High Areal Capacity Cation and Anionic Redox Solid-State Batteries Enabled by Transition Metal Sulfide Conversion.

Pure sulfur (S 8 and Li 2 S) all solid-state batteries inherently suffer from low electronic conductivities, requiring the use of carbon additives, resulting in decreased active material loading at the expense of increased loading of the passive components. In this work, a transition metal sulfide in combination with lithium disulfide is employed as a dual cation-anion redox conversion composite cathode system. The transition metal sulfide undergoes cation redox, enhancing the electronic conductivity, whereas the lithium disulfide undergoes anion redox, enabling high-voltage redox conducive to achieving high energy densities. Carbon-free cathode composites with active material loadings above 6.0 mg cm -2 attaining areal capacities of ∼4 mAh cm -2 are demonstrated with the possibility to further increase the active mass loading above 10 mg cm -2 achieving cathode areal capacities above 6 mAh cm -2 , albeit with less cycle stability. In addition, the effective partial transport and thermal properties of the composites are investigated to better understand FeS:Li 2 S cathode properties at the composite level. The work introduced here provides an alternative route and blueprint toward designing new dual conversion cathode systems, which can operate without carbon additives enabling higher active material loadings and areal capacities.