Metal Lithium Precipitation Detection in Li-Ion Batteries

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Solution Overview

Problem

Existing methods for determining whether metal lithium is precipitated in lithium ion secondary batteries are complex and require constant voltage control, making it difficult to diagnose precipitation in vehicle electrical systems, and cannot distinguish between metal lithium precipitation and normal usage degradation.

Innovation Solution

A determination system that performs constant current discharge on the battery until a predetermined low state of charge is reached, then measures the natural increase in voltage after discharge termination, comparing it to a threshold to determine if metal lithium is precipitated, without relying on constant voltage control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If constant voltage control is used to determine metal lithium precipitation, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improvedetermination accuracyVSAvoidpower supply system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The invention extracts only the necessary measurement function from the complex constant voltage control system. By using constant current discharge followed by open-circuit voltage measurement, it removes the need for complex constant voltage control hardware while retaining the ability to detect metal lithium precipitation through voltage recovery behavior.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of applying constant voltage and measuring current (conventional approach), the invention inverts the approach by applying constant current and measuring voltage recovery. This inversion simplifies the power supply requirements while maintaining diagnostic capability for metal lithium precipitation.

Inventive Principle:

Principle #13The other way round (Inversion)

2Measurement precision

If constant voltage charge is performed to inspect battery internal state, then measurement precision is improved, but ease of operation deteriorates

Engineering Contradiction:

Improveinternal state detection accuracyVSAvoidoperational simplicity

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The invention extracts only the essential measurement capability from complex charge protocols. By using simple constant current discharge followed by open-circuit voltage monitoring, it eliminates the need for sophisticated constant voltage control operations while maintaining the ability to detect battery internal state changes indicative of metal lithium precipitation.

Inventive Principle:

Principle #2Taking out (Extraction)

3Loss of information

If conventional inspection methods are used, then information about capacity decrease is acquired, but reliability of determination deteriorates

Engineering Contradiction:

Improvecapacity informationVSAvoidprecipitation determination reliability

Core Design Contradiction:

Loss of informationVSReliability

Solution Approach 1:

The invention performs preliminary constant current discharge to a predetermined low state of charge before measuring voltage recovery. This preliminary action prepares the battery in a standardized state that enhances the reliability of subsequent voltage recovery measurements for detecting metal lithium precipitation, while also providing capacity information.

Inventive Principle:

Principle #10Preliminary action

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 determination of metal lithium precipitation without complex power supply systems, allowing for timely battery replacement and improving diagnostic accuracy in vehicle applications.

Implementation Method 1

a discharging unit that causes the lithium ion secondary battery to perform constant current discharge until a voltage of the lithium ion secondary battery becomes a voltage corresponding to a predetermined low state of charge

Methodology Applied

Scientific EffectElectrochemical discharge: Battery (electricity)

Implementation Method 2

a natural increase acquisition unit that acquires a natural increase in voltage of the lithium ion secondary battery after the constant current discharge is terminated

Methodology Applied

Scientific EffectPolarization relaxation:

Data Source

PatentUS8686691B2Determination system and determination method for determining whether metal lithium is precipitated in a lithium ion secondary battery, and vehicle equipped with the determination system

Publication Date: 2014.04.01 TOYOTA JIDOSHA KK

AI summary

A determination system for determining whether metal lithium is precipitated in a lithium ion secondary battery includes: a discharging unit that causes the lithium ion secondary battery to perform constant current discharge until a voltage of the lithium ion secondary battery becomes a voltage corresponding to a predetermined low state of charge; a natural increase acquisition unit that acquires a natural increase in voltage of the lithium ion secondary battery after the constant current discharge is terminated; and a precipitation determining unit the compares the acquired natural increase with a predetermined threshold, that determines that the metal lithium is not precipitated when the natural increase is larger than or equal to the threshold, and that determines that the metal lithium is precipitated when the natural increase is smaller than the threshold.