Pouch Cell Gas Measurement Using Pressure-Dependent Buoyancy
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Solution Overview
Problem
Existing methods for determining the amount of gas in lithium-ion pouch cells are either limited to initial gas formation measurement, require destructive testing, or are influenced by electrolyte solubility and temperature, making it difficult to monitor gas formation over time and under various conditions.
Innovation Solution
A method involving immersion of the battery cell in a non-conductive liquid at defined ambient pressures, measuring buoyancy forces, and using the ideal gas law to calculate the amount of gas present, allowing for non-destructive, repeated measurements at different temperatures and pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the volume change of pouch cells is measured to determine gas formation, then initial gas formation can be measured, but the method fails when the pouch cell is completely filled with gas and volume no longer changes
Solution Approach 1:
The patent changes the measurement parameter from volume change to mass change. By measuring the mass of the pouch cell at different states of charge and temperatures, the method can determine gas formation even when the cell volume is completely filled and no longer changes. This parameter transformation resolves the limitation of the volume-based method.
2Measurement precision
If the pouch cell is opened in a vacuum to determine gas amount, then the gas volume can be derived from pressure rise, but the pouch cell must be destroyed
Solution Approach 1:
The patent replaces the destructive mechanical opening method with a non-destructive mass measurement method. By using a precision balance to measure mass changes of the sealed pouch cell under different conditions, the gas amount can be determined without destroying the cell structure, enabling repeated measurements on the same cell.
3Measurement precision
If gas amount is determined by opening in vacuum, then measurement can be performed, but a very large number of pouch cells must be tested to create models
Solution Approach 1:
The patent enables the same pouch cell to serve multiple measurement purposes through repeated non-destructive testing. The cell can be measured at different states of charge and temperatures without being destroyed, allowing a single cell to provide data for creating gas formation models under various utilization scenarios, thereby eliminating the need to test a very large number of cells.
4Measurement precision
If gas amount is determined by vacuum opening method, then measurement can be performed, but the determined amount is significantly influenced by gas solubility in electrolyte which depends on pressure and temperature
Solution Approach 1:
The patent performs measurements at multiple states of charge and temperatures to track gas formation continuously. By measuring the mass of the pouch cell at different operational conditions and comparing these measurements, the method can distinguish between mass changes due to gas formation versus mass changes due to solubility variations, thereby compensating for the solubility influence and obtaining accurate gas formation data.
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
Enables accurate, non-destructive determination of gas amounts in battery cells over time and under varying conditions, including those with high internal gas pressures, by accounting for temperature-dependent solubility and using controlled ambient pressures.
Implementation Method 1
a lifting force is generated that acts in the opposite direction of a downforce of the battery cell; the buoyancy force—which is dependent on the ambient pressure—of the battery cell in the liquid is measured
Implementation Method 2
the amount of gas present in the battery cell is measured, taking into account the second ambient pressure, the buoyancy force ascertained for the second ambient pressure, the temperature of the liquid and the density of the liquid
Data Source
AI summary
A method for determining the amount of a gas present in a battery cell, whereby the battery cell has an initial volume, comprises at least the following steps: a) immersing the battery cell into a non-conductive liquid having a defined density at a first ambient pressure; b) generating a lifting force that acts in the opposite direction of a downforce of the battery cell; c) changing the first ambient pressure to a second ambient pressure, and measuring the buoyancy force—which is dependent on the ambient pressure—of the battery cell in the liquid; and d) measuring the amount of gas present in the battery cell, taking into account the first and second ambient pressures, the buoyancy forces ascertained for these ambient pressures, the temperature of the non-conductive liquid and the density of the liquid.