Polyimide Separator Labyrinth Porosity for Battery Safety
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Solution Overview
Problem
Lithium ion cells face safety concerns due to lithium dendrite growth and internal short circuits, particularly under high mechanical, thermal, and electrical stress, which conventional polyolefin and high-melting polyimide separators fail to adequately address.
Innovation Solution
A polyimide-based separator with labyrinth porosity and a ceramic-based coating is used, featuring culs-de-sac channels that prevent direct communication between electrodes, combined with a binder and ceramic particles for enhanced stability and safety, utilizing a lithium ion-conducting ceramic to improve high-current capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polyolefin separators are used, then manufacturing cost is reduced, but thermal stability and mechanical strength deteriorate at high temperatures
Solution Approach 1:
The patent employs a composite separator structure consisting of a polyolefin base layer combined with a polyimide coating layer. This composite design allows the separator to maintain the manufacturing advantages of polyolefin while gaining the high thermal stability of polyimide, effectively resolving the contradiction between manufacturing cost and thermal stability.
2Temperature
If high-melting polyimide separators are used, then thermal stability is improved, but mechanical strength and safety under stress deteriorate
Solution Approach 1:
The patent creates a composite separator where a polyimide coating layer is applied over a polyolefin base layer. The polyolefin provides mechanical strength and flexibility, while the polyimide coating contributes thermal stability. This composite approach resolves the contradiction between thermal stability and mechanical strength by combining the advantages of both materials.
3Use of energy by moving object
If open porosity separators are used, then lithium ion conductivity is improved, but safety deteriorates due to dendrite growth
Solution Approach 1:
The patent applies a polyimide coating layer with specific porosity characteristics on the surface of the polyolefin separator. This creates a localized structure where the coating layer provides dendrite prevention while the underlying polyolefin maintains high lithium ion conductivity through its open porosity. The local quality modification resolves the contradiction between conductivity and safety.
Solution Approach 2:
The patent transforms the potential harm of open porosity (dendrite growth path) into a benefit by introducing a polyimide coating layer that blocks dendrite propagation while preserving ion transport. The coating converts the harmful open channel structure into a protected pathway, allowing high conductivity without compromising safety.
4Use of energy by moving object
If separator porosity is increased, then lithium ion conductivity is improved, but structural integrity deteriorates under mechanical loads
Solution Approach 1:
The patent uses a composite structure where the polyolefin base layer provides mechanical strength and structural integrity, while the polyimide coating layer contributes to ion conductivity and surface protection. This composite design resolves the contradiction between porosity-induced conductivity and structural integrity by assigning different functional roles to each layer.
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 significantly enhances the safety and stability of lithium ion cells by preventing lithium dendrite growth and maintaining structural integrity under thermal and mechanical loads, offering improved intrinsic safety and high-current performance.
Implementation Method 1
the porosity of the separator takes the form of labyrinth porosity. This means that the separator has a number of labyrinthine channels which represent, so to speak, culs-de-sac, which do not extend continuously from one side of the separator to its other side
Implementation Method 2
a composite coating comprising at least one binder and also ceramic particles
Implementation Method 3
a porous, ceramic-based coating which is applied on at least one side of the polyimide-based separator
Implementation Method 4
utilizing a lithium ion-conducting ceramic to improve high-current capability
Implementation Method 5
Other separators used, made of plastic which is high-melting, are known from U.S. Pat. No. 7,112,389 B1 and are more stable both thermally and mechanically than polyolefin-based separators
Data Source
AI summary
A galvanic element includes at least one lithium-intercalating and at least one lithium-deintercalating electrode. A positive electrode and a negative electrode are separated by a polyimide-based separator that has a labyrinth porosity. The polyimide-based separator is configured at least on one side with a porous, ceramically-based coating that comprises a binder and ceramic particles.