Incorporation of halogen (Cl, Br, I) in Li-P-S-O system for exploring new sulfide solid electrolytes with high conductivity and superior electrochemical performance in solid-state batteries

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 Li10GeP2S12 (LGPS) structured SEs. In all prepared SEs, Li3.3PS3.7O0.3Br0.1 and Li3.3PS3.7O0.3I0.1 compositions show highest conductivities of 0.77 mS cm -1 and 0.93(≈ 1.0) mS cm -1 at 25 °C. These compounds also show superior stability against lithium metal in symmetric cells as well as in full SSB cells tested with LiNi0.8Co0.15Al0.05O2 (NCA) cathode and graphite anode. The instability of sulfide based SEs in ambient environment is a major issue, whereas, our prepared compounds Li3.3PS3.7O0.3Br0.1 and Li3.3PS3.7O0.3I0.1 show 5 times higher stability in ambient environment conditions as compared to non-doped Li3.2PS3.7O0.3. In-situ EIS study performed on full SSB as prepared and after chargedischarge cycles have revealed the contribution of interfacial reactions on impedance. The study also shows higher interfacial resistances in full SSB with Li-metal anode as compared graphite anode. At the end, post-mortem analysis of full SSB cell as well as SE-Li interfacial study was conducted by SEM and elemental mapping to observed the changes in the electrodes and electrolyte before and after charge-discharge cycles. Therefore, the present work reports sulfide based new SEs with high conducting and better stability, and their interfacial studies.