Rechargeable Battery Short-Circuit Screening via Nyquist Impedance
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Solution Overview
Problem
Existing methods for detecting internal short circuits in rechargeable batteries are time-consuming and limited in screening ability, posing safety risks due to potential heat generation and ignition.
Innovation Solution
A method using AC impedance analysis to detect defects in rechargeable batteries by measuring AC impedance at various frequencies, building an equivalent circuit model, and calculating specific time constants or slope values to identify internal short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage drop monitoring method is used to detect internal short circuits, then detection accuracy is improved, but detection time increases significantly (3 to 14 days required)
Solution Approach 1:
The patent replaces the time-consuming voltage drop monitoring method with AC impedance spectroscopy, substituting a slow electrochemical monitoring approach with a faster electrical measurement technique. The AC impedance method measures impedance magnitude and phase difference across frequency ranges to detect internal short circuits, reducing detection time from days to minutes while maintaining detection accuracy.
Solution Approach 2:
The patent changes the measurement parameters from voltage drop over time to AC impedance characteristics (magnitude and phase difference) across frequency. By measuring impedance at multiple frequencies and analyzing the phase difference between voltage and current signals, the method achieves rapid detection of internal short circuits without requiring extended monitoring periods.
2Reliability
If conventional voltage drop method is used, then internal short circuits can be detected, but screening ability is limited
Solution Approach 1:
The patent adds a new dimension to defect detection by measuring both magnitude and phase difference of AC impedance across frequency ranges. This multi-dimensional approach (frequency, magnitude, phase) provides richer information about battery health and internal short circuits, significantly improving screening ability and detection reliability compared to single-parameter voltage monitoring.
Solution Approach 2:
The patent introduces AC impedance as an intermediary parameter that reflects the electrochemical state of the battery. By measuring impedance characteristics rather than directly monitoring voltage drop, the method achieves both reliable defect detection and improved screening efficiency, as impedance changes provide early indicators of internal issues.
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
This method allows for quick and accurate detection of internal short circuits in rechargeable batteries, improving safety and reducing the time required for diagnostic testing compared to conventional methods.
Implementation Method 1
The AC impedance method is a method of analyzing the magnitude and phase difference of impedance by measuring the impedance according to the frequency while applying alternating current with a small amplitude at different frequencies, that is, a method of analyzing the characteristics of an electrochemical system based on the impedance of the electrochemical reaction depending on the AC frequency.
Data Source
AI summary
Detecting a defect in a rechargeable battery includes measuring an output signal by applying an input signal to the battery while modulating frequency, calculating an AC impedance according to the frequency and the output signal, Nyquist plotting the AC impedance and building an equivalent circuit model based on the plot, calculating a product of a charge transfer resistance and an electric double layer capacitance in the model as a time constant or calculating a slope of a straight line appearing in a low-frequency region in the plot, comparing the time constant with a predetermined time constant or comparing an absolute value of the calculated slope of the straight line with a predetermined slope absolute value, and determining the battery is defective when the time constant is less than the predetermined time constant or when the absolute value of the calculated slope is smaller than the predetermined slope absolute value.