Atomic-Resolution Study of Complex Oxides for Multi-Valent Ion Battery Cathodes

As the world transitions from fossil fuels to renewable energy sources, demand for energy-dense battery materials will continue to rise. Today, the most common battery technology in electric vehicles and portable devices is based upon Li-ion transport between a transition metal oxide cathode and a graphite anode. Despite their popularity, graphite anode Li-ion batteries inherently offer lower capacities than metal anode batteries. However, Lithium metal anode batteries present environmental concerns over the safety of their disposal and safety concerns from dendrite formation upon cycling. Moreover, Li shortages have highlighted the need for batteries based upon the ion transfer other than Li-ions.<br/>Therefore, the focus has shifted towards the development of multi-valent ion batteries which should enable the usage of metal anodes. Promising candidate materials that have emerged from this search are transition-metal spinel oxides, some of which exhibit high capacities especially in nano-sized crystals. For example, recent reports demonstrate that despite the presence of complex structural defects V₂O₄ nanocrystals are capable of cycling Mg²⁺ at capacities greater than Cr and Mn spinel counterparts.<br/>In this contribution, I will discuss results from several different transition metal oxide spinels and demonstrate how atomic resolution scanning transmission electron microscopy (STEM) techniques, including electron energy loss measurements (EELS) and x-ray energy dispersive spectroscopy (XEDS) and in-situ electro-chemical cycling can be used to elucidate the extend of multi-valent ion intercalation and the effects of electrolyte induced corrosion on the surface structure of the oxide cathodes. The structural information will also be directly correlated to battery performance data, XAS measurements and first-principles density functional theory (DFT) calculations.