3D Asymmetric Bilayer Garnet Hybridized High-Energy-Density Lithium-Sulfur Batteries

Abstract

Li7La3Zr2O12 (LLZO) has high ionic conductivity and stability against a Li metal anode making it a promising solid electrolyte for Lithium-Sulfur batteries. However, typically reported discharge capacity does not achieve theoretical. Therefore, we addressed this by forming a stable sulfur cathode/LLZO interface through a poly(ethylene oxide) (PEO)-based interlayer, with a small amount of catholyte used to maintain physical contact and ionic conduction between sulfur cathode and the PEO-based interlayer. With a thin bilayer LLZO and the stabilized sulfur cathode/LLZO interface, the hybridized Li-S batteries achieved an initial discharge capacity of 1307 mAh/g at a current density of 0.2 mA/cm2 (0.03C) at room temperature (22°C) without any indication of a polysulfide shuttle. With specific optimization, an energy density of 1308 Wh/L and 485 Wh/kg is achievable.The mechanisms regarding the cell stabilization are presented: 1). X-ray Diffraction and X-ray Photoelectron Spectroscopy indicate that the PEO-based interlayer which physically separates the sulfur cathode and LLZO, is both chemically and electrochemically stable with LLZO. 2). Due the physical separation between liquid electrolyte and LLZO through the PEO-based film, the proton/Li+ exchange with the moisture in liquid electrolytes was avoided. 3). PEO-based interlayer can adapt to the stress/strain associated with sulfur volume expansion during lithiation to protect LLZO from failure.