Battery SOC Estimation Using Temperature Rate Change Detection

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Solution Overview

Problem

Existing methods for estimating the state of charge (SOC) of secondary batteries, such as those described in WO 2017/010475, are inaccurate when charging and discharging currents vary, particularly in lithium iron phosphate (LFP) batteries, due to variations in cathode potential and anode potential that cannot be accurately detected.

Innovation Solution

A power storage amount estimating device that utilizes a temperature acquisition unit to detect temperature changes during charging or discharging, a change determining unit to identify variations in temperature change rates, and a power storage amount estimating unit to estimate the battery's power storage amount based on these changes, independent of voltage detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If voltage detection method is used to detect anode stage change, then measurement precision is improved, but reliability deteriorates when current varies due to cathode potential estimation errors and CCV voltage variations

Engineering Contradiction:

Improveanode potential detection accuracyVSAvoidestimation accuracy under variable current

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent introduces temperature as an intermediary parameter to detect anode stage changes. Instead of directly measuring potential (which requires complex estimations), the system uses temperature acquisition units to detect temperature changes that occur during anode stage transitions. This intermediary approach bypasses the need for cathode potential estimation and CCV voltage corrections, providing reliable detection under variable current conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the electrical measurement system (voltage detection) with a thermal measurement system (temperature detection). By substituting the mechanical/electrical measurement approach with thermal sensing, the system eliminates the problems associated with potential estimation errors and resistance variations, achieving more reliable stage change detection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If constant current charging/discharging is maintained to enable voltage-based stage detection, then measurement precision is improved, but productivity deteriorates due to inability to adapt to vehicle operating conditions

Engineering Contradiction:

Improvestage change detection accuracyVSAvoidcharging/discharging efficiency

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent enables dynamic current adjustment during charging and discharging operations. By using temperature-based stage detection, the system can accurately identify stage transitions even when current varies dynamically according to vehicle needs. This allows the battery management system to optimize charging/discharging rates without compromising stage detection accuracy, thereby improving overall system productivity and adaptability.

Inventive Principle:

Principle #15Dynamics

3Productivity

If high current charging/discharging is performed to improve productivity, then productivity is improved, but measurement precision deteriorates as voltage-based detection becomes unreliable

Engineering Contradiction:

Improvecharging/discharging rateVSAvoidanode stage change detection accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent uses temperature as an intermediary that remains effective for detecting anode stage changes even under high current conditions. While high current causes significant polarization and resistance effects that degrade voltage-based detection, the thermal response of the anode material during stage transitions remains detectable through temperature acquisition units, maintaining measurement precision at high productivity levels.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

Accurately estimates the power storage amount of secondary batteries by detecting anode stage changes through temperature variations, improving estimation accuracy and reliability.

Implementation Method 1

a temperature acquisition unit for acquiring a temperature change during charging or discharging of the secondary battery

Methodology Applied

Scientific EffectTemperature change detection:

Data Source

PatentUS20250327868A1Power storage amount estimating device

Publication Date: 2025.10.23 TOYOTA JIDOSHA KK

AI summary

A change in temperature during charging or discharging of the secondary battery is acquired, it is determined whether or not the change rate of the temperature change has varied, and when it is determined that the change rate of the temperature change has varied, it is estimated that the power storage amount of the secondary battery becomes a predetermined power storage amount.