# Solid‐State Nuclear Magnetic Resonance Investigations of the Lithium‐ and Sodium‐Storage Mechanisms of Pyrolytic Phosphorus‐Carbon Composites

## TL;DR

This paper uses nuclear magnetic resonance to study how lithium and sodium ions are stored in phosphorus-carbon composites used in batteries.

## Contribution

The study provides a detailed mechanistic analysis of ion storage in phosphorus-doped turbostratic graphite microspheres using solid-state NMR.

## Key findings

- Lithium intercalation involves Li3P formation from trapped white phosphorus and lithiated phosphorus atoms in the graphitic lattice.
- Sodiation follows a similar mechanism but lacks evidence of a dual-sodiated doped-phosphorus environment.
- Reversible ion storage is enabled by carbon-encapsulated phosphorus adopting a red phosphorus-like local structure.

## Abstract

Phosphorus‐doped carbons provide a balance between the electrochemical stability of graphitic lattices and the high energy density of phosphorus materials when used in lithium and sodium‐ion batteries. Herein, a comprehensive ex situ 31P, 7Li, and 23Na solid‐state nuclear magnetic resonance analysis of the intercalation mechanism of novel, stable, dual‐phase phosphorus‐doped, and phosphorus‐encapsulated turbostratic graphite microspheres is presented. Results indicate that lithium intercalation occurs through the formation of Li3P from white phosphorus trapped within the graphitic layers, with the involvement of lithiated phosphorus atoms within the graphitic lattice. A dual‐lithiated carbon doped‐phosphorus environment is tentatively proposed at low voltages. Sodiation occurs through a similar mechanism; however, no evidence of a dual‐sodiated doped‐phosphorus environment is observed. Upon removal of ions, carbon‐encapsulated phosphorus with a local structure similar to red phosphorus forms, which subsequently allows effective reversible ion storage.

Phosphorus–carbon composites as battery electrode materials benefit from the high capacity of phosphorus and the stability of carbon. Understanding the ion‐storage mechanisms in these materials is crucial for their development. An analysis of the lithiation and sodiation mechanisms of a phosphorus–carbon composite is undertaken here utilizing ex situ solid‐state nuclear magnetic resonance, allowing a mechanistic insight into the multiple reactions that occur in these systems.© 2025 WILEY‐VCH GmbH