Microstructure of Lithium Metal Electrodeposited at the Steel|Li6PS5Cl Interface in “Anode-Free” Solid-State Batteries

Recent research shows that integrating lithium metal anodes can enhance battery energy density, but the high reactivity of lithium requires handling under inert conditions to avoid degradation. To overcome this, reservoir-free cells (RFCs) are explored, where lithium metal is electrodeposited at the current collector (CC) and solid electrolyte (SE) interface during initial charging. The electrochemical properties of electrodeposited lithium are influenced by its morphology and microstructure, which impact lithium discharge capacity and pore formation. However, little is known about how to control the microstructure of electrodeposited lithium. This work experimentally characterizes the lithium microstructure at the steel|Li₆PS₅Cl interface using cryogenic ion beam milling, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD), focusing on the effects of electrodeposition current density and lithium layer thickness. The results show that layer thickness, not current density, primarily governs the lithium microstructure. This “specimen thickness effect” is qualitatively described using a Monte Carlo Potts model and indicates that electrodeposited lithium metal quickly equilibrates at room temperature.