Electron microscopy studies of aqueous Zn-ion battery reaction mechanisms*

The high theoretical capacities, safety, and low cost of aqueous Zn-ion batteries (ZIBs) with MnO₂ cathodes make them attractive alternates to Li-ion batteries; however, details regarding the dominant energy storage mechanism remain under debate. Manganese oxide materials hold complexity for characterization due to the multiple polymorphs that the material can adopt including a variety of layered as well as tunneled structures.  Further, the fundamental building block of the materials is based on manganese centers surrounded by oxygen typically in an octahedral arrangement. 

Here electron microscopy is utilized to study the mechanistic details of ZIBs with MnO₂ cathodes when tested in mildly alkaline media. The local analysis is well suited to investigate materials as prepared and after electrochemical activity.  The structural details can be elucidated.  The surface condition of the samples is examined and using electron energy loss spectroscopy (EELS) the oxidation state of the manganese centers can be determined.  Careful data collection and analysis sheds light on this complex family of materials and their electrochemistry.