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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. 

The development of the multivalent electrolytes is a critical component to advance polyvalent energy storage technology. In this work, a new and simple nonaqueous zinc electrolyte is developed and investigated where a secondary amine is introduced as a cosolvent. The addition of dimethylamine (DMA) as a cosolvent in THF facilitates the solubilization of Zinc (II) bis(trifluoromethanesulfonyl)imde (Zn(TFSI)₂) and results in a homogeneous electrolyte with reversible plating of zinc achieved at high coulombic efficiencies. The electrochemical properties of the developed electrolyte and the effects of the cosolvent and salt concentrations are systematically investigated. It was found that increasing the ratio of the cosolvent DMA in THF for a Zn(TFSI)₂electrolyte leads to more facile kinetics, better ion solubilization, and higher ion mobility evidenced by up a significant increase in conductivity as well as the plating/stripping current densities. Increased Zn(TFSI)₂salt concentration in a 2.0 M DMA in THF solvent mixture not only leads to a higher current density and conductivity, but also a higher molar conductivity due to a redissociation mechanism. The findings in this study are relevant and important to further understand and characterize multivalent electrolytes from a simple and effective electrolyte design strategy.