Thermodynamic\nand Kinetic Properties of the Lithium–Silver\nSystem

A carbon–silver anode has recently been shown\nto suppress\ndendrite formation in all-solid-state lithium-ion batteries. The role\nthat silver plays in enabling the reversible deposition and stripping\nof lithium remains unknown. Furthermore, very little is known about\nthe thermodynamic and kinetic properties of Li<sub><i>x</i></sub>Ag<sub>1–<i>x</i></sub> alloys. Here, we report\non an in-depth first-principles study of phase stability and diffusion\nmechanisms in the Li–Ag alloy system. We identify two new intermetallic\nphases that are predicted to be stable in Li-rich Li<sub><i>x</i></sub>Ag<sub>1–<i>x</i></sub> alloys with stoichiometries\nof Li<sub>3</sub>Ag and Li<sub>11</sub>Ag<sub>2</sub>. Our calculations\nshow that the peculiar and highly anharmonic energy surface of pure\nLi along the Bain and Burgers paths persists upon the addition of\nAg to BCC Li. This has important implications for room-temperature\nphase stability and mechanical properties. We have also performed\na systematic study of diffusion mechanisms in the Li<sub><i>x</i></sub>Ag<sub>1–<i>x</i></sub> alloy system as a\nfunction of alloy concentration <i>x</i>. Diffusion in alloys\nand intermetallics is mediated by vacancies. High vacancy formation\nenergies are predicted in the Li<sub><i>x</i></sub>Ag<sub>1–<i>x</i></sub> alloy, especially in Ag-rich FCC\nsolid solutions. Complex diffusion mechanisms are identified in the\nB2 and γ-brass intermetallic phases that include two-atom hops\nand second-nearest neighbor hops. The migration barriers are found\nto decrease with increasing Li concentration, with predictions of\nexceptionally low migration barriers of 0.1 eV in the D0<sub>3</sub> Li<sub>3</sub>Ag phase.