Crosslinked Polyolefin Separator for High Meltdown Temperature
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Solution Overview
Problem
Conventional crosslinked polyolefin separators for lithium secondary batteries have low meltdown temperatures, leading to safety concerns due to the insufficient difference between shutdown and meltdown temperatures, which can result in hot box test failures.
Innovation Solution
A method for manufacturing a crosslinked polyolefin separator involving the use of polyolefin and polyolefin elastomer with a specific weight ratio, reactive extrusion with alkoxy silane, and subsequent stretching and moisture crosslinking to achieve a high meltdown temperature and low shutdown temperature, ensuring improved safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional polyolefin separator is used, then the manufacturing process is simple, but the meltdown temperature is low resulting in insufficient safety margin between shutdown and meltdown temperatures
Solution Approach 1:
The patent applies preliminary action by incorporating silane grafting during the extrusion process before the final separator formation. The silane-modified polyolefin is prepared in advance with controlled grafting degree, which enables subsequent moisture-induced crosslinking to achieve high meltdown temperature without requiring complex post-processing steps. This preliminary modification of the polymer structure allows the separator to develop enhanced thermal stability through crosslinking after manufacturing.
Solution Approach 2:
The patent employs parameter changes by controlling the silane content and grafting degree during extrusion to optimize the crosslinking density. By adjusting the silane concentration and extrusion parameters, the manufacturing process achieves controlled crosslinking that raises the meltdown temperature while maintaining processability. The crosslinking degree is tuned to ensure the meltdown temperature exceeds the shutdown temperature by sufficient margin, resolving the thermal safety issue.
2Temperature
If silane crosslinking is performed to increase meltdown temperature, then the thermal safety is improved, but the silane crosslinking uniformity is poor leading to inconsistent performance
Solution Approach 1:
The patent applies local quality by ensuring uniform silane distribution throughout the polyolefin matrix during the extrusion process. The silane-modified polyolefin is processed to achieve homogeneous local composition, which enables uniform crosslinking density throughout the separator structure. This local uniformity in silane distribution and crosslinking density ensures consistent meltdown temperature and thermal safety performance across different regions of the separator.
Solution Approach 2:
The patent uses preliminary action by pre-grafting silane groups to the polyolefin chains during extrusion with controlled reaction conditions. This preliminary silane incorporation ensures uniform distribution of crosslinking sites before separator formation and moisture exposure. The controlled grafting process creates homogeneous silane content throughout the material, which subsequently leads to uniform crosslinking and consistent thermal properties across the entire separator.
3Temperature
If the shutdown temperature is reduced to improve safety margin, then the thermal safety is improved, but the ionic conductivity may be affected due to premature shutdown
Solution Approach 1:
The patent applies parameter changes by selecting polyolefin materials and silane modifiers with appropriate melting and crosslinking characteristics. The shutdown temperature is optimized to a value that provides sufficient safety margin below the crosslinked meltdown temperature while remaining above the operating temperature range. This parameter optimization ensures that the separator maintains porosity and ionic conductivity during normal operation, then shuts down at an appropriate safety temperature, and finally achieves high meltdown resistance through crosslinking.
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 method produces a crosslinked polyolefin separator with enhanced silane crosslinking uniformity and a significant increase in meltdown temperature while maintaining a low shutdown temperature, thereby improving the safety of lithium secondary batteries.
Implementation Method 1
reactive extrusion of a silane grafted polyolefin composition
Implementation Method 2
crosslinking the heat-set porous membrane in the presence of moisture
Implementation Method 3
extracting the first diluent and the second diluent from the stretched sheet to produce a porous membrane
Data Source
AI summary
The present disclosure relates to a method for manufacturing a crosslinked polyolefin separator including putting a polyolefin and a polyolefin elastomer into an extruder first, and putting an alkoxy silane containing a carbon-carbon double bond functional group, an initiator and a crosslinking catalyst, and a separator. The present disclosure provides a method for manufacturing a crosslinked polyolefin separator with high meltdown temperature and low shutdown temperature and a separator manufactured thereby.