Battery Cell Capacity Diagnosis via Q-V Curve Analysis

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Solution Overview

Problem

Existing methods for diagnosing battery cell capacity from Q-V curves are limited in accuracy and efficiency, particularly in considering capacity deterioration factors such as voltage differences and changes in inclination.

Innovation Solution

A diagnostic device and method that calculate battery cell capacity by comparing measurement Q-V curves with reference Q-V curves, using calculators to determine capacity deterioration and temporary maximum capacity based on voltage differences and inclination ratios.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If battery capacity is diagnosed using Q-V curve comparison methods, then diagnostic accuracy is improved, but diagnostic time increases

Engineering Contradiction:

Improvecapacity diagnosis accuracyVSAvoiddiagnostic time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The Q-V curve analysis is segmented into multiple inclination regions (first, second, third inclinations) corresponding to different charge/discharge stages. Each region is analyzed independently to calculate specific capacity deterioration components, enabling comprehensive diagnosis without requiring exhaustive curve analysis, thus balancing accuracy with efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Reference Q-V curves are pre-established for different battery types and conditions. During diagnosis, these pre-prepared reference curves are directly compared with measurement curves, eliminating the need to create reference data during the diagnostic process itself, thereby reducing diagnostic time while maintaining accuracy.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If detailed Q-V curve analysis is performed to diagnose capacity deterioration, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improvecapacity deterioration detection accuracyVSAvoiddiagnostic system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

Complex physical battery testing and disassembly are replaced with computational analysis of Q-V curve data. The diagnostic system uses algorithmic processing of voltage and current integration data to detect capacity deterioration, substituting mechanical/physical diagnostic methods with mathematical modeling and data processing.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system analyzes changes in curve inclination parameters (slope, curvature) rather than absolute values. By monitoring parameter variations such as the first, second, and third inclinations of the Q-V curve, the system detects capacity deterioration with high precision while keeping the analytical framework relatively simple.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If multiple calculation methods are used to account for different deterioration factors, then reliability is improved, but ease of operation deteriorates

Engineering Contradiction:

Improvediagnosis reliabilityVSAvoidoperational simplicity

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

Multiple deterioration analysis methods are merged into a unified Q-V curve comparison framework. Different inclination analyses (first, second, third inclinations) and multiple calculation approaches are integrated into a single diagnostic process, maintaining comprehensive reliability while presenting a unified, easier-to-operate interface.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The diagnostic system is designed to handle multiple battery types and deterioration conditions through a universal Q-V curve analysis methodology. The same basic framework accommodates different battery chemistries and degradation patterns, reducing operational complexity while maintaining broad applicability and reliability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentEP4166965B1Diagnostic device, diagnostic method, and computer diagnostic program

Publication Date: 2025.04.23 YOKOGAWA ELECTRIC CORP

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Figure 5

AI summary

A diagnostic device (1) includes: a calculator (5) configured to calculate a value related to a capacity of a battery cell based on a result of comparison between a measurement Q-V curve and a reference Q-V curve, the measurement Q-V curve indicating a relation between a voltage and an integrated current amount that are obtained from measurement data of the battery cell. The calculator (5) includes at least one of: a first calculator (51) configured to calculate an amount of capacity deterioration caused by a voltage difference between the measurement Q-V curve and the reference Q-V curve by multiplying an inclination of the measurement Q-V curve by the voltage difference; or a second calculator (52) configured to calculate a temporary maximum capacity after capacity deterioration caused by a change in the inclination of the measurement Q-V curve to an inclination of the reference Q-V curve by multiplying a ratio between the inclination of the measurement Q-V curve and the inclination of the reference Q-V curve by a reference maximum capacity.