A Li-rich layered sulfide as cathode active material in all-solid-state Li-metal batteries.

Great hopes are placed on all-solid state Li-metal batteries (ASSB's) to boost the energy density of the current Li-ion technology. Though, these devices still present a number of unresolved issues that keep them far from commercialization such as interfacial instability, lithium dendrite formation and lack of mechanical integrity during cycling. To mitigate these limiting aspects, the most advanced ASSB systems presently combine a sulfide or oxide-based solid electrolyte (SE) with a coated Li-based oxide as positive electrode and a lithium anode. Through this work we propose a different twist by switching from layered oxides to layered sulfides as active cathode materials. Herein we present the performance of a Li-rich layered sulfide of formula LiTiFeS (LTFS) in room temperature operating all-solid state batteries, using -Li3PS4 as a solid electrolyte and both InLi and Li anode materials. These batteries exhibit good cyclability, small polarization and, in the case of Li anode, no initial irreversible capacity. At a side of this work, we also suggest the possibility of using this Li-rich sulfide mixed with oxide cathode materials as part of the positive electrode in ASSB's in order to improve the cathode/sulfide SE interface. Our proof of concept using LiNi0.6 Mn0.2Co0.2O2 (NMC 622) showed that the addition of a small amount of LTFS had a direct positive impact in the battery performance.