Potential of compositional complex oxide in reversible electrochemical energy storage

Abstract

Compositional complex or high entropy materials, due to their unique phase stabilization mechanism, have ushered exciting research opportunities for material property design on many fronts, and perhaps more importantly, given rise to prospect of developing fundamental understanding of complex material systems whereby material functions may be tailored to fit various application needs simultaneously. In the area of electrochemical energy storage, high entropy materials have shown promising results both in storage capacity and longevity in lithium ion batteries owing to their efficient conversion type reaction mechanism, which can pave the way for more sustainable energy storage in the near future. Moreover, high entropy materials tend to retain structural integrity more than traditional binary or ternary metal complex and show interesting results insofar as the attributes of constituents, which can range from mechanical to electronic properties, may be aggregated and manifested in a single combined phase, and in some cases the single combined phase is imparted with superior attributes than the phase mixture of aggregated whole. Research into the underpinnings of this phenomenon can enable design of complex material systems with potential to address many challenges faced in the broader community today. A compositional complex oxide (V0.25Mn0.25Fe0.25Co0.25)1-xNixO was synthesized and characterized in this paper. Its structural properties entailed a mixture a primary spinel and secondary triclinic phases crystallized in predominantly nanometer sized grains with near equimolar composition of transition metals sans nickel. Elemental composition was in uniform distribution, and oxidation states were multi-valent. Cyclic voltammetry, galvanostatic and electrochemical impedance data altogether concur and support for a conversion type reaction consisted of equally fast surface kinetic and long range diffusion, with high probability of entropic stabilization. The findings show convincing connection between structural and compositional material properties and electrochemical responses. Further studies are necessary to shed light on the pertaining fundamentals.