Thermodynamics and kinetics of lithium at the silver-lithium battery interface

Abstract

Silver interlayers have been shown to enable smooth lithium deposition and cycling in anode-free solid-state batteries. Here, we report the atomic structure of the Ag and Li interface, showing that Li preferentially plates as FCC on both the (111) and (100) Ag surfaces. This forms an energetically favorable coherent interface with Ag, while the BCC phase forms a semi-coherent interface due to large lattice mismatch. We also calculate vacancy formation energies and migration energies for Li diffusion through the interface. We show that vacancy formation energies increase at the interface, leading to an energetic driving force for vacancies to diffuse away from the interface. Additionally, the migration barriers for vacancies from the Ag to the Li are small (29 meV), and therefore promote rapid alloying between Ag and Li. Rapid Li diffusion kinetics directly at the interface leads to smooth deposition of Li, reducing the onset of dendrites. However, diffusion in the 2nd and 3rd Li layers is slower compared to bulk FCC or BCC Li, leading to kinetically hindered alloying when multiple layers of pure Li form. The diffusion kinetics for Ag nanoparticles may be improved by alloying with Mg to expand the Ag lattice constant while forming a solid solution with both Ag and Li.