Solid-Electrolyte-Free O3-Li x TiS2 Cathode for High-Energy-Density All-Solid-State Lithium-Metal Batteries

Composites made of high-capacity and high-potential LiNi x Mn y Co1-x-y O2 (NMC) lamellartransition-metal oxides and S-based ionic conductors are primarilyused as positive electrodes in all-solid-state batteries (ASSBs).However, NMC coatings are necessary to prevent the chemical reactivityof oxygen and sulfur at the expense of some penalty in capacity andin ionic conduction. To overcome these problems, the current trendis to move to S-based positive electrodes, which exhibit higher electronicand ionic conductivities and no S-O reactivity. Herein we succeedin preparing highly divided O3-Li x TiS2 powders by ball milling, which can be used as a positiveelectrode free of the electrochemically dead solid electrolyte (SE)in ASSBs that shows energy densities of more than 350 Wh/kg and stablecycling under low pressures down to 1 bar. These enhanced performanceswere rationalized by Li-7 NMR measurements that revealeda decrease in the site-to-site activation energy barrier with increasingball-milling time. This finding, based on diffusion considerationsassociated with particle size reduction, can be generalized to other3D metal sulfides and provides insights on the benefits of using aSE-free and C-free design relying on highly divided Li-containingsulfides to boost energy densities in ASSBs.