Silane-Grafted Polyolefin Separator for Uniform Melt-Down Behavior
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Solution Overview
Problem
Conventional crosslinked polyolefin separators exhibit non-uniform crosslinking, leading to high surface resistance and difficulty in maintaining a consistent melt-down temperature across the thickness direction, which affects the safety and performance of lithium secondary batteries.
Innovation Solution
A crosslinked polyolefin separator is manufactured using a controlled introduction of diluting agents and a silane-crosslinking process, ensuring uniform crosslinking throughout the thickness direction by adjusting the ratio of IR peak intensities and crosslinking density, thereby reducing surface resistance and enhancing melt-down temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If crosslinking is performed using conventional methods with diluting agents and crosslinking agents, then the melt-down temperature of the separator is increased, but non-uniform crosslinking occurs with intensive crosslinking only on the surface
Solution Approach 1:
The silane-modified polyolefin is prepared in advance with grafted silane groups, but the actual crosslinking reaction is delayed until the separator is formed. This preliminary preparation allows the crosslinking agents to be uniformly distributed throughout the material before the crosslinking reaction occurs, preventing surface-only crosslinking while maintaining high melt-down temperature.
Solution Approach 2:
Silane-modified polyolefin acts as an intermediary substance that bridges the polyolefin matrix and crosslinking agents. The grafted silane groups (Si-OH) serve as intermediate reactive sites that facilitate uniform crosslinking throughout the separator thickness, rather than allowing direct surface-only crosslinking between diluting agents and crosslinking agents.
2Temperature
If crosslinking occurs intensively on the separator surface, then the melt-down temperature increases, but pores cannot be formed on the separator surface causing increased resistance
Solution Approach 1:
The separator structure with pores is formed in advance through the phase separation process using diluting agents, before the crosslinking reaction occurs. This ensures that the pore structure is established throughout the separator including the surface, and subsequent crosslinking does not block pore formation, thus maintaining low resistance while achieving high melt-down temperature.
Solution Approach 2:
The crosslinking reaction conditions are carefully controlled by adjusting parameters such as crosslinking temperature, time, and catalyst concentration to achieve uniform crosslinking throughout the separator thickness. This prevents excessive surface crosslinking that would block pores, while ensuring sufficient crosslinking to raise the melt-down temperature.
3Strength
If diluting agent and crosslinking agent are used together, then crosslinking is achieved, but side reactions occur between the two agents
Solution Approach 1:
The diluting agents are completely removed from the separator through extraction processes before the crosslinking reaction occurs. This separation eliminates the source of side reactions between diluting agents and crosslinking agents, while the silane-modified polyolefin retains its crosslinking capability through the grafted silane groups that remain on the polymer chains.
Solution Approach 2:
The diluting agents serve as temporary, disposable substances used only during the phase separation process to create pores. They are completely extracted afterward, leaving no residual substances that could cause side reactions during crosslinking, while still having served their purpose of creating the desired porous structure.
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 results in a separator with reduced surface resistance and uniform thermal properties, improving the safety and performance of electrochemical devices by maintaining a higher melt-down temperature and preventing surface over-crosslinking.
Implementation Method 1
a crosslinked polyolefin separator which includes silane-crosslinked polyolefin
Implementation Method 2
silane crosslinking shows an Infrared Spectroscopy (IR) peak intensity of 0.001-0.012 in the thickness direction of the separator
Implementation Method 3
when using crosslinking, a diluting agent required for forming pores
Data Source
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AI summary
The present disclosure relates to a method for manufacturing a crosslinked polyolefin separator, including the steps of: (S1) introducing polyolefin having a weight average molecular weight of 200,000-1,000,000, a first diluting agent, alkoxysilane containing a carbon-carbon double bonded group, an initiator and a crosslinking catalyst to an extruder, followed by mixing; (S2) introducing a second diluting agent to the extruder, followed by mixing, to carry out reactive extrusion of a silane-grafted polyolefin composition; (S3) molding and orienting the reactive extruded silane-grafted polyolefin composition in the form of a sheet; (S4) extracting the first diluting agent and the second diluting agent from the oriented sheet to obtain a silane-grafted polyolefin porous membrane; (S5) thermally fixing the porous membrane; and (S6) crosslinking the porous membrane in the presence of water. According to the method, it is possible to provide a separator which shows a decrease in intensive silane crosslinking on the surface thereof.