Ionic Conductivity and Electronic Insulation in a Nanoscale Interlayer for Improved Solid Electrolyte Performance

Abstract

Growing demands for versatile, high-energy-density energy storage bring inorganic solid electrolytes to the forefront of research for future battery designs. Dendrite formation and subsequent electrical shorting in solid electrolytes, however, present a critical obstacle to their widespread implementation in energy storage devices. Based on research that suggests a dependence of dendrite formation on the electronic conductivity of a solid electrolyte, we propose the rational design of a thin (<100 nm), conformal layer of electronically insulating, ionically conductive material at the interface between garnet-type LLZO electrolyte and a metallic Li-Sn alloy anode. Selection of the solid electrolyte LiPON as the material for the electronically insulating layer facilitated application by atomic layer deposition, a technique which ensured continuity across the garnet substrate surface. The LiPON layer enabled dendrite inhibition while promoting ionic conductivity through the electrolyte matrix over a long cycle life. Potential step chronoamperometry and electrochemical impedance spectroscopy performed on the LiPON-coated LLZO electrolyte matrix demonstrate the excellent electronic insulating ability of the applied layer, as evidenced by a dramatic drop of over two orders of magnitude in the electronic leakage current while maintaining practical ionic conductivity. In a galvanostatic cycling protocol of over 200 h (100 cycles) using a maximum current of 0.1 mA⸱cm-2, symmetric coin cells consisting of LiPON-coated LLZO with Li alloy electrodes successfully demonstrated superior electrochemical stability and longer cycle life compared to a bare LLZO control. Our observations, confirmed by various spectroscopic techniques and post-cycling electron microscopy for visualization of Li dendrites and interface characteristics, support a new understanding of the possible failure mechanisms in LLZO solid electrolyte. Our simple and adaptable strategy yields new insight for the design of other dendrite-free solid-state electrolytes.