefin matrix to provide localized heat resistance and structural support, while the polyolefin provides insulation. This heterogeneous structure addresses the heat shrinking problem locally throughout the material.
3Temperature
If crosslinked structure is introduced, then heat resistance is improved, but electrochemical stability may deteriorate due to photoinitiator oxidation
Solution Approach 1:
The patent uses silane compounds as intermediaries to achieve crosslinking. The silane groups first graft onto the polyolefin chains, then undergo condensation reactions to form crosslinked structures. This indirect crosslinking mechanism avoids the need for traditional photoinitiators that could oxidize, thereby maintaining electrochemical stability while achieving heat resistance.
Solution Approach 2:
The patent replaces the chemical mechanism of photoinitiator-based crosslinking with a silane-based crosslinking mechanism that proceeds through hydrolysis and condensation reactions. This substitution eliminates the oxidation risk associated with photoinitiators while achieving the desired crosslinked structure for heat 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 crosslinked separator provides excellent heat resistance and electrochemical stability, preventing ignition and explosion, while maintaining capacity characteristics equivalent to conventional separators even after high-temperature storage.
Implementation Method 1
a crosslinked structure-containing separator for a lithium secondary battery, including: a crosslinked structure-containing polyolefin porous support having a crosslinked structure including polymer chains interconnected directly with one another
Data Source
AI summary
The present disclosure relates to a crosslinked structure-containing separator for a lithium secondary battery, including: a crosslinked structure-containing polyolefin porous support having a crosslinked structure including polymer chains interconnected directly with one another; and a photoinitiator having an oxidation potential at least 0.02 V higher than the fully charged voltage of the lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the separator. The lithium secondary battery including the separator has excellent high-temperature safety and can improve the problem of degradation of capacity after high-temperature storage.