Enhancement of ionic conductivity in novel LiON-AlO_x multilayer heterostructures prepared by atomic layer deposition

A novel heterostructured multilayer thin-film solid electrolyte consisting of LiON-AlO_x was synthesized by atomic layer deposition (ALD). The ALD-derived films were grown about 200 °C on SiO₂/Si substrate by an alternating deposition of lithium oxynitride (LiON) and AlO_x sublayers with 1–6 nm thickness and then characterized by various methods for roughness, homogeneity, crystallinity, thickness, composition, chemical environment, and ionic conductivity. The desired layer-by-layer structure of the films was confirmed by both high-resolution transmission electron microscopy and time-of-flight secondary ion mass spectrometry. Compared to pure LiON films without insulating AlO_x interlayers, the ionic conductivities of multilayer LiON-AlO_x films with various nanoscale sublayers are enhanced due to channeling effects between the heterointerfaces of nanoscale sublayers, while the activation energies are increased due to the incorporation of non-conducting AlO_x sublayers. Thickness-dependent conductivity of the multilayer LiON-AlO_x films indicates that 3.2 nm of LiON sublayer alternatively combined with 1 nm AlO_x sublayer has the best conduction performance. The film with 15 bilayers exhibits a conductivity of 6.2 × 10⁻⁴ S/cm at 160 °C with an activation energy of 0.57 eV.