Enhanced Li-metal interphase stability of argyrodite Li6+xSixP1-xS5Cl solid electrolytes by silicon substitution

Abstract

Lithium-ion batteries are being used in various applications from small electronic devices to transportation vehicles. However, the flammable liquid electrolyte further accelerates the fire in the event of thermal runaway exceeding 800 °C. Due to this safety issues, researches on solid electrolytes are actively underway. Among the types of solid electrolytes, Li-Argyrodite Li6PS5Cl sulfide solid electrolytes are attracting attention due to their high ionic conductivity, but chemical species such as Li2S, LiCl, and Li3P are formed at the Li-metal interface. These chemical species increase interfacial resistance, and Li3P has electron conductivity, which causes the formation of a non-homogeneous solid electrolyte interphase (SEI) layer. In this study, solid-state substitution of Si in Li6PS5Cl, a sulfide solid electrolyte with an argyrodite mineral structure, confirmed the improvement of ionic conductivity and stability at the Li-metal interface. As Si was substituted, the ionic conductivity is improved from 2.59 x 10-4 S cm-1 to 5.22 x 10-4 S cm-1. Enhancement of critical current density was confirmed by using Li|Li6+xSixP1-xS5Cl|Li symmetric cell. Through Li-metal interface analysis, it was confirmed that LixSi species were formed at the interface and it served as a passivation layer. In particular, through impedance analysis, it was confirmed that the increase in resistance corresponding to the SEI layer was greatly alleviated. Finally, the applicability of Si-substituted Li6PS5Cl to an all-solid-state battery using Li-metal as an anode was presented.