Battery Separator Testing for Ionic Conduction and Short Resistance
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Solution Overview
Problem
Current battery separator tests, primarily derived from the textile industry, fail to accurately predict performance in lithium-ion batteries due to their inability to simulate the actual conditions within the battery, particularly regarding air and liquid flow, vacuum environments, and internal shorting resistance.
Innovation Solution
A complex method involving multiple measurements such as ionic conduction, wettability under vacuum, internal short resistance, and tension strength testing, using a squeeze electrode setup that mimics the battery environment, to assess the performance of battery separators more accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional air permeability testing (Gurley measurement) is used, then the test method is simple and familiar, but it fails to accurately predict separator performance in lithium-ion batteries because there is no air flow in the actual battery
Solution Approach 1:
The patent creates a simplified battery model that copies the essential structure and conditions of a real lithium-ion battery (separator between electrodes, electrolyte injection, vacuum environment) to perform testing. This allows measurement of ionic conduction under conditions that simulate actual battery operation, providing accurate performance prediction without requiring a full-scale battery.
Solution Approach 2:
The patent replaces the mechanical air flow measurement system (Gurley tester) with an electrical measurement system that measures ionic conduction. Instead of forcing air through the separator and measuring resistance to air flow, the patent uses electrochemical cells to measure ion transport properties, which directly correlate with actual battery performance.
2Measurement precision
If wettability testing is performed in air, then the test is simple to perform, but it does not reflect the vacuum conditions and multi-phase interfaces present in actual battery operation
Solution Approach 1:
The patent performs wettability testing in a vacuum environment rather than in air, which better simulates the actual battery conditions during electrolyte injection. The vacuum environment eliminates interference from air and accurately reflects the multi-phase interfaces (electrolyte, cathode, anode, separator, vacuumed residue air) that affect separator performance in real batteries.
3Measurement precision
If puncture strength testing is performed on unsupported separator, then the test is simple to perform, but it does not account for the support provided by cathode and anode in actual battery operation
Solution Approach 1:
The patent segments the battery into essential components (electrodes and separator) to create a simplified test model. By isolating these key elements and arranging them in a layered structure, the patent can test separator performance under conditions that reflect actual battery operation without the complexity of a complete battery assembly.
Solution Approach 2:
The patent introduces an intermediary testing setup where electrodes are placed on either side of the separator, simulating the support structure provided by cathode and anode in real batteries. This intermediary configuration allows the separator to be tested in a manner that reflects its actual operational conditions, improving the accuracy of internal shorting resistance prediction.
4Use of energy by moving object
If thinner separators are used to improve energy density, then battery energy density increases, but the separator becomes more vulnerable to internal shorting and requires more accurate testing
Solution Approach 1:
The patent changes the testing parameters from mechanical strength measurements to ionic conduction measurements, which are more sensitive and relevant for thin separators. By measuring ion transport properties rather than mechanical strength, the patent can detect subtle differences in separator performance that are critical for safety, especially for thinner separators where mechanical properties may be similar but ionic conduction characteristics differ.
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 proposed method provides a more accurate prediction of battery separator performance, addressing the limitations of existing tests by simulating real battery conditions and improving the assessment of internal shorting resistance, which is critical for safety in lithium-ion batteries.
Implementation Method 1
Separators must allow for the flow of ions across the battery separator during normal battery charge and discharge cycles. For polymeric separators, typically these need to be wet with liquid electrolyte to allow for ionic conduction.
Implementation Method 2
Battery separators should also be chemically and electronically stable, i.e., not reactive or minimally reactive with other components in the battery like the electrolyte and the electrode materials.
Implementation Method 3
Wettability testing measures the time required for separator material to become completely wetted when it comes in contact with liquid electrolyte.
Data Source
AI summary
Disclosed herein are new or improved method for measuring battery separators that are more suitable for modern battery separators and may more accurately predict performance in the battery. Also disclosed are characteristics of an ideal separator that may be measured according to the new or improved methods herein. The ideal separator may comprise one of more of the following properties: low electrical resistance (ER)/σi approaching infinity; σe approaching zero when the separator is dry or wet with electrolyte; low or no volume (higher Wh/l); low or no weight (high Wh/kg); anti-compression (z-performance, wet); super strong (XYZ direction strength for processing when dry and wet); all temperature stability (mechanical, electrical, and electro-chemical when wet and dry); and ability to apply infinite force when measuring ISR.