Battery Defect Detection Using AC Impedance Time Constants
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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 thermal energy conversion and accidents.
Innovation Solution
A method using AC impedance spectroscopy to analyze the impedance changes based on frequency, constructing an equivalent circuit model, and calculating time constants to quickly and accurately detect internal short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage drop 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, which uses electrical impedance measurements at different frequencies to detect internal short circuits. This substitution of measurement methodology enables rapid detection within minutes while maintaining high accuracy through frequency-dependent impedance analysis.
Solution Approach 2:
The patent introduces frequency as a new parameter for defect detection by measuring impedance at multiple frequencies. By analyzing how impedance varies with frequency, the method can quickly identify internal short circuits through characteristic impedance patterns, eliminating the need for prolonged voltage monitoring and achieving both speed and accuracy.
2Productivity
If conventional detection methods are used, then screening capability is limited, but device complexity remains low
Solution Approach 1:
The patent employs periodic AC signals at different frequencies to probe the battery's impedance characteristics. By applying sinusoidal voltages at multiple frequency points and measuring the resulting current responses, the system efficiently screens for internal short circuits through frequency-domain analysis, significantly improving productivity while using standard electrochemical measurement equipment.
Solution Approach 2:
The patent adds the frequency dimension to the impedance measurement, transforming a single-point DC measurement into a multi-frequency AC analysis. This dimensional expansion enables more informative defect detection by capturing frequency-dependent impedance behavior, enhancing screening efficiency without requiring fundamentally new equipment beyond standard electrochemical workstations.
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 rapid and precise identification of battery defects, particularly internal short circuits, improving safety by reducing detection time and enhancing screening efficiency.
Implementation Method 1
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
Implementation Method 2
calculating a product of a charge transfer resistance component Rct and an electric double layer capacitance component Cdl in the equivalent circuit model as a time constant
Implementation Method 3
calculating a product of a charge transfer resistance component Rct and an electric double layer capacitance component Cdl in the equivalent circuit model as a time constant
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
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.