Battery SoH Estimation Using Double-Layer Voltage Modeling
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Solution Overview
Problem
Existing methods for accurately estimating the state of charge (SoC) and state of health (SoH) of rechargeable batteries are either too time-intensive, not accurate enough, or unsuitable for real-time applications due to issues with voltage measurement errors, temperature dependence, aging effects, and complexity of equivalent circuit models.
Innovation Solution
A novel approach using a combined physical diffusion and electrical model that generates equations describing voltage at the anode and cathode double-layers, allowing for the determination of SoH by establishing a relationship between solved double-layer characteristics and SoC, utilizing a single battery model with lumped parameters to accurately profile battery electrochemical states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If open circuit voltage (OCV) monitoring is used for SoC estimation, then accuracy is improved, but the method requires long resting time (more than 3 hours) which makes it unsuitable for real-time applications
Solution Approach 1:
The patent transforms the static OCV measurement approach into a dynamic method by continuously monitoring terminal voltage during active charging and discharging operations. The system uses real-time voltage measurements combined with ampere-hour counting to estimate SoC without requiring the battery to be in a static resting state, thereby eliminating the 3+ hour waiting period while maintaining accuracy through continuous adaptation to changing battery conditions.
Solution Approach 2:
The patent pre-calibrates the relationship between terminal voltage and SoC across the full charge range during battery manufacturing or initial setup. This preliminary characterization allows the system to use simple real-time voltage measurements during operation to estimate SoC accurately without requiring subsequent long resting periods for OCV stabilization, enabling real-time monitoring from the start of battery use.
2Measurement precision
If equivalent circuit models (ECM) are made more accurate to improve electrochemical state estimation, then measurement precision is improved, but device complexity increases making it unsuitable for low-cost computing units
Solution Approach 1:
The patent divides the complex battery system into two independent but complementary estimation components: (1) a simple ampere-hour counter for tracking charge/discharge quantity, and (2) a terminal voltage sensor for measuring instantaneous voltage. This segmentation allows each component to remain computationally simple while their combined output provides accurate SoC and SoH estimation, avoiding the need for complex unified equivalent circuit models.
Solution Approach 2:
The patent changes the estimation approach from using complex dynamic parameters (multiple RC circuits, polarization effects) to using simple static or quasi-static parameters (terminal voltage and cumulative charge). By focusing on parameters that can be directly measured or easily integrated, the system achieves accurate electrochemical state estimation without requiring complex computational models that would burden low-cost microcontrollers.
3Productivity
If ampere hour counting (AHC) is used for SoC estimation, then real-time capability is improved, but accuracy deteriorates due to current sensing errors that accumulate over time
Solution Approach 1:
The patent implements a feedback mechanism where the terminal voltage measurement continuously monitors the battery state and provides correction information to the ampere-hour counting algorithm. When the measured terminal voltage deviates from the expected voltage based on cumulative charge, the system adjusts the SoC estimate accordingly, preventing error accumulation and maintaining long-term accuracy while preserving real-time estimation capability.
Solution Approach 2:
The patent introduces terminal voltage as an intermediary measurement that bridges the gap between cumulative charge and actual SoC state. The voltage measurement acts as a mediator that validates and corrects the integrated charge data, allowing the system to maintain the real-time advantages of AHC while eliminating its primary weakness of error accumulation through the mediating voltage feedback.
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 method provides accurate and compact battery equivalent models for real-time SoC and SoH estimation, overcoming previous limitations by simplifying parameter extraction and improving accuracy with low-cost computing devices, while accurately predicting battery behaviors and impedance.
Implementation Method 1
During a charging cycle ionic electrolytic particles within the electrolyte migrate from the cathode assembly to the anode double layer and via a diffusion process diffuse into the plurality of anode slices. During a discharge cycle the ionic electrolytic particles within the electrolyte migrate from the anode assembly to the cathode double layer and via a diffusion process diffuse into the plurality of cathode slices.
Data Source
AI summary
A method of determining state of health (SoH) of a battery is disclosed which includes receiving a predetermined open circuit voltage (VOC) vs. a state of charge (SoC) characteristics for a pristine battery, establishing a single battery model including physical diffusion characteristics and electrical characteristics based on lumped parameters thereby modeling diffusion resistance and capacitance of particles in the electrodes of the battery as well as electrical characteristics based on electrical resistance and capacitance from one electrode assembly to another, thereby generating equations describing voltage at the associated double-layers, solving the double-layer equations, thereby generating solutions for the double-layer electrical characteristics, and establishing a relationship between the solved double-layer characteristics and the SoC, thereby determining a SoH of the battery based on said relationship.