Lithium germanium thiophosphate (LGPS) is an attractive solid-state electrolyte material due to its exceptionally high ionic conductivity, which rivals organic liquid electrolytes. Despite this potential, other properties have impeded its adoption into solid-state batteries, particularly the poor voltage stability of the material at potentials near that of high voltage cathodes or lithium metal. Aluminum nitride (AlN) can serve as an anodic protection interlayer between LGPS and lithium metal, enhancing cell performance. AlN is grown via plasma-enhanced ALD at 250 °C using TMA and both N2 and NH3, but the deposited films show significant oxygen contamination originating from the plasma and lack crystallinity. Galvanostatic cycling and electrochemical impedance spectroscopy show that LGPS-coated cells perform better than bare cells, with expected lifetimes >3x greater in certain cases. Finally, XPS line scans highlight the slow room-temperature reactivity between AlN and evaporated lithium, and a computational model is built to aid further XPS experiments.