Battery State-of-Health Estimation via Open-Circuit Voltage Relaxation
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Solution Overview
Problem
Existing methods for determining the state-of-health (SOH) of rechargeable batteries, such as lithium batteries, are either complex, expensive, time-consuming, or unable to accurately account for factors like internal resistance changes and temperature effects, making them unsuitable for real-time monitoring in critical applications.
Innovation Solution
A method that calculates the SOH of a battery by charging it to maximum potential, waiting a predetermined period, and then using the open-circuit voltage (OCV) to determine the state-of-charge (SOC) through a second-order polynomial equation, allowing for the estimation of permanent capacity loss without requiring complex mathematical computations or offline testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If internal resistance measurement is used to estimate SOH, then the measurement process is simple, but the estimation accuracy is insufficient because it disregards factors like internal resistance changes over time and temperature effects
Solution Approach 1:
The patent changes the measurement parameter from internal resistance alone to open-circuit voltage (OCV) after a predetermined time period following charging. This parameter change captures the relaxation effect and impedance changes over time, providing more accurate SOH estimation while maintaining measurement simplicity through a single voltage reading.
Solution Approach 2:
The patent introduces a preliminary action step of waiting for a predetermined time period after charging before measuring the OCV. This allows the battery to stabilize and the relaxation effect to manifest, ensuring accurate capture of impedance changes without requiring complex continuous monitoring during the charging process.
2Measurement precision
If full/partial discharge test is used to determine SOH, then the measurement accuracy is high, but the method is expensive, time-consuming, and requires the battery to be offline
Solution Approach 1:
Instead of performing a complete full discharge test, the patent uses a partial action approach by measuring the OCV at a specific point in time after charging. This single measurement at a predetermined time period provides sufficient information for SOH estimation without requiring the battery to be discharged completely or taken offline for extended periods.
Solution Approach 2:
The patent performs a preliminary charging action to a predetermined voltage level before the OCV measurement. This prepares the battery in a known state, allowing the subsequent OCV measurement to accurately reflect the SOH without requiring a full discharge cycle, thereby reducing testing time and maintaining battery availability.
3Loss of information
If traditional SOC indication based on terminal voltage is used, then the charge status can be indicated, but the method fails to capture the returnable capacity through cumulative stress-life due to impedance increase in aged cells
Solution Approach 1:
The patent changes the measurement parameter from immediate terminal voltage to open-circuit voltage after a predetermined time period. This temporal parameter change allows the measurement to capture the relaxation effect and impedance characteristics that develop over time, providing accurate information about returnable capacity in aged batteries while maintaining the familiar voltage-based indication approach.
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 provides a simple, accurate, and real-time measurement of a battery's SOH, independent of its application, enabling effective monitoring of battery capacity in various fields like medical devices and aircraft emergency power systems.
Implementation Method 1
rechargeable batteries age and degrade causing a decrease in the batteries' ability to hold a charge
Implementation Method 2
The SOC is the quantification (in percentage (%)) of the usability of the cell in terms of its relative charge level. A traditional SOC indication for a lithium cell is generally related to the terminal voltage of the cell during a stabilized open-circuit stand.
Data Source
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AI summary
A system and method use an open-circuit voltage (OCV) method of calculating a state-of-health (SOH) of a chemical battery. The OCV system and method includes charging the battery to a maximum charge potential, determining an open-circuit voltage (OCV) of the battery after waiting a predetermined period of time after completion of the charging, and determining the SOH of the battery based on the determined OCV of the battery. Another system and method use a time-to-charge (TTC) method of calculating a state-of-health (SOH) of a chemical battery. The TTC system and method includes monitoring and storing a charge time of the battery in a memory and scaling the stored charge time to form an SOH indication.