Slurry-Processed Glass-Ceramic LI2S-P2S5-LiI Electrolyte for All-Solid-State Li-Ion Batteries

Abstract

Lithium-ion batteries (LIBs) have widely been used as power sources for from small electronic devices to large-scale systems such as electric and plug-in hybrid electric vehicles, mostly due to their high power and high energy density. However, the organic electrolyte in commercial LIBs has evoked safety issues, making all-solid-state LIBs with inorganic solid electrolyte an alternative of conventional organic electrolyte batteries. Solid electrolytes are not only safer and more reliable than liquid electrolytes in thermochemical point of view but also more compatible with Li metal anode and high voltage cathode materials. Among solid electrolytes, sulfide-based electrolytes have received great attention because of their high lithium ion conductivities of 10-4 to 10-2 S cm-1 at room temperature, comparable to organic electrolytes. In most studies, however, the solid electrolytes were pressed into a pellet under extremely high pressure to increase the ionic conductivity by minimizing the void and interface between electrolyte particles. This method is not suitable for the practical cell fabrication considering the scale-up manufacture. Moreover, although the electrochemical stability of sulfide-based solid electrolytes with cathode materials was improved by an interphase coating such as LiNbO3, the stability with the anode, especially with Li metal, has not been fully studied yet, mostly reporting a short-term stability evaluated by cyclic voltammetry. In this study, we evaluate long-term electrochemical stabilities of sulfide-based solid electrolytes, LGPS (Li10GeP2S12), LPS (Li7P3S11), and LPSI (Li2S-P2S5-LiI glass-ceramic and Li7P2S8I) with respect to Li metal. Area specific interfacial resistances of the solid electrolytes were characterized by using a DC cycling method, i.e., a repeated long-term charge/discharge over 100 hours with the current density of 0.1 mA/cm2 and the duty cycle of 1 hour. Then, we demonstrate a slurry-processed all-solid-state cell with Li metal anode, LPSI glass-ceramic electrolyte, and a composite cathode, where a mixture of LiNbO3-coated LiNi0.6Mn0.2Co0.2O2, LPSI solid electrolyte, carbon black, and binder dissolved in an appropriate solvent was slurry-coated and, after drying and pressing, LPSI electrolyte slurry was coated on top of the cathode layer. The cell performances of the slurry-processed all solid-state LIB cells are evaluated in comparison with pellet-type cells.