(Invited) In Operando and in Situ techniques for Intercalation Compounds in Li-Ion and All-Solid-State Batteries

Abstract

We will present the results and supporting video files of several in operando techniques used to study lithium-ion and solid-state batteries, such as in situ scanning electron microscopy (SEM), in situ transmission electron microscopy (TEM), in situ Raman spectroscopy, in situ X-ray diffraction and in situ UV visible. These studies help understand several mechanisms, including volume expansion of anodes such as Si (300%), lithium metal (20%), graphite (10%) and LTO (0%). They are also used to measure the thickness of the anode, cathode and electrolyte through the charge/discharge cycle. The mechanism of lithium dendrite was also studied and its details will be presented.Blend-based solid polymer electrolyte (SPE) lithium-sulfur cells were studied in operando using two techniques: SEM and ultraviolet-visible absorption spectroscopy (UV-vis). During the operation of these cells, extensive polysulfide dissolution in the solid polymer electrolyte (cross-linked polyethylene oxide) leads to the formation of a catholyte. A clear micrograph of the thick passivation layer on the sulfur-rich anode and the decreased SPE thickness due to cycling confirmed the failure mechanism: capacity decays by reducing the amount of active material and by contributing to a charge-inhibiting mechanism called polysulfide shuttle. The formation of elemental sulfur is clearly visible in real time during the charge process beyond 2.3 V. The non-destructive in operando UV-vis study also showed the presence of characteristic absorption peaks evolving with cycling, demonstrating the accumulation of various polysulfide species, and the predominant formation of S4 2- and of S6 2- during discharge and charge, respectively. This finding implies that the charge and discharge reactions are not completely reversible and proceed along different pathways.