In this study, thermal atomic-layer deposition (ALD) is utilized to deposit a film of lithium phosphorus oxynitride (LiPON) to improve the solid-electrolyte performance of thin-film lithium batteries, increasing their viability for high-energy-storage applications. This technique enabled the successful fabrication of a carbon-free LIPON film using a deposition sequence constructed on the basis of a phosphate backbone and film deposition temperatures of 400-500 degrees C. The obtained film has an ionic activity of 3.2 x 10(-7) S cm(-1) and an activation energy of 0.57 eV, values that are largely equivalent to those of sputtered LiPON films. Characterization of the film revealed that the thermal ALD-based film deposition is highly conformal, as the LiPON film is deposited deep (several hundreds of nanometers) into the grain boundaries of the lithium cobalt dioxide and the pores in this film are several tens of nanometers in diameter. These findings suggest that the use of thermal ALD to deposit LiPON films has a wide range of potential applications in battery technologies. (C) 2016 The Electrochemical Society. All rights reserved.