Crosslinked Li-Ion Battery Separator for Heat Resistance and Shutdown
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Solution Overview
Problem
Current lithium ion secondary battery separators face challenges in achieving high-temperature membrane rupture resistance, low temperature shutdown function, and stable cycle characteristics due to limitations in silane crosslinking methods, leading to potential safety issues and reduced battery performance.
Innovation Solution
A separator for lithium ion batteries comprising a silane-modified polyolefin that crosslinks when in contact with the electrolyte solution, with a specific weight ratio of silane-modified polyolefin to polyethylene, and a crosslinking method that avoids the use of dehydrating condensation catalysts, allowing for controlled crosslinking during the production process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If silane crosslinking is performed using dehydrating condensation catalysts during separator production, then high-temperature membrane rupture resistance is improved, but internal stress and deformation occur during production
Solution Approach 1:
The separator is pre-modified with silane groups during manufacturing, but the actual crosslinking reaction is postponed to occur later during battery formation or initial charging cycles. This preliminary preparation allows the separator to gain heat-resistant properties without undergoing crosslinking-induced deformation during production, as the crosslinking occurs after the battery assembly is complete.
Solution Approach 2:
The patent employs a two-stage approach where silane modification is performed beforehand during separator production, but the crosslinking reaction is cushioned or delayed to occur later under controlled conditions. This prevents the harmful effects of crosslinking (internal stress and deformation) during manufacturing while still achieving the desired high-temperature resistance through subsequent controlled crosslinking during battery operation.
2Reliability
If polyolefin separator is used to ensure chemical inertness, then electrochemical stability is improved, but affinity with electrolyte solution and Li ion permeability are reduced
Solution Approach 1:
The patent applies local quality modification by introducing silane groups at specific locations on the polyolefin separator chains. The bulk polyolefin structure maintains its chemical inertness and electrochemical stability, while the localized silane groups provide enhanced electrolyte affinity and facilitate Li ion permeation. This localized modification allows the separator to simultaneously exhibit both electrochemical stability and improved ion transport properties.
Solution Approach 2:
The patent creates a composite structure combining polyolefin base material with silane-modified regions. The polyolefin provides the fundamental chemical inertness and structural integrity, while the silane-modified portions contribute improved electrolyte wettability and ion conductivity. This composite approach allows the separator to integrate multiple functional properties that neither material alone could provide.
3Volume of moving object
If separator thickness is reduced to improve battery energy density, then battery size is reduced, but mechanical strength and safety are compromised
Solution Approach 1:
The patent changes the physical and chemical parameters of the separator material through silane modification and subsequent crosslinking. The crosslinked gel structure fundamentally alters the mechanical properties of the separator, providing enhanced strength and dimensional stability. This parameter change allows the use of thinner separator designs that would otherwise be mechanically insufficient, thereby reducing battery size while maintaining safety.
Solution Approach 2:
The patent employs a composite gel structure formed by crosslinked silane-modified polyolefin chains within the separator matrix. This composite structure provides exceptional mechanical strength and thermal stability relative to the thin film geometry. The crosslinked gel network acts as a reinforcing phase that compensates for the reduced thickness, enabling thin separators to maintain adequate mechanical strength and safety performance.
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 provides a separator with improved high-temperature puncture resistance, low temperature shutdown function, and enhanced cycle stability, reducing the risk of internal stress and deformation, while ensuring safety and productivity in battery production.
Implementation Method 1
silane crosslinking reaction of the silane-modified polyolefin is initiated when it contacts with the electrolyte solution
Implementation Method 2
separators must have both an active shutdown function and high membrane rupture temperature
Implementation Method 3
a solid electrolyte interface (SEI) is formed by chemical reaction during initial charge
Data Source
Figure 1~2
Figure 3
Figure 4(a)~4(b)
AI summary
A separator for an electricity storage device comprising 5 to 40 weight% of a silane-modified polyolefin and 60 to 95 weight% of a polyolefin other than the silane-modified polyolefin, wherein the transition temperature, determined as described in the specification, is 135°C to 150°C for the rubber plateau and the crystal melt flow region, in the temperature-dependent change of the storage modulus of the separator for an electricity storage device.