Magnesium−sulfur batteries are considered as attractive energystorage devices due to the abundance of electrochemically active materials and high theoretical energy density. Here we report the mechanism of a Mg−S battery operation, which was studied in the presence of simple and commercially available salts dissolved in a mixture of glymes. The electrolyte offers high sulfur conversion into MgS in the first discharge with low polarization. The electrochemical conversion of sulfur with magnesium proceeds through two well-defined plateaus, which correspond to the equilibrium between sulfur and polysulfides (high-voltage plateau) and polysulfides and MgS (low-voltage plateau). As shown by XANES, RIXS (resonant inelastic X-ray scattering), and NMR studies, the end discharge phase involves MgS with Mg atoms in a tetrahedral environment resembling the wurtzite structure, while chemically synthesized MgS crystallizes in the rock-salt structure with octahedral coordination of magnesium.

Development of magnesium sulfur battery is accompanied with all known difficulties present in Li-S batteries, however with even more limited choice of electrolytes. In the present work, the influence of current collector on electrochemical mechanism was investigated in light of different reports where improved behavior was ascribed to electrolyte. Notable differences in cycling behavior are reported when Al current collector is replaced by Cu current collector independent of electrolyte. The initial reduction of sulfur follows similar reaction path no mater of current collector but formation of MgS can be in competition with formation of CuS in the presence of Cu cations. With the subsequent cycling cells prepared from cathodes deposited on Cu current collector show decrease in the voltage and formation of single plateau during cycling. The change corresponds to the involvement of Cu into the reaction and formation of redox couple Mg/CuS as determined by Cu Kedge XANES measurements. Corrosion of Cu foil is identified by SEM and serves as a source of Cu cations for the chemical reaction between Cu and polysulfides. Mg/CuS redox couple shows improved cycling stability, but theoretical energy density is severely reduced due to substitution of S with CuS as cathode active material.

Abstract

Ca metal anode rechargeable batteries are seen as a sustainable high-energy density and high-voltage alternative to the current Li-ion battery technology due to the low redox potential of Ca metal...

Commercial LiMn2O4 powder was used as the base material for probing magnesiation, cycling behavior, and structural stability/changes in (MgxLi1-x)Mn2O4 spinel cathodes in aqueous Mg(NO3)2 and non-aqueous Mg(TFSI)2/diglyme and Mg(Mg(HFIP)2 − 2Al(HFIP)3/diglyme electrolytes. Each of the samples was delithiated and, then, magnesiated electrochemically in the corresponding electrolyte. The electrochemical activity of the cathode cycled in aqueous electrolyte showed high reversibility during the oxidation process; however, large polarization and a relatively fast capacity fading were the culprits of the system. Cycling in Mg(TFSI)2/diglyme electrolyte solution resulted in much lower initial specific capacity compared to an aqueous counterpart, as well as a much faster failure. On the other hand, cycling in Mg(HFIP)2 − 2Al(HFIP)3/diglyme electrolyte solution demonstrated excellent cycling performance with very low polarization in the first cycles. The observed voltages for this system were near theoretical values for the Mg insertion. Although the electrochemical measurements suggest reversible magnesiation, detailed structural and analytical STEM investigation revealed the differences in the atomic structure and Mn valence of all three cathode samples upon cycling. The electrolytes’ influence on the structural rearrangement during Mg insertion is discussed for each of the three systems.

No abstract

Sedimentation is a naturally occurring process of allowing particles in water bodies to settle out of the suspension under a gravity effect. In this study, the sediments of the Drava River were fully investigated to determine the heavy metal concentrations along the river and their potential reuse in the construction sector. Naturally dehydrated sediments from the Drava River were tested as an additive for the production of fired bricks. The dredged sediments were used as a substitute for natural brick clay in amounts up to 50% by weight, and it was confirmed that up to 20% by weight of the added sediment could be used directly in the process without critically affecting performance. Finally, the naturally dehydrated sediments were also evaluated for their use as a filling material in the construction of levees. The natural moisture content of the dehydrated sediment was too high for it to be used without additives, so quicklime was added as an inorganic binder. The test results showed an improvement in the geotechnical properties of the material to such an extent that it is suitable as a filling material for levees.

The search for low cost and environmental friendly intercalation cathode materials offering high power density in rechargeable ion‐exchange batteries is driven by the limitations of the existing Li‐ion technology. At present, the use of the lithium metal as a negative electrode is restricted to the use of specific polymer electrolytes 1 which hinder the formation of the dendrites. Therefore, the graphite negative electrodes are employed. However, they reduce the theoretical capacity density from 2046 mAh cm ‐3 to ~850 mAh cm ‐3 and drastically increase costs. Here, the application of multivalent battery technology that pairs an intercalation cathode with the metal electrode thus allowing for higher energy density and lower costs, is desired 2 . Among the candidates, Mg metal that possesses high volumetric specific capacity of 3833 mAh cm ‐3 , exhibits no dendrite growth on deposition 2 , is safe to handle in ambient atmosphere and largely available, is of special interest 3 . Various materials have shown the initial promise for multivalent intercalation, including Chevrel phase Mo 6 S 6 , layered V 2 O 5 , graphitic fluoride, etc. However, owing to the limited mobility of Mg ions and possible concurrent insertion of water and/or protons, the cycling stability of these host materials has been shown insufficient. The promising candidates for the cathode materials that display higher voltages than Chevrel phases are variants of manganese oxide. In this study we have chosen a MgMn 2 O 4 spinel and (Mg x Na y )Mn 2 O 4 birnessite phases. These materials crystal structures employ different mechanisms for keeping the stability upon cycling and allow for Mg de/insertion, which was performed in magnesium nitrite aqueous electrolyte. The aim of the study was to investigate the possible Mg insertion mechanisms in both materials prior assembling a battery by correlating the cyclic voltammetry (CV) results with the structural and compositional changes of these cathode materials by S/TEM at the atomic level upon increasing number of cycles. The spinel phase was prepared by the delithiation of the commercially available LiMn 2 O 4 spinel in 0,1 M Mg(NO 3 ) 2 aqueous electrolyte and its following magnesiation. The Mg containing birnessite phase was synthesized by the rout described by Aronson and coworkers via Na‐birnessite phase 4 . The STEM‐EDX confirmed partial exchange of Na over Mg with the Mg occupying fully the smaller particles and only the outer shells of the larger particles. Same behavior was observed in the spinel material, where the small particles had a higher Mg content than the large particles (above 200 nm). Both materials were then put through the CV tests to explore the Mg de/insertion mechanisms. Plots in Fig 1 (a,c) show that both spinel and birnessite structures can reversibly insert the Mg ions. The complete stabilization of the CV curve was observed in both materials at around the 20 th cycle (Fig. 1 a,c). STEM‐ABF images (Fig. 1 b,d) were taken from the material after the third cycle, when the initial changes of structure due to the Mg de/insertion took place. The ABF technique allowed for the visualization of the lighter Mg and O atoms that can be vaguely seen in case of spinel structure. The ABF imaging of birnessite, in its turn, confirmed the presence of extra O atoms belonging to the crystal water interlayer that has been reported to play a crucial role in the layered cathode materials by enhancing the ion diffusion as well as suppressing the Mn 2+ dissolution 5 .