Battery Impedance Diagnosis by Nyquist Inflection-Point Comparison

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Solution Overview

Problem

Current battery diagnosing technologies face challenges in accurately predicting the state of lithium secondary batteries due to limitations in distinguishing inductance and resistance components during impedance measurements, leading to inadequate accuracy in diagnosing battery health, especially when reusing batteries in energy storage systems or electric vehicles.

Innovation Solution

A battery diagnosing apparatus that measures impedance using an AC voltage and generates a Nyquist diagram, extracts an inflection point, and compares it with stored impedance reference values to diagnose the battery, eliminating the need for equivalent circuit models and minimizing the influence of measurement probe components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If electrochemical impedance spectroscopy (EIS) with equivalent circuit model is used for battery diagnosis, then measurement can be performed, but accuracy is insufficient due to inability to distinguish inductance and resistance components from measurement probe vs battery itself

Engineering Contradiction:

Improvebattery diagnosis accuracyVSAvoidequivalent circuit model complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts and removes the measurement probe components (inductance and resistance) from the impedance measurement data through subtraction. By separately measuring the probe components and subtracting them from the total measurement, the patent isolates the true battery impedance, thereby improving measurement accuracy without requiring complex equivalent circuit modeling.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent performs additional measurements beyond the basic EIS measurement - specifically measuring the open circuit voltage and separately characterizing the measurement probe components. This excessive action of measuring extra parameters enables accurate separation and subtraction of probe effects, resolving the accuracy issue without needing complex equivalent circuit models.

Inventive Principle:

Principle #16Partial or excessive action

2Measurement precision

If inductance component of measurement probe is considered, then measurement can be performed, but high frequency band resistance component (SEI) shows large deviation affecting diagnosis accuracy

Engineering Contradiction:

Improvehigh frequency resistance measurement accuracyVSAvoidmeasurement probe inductance interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful inductance effect into a beneficial measurement by deliberately measuring the probe's inductance component separately and using it for compensation. By characterizing the probe's inductance and systematically subtracting its effect from the total measurement, the patent transforms the previously problematic inductance into a correctable parameter, improving high-frequency resistance measurement accuracy.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If equivalent circuit model is used to extract element constants, then diagnosis can be performed, but perfect equivalent circuit model cannot be implemented leading to insufficient accuracy

Engineering Contradiction:

Improvebattery state prediction reliabilityVSAvoidequivalent circuit model implementation difficulty

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical/mathematical equivalent circuit model approach with a direct electrical measurement and subtraction approach. Instead of fitting data to complex circuit models, the patent directly measures impedance at multiple frequencies and subtracts probe components, eliminating the need for equivalent circuit model implementation while improving reliability of battery state prediction.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 approach enhances the accuracy and speed of battery diagnosis, allowing for effective classification of battery levels and improving the reliability of battery health assessment, particularly in reusing battery modules or packs.

Implementation Method 1

as one of conventional representative techniques for diagnosing a battery, there is a method using electrochemical impedance spectroscopy (EIS)

Methodology Applied

Scientific EffectElectrochemical impedance spectroscopy:

Implementation Method 2

A battery generates electrical energy through electrochemical oxidation and reduction reactions

Methodology Applied

Scientific EffectElectrochemical oxidation and reduction reactions: Redox Reactions

Data Source

PatentUS20240036115A1Battery diagnosing apparatus and method

Publication Date: 2024.02.01 LG ENERGY SOLUTION LTD

AI summary

Discussed is a battery diagnosing apparatus that may include an impedance measuring module configured to measure an impedance according to a change of frequency while applying an alternating current (AC) voltage to a target battery, a memory module configured to store an impedance reference value per frequency, and a processor configured to generate a Nyquist diagram for an impedance measurement value of the target battery measured by the impedance measuring module, extract an inflection point from the generated Nyquist diagram, and compare a value within a predetermined frequency range centering around the extracted inflection point with the impedance reference value per frequency stored in the memory module to diagnose the target battery.