The Zintl-Klemm Concept in the Amorphous State: A Case Study of Na-P Battery Anodes

The Zintl-Klemm concept has long been used to explain and predict the bonding, and thereby the structures, of crystalline solid-state materials. We apply this concept to the amorphous state, examining as an example the diverse disordered Na-P phases that can form in sodium-ion battery anodes. Using first-principles simulations combined with state-of-the-art machine-learning methods, we provide atomic-scale insight into the structural and energetic behaviour of amorphous Na-P phases. We evaluate the applicability of the Zintl-Klemm rules in the amorphous state and discuss implications for future work.