Local structure of glassy lithium phosphorus oxynitride thin films: a combined experimental and ab initio approach

TL;DR

This study combines experimental spectroscopy and ab initio calculations to elucidate the local atomic structure of LiPON thin films, revealing that their stability stems from a glassy phosphate-based network with nitrogen incorporation.

Contribution

It provides a detailed structural model of LiPON using combined spectroscopic and computational methods, clarifying its amorphous phosphate monomer network and nitrogen roles.

Findings

LiPON's structure is mainly isolated phosphate monomers with nitrogen in specific sites.

The glassy structure contributes to its stability and mechanical flexibility.

Experimental and computational results are consistent in identifying the local atomic arrangements.

Abstract

Lithium phosphorus oxynitride (LiPON) is an amorphous solid-state lithium ion conductor displaying exemplary cyclability against lithium metal anodes. There is no definitive explanation for this stability due to the limited understanding of the structure of LiPON. We provide a structural model of RF-sputtered LiPON via experimental and computational spectroscopic methods. Information about the short-range structure results from 1D and 2D solid-state nuclear magnetic resonance experiments investigating chemical shift anisotropy and dipolar interactions. These results are compared with first principles chemical shielding calculations of Li-P-O/N crystals and ab initio molecular dynamics-generated amorphous LiPON models to unequivocally identify the glassy structure as primarily isolated phosphate monomers with N incorporated in both apical and as bridging sites in phosphate dimers. Structural results suggest LiPON's stability is a result of its glassy character. Free-standing LiPON films are produced that exhibit a high degree of flexibility highlighting the unique mechanical properties of glassy materials.