Solid-state divalent ion conduction in ZnPS_3

Abstract

Rechargeable Li-ion batteries revolutionized portable energy storage, but the fundamental limitations imposed by intercalation chem. and the cost assocd. with common components in Li-ion cells drive the need for new batteries. The search for these so called "beyond Li-ion" technologies include systems based on conversion cathodes, multi-electron intercalation cathodes, and new working ions, to name a few. Here, we focus on chemistries that employ divalent working ions. Divalent ions are promising alternatives to Li-based chem. as they enable reversible metal anodes while using abundant and inexpensive resources. The intricacies of divalent cation electrochem. range from the complex coordination complexes in electrolyte solns., to unstable interfaces, to difficulties in divalent cation conduction in the solid-state. We will explore aspects of these key challenges in the context divalent ion cond. in the solid-state. To begin understanding the fundamental mechanisms of solid-state divalent ion diffusion, we have developed and characterized an electronically insulating, divalent ion conductor. ZnPS_3 supports Zn^(2+) conduction with low activation energies, thanks to the [P_2S_6]^(4-) polyanion. The ion diffusion pathways in ZnPS_3 and future strategies towards higher cond. materials will be discussed.