Role of Halogen Elements in Conductivity and Electrochemical Stability of Sulfide Based Solid Electrolytes

All-solid-state batteries (ASSBs) are a promising candidate for future energy storage technology with better safety and higher energy density [1]. Safety of solid state batteries come from solid electrolytes used instead of organic liquid electrolytes in conventional Li-ion batteries. The various types of solid electrolytes have already been reported for SSBs which can be divided into oxides, sulfides, halides and polymers based on their properties, advantages and disadvantages [2]. Among them, sulfide based solid electrolytes have advantages over other due to high conductivity and ductile nature of sulfides [3]. The discovery of Li 10 GeP 2 S 12 solid electrolyte called LGPS structured sulfide electrolyte have shown great potential to replace liquid electrolyte as ionic conductivity of LGPS was found 1.2×10 -2 S cm -1 at room temperature comparable to the conductivity of organic liquid electrolyte [4]. However, Li 10 GeP 2 S 12 electrolyte suffers with poor cyclability in solid state batteries due to reduction of Ge +4 ions to Ge 0 , and instable against lithium metal anode [5, 6]. The solid electrolytes (SEs) with high conductivity and better stability against lithium metal are most important requirements for successful commercialization of solid state battery (SSB) technology. Therefore, in the search for new SEs with above mentioned qualities, halogen elements (Cl, Br, I) are explored in Li-P-S-O system to prepare Li 10 GeP 2 S 12 (LGPS) structured SEs. In all prepared SEs, LPSOBr and LPSOI compositions show highest conductivities of 0.55 mS cm -1 and 0.67 mS cm -1 at 25 °C. The phase identification of newly synthesized solid electrolytes is done by X-ray diffractometer technique along with Rietveld refinement analysis. The conductivity of prepared solid electrolytes is determined by electrochemical impedance spectroscopy. These similar compounds also show superior stability against lithium metal in symmetric cells (Li/Ses/SE) as well as in full SSB cells (NCA/SEs/graphite) tested with LiNi 0.8 Co 0.15 Al 0.05 O 2 cathode and graphite anode. These compounds also show 5 times higher stability in ambient environment conditions as compared to non-doped LPSO compound. References: Nikodimos et al. Adv. Energy Mater. 2022, 2202854 Scrosati et al., Power Sources 195, 2010, 2419. Zhang et al., Energy Storage Mater. 10, 2018, 139-159. Jiang et al., ACS Appl Mater Interfaces 12, 2020, 54662-70. Kamaya et al., Mater., 10, 2011, 682–686. Neveu et al., Power Sources 467, 2020, 228250.