Title: Structure and charge monitoring of Prussian Blue analogous battery materialsby operando XRD and XAS

Abstract

Nowadays, electrochemical energy storage plays a major societal role due to its widespread technological applications. Host nanostructured materials having a crystal structure with insertion sites, channels and/or interlayer spacings, allows the rapid insertion and extraction of lithium and sodium ions with generally little lattice strain. Therefore they are used as electrode materials for batteries. X-ray absorption spectroscopy is a synchrotron radiation based technique that is able to provide information on local structure and electronic properties in a chemically selective mode. Operando synchrotron radiation x-ray powder diffraction (SR-XRPD) experiments allow monitoring the extended structure of a material during the intercalation/release process of ions. Both techniques were adopted in the study intercalation site, charge modification, and lattice modification of battery materials. In addition to ex situexperiment, dynamic processes occurring in batteries can be studied by operando modality. Operando experiments provide a realistic representation of the reaction behavior occurring at electrodes The potentiality of the joint XAS-XRD approach in the newly proposed Prussian Blue-like cathodes materials for rechargeable batteries is here underlined.In our group, a series of PBAs have been synthesized, such as copper hexacyanoferrate (CuHCF), manganese hexacyanoferrate (MnHCF), titanium hexacyanoferrate (TiHCF), multi-metal doped hexacyanoferrate, as well as copper nitroprusside etc. In particular, this talk will be summarize results obtained in the case of copper, manganese, and the titanium analogs. As an example, the electrochemical activity of MnHCF without extensive dehydration was investigated by varying the interstitial ion content through a joint approach using operando x-ray absorption fine structure (XAFS) spectroscopy and multivariate curve resolution with alternating least squares algorithm (MCR ALS), with the intent to assess the structural and electronic modifications occurring during sodium release and lithium insertion as well as the overall dynamic evolution of the system. The study is also complemented to the and operando XRPD. It was found that only a minor volume change (about 2%) is recorded upon cycling the electrode material against lithium.