In Situ/ Operando Methods of Characterizing All-Solid-State Li-Ion Batteries: Understanding Li-Ion Transport during Cycle

Clean energy is an utmost need for the betterment of society. Li-ion batteries (LIBs) have been the clean-energy choice for several decades. However, with the increasing demand for batteries with high specific energy, the current state-of-the-art LIB technology is becoming unsatisfactory because of the capacity fade and low potential window encountered when using liquid-based electrolytes. Conversely, solid Li-ion conductors are capable of widening the cell-potential window and adding safety features to the LIB system. Nevertheless, the development of all-solid-state batteries (ASSBs) faces several challenges, starting from ion transport through solid components to interface reactions, leading to increased cell resistance. The current review focuses on the use of in situ/operando techniques to explore such challenges in ASSBs. X-ray and neutron diffraction techniques can be used to evaluate the phase evolution and impurity formation in solid Li-ion conductors. Energy-dispersive X-rays can provide information about intermittent products during the battery cycle. Imaging techniques can provide direct visualization of changes that occur in cell components during cycles. Operando techniques are further discussed to estimate the residual gas evolution in such ASSBs. Overall, this review discusses the cause of cell death and capacity fade in ASSBs.