Temperature-Induced Precipitation of V2O5 in Vanadium Flow Batteries—Revisited

The maximum operation temperature of the vanadium solution in vanadium flow batteries is typically limited to 40 °C to prevent the damaging thermal precipitation of V2O5. Therefore, the operation of batteries at high ambient temperatures is an important aspect to tackle for stationary storage. In the present work, a comprehensive study of the high temperature stability of redox solutions for vanadium flow batteries was performed. In particular, focus was placed on a comparison between batch and in operando precipitation experiments. It was found that, despite being a widely used method in the literature, caution should be taken when assessing the precipitation through capacity fade due to the large influence of external oxidation and cycling parameters, plausibly leading to an incorrect interpretation of the results. The in operando experiments consistently show a precipitation temperature almost 10–20 °C higher than in the batch tests at a 100% state of charge for the same time lapse.

Extended Model for Prediction of Transition from Internal to External Oxidation in Steels: Comparison between Analytical/Semi-Analytical and Numerical Approaches

The aim of this paper is to present a model that predicts the transition from internal to external oxidation. This variant is based on the simultaneous resolution of the diffusion equations and the equilibrium equation that stems from the assumption of the local instantaneous thermodynamic equilibrium. It accounts for the possible formation of large precipitates fractions that may act as diffusion barriers. This effect is modeled by introducing a dependence of the diffusion coefficients upon the mass fraction of precipitates. As a counterpart, it is generally impossible to solve the non-linear equations of the model analytically. Thus, a semi-analytical and a finite elements models are presented.

Effect of Copper and Annealing Dew Point on Oxidation Behavior of C-Si-Mn Steels

The effect of copper on oxidation behavior of a C-Si-Mn steel was investigated. The samples were heated to 820°C and held for 75s under four different dew points with 5vol% hydrogen. The results of glow discharge optical emission spectrometry (GDOES), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis techniques revealed the differences in oxidation. It is proposed that the steel containing 0.3 wt.% copper has less external oxidation of silicon and manganese compared to the steel containing no copper for all different dew points. As researched in this paper the external oxidation of C-Si-Mn steels would be suppressed by adding copper.