Life Aging Effect as a Conditioning Process that Regulates the Performance of the Halogen-Free Mg Electrolyte.

Studying the interplay between the electrochemical performance and the electrolyte conditioning process is crucial for building an efficient magnesium battery. In this work, we use halogen-free electrolyte (HFE) based on Mg(NO3)2 in acetonitrile (ACN) and tetraethylene glycol dimethyl ether (G4) to study the effect of the aging time calendar on its electrochemical properties. The characterization techniques confirm apparent changes occurring in the bulk speciation and the Mg2+ solvation barrier of the aging HFE relative to the as-prepared fresh HFE. The overpotential of Mg plating/stripping and bulk resistance of the aging HFE is reduced relative to the as-prepared fresh HFE. Mg-S cells using aged HFE deliver high specific capacities (586 mA h/g), higher Coulombic efficiencies, and higher cycle life (up to 30 cycles at 25 °C) relative to Mg-S cells with fresh HFE that deliver a specific capacity of ∼535 mA h g-1, low Coulombic efficiency, and short cycle life at a current density of 0.02 mA cm-2. The present findings provide a new concept describing how the aging process regulates the electrochemical performance of the HFE and enhances the cycle life of Mg-S batteries.

Nanosynthesis and Characterization of Cu1.8Se0.6S0.4 as a Potential Cathode for Magnesium Battery Applications.

Copper selenide (Cu-Se) and copper sulfide (Cu-S) are promising cathodes for magnesium-ion batteries. However, the low electronic conductivity of Cu-Se system results in a poor rate capability and unsatisfactory cycling performance. Mg-ion batteries based on the Cu-S cathode exhibited large kinetic barriers during the recharging process owing to the presence of polysulfide species. This work attempts to circumvent this dilemma by doping Cu1.8Se by sulfur, which replaces the selenium in the CuSe lattice to form Cu1.8Se0.6S0.4 nanocrystalline powder. The presence of sulfur will increase the electronic conductivity, and the presence of selenium will mitigate the effect of polysulfide species that hinder the kinetics of Mg2+. Herein, a Cu1.8Se0.6S0.4 nanocrystalline powder was synthesized by the solid-state reaction, yielding a highly pure and stoichiometric powder. The crystallographic structure of the nanopowder and the conversion-type storage mechanism have been attested via ex situ X-ray diffraction and energy-dispersive X-ray analysis. The nanocrystalline feature of Cu1.8Se0.6S0.4 was demonstrated by high-resolution transmission electron microscopy. An apparent surface morphology change during the charging/discharging process has been visualized by a field emission scanning electron microscope. Diffuse reflectance spectroscopy has discussed the variation of the band gap during charging and discharging. The full Mg/Cu1.8Se0.6S0.4 cells presented an initial discharge capacity of 387.99 mAh g-1 at a current density of 0.02 mA cm-2; moreover, they show moderate diffusion kinetics with DMg2+ ≈ 10-15 cm-2 s-1.

Probing the effect of ethylene carbonate on optimizing the halogen-free electrolyte performance for Mg sulfur batteries.

Magnesium metal batteries attract great attention for their high volumetric capacity and safety as a post-lithium choice. The strategy of adding organic plasticizer may bring new insights into designing halogen-free electrolytes for the further development of magnesium-sulfur batteries. The high charge density of Mg2+ results in a high desolvation barrier and low interfacial Mg2+ transfer kinetics due to the strong coulombic interactions of Mg2+ ions with anions and solvent molecules. In this study, we test the effect of the stoichiometric ratio of ethylene carbonate (EC) as an organic additive on the electrochemical performance of halogen-free electrolyte (HFE) based on Mg(NO3)2 in acetonitrile (ACN) and tetraethylene glycol dimethyl ether (G4). Through various characterization methods, the introduction of EC perturbs the bonding scheme of the HFE electrolyte, enhances the ionic conductivity, reduces the relaxation time, and forms a resistive solid electrolyte interphase (SEI). The assembled Mg-S full cell using modified HFE (HFE_EC) delivers initial specific capacities of 900 m Ag-1 with a cycle life of up to 10 cycles in the case of activating the cell with electrochemical conditioning. This study sheds light on the interplay of EC and the interfacial kinetics in Mg batteries and opens a door for designing novel magnesium electrolytes.

The role of MgBr2 to enhance the ionic conductivity of PVA/PEDOT:PSS polymer composite.

A solid polymer electrolyte system based on poly(vinyl alcohol) (PVA) and poly(3,4-Etylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS) complexed with magnesium bromide (MgBr2) salt was prepared using solution cast technique. The ionic conductivity is observed to increase with increasing MgBr2 concentration. The maximum conductivity was found to be 9.89 × 10(-6) S/cm for optimum polymer composite film (30 wt.% MgBr2) at room temperature. The increase in the conductivity is attributed to the increase in the number of ions as the salt concentration is increased. This has been proven by dielectric studies. The increase in conductivity is also attributable to the increase in the fraction of amorphous region in the electrolyte films as confirmed by their structural, thermal, electrical and optical properties.