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Studying the interplay of 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 aging HFE is reduced relative to the as-prepared fresh HFE. Mg-S cells using aged HFE deliver high specific capacities (586 mAh/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 mAh 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 HFE and enhance the cycle life of Mg-S batteries. 

The formation and evolution of the dynamic solid electrolyte interphase (SEI) at the Si anode/electrolyte interface are yet to be completely understood to solve irreversible capacity loss and increase battery cycle life. Herein, the evolution of SEI and its dynamic properties at the Si anode/electrolyte interface are investigated in two electrolyte systems, a 1.2 M LiPF 6 in EC: EMC 3:7 (wt%) electrolyte (referred to as Gen2) and a 1.2 M LiTFSI in EC: EMC 3:7 (wt%) electrolyte (referred to as LiTFSI). Two lithiation stages are studied: the pre-lithiation ( pre-Li ) SEI stage and the post-lithiation ( post-Li ) stage. Findings reveal at the pre-Li , SEI formation starts at an early potential and contributes to the greater mass gain in the Si/Gen2, and it is dominated by the formation of a non-uniform F- and P-rich layer in Si/Gen2, in contrast to a homogeneous F- and C-containing layer at the Si/LiTFSI interphase. The initially formed SEI in LiTFSI further benefits the charge transfer kinetics. At the post-Li stage, a more substantial SEI evolution is observed at Si/LiTFSI. This study offers a foundational understanding of the SEI dynamic evolution with electrolyte dependence. Findings from this report offer important insights into solving the complex SEI stability issues on Si.