Non-equilibrium Ion Transport in a Hybrid Battery Material

Abstract

Hybrid materials, which combine inorganic and molecular components, often exhibit structural flexibility that enables unusual functional responses. Among them, Prussian blue analogues (PBAs) are a promising class for post-lithium battery technologies. Here, we show that non-equilibrium transformation processes govern the charge-storage mechanism of a PBA electrode, K2Mn[Fe(CN)6]. Ostensibly, this behavior mirrors that observed in high-rate cycling of conventional cathodes such as LiFePO4, yet arises here for fundamentally different reasons -- namely, low elastic moduli and cooperative distortions inherent to the hybrid framework. Using \emph{operando} methods, we show that framework flexibility limits transport kinetics and promotes collective, metastable pathways. Our results highlight new directions for PBA cathode optimisation, but also suggest a broader relevance of non-equilibrium mechanisms for mass transport in hybrid materials beyond PBAs alone.