Coated Polyethylene Separator for High-Temperature Pore Shutdown
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Solution Overview
Problem
Lithium-ion batteries face thermal safety issues at high temperatures, leading to intermittent cycling performance degradation and increased risk of fires and explosions due to reactions between positive and negative electrodes.
Innovation Solution
A separator with a polyethylene base film and a coating, where the pore closing temperature difference and porosity are controlled within specific ranges, along with a tailored electrolyte composition, to block reactions between electrodes and suppress thickness swelling, enhancing high-temperature performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional separator is used, then the battery can operate at high temperatures, but the pores remain open allowing reactions between electrodes leading to thermal runaway
Solution Approach 1:
The separator utilizes phase transition of the coating material from solid to liquid state at elevated temperatures. The coating layer undergoes melting at a specific temperature range (3-17°C below base film), causing pores to close automatically and block electrode reactions, thereby preventing thermal runaway while maintaining normal operation.
Solution Approach 2:
The separator employs a composite structure consisting of a polyethylene base film combined with a coating layer containing heat-responsive materials. This composite design allows the separator to exhibit both mechanical strength from the base film and temperature-responsive pore closing capability from the coating, resolving the contradiction between maintaining open pores for ion transport and closing pores for safety.
2Reliability
If the pore closing temperature of the separator is too close to the base film, then the coating provides minimal additional protection, but if too far apart, the separator structure becomes unstable
Solution Approach 1:
The invention optimizes the pore closing temperature parameter by selecting coating materials with specific melting points that are 3-17°C lower than the base film. This parameter control ensures the coating activates before the base film, providing effective pore closure while maintaining structural stability through the coordinated temperature response of the composite structure.
3Productivity
If the porosity is too high, then ion transport is efficient, but the separator cannot effectively block electrode reactions during thermal events
Solution Approach 1:
The coating layer performs preliminary pore closure action at a temperature threshold before thermal runaway occurs. By designing the coating to melt and close pores at 3-17°C below the base film temperature, the system proactively blocks ion transport and electrode reactions in advance of catastrophic failure, sacrificing some high-temperature ion transport to ensure thermal safety.
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 effectively improves the drop performance and intermittent cycling performance of lithium-ion batteries at high temperatures by quickly closing pores and forming uniform solid electrolyte interface films, reducing gas generation and lithium precipitation, thereby enhancing safety and longevity.
Implementation Method 1
a pore closing temperature of the separator is T1, a pore closing temperature of the polyethylene base film is T2, and 3° C.≤T2−T1≤17° C.
Implementation Method 2
the separator has a porosity P of 15% to 55% after being placed at 110° C. for 10 min
Data Source
AI summary
A separator includes a polyethylene base film and a coating provided on at least one surface of the polyethylene base film, where a pore closing temperature of the separator is T1, a pore closing temperature of the polyethylene base film is T2, and 3° C.≤T2−T1≤17° C.; and the separator has a porosity P of 15% to 55% after being placed at 110° C. for 10 min. When the separator is used, during drop process of the secondary battery, a pore closing tendency of the separator can block reactions between positive and negative electrodes. This can improve the drop performance of the secondary battery at high temperatures and effectively improve the intermittent cycling performance of the secondary battery at high temperatures.