Battery SOC Evaluation Using Finite-Rate Voltage Scans
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Solution Overview
Problem
Lithium-based battery cells face challenges in accurately determining state of charge (SOC) and controlling charging due to hysteretic behavior in silicon electrodes, which complicates the interpretation of open-circuit voltage (OCV) measurements and leads to rate-dependent and rate-invariant charge/discharge relationships.
Innovation Solution
A method involving finite-rate voltage scans to establish dynamic equilibrium relationships between OCV and SOC, using mathematical expressions and algorithmic code to determine the rate-invariant and rate-dependent charge/discharge relationships, and controlling charging based on the present SOC state, with specific relationships and stress functions to model the behavior of silicon electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional OCV measurement methods are used for battery cells with silicon electrodes, then the measurement process is simple, but the SOC determination accuracy deteriorates due to hysteresis effects
Solution Approach 1:
The patent implements a dynamic measurement approach by performing voltage scans at multiple different rates (e.g., 0.1 mV/s, 1 mV/s, 10 mV/s) to capture the rate-dependent hysteresis behavior of silicon electrodes. This dynamic characterization allows the system to adapt measurements to the specific hysteresis conditions, significantly improving SOC determination accuracy compared to static single-rate methods.
Solution Approach 2:
The patent changes the measurement parameters by conducting voltage scans at multiple rates and in both charging and discharging directions. This parameter variation reveals the hysteresis loops characteristic of silicon electrodes, enabling the system to distinguish between rate-invariant and rate-dependent behaviors and thereby accurately determine SOC despite the complexity introduced by hysteresis effects.
2Measurement precision
If voltage scans are performed at multiple rates to capture hysteresis behavior, then SOC determination accuracy improves, but the measurement time increases
Solution Approach 1:
The patent applies partial action by selecting a subset of scan rates that provide sufficient characterization of hysteresis behavior without performing exhaustive measurements at all possible rates. The system identifies the minimum necessary measurement effort to capture the essential hysteresis loops, thereby reducing measurement time while maintaining adequate SOC determination accuracy.
Solution Approach 2:
The patent performs preliminary characterization of the battery cell's hysteresis behavior during initial cycles or calibration phases. This preliminary action establishes the rate-dependent relationships and hysteresis parameters in advance, allowing subsequent SOC determinations to use pre-characterized models rather than performing full multi-rate scans each time, thus reducing operational measurement time.
3Measurement precision
If rate-dependent and rate-invariant charge/discharge relationships are modeled separately, then the accuracy of charging control improves, but the computational complexity increases
Solution Approach 1:
The patent segments the charge/discharge behavior into distinct rate-dependent and rate-invariant components. By separating these relationships, the system can apply appropriate modeling approaches to each component independently, improving the accuracy of charging control while managing computational complexity through modular processing of different behavioral aspects.
Solution Approach 2:
The patent introduces an intermediary computational layer that processes the multi-rate voltage scan data to extract hysteresis parameters and establish the separate rate-dependent and rate-invariant relationships. This intermediary processing step transforms raw measurement data into structured models that can be efficiently used for charging control, balancing accuracy requirements with computational feasibility.
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 allows for accurate determination of SOC and controlled charging, accounting for hysteretic effects and transient behaviors, improving the reliability and efficiency of lithium-based battery cells by capturing rate-invariant and rate-dependent behaviors.
Implementation Method 1
Lithium-based battery cells face challenges in accurately determining state of charge (SOC) and controlling charging due to hysteretic behavior in silicon electrodes
Implementation Method 2
executing a second finite-rate voltage scan associated with a state of dynamic equilibrium in which the scanned voltage follows an oxidation branch of a relationship between OCV and the SOC
Implementation Method 3
executing a first finite-rate voltage scan associated with a state of dynamic equilibrium in which the scanned voltage follows a reduction branch of a relationship between OCV and the SOC
Data Source
AI summary
A method for determining a state of charge (SOC) of a rechargeable battery cell includes determining a rate-invariant charge/discharge relationship between an open-circuit voltage (OCV) and a state of charge (SOC). This includes a first finite-rate voltage scan following a reduction branch of a relationship between OCV and the SOC, and executing a second finite-rate voltage scan following an oxidation branch of a relationship between OCV and the SOC. A rate-dependent charge/discharge relationship between the OCV and the SOC is determined during scanned voltage transitions between the reduction and oxidation branches. A present SOC state is determined based upon an electrical potential, the rate-invariant charge/discharge relationship between the OCV and the SOC, and the rate-dependent charge/discharge relationship between the OCV and the SOC during a voltage-scan reversal that occurs when the scanned voltage transitions between the reduction and oxidation branches.