Synthesis of sulfur based solid electrolytes for lithium ion batteries and investigation of electrode electrolyte interface

This thesis aims to enhance the electrochemical performance of lithium-sulfur batteries through the synthesis high ionic conductive Li7P3S11 solid electrolyte and its adoption into an all-solid-state battery. An artificial solid electrolyte layer was formed on lithium anode surface with Li3N and MoS2 phases to prevent the formation of unstable solid electrolyte interfaces. All-solid-state batteries are constructued where surface-modified lithium, Li7P3S11 and sulfur based composites were utilized as anode, solid electrolyte and cathode respectively. Besides, solid electrolytes with low activation energy barrier with intrinsic electrochemical stability were synthesized by doping sulfur into oxide based solid electrolytes to partially replace oxygen atoms with sulfur. In this regard, Li1.3Al0.3Ti1.7(PO4)3(LATP) solid electrolyte was doped with sulfur through sulfur-amine chemistry. Stability of the electrode-electrolyte interface was analyzed by long-term chronoamperometry and chronovoltammetry analyses where Elecrochemical Impedance Spectroscopy, Cyclic Voltammetry and Galvanostatic Charge-Discharge tests were conducted to determine the electrochemical performance of the batteries. Our results indicate that surface modified Lithium anodes impart better electrochemical stability and capacity retention upon cycling through preventing the formation of undesired phases in the solid electrolyte interface. Besides, our studies focued on to develop high electrochemical window materials shows 10,1% decreased lithium ion difusion activation energy barrier with 5,21x10-4 S/cm ionic conductivity in sulfur-doped LATP crystal structures.