An Electron/Ion Dual Conductive Integrated Cathode Using Cationic/Anionic Redox for High-Energy-Density All-Solid-State Lithium-Sulfur Batteries

All-solid-state lithium-sulfur batteries (ASSLSB), composed of sulfur cathode and lithium metal anode with high theoretical capacity, have a potentially higher energy density by weight than a typical lithium-ion battery (LIB). However, due to insulating sulfur, a relatively large proportion of electronic (carbon) and ionic (solid electrolyte) conductors are mixed for cathode fabrication, leading to inferior practical capacity. Herein, we report a novel integrated cathode Li2S-LiI-MoS2 which has relatively high electronic and ionic conductivities (the order of 10-4 S cm-1) without any carbon and solid electrolyte. The ASSLSB with integrated Li2S-LiI-MoS2 cathode delivers a remarkably high energy density of 1020 Wh kg-1 at the cathode level at room temperature. By applying precise X-ray diffraction, pair distribution function analysis and X-ray computed tomography, it is found that the formation of an ionic conducting phase composed mainly of LiI during discharge is responsible for the high rate capability. Furthermore, X-ray absorption fine structure (XAFS) has also revealed the charge compensation mechanism and ascertained the involvement of both Mo 3d and S 3p orbitals during the charging and discharging process. It is believed the strategy will pave the way for developing high practical energy density at room temperature for all-solid-state batteries. Without carbon and solid electrolyte added into cathode composite, the Li2S-LiI-MoS2 cathode could deliver capacity of 530 mAh g-1 on the cathode level, leading to 1020 Wh kg-1 with Li metal as anode. The metallic phase LixMoS2 provides electron transport and LiI-rich domain benefits lithium-ion transport during charge process, which enables good rate capability at room temperature.image