All-solid-state lithium batteries (ASSLBs) based on sulfide solid electrolytes (SEs) have received great attention because of the high ionic conductivity of the SEs, intrinsic thermal safety, and higher energy density achievable with a Li metal anode. However, studies on practical slurry-cast composite electrodes show an extremely limited battery performance than the binder-free pelletized electrodes because of the poor interfacial robustness between the active materials and SEs by the presence of a polymeric binder. Here, we employ a low-temperature post-sintering process for the slurry-cast composite electrodes in order to overcome the binder-induced detrimental effects on the electrochemical performance. The LiI-doped LiPS SEs are chosen because the addition of iodine not only improves the Li-ion conductivity and Li metal compatibility but also lowers the glass-transition and crystallization temperatures. Low-temperature post-sintering of composite cathodes consisting of a LiNiCoMnO-active material, LiI-doped LiPS SE, polymeric binder, and conducting agent shows a significantly improved electrochemical performance as compared to a conventional slurry-cast electrode containing pre-annealed SEs. Detailed analyses by electrochemical impedance spectroscopy and galvanostatic intermittent titration technique confirm that post-sintering effectively reduces the interfacial resistance and enhances the chemomechanical robustness at solid-solid interfaces, which enables the development of practical slurry-cast ASSLBs with sulfide SEs.

Development of a tangible solid state battery has received great attention but there are various engineering challenges to overcome, especially for the scalable processing and the use of Li metal anode. In order to tackle these issues, we first evaluated the electrochemical stability of thio-LISICON solid electrolytes, i.e., Li 10 GeP 2 S 12 (LGPS), Li 7 P 3 S 11 (LPS), and Li 7 P 2 S 8 I (LPSI), where the glass-ceramic LPSI electrolyte showed a superior compatibility with Li metal. Moreover, a superionic conductivity of 1.35 × 10 −3 S/cm could be achieved by optimizing the wet mechanical milling and the low-temperature annealing processes. Using this superior LPSI solid electrolyte, we evaluated the electrochemical performance of pellet-type and slurry-type all-solid-state cells with LiNbO 3 -coated LiNi 0.6 Co 0.2 Mn 0.2 O 2 (LNO-NCM622)/LPSI composite cathode and Li metal anode. The initial discharge capacity of ∼150 mAh/g was achieved for the pellet-type test cell and ∼120 mAh/g for the slurry-type cell. Comparing the interfacial resistances of the two types of cells, strategies to enhance the performance and realize a scale-up fabrication of all-solid state Li-ion batteries are discussed.

In order to envisage a sulfide electrolyte based all-solid-state Li battery considering the use of Li metal as the anode as well as a scalable cell fabrication process, we evaluated the long-term electrochemical stability of various lithium conducting sulfide superionic conductors interfaced with Li metal anode. Among them, Li 2 S-P 2 S 5 -LiI glass-ceramic electrolyte, which showed a superior compatibility with Li metal as well as a comparable ionic conductivity of 1.35 x 10 -3 S/cm, was used as the electrolyte for a slurry-processed all-solid state Li-ion cell. The discharge capacity of the slurry-type cell retained ~88% compared with that of a typical pellet-type one. The porous nature of the slurry-coated layer as well as the hindering effect of a polymeric binder, however, resulted in large overpotentials during charge and discharge. A strategy for further study to overcome these detrimental effects of slurry-processing was discussed.