Vanadium Redox Flow Battery State of Charge Determination
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Solution Overview
Problem
Existing methods for determining the state of charge (SoC) of vanadium redox flow batteries face challenges due to non-linear relationships between absorbance and vanadium species mixture ratios, especially for the positive electrolyte, leading to inaccurate measurements and interference with battery operation.
Innovation Solution
A method involving the determination of absorbance at specific wavelengths, comparison against look-up graphs, and estimation of vanadium species concentrations using simultaneous equations to accurately calculate the fraction of VIV and VV in the positive electrolyte, allowing for independent measurement of the state of charge without relying on electrochemical methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If spectroscopy is used to measure absorbance for determining state of charge, then measurement can be performed without extra electrodes, but the relationship between absorbance and vanadium species concentration becomes non-linear due to complex formation
Solution Approach 1:
The patent transforms the non-linear absorbance-concentration relationship into a linear one by measuring excess absorbance at multiple wavelengths and using ratio calculations. This parameter transformation approach converts the complex spectral data into a linear relationship that can be accurately correlated with vanadium species concentration, resolving the measurement precision issue while maintaining the electrode-free advantage
Solution Approach 2:
The patent introduces excess absorbance ratio as an intermediary parameter between the raw absorbance measurements and the vanadium species concentration. By calculating the ratio of excess absorbance at different wavelengths, it creates a new measurement parameter that linearly relates to concentration, thereby solving the non-linearity problem without requiring additional electrodes or complex setup
2Measurement precision
If reference electrodes are placed in half cells to determine state of charge, then electrochemical measurement can be performed, but the reference electrode solution can be easily contaminated and interfere with battery operation
Solution Approach 1:
The patent replaces the electrochemical measurement system (reference electrodes) with an optical measurement system (spectroscopy). This substitution eliminates the need for reference electrodes that can be contaminated, while providing independent measurement capability. The optical method measures absorbance directly in the electrolyte without introducing foreign solutions or electrodes that could interfere with battery operation
3Device complexity
If electrochemical methods are used to measure state of charge, then measurement can be performed using existing electrodes, but the measurements are not independent and vary with electrode behavior changes
Solution Approach 1:
The patent replaces electrochemical measurement methods with optical spectroscopy, providing an independent measurement pathway that does not depend on electrode behavior. The absorbance measurements reflect the actual vanadium species concentration in the electrolyte independently of electrode surface states, leakage currents, or other electrochemical variations, thereby ensuring measurement reliability and independence
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 enables accurate and independent measurement of the state of charge for both half-cells, reducing interference and providing reliable data even with changes in vanadium concentration, thus improving the control and maintenance of vanadium redox flow batteries.
Implementation Method 1
Spectroscopy can be used to accurately measure the concentration of species in solution by measuring the absorbance of the solution at different wavelengths
Data Source
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Figure 3(a)~3(d)
AI summary
The invention relates to a method for determining VIV or Vv concentration in mixtures of VIV and Vv solutions, the method comprising the steps of determining the absorbance of the solution at at least one wavelength; and calculating the concentration of the VIV and Vv solution based on the absorbance. In one embodiment the VIV, Vv and/or total vanadium concentration in a solution is calculated based on the fact that the absorbance at a specific wavelength can be predicted by taking into account the formation of vanadium complexes.