Evaluation of Porous Lithium Lanthanum Zirconium Oxide (LLZO) Anode Host Structures for Li-Metal Batteries

Abstract

Lithium metal batteries are considered to be a leading candidate for next generation batteries due to their higher energy density and potential for safer operation when combined with solid-state electrolyte materials. However, they are still facing different challenges. A key challenge of lithium metal batteries is the volume expansion over cycling due to the non-uniform deposition of lithium on the anode leading to lithium dendrite formation compromising the battery safety, and poor lifetime. Herein, we report the use of porous Lithium Lanthanum Zirconium Oxide (LLZO) anode structures, in which lithium from the cathode is deposited into the pores during initial charging. The goal of this study is to study postmortem the lithium deposition in the porous host after different cycling conditions to measure the 7Li and 6Li isotopes depth profile by nuclear reaction analysis (NRA), namely, Proton Induced γ-Ray Emission (PIGE) and by Deuteron Induced Particle Emission (DIPE), respectively. The advantages of using NRA are that it gives an absolute measurement of Lithium without sample reliant calibration, it is a nondestructive technique, highly selective for specific light nuclides such as Lithium, and it is not affected by coordination effect.We demonstrate two different fabrication methods of porous LLZO structures, namely, electrospinning and electrospraying. Then, the fabricated LLZO structures are tested electrochemically using a half cell configuration to examine plating/stripping behavior as a function of current density and to track the overpotential evolution over cycling. Finally, the cycled anodes are investigated using NRA in particular Li concentration inside porous anode, at separator/anode interface and anode/current collector interface. Characterizing the concentration gradient of Li species within the porous and at the various interfaces can help define the current density limitations of solid-state Li metal batteries and identify Li loss failure modes so that cell lifetime can be improved.