scholarly journals Monitoring the State of Charge of the Positive Electrolyte in a Vanadium Redox-Flow Battery with a Novel Amperometric Sensor

Batteries ◽  
2019 ◽  
Vol 5 (1) ◽  
pp. 5 ◽  
Author(s):  
Isabelle Kroner ◽  
Maik Becker ◽  
Thomas Turek
Keyword(s):  
Gas Diffusion ◽  
The State ◽  
State Of Charge ◽  
Vanadium Redox Flow Battery ◽  
Rotating Disc ◽  
New Approach ◽  
Long Term Stability ◽  
The Individual ◽  
Vanadium Redox

Vanadium redox-flow batteries are a promising energy storage technology due to their safety, long-term stability, and independent adjustability of power and capacity. However, the vanadium crossover through the membrane causes a self-discharge, which results in a capacity shift towards one half cell. This leads to a gradual decrease in its efficiency over time. Capacity balancing methods for compensation of this effect require a reliable online state of charge (SoC) monitoring. Most common methods cannot provide exact values of the individual concentration of each species in both electrolytes. In particular, the state of the positive electrolyte cannot yet be precisely determined. In this work, an amperometric SoC monitoring is proposed as a new approach. First, the suitability of the principle is investigated with a rotating disc electrode (RDE). Then, a sensor based on a gas diffusion layer (GDL) is developed and tested in the positive electrolyte. The dependencies between oxidative current and V(IV)-concentration are examined as well as those between reduction current and V(V)-concentration. Using both relationships, a reliable measurement of all relevant concentrations is possible.

Photometrical Determination of the State-of-Charge in Vanadium Redox Flow Batteries Part II: In Combination with Open-Circuit-Voltage

2019 ◽  
Vol 233 (12) ◽  
pp. 1695-1711 ◽  
Author(s):  
Jan Geiser ◽  
Harald Natter ◽  
Rolf Hempelmann ◽  
Bernd Morgenstern ◽  
Kaspar Hegetschweiler
Keyword(s):  
Open Circuit Voltage ◽  
Open Circuit ◽  
The State ◽  
State Of Charge ◽  
Vanadium Redox Flow Battery ◽  
Term Operation ◽  
Partial State ◽  
Set Up ◽  
Vanadium Redox

AbstractBy means of in-situ UV/Vis/NIR spectrometry, separately both in the anolyte as well as in the catholyte of a vanadium redox flow battery (single cell) partial state-of-charge values are determined online. The UV/Vis/NIR spectroscopic experimental set-up is calibrated using the state-of-charge value determined from measurements of the open-circuit-voltage (OCV) in the pristine state of the battery which is related to Nernst’s equation taking into account also H+ formation/consumption during the V4+/V5+ redox process. The comparison of both partial state-of-charge values indicates a possible imbalance of the battery, which can occur after long-term operation.

scholarly journals A Novel State of Charge Estimating Scheme Based on an Air-Gap Fiber Interferometer Sensor for the Vanadium Redox Flow Battery

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 291 ◽  
Author(s):  
Chao-Tsung Ma
Keyword(s):  
Real Time ◽  
Remote Monitoring ◽  
Strong Acid ◽  
Air Gap ◽  
The State ◽  
State Of Charge ◽  
Vanadium Redox Flow Battery ◽  
Redox Flow Battery ◽  
Flow Battery ◽  
Vanadium Redox

Real-time and remote monitoring of the state of charge (SOC) of a vanadium redox flow battery (VRFB) is technically desirable for achieving advanced compensation functions of VRFB systems. This paper, for the first time, proposes a novel SOC monitoring scheme based on an air-gap fiber Fabry–Perot interferometer (AGFFPI) sensor for the VRFB. The proposed sensing concept is based on real-time sensing of the refractive index (RI) of the positive electrolyte, which is found closely correlated to the VRFB’s SOC. The proposed SOC estimating scheme using fiber sensor has a number of merits, e.g., being precise, having lightweight, having strong acid resistance, and being easy to incorporate the state-of-the-art fiber communication technology for remote monitoring. It is found that the RI of the positive electrolyte solution exhibits distinct and linear variations in accordance with changes of the VRFB’s SOC value. Using the linear relationship between the electrolyte’s RI and SOC, a real-time SOC monitoring mechanism can be readily realized by the proposed AGFFPI. In this paper, existing SOC detecting methods for VRFB are firstly reviewed. The details concerning the proposed detecting method are then addressed. Typical experimental results are presented to verify the feasibility and effectiveness of the proposed SOC estimating scheme.

Photometrical Determination of the State-of-Charge in Vanadium Redox Flow Batteries Part I: In Combination with Potentiometric Titration

2019 ◽  
Vol 233 (12) ◽  
pp. 1683-1694 ◽  
Author(s):  
Jan Geiser ◽  
Harald Natter ◽  
Rolf Hempelmann ◽  
Bernd Morgenstern ◽  
Kaspar Hegetschweiler
Keyword(s):  
Potentiometric Titration ◽  
Nir Spectroscopy ◽  
The State ◽  
State Of Charge ◽  
Vanadium Redox Flow Battery ◽  
Absorption Coefficients ◽  
Vanadium Concentration ◽  
Redox Flow Batteries ◽  
Flow Batteries ◽  
Vanadium Redox

AbstractThe stepwise oxidation of vanadium ions in electrolytes, as used in all vanadium redox flow batteries (VRFB), is studied offline by a combination of potentiometric titration and simultaneous UV/Vis/NIR spectroscopy. Eight different total vanadium concentrations between 0.2 mol L−1 and 1.6 mol L−1 have been investigated. The analyte (titrand, V2+ solution) is the anolyte (V2+/V3+ side) of a fully charged laboratory vanadium redox flow battery (VRFB). Absorption maxima are observed at λ = 850 nm for V2+ and at λ = 400 nm for V3+, the corresponding absorption coefficients are determined. In the former case an extrapolation procedure is necessary because during transfer from the VRFB to the titration cell, oxidation to V3+ by ambient oxygen cannot completely be avoided. Based on the knowledge of the absorption coefficients, via simultaneous photometry of V2+ and V3+, the state-of-charge of the anolyte of a VRFB can be determined. In the catholyte (V4+/V5+ side) of a VRFB the formation of an intermediate mixed valence VIV–VV complex at large vanadium concentration prevents a simple photometric SOC determination.

A Constrained Extended Kalman Filter for State-of-Charge Estimation of a Vanadium Redox Flow Battery With Crossover Effects

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Victor Yu ◽  
Alex Headley ◽  
Dongmei Chen
Keyword(s):  
Kalman Filter ◽  
Extended Kalman Filter ◽  
State Of Charge ◽  
Physical Models ◽  
Vanadium Redox Flow Battery ◽  
Vanadium Concentration ◽  
Capacity Loss ◽  
Crossover Effects ◽  
Vanadium Redox

One of the main issues with vanadium redox flow batteries (VRFBs) is that vanadium ions travel across the membrane during operation which leads to a concentration imbalance and capacity loss after long-term cycling. Precise state-of-charge (SOC) monitoring allows the operator to effectively schedule electrolyte rebalancing and devise a control strategy to keep the battery running under optimal conditions. However, current SOC monitoring methods are too expensive and impractical to implement on commercial VRFB systems. Furthermore, physical models alone are neither reliable nor accurate enough to predict long-term capacity loss due to crossover. In this paper, we present an application of using an extended Kalman filter (EKF) to estimate the total vanadium concentration in each half-cell by combining three voltage measurements and a state prediction model without crossover effects. Simulation results show that the EKF can accurately predict capacity loss for different crossover patterns over a few hundred cycles.

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