The structural accommodations, essential to the processes of insertion of the Li-ion inside the materials of the battery, are strongly dependent on the kinetics of the electrochemical reaction. Thus, the quantification of these structural inhomogeneities, their interfaces and their evolutions according to the state of charge and the electrochemical cycling regime is the key to better understand the processes at the origin of the degradation of the retentions in capacity for the Li-ion batteries. For example, knowledge of the spatial distribution of phase, orientation, grain boundary, and strain is crucial to obtain a complete picture of the phenomena occurring during material operation.

Recently, new in situ/operando analytical tools have been developed to monitor structural and chemical transformations, which have allowed important advances in the knowledge of dynamical processors. Liquid cell TEM is a developing technique that allows us to apply the powerful capabilities of the electron microscope to image and analyze materials immersed in liquid. The liquid/bias cell (Protochips) consists of silicon nitride windows on silicon support called E-chip, which separates the liquid from the vacuum of the microscope and confines it in a thin enough layer for TEM imaging. The importance of liquid cell microscopy in electrochemistry is that liquid cell experiments allow direct imaging of key phenomena during battery operation and relate structural and compositional changes to electrochemical behaviors. Different interesting results on monitoring dynamical processes occurring in a wide variety of electrochemical systems, such as LiFePO4, NMC811, LMNO and solid state will be presented here.

4D-STEM techniques yielding structure and strain maps were used to locally probe the crystallographic information of active material crystals and correlate it to the spatial occupancy of Li-ion during the electrochemical cycle. Liquid mass spectrometry analysis was also used to monitor the evolution of the liquid electrolyte during the formation of SEI on the surface of the negative electrode. Structural refinement of an individual cathode grain was achieved using 3DED (electron diffraction tomography) techniques revealing changes in lattice parameters after an in situ electrochemical delithiation process. The ability to couple emerging analytical techniques with liquid electrochemical cell TEM paves new way in energy material characterization, in particular in the study of the dynamic phenomena occurring during the operation which are until now inaccessible to the primary particle scale.