Crosslinked Polyolefin Separator for High-Temperature Battery Safety
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Solution Overview
Problem
Lithium secondary batteries face safety issues due to low melting point separators like polyethylene, leading to potential ignition and explosion, and existing solutions like PE/PP/PE trilayer separators complicate manufacturing or produce undesired byproducts.
Innovation Solution
A crosslinked polyolefin separator with specific rheological properties (tan(δ) ≤ 0.3, 'a' value of 0.03-0.25, and direct UV crosslinking of polyolefin fibrils maintains elasticity and high meltdown temperature, ensuring safety and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separator is used in lithium secondary batteries, then safety is improved by preventing internal short circuits, but battery output is reduced due to impedance at the interface between the separator and electrode
Solution Approach 1:
The patent applies parameter changes by modifying the surface properties of the separator through plasma treatment. This treatment alters the surface energy and chemical composition of the separator, enabling better wettability and adhesion with the electrode. The plasma treatment introduces polar groups and increases surface roughness at the microscopic level, which improves the contact area and reduces interfacial impedance without changing the bulk properties of the separator, thus maintaining safety while enhancing power output.
2Strength
If the surface energy of the separator is increased to improve adhesion with the electrode, then manufacturing complexity increases due to additional treatment steps
Solution Approach 1:
The patent replaces complex multi-step chemical treatments with a single plasma treatment process. Instead of using multiple chemical coatings or adhesives that would require sequential application and curing steps, the plasma treatment achieves the desired surface energy increase and adhesion improvement in one step. This substitution of mechanical/chemical complex processes with a plasma physical-chemical process simplifies the manufacturing procedure while achieving the same or better adhesion results.
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 separator maintains strength and insulating properties at high temperatures, preventing short circuits and enhancing safety by increasing meltdown temperature while maintaining porosity and air permeability.
Implementation Method 1
a surface treatment step for treating a surface of the porous polymer separator with plasma
Implementation Method 2
a surface treatment step for treating a surface of the porous polymer separator with plasma, and a surface treatment step for forming a silane coupling agent layer on the porous polymer separator
Data Source
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AI summary
Disclosed is a separator for a lithium secondary battery including a porous polyolefin substrate and showing a tan(δ) of 0.3 or less in the storage-loss modulus curve. Also disclosed is an electrochemical device including the separator. The separator shows low viscosity but high elasticity at high temperature. Therefore, the separator maintains its strength at high temperature and ensures resistance against external force in the state of high-temperature exposure, and thus can provide a lithium secondary battery with improved safety. In addition, according to an embodiment of the present disclosure, it is possible to obtain a crosslinked polyolefin separator through a simplified process, unlike the related art.