Dissolution and Reprecipitation of Sulfur on Carbon Surface

Further understanding of the redox process of lithium polysulfides (PSs) on carbon surface is helpful to design Li/S batteries with better performance. “Shuttle mechanism” can explain the low coulomb efficiency and self-discharge of a Li/S battery, but it cannot explain the fact that battery performance is closely affected by electrolyte volume and sulfur load. This paper aims to reveal main redox process of PSs on surface of carbon by examining cathodic behavior with different electrolyte volume and sulfur load. SEM photos and Impedance Spectra of cathode before and after 1st discharge were compared, it was found that the discharge process is the continuous dissolution of sulfur composited with carbon into the electrolyte to form PSs, at the same time, PSs re-precipitates sulfur on the surface of cathode through disproportionation reaction to form a solid film. CV curves showed that the solid film passivates electrode, and the electrode is activated only when potential sweeps negatively and Li2S is generated. When lean electrolyte is used, there is fluctuation in CV curves, which proves that the dissolution-reprecipitation of sulfur is the main process of cathode. The discharge-charge curves of cathodes with different sulfur load were compared, it was found that there is wavy fluctuation in the discharge curve with high sulfur load, which proves again that the sulfur reaction dominates the electrode process.

Reactive pathways toward parasitic release of singlet oxygen in metal-air batteries

The superoxide disproportionation reaction is a key step in the chemistry of aprotic metal oxygen batteries that controls the peroxide formation upon discharge and opens the way for singlet oxygen release. Here we clarify the energy landscape of the disproportionation of superoxide in aprotic media catalyzed by group 1A cations. Our analysis is based on ab initio multireference computational methods and unveils the competition between the expected reactive path leading to peroxide and an unexpected reaction channel that involves the reduction of the alkaline ion. Both channels lead to the release of triplet and singlet O2. The existence of this reduction channel not only facilitates singlet oxygen release but leads to a reactive neutral solvated species that can onset parasitic chemistries due to their well-known reducing properties. Overall, we show that the application of moderate overpotentials makes both these channels accessible in aprotic batteries.

Highly Stable Titanium-Manganese Single Flow Batteries for Stationary Energy Storage

Manganese-based flow batteries have attracted increasing interest due to their advantage of low cost and high energy density. However, the sediment (MnO2) from Mn3+ disproportionation reaction creates the risk to...

Influence of the acidity of the iodous acid solution system on the kinetics of the disproportionation reaction

Influence of the acidity of the iodous acid (HOIO) solution system on the kinetics disproportionation reaction is examined in aqueous sulfuric acid solution (0.125 moldm-3 ). The disproportionation reaction rate constants were determined at 285, 291, 298 and 303 K based on data obtained under stationary conditions. The calculated rate constants increase with increasing temperature for different values of iodous acid and iodate concentrations. The average activation energy of 46 kJmol-1 was determined for the chosen temperature interval, by a graphical method. The values of pseudo-equilibrium concentrations of kinetically important and catalytic species H+ , H2OI+ i IO3 - in the disproportionation reaction were determined for the given experimental conditions based on the equilibrium dissociation reactions of sulfuric and iodous acids in the quasi-stationary state. The estimated values of sulfuric and iodous acid are predominant and higher than the concentration of the protonated ion of H2OI+ .