Low temperature plasma-enhanced atomic layer deposition of sodium phosphorus oxynitride with tunable nitrogen content

Abstract

Atomic layer deposition (ALD) is a key technique in processing new materials compatible with complex architectures. While the processing space for Li-containing ALD thin films has been relatively well explored recently, the space for other alkali metal thin films (e.g., Na) is more limited. Thermal ALD and plasma-enhanced ALD (PEALD) lithium phosphorus oxynitride [Kozen et al., Chem. Mater. 27, 5324 (2015); Pearse et al., Chem. Mater. 29, 3740 (2017)] processes as well as analogous thermal sodium phosphorus oxynitride (NaPON) (Ref. 13) have been previously developed as conformal ALD solid state electrolytes. The main difference between the Na and Li processes is the alkali tert-butoxide precursor (AOtBu, A = Li, Na). One would expect such an isoelectronic substitution with precursors that have similar structure and properties to correlate with a similarly behaved ALD process. However, this work demonstrates that the PEALD NaPON process unexpectedly behaves quite differently from its Li counterpart, introducing some insight into the development of Na-containing thin films. In this work, we demonstrate process development and characterization of an analogous low temperature (250 °C) PEALD of NaPON. This process demonstrates significant tunability of N coordination states by varying plasma nitrogen exposure time. Electrochemical characterization showed an ionic conductivity of 8.2 × 10−9 S/cm at 80 °C and activation energy of 1.03 eV. This first instance of low temperature NaPON deposition by PEALD shows promise for further development and understanding of more versatile processing of Na thin film materials.

Li, Na, K, Mg, Zn, Al, and Ca Anode Interface Chemistries Developed by Solid‐State Electrolytes

“…[226] XPS results clarify the presence of Na + -O − ,═P−, O − -Na═, doubly-coordinated N (P-N═P), and triply coordinated N (P-N<P 2 ). Fontecha et al [227] also reported NaPON using PEALD for 150-350 °C and obtained 𝜎 Na + ≈8.2 nS cm −1 at 80 °C. N content and coordination states of N (N d or N t ) in NaPON or LiPON are crucial for high-ion mobility.…”

“…Table 1 provides the state‐of‐the‐art multivalent SEs and their properties. [ 10–12,32,39,102,112–232 ]…”

“…Fontecha et al. [ 227 ] also reported NaPON using PEALD for 150–350 °C and obtained σ Na + ≈8.2 nS cm −1 at 80 °C. N content and coordination states of N (N d or N t ) in NaPON or LiPON are crucial for high‐ion mobility.…”

Dynamic Electrode–Electrolyte Intermixing in Solid-State Sodium Nano-Batteries

“…Enabled by our recent developments of both thermal and plasma-based ALD processes for sodium phosphorus oxynitride (NaPON), we present a proof-of-principle nanoscale Na-SSB. The electrochemical couple is formed by an ALD V 2 O 5 cathode (40 nm) and a thermally evaporated Na metal anode (1000 nm).…”

“…This becomes a major concern when constructing all-SSBs, where interface stabilization is arguably the most prescient hurdle for developing successful SSBs. 10,29,32−34 Enabled by our recent developments of both thermal 35 and plasma-based 36 ALD processes for sodium phosphorus oxynitride (NaPON), we present a proof-of-principle nanoscale Na-SSB. The electrochemical couple is formed by an ALD V 2 O 5 cathode (40 nm) and a thermally evaporated Na metal anode (1000 nm).…”