Atomic Layer Deposition of Sodium Phosphorus Oxynitride: a Conformal Solid-State Sodium-ion Conductor.

The development of novel materials that are compatible with nanostructured architectures is required to meet the demands of next-generation energy storage technologies. Atomic layer deposition (ALD) allows for the precise synthesis of new materials that can conformally coat complex 3D structures. In this work, we demonstrate a thermal ALD process for sodium phosphorus oxynitride (NaPON), a thin-film solid-state electrolyte (SSE) for sodium-ion batteries (SIBs). NaPON is analogous to the commonly used lithium phosphorus oxynitride SSE in lithium-ion batteries. The ALD process produces a conformal film with a stoichiometry of Na4PO3N, corresponding to a sodium polyphosphazene structure. The electrochemical properties of NaPON are characterized to evaluate its potential in SIBs. The NaPON film exhibited a high ionic conductivity of 1.0  10-7 S/cm at 25 °C and up to 2.5  10-6 S/cm at 80°C, with an activation energy of 0.53 eV. In addition, the ionic conductivity is comparable and even higher than the ionic conductivities of ALD fabricated Li+ conductors.1-4 This promising result makes NaPON a viable SSE or passivation layer in solid-state SIBs.