Study of the Sodiation Dynamics within Individual Particles of Active Materials for Na-ion Batteries by Electrochemical TEM Operando Measurement – DESTINa-ion_Operando

SUMMARY: The main objective of the DESTINa-ion_Operando project is the development of instrumental methodologies based on in situ liquid / electrochemical TEM for studying the lithiation dynamics (and sodiation) in individual particles of positive electrode materials for Li-ion (and Na-ion) batteries. The inhomogeneity of ion insertion reactions within crystals is strongly dependent on the solid-liquid (liquid crystal / electrolyte) and solid-solid (crystal / current collector) interfaces, and is the source of the constraints, fractures mechanisms and migrations of elements (V, Mn, O) which degrade the reversibility of electrochemical reactions. These defects of uniformity present at the nanometric scale are at the origin of the difficulties of interpretation between the evolution the electrochemical properties and the mechanisms of insertion of the ions. In addition, these structural adjustments essential to ion insertion processes are highly dependent on the kinetics of electrochemical reaction. Thus, the quantification of these structural inhomogeneities, their interfaces and their evolutions as a function of the state of charge and the electrochemical cycling regime is the key points to providing a better understanding of the processes that cause the degradation of retentions in capacity for Na-ion and Li-ion batteries. We propose in this project to develop two Operando experimental approaches based on the use of our electrochemical TEM sample holder in order to follow, in real time (fast camera) and on the nanometric scale, the structural modulations induced by the mechanisms of insertion into individual crystals. The developments will be on the one hand, from electron diffraction in tomography mode [1] and dark field imaging, and on the other hand, from phase mapping and crystalline orientation (ASTAR ). The use of a fast camera (Gatan Oneview) very suitable for electron diffraction will allow precisely quantifying the reaction dynamics (30 to 300 fps) [2] even for very high current densities. These Operando TEM studies will be complemented by "nanoprobe" X-ray synchrotron (ESRF) measurements that allow for X-ray diffraction and XANES absorption measurements as well as X-ray fluorescence with a spatial resolution of 20 to 50 nm. according to the technique. Our XRD electrochemical cell developed at LRCS for synchrotron lines will be used to perform Operando electrochemical measurements. The monitoring of intercalation dynamics by these different techniques will help to better understand kinetic phenomena by linking the morphological, structural and chemical properties. We will focus on 2 positive electrode materials, one for Li-ion batteries, LiNi1/2Mn3/2O4 high spinel structural oxide, which is a very interesting candidate for lithium-ion type batteries energy, and the other for power-type Na-ion batteries, fluorinated vanadium phosphate Na3V2(PO4)2F3 (NVPF) of interest because chemically stable. DESTINa-ion_Operando aims to open a new path in the understanding of phenomena limiting the performance of electrochemical energy storage devices. This project is located in the scientific axis "transverse domains" (E.8), "sensor, instrumentation" (8.12).