Li-Rich Layered Sulfide as Cathode Active Materials in All-Solid-State Li–Metal Batteries

Great hopes are placed on all-solid-state Li–metal batteries (ASSBs) to boost the energy density of the current Li-ion technology. However, 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 the 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 Li_1.13Ti_0.57Fe_0.3S₂ (LTFS) in room temperature operating all-solid-state batteries, using β-Li₃PS₄ as SE and both InLi and Li anode materials. These batteries exhibit good cyclability, small polarization and, in the case of the Li anode, no initial irreversible capacity. We also suggest the possibility of using this Li-rich sulfide mixed with oxide cathode materials as part of the positive electrode in ASSBs in order to improve the cathode/sulfide SE interface. Our proof of concept using LiNi_0.6 Mn_0.2Co_0.2O₂ (NMC 622) showed that the addition of a small amount of LTFS had a direct positive impact in the battery performance.