# Probing the Surface Chemistry of Lithium Nitridation

## TL;DR

This study investigates how lithium reacts with nitrogen gas to form Li3N, finding that surface oxidation and trace gases hinder nitridation.

## Contribution

The paper provides new insights into the conditions and mechanisms of lithium nitridation using in situ APXPS.

## Key findings

- Li3N formation is not detected at nitrogen pressures ≤10 mTorr.
- Surface Li3N reacts rapidly with trace CO2 at higher pressures.
- Oxidation by O2, CO2, or H2O inhibits Li3N formation on lithium surfaces.

## Abstract

Chemical synthesis of Li3N through lithium
nitridation
has potential to advance rechargeable battery and nitrogen fixation
technology. However, studies of the conditions for forming Li3N on the lithium surface via nitrogen gas exposure report
contradictory findings, such as the spontaneous reaction of Li with
pure N2, the impossibility of forming Li3N through
pure Li and N2 interaction, the requirement of trace H2O to catalyze the reaction, and evidence to the contrary.
In this study, ambient pressure X-ray photoelectron spectroscopy (APXPS)
was applied to evaluate the in situ chemical evolution of the lithium
metal surface under nitrogen gas up to 800 mTorr. At pressures ≤10
mTorr, no Li3N was detected. At higher pressures, surface
Li3N rapidly reacts with trace CO2. Additionally,
because metallic lithium is readily oxidized by trace gases, the atomic
nitrogen concentration of the lithium surface remains below 2%. When
nitridation follows oxidation by O2 gas, CO2 gas, or H2O vapor, surface Li3N formation
is inhibited. These results suggest that nitrogen gas can diffuse
through the oxidized lithium metal surface to react with subsurface
metallic lithium.