(Keynote) Dynamics in Prussian Blue Analogs-Based Batteries Revealed By X-Ray Techniques
Authors: Giorgetti Marco , Li Min , Maisuradze Mariam , Sciacca Rosalinda 
Published: November 2022

A key factor for the developing of post-lithium batteries is represented by suitable active materials to be used in the positive and the negative electrodes. Host nanostructured have insertion sites, channels and/or interlayer spacings allowing the rapid insertion and extraction of the required ions, occurring generally with little lattice strain, with concomitant reduction/oxidation of an active metal belonging to the host. In this context Prussian Blue Analogs (PBA) offer an interesting host material for a wide variety of cations, which is also characterized by an appropriate electroactive bimetallic network.
Dynamic processes occurring in batteries can be studied by operando modality, which provide a realistic representation of the electrochemical reactions occurring at the electrodes, or in ex situ modality, which reflect a given state of charge (SOC) of the electrode material. Monitoring the local structure around the metallic sites as well as the periodic structure can be performed using spectroscopic methods and in particular X-rays. X-ray absorption spectroscopy (XAS) is a synchrotron radiation-based technique that provide both electronic and structural information on a selected atomic species in a sample. General guidelines are presented in order to give a useful guide for a correct interpretation of the EXAFS spectra of this class of compounds, which is characterized by close, but sufficiently separated, discontinuities of the absorption coefficient due to contiguous transition metal K-edges. The dynamic of the ions insertion/release electrochemical reaction can further be investigated by adopting a chemometric approach using a multivariate curve resolution with alternating least squares algorithm (MCR-ALS), with the intent to assess the number of species involved and their evolutions during the electrochemical process. X-ray powder diffraction (XRPD) experiments allow monitoring the periodic structure of a material following the intercalation/release process of the ions involved. The potentiality of the joint XAS-XRD approach in the newly proposed PBA cathodes materials for rechargeable batteries is here highlighted, giving emphases on the copper hexacyanoferrate, copper nitroprusside, and manganese hexacyanoferrate electrodes.
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