Battery Capacity Estimation Using Open-Circuit Voltage Correlation
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Solution Overview
Problem
Existing methods for on-line characterization of electrochemical systems, such as batteries, are challenging due to noisy environments and require a reference electrode or complete discharge, making real-time battery capacity estimation in metal-ion batteries, especially for lithium-ion batteries, inaccurate and impractical.
Innovation Solution
A method that correlates electrode open-circuit voltage with electrode state of charge and active-material capacity using look-up tables or equations, allowing for real-time monitoring and estimation of battery capacity without a reference electrode or complete discharge, by identifying key times for open-circuit voltage measurements and integrating current, and using non-linear curve minimization techniques like the Nelder-Mead method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the coulomb counting method is used to estimate battery capacity, then the method is simple to implement, but it requires complete discharge which is not suitable for online diagnostics
Solution Approach 1:
The patent extracts the essential information needed for capacity estimation (open-circuit voltage and state of charge relationships) from the complete discharge requirement, allowing capacity to be estimated online without performing a full discharge cycle. This separates the measurement requirement from the operational constraint.
Solution Approach 2:
The patent performs preliminary characterization offline to establish the open-circuit voltage versus state of charge relationship and capacity fade models. This preliminary work enables subsequent online capacity estimation without requiring complete discharge during actual operation.
2Loss of information
If conventional capacity estimation methods are used, then they can provide capacity information, but they lead to errors in battery state calculations due to inaccurate capacity data
Solution Approach 1:
The patent implements a feedback mechanism where the estimated capacity is continuously used to update state of charge calculations, and the open-circuit voltage measurements provide feedback to refine the capacity estimation. This closed-loop approach improves the accuracy of battery state calculations by using the most current capacity information.
Solution Approach 2:
The patent accounts for capacity fade over time by dynamically adjusting the capacity parameter based on the relationship between open-circuit voltage and state of charge. This parameter change approach ensures that capacity information remains accurate throughout the battery's operational life, improving state calculation precision.
3Productivity
If online capacity monitoring is implemented, then real-time battery state information is available, but the noisy environment makes characterization difficult
Solution Approach 1:
The patent uses open-circuit voltage as an intermediary measurement that can be obtained in noisy environments without direct physical contact with the battery terminals during operation. The open-circuit voltage serves as a mediator that translates complex battery state information into a measurable quantity that is less susceptible to environmental noise.
Solution Approach 2:
The patent replaces direct electrical measurement methods that are sensitive to noise with electrochemical-based open-circuit voltage measurements. This substitution uses the battery's own electrochemical properties as the measurement basis, which is inherently more robust to external electrical noise and interference.
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 and reliable real-time monitoring of battery capacity and state of health, predicting future capacity and health, even in aged batteries, by maintaining the OCV-capacity relationship constant over the battery's life, primarily focusing on lithium loss for capacity fade estimation.
Implementation Method 1
correlating electrode open-circuit voltage with electrode state of charge for a selected electrode
Implementation Method 2
the capacity of a cell can be estimated by fully discharging it and integrating the measured current (coulomb counting method)
Implementation Method 3
A non-linear curve minimization technique may be used to acquire the electrode capacity and the active-material capacity at the beginning of life of the battery
Data Source
AI summary
In some variations, a method of real-time monitoring of battery capacity comprises correlating electrode open-circuit voltage with electrode state of charge for a selected electrode; compiling a look-up table to correlate the electrode open-circuit voltage with the electrode capacity at different values of the active-material capacity; during real-time operation, identifying first and second times at which battery terminal voltages are approximated as battery open-circuit voltages; and calculating battery capacity based on the difference in battery open-circuit voltages at the first and second times, current integration, and the look-up table. No reference electrode is needed, and a complete battery charge/discharge is not necessary to determine the capacity. This technique can therefore be implemented on-board and in real time to provide reliable capacity estimation even as the battery ages. The methods are applicable to various metal-ion secondary battery systems, including lithium-ion batteries, with different material chemistries.