Manufacturing and testing of thin-film electrochemical cells in liquid electrolyte on a chip intended for TEM observation in operando experiments

In operando experiments aim to perform in situ measurements of an electrochemical cell on a chip using transmission electron microscopy (TEM) during operation, which is a crucial requirement for understanding the fundamental physical and electrochemical phenomena taking place in a battery. These findings can enhance the understanding of electrochemical cells' behaviour and pave the way for designing more efficient and effective electrochemical energy-storage devices. Hence, the aim of this project is manufacturing a thin-film cell suitable for in operando TEM measurements by testing different chip designs and liquid electrolytes. This kind of cells require electrodes thinner than a few hundred nanometers, but typical commercial active material powders mainly consist of micrometric particles. So, this dissertation is focused on designing a process to prepare suitable cells from commercial materials. To accomplish this, particle size selection of LiMn2O4 was performed using separation methods. Having the ability to both deintercalate and intercalate, LiMn2O4 is used as active material for all electrodes in the thin-film cell. Therefore, nanoparticles are selected by centrifugation suspended in ethanol. Dynamic Light Scattering is employed to characterize their size and concentration to study the effects of the solvent, the centrifugation speed, and the use of filters. Then, adequate particles are drop casted on the chip with Polyvinylidene Fluoride (PVDF) in N-Methyl-2-pyrrolidone (NMP) to adhere them onto the surface. This particle distribution on the chip can be observed in Scanning Electron Microscopy (SEM). It was possible to demonstrate with planar microcells on chips electrochemical features that reproduce those typically shown by macroscopic cells. For example, 5 M LiNO3 had a good CV performance with 70 nA for the oxidation peak and -55 nA for the reduction one when selected depositing LiMn2O4 particles with 500 rpm centrifugation. The cell collectors represen