Session 2C — Symposium: “Electrochemical Energy Storage and Sustainability”

Organizers: S Sampath (IISc, Bengaluru) and K Vijayamohanan Pillai (IISER, Tirupati)

Stress-induced degradation of electrode materials in alkali metal-ion batteries View Presentation

Electrode materialsfor alkali metal-ion cells (such as Li-ion, Na-ion, K-ion battery systems) undergo a host of changes, such as phase transformations, structural transformations and dimensional changes during electrochemical insertion/removal of the corresponding alkali metal-ions; which, in turn, lead to stress development and concomitant mechanical degradation of the electrodes. Furthermore, irreversible reactions at the electrode/electrolyte interfaces also cause modifications to such interfaces, especially by way of formation of an additional layer that is commonly known as solid electrolyte interface (SEI). Such changes and degradations of the electrode materials and interfaces, which take place during electrochemical cycling, influence the electrochemical behavior and performances; in particular, the reversible capacity that can be practically obtained, the cyclic stability, cell impedance and voltage hysteresis. In fact, the above aspects turn out to be some of the major bottlenecks towards further enhancing the energy density and improving the safety aspects of the Li-ion battery system. There have been various attempts to understand the electrode stresses via post-cycling observations and/or mathematical modelling. However, evaluating and fully understanding the electro-chemo-structural-mechanical aspects via ex-situ experiments is neither truly feasible, nor reliable, because the stress states depend critically on the state-of-charge, electrochemical potential and surroundings of the concerned electrodes. Thus, in-situ experiments are needed for evaluating/understanding them more thoroughly; and eventually addressing them in a systematic manner and in comprehensive terms. In the above contexts, after a more generic introduction to the degradation/aging mechanisms in alkali metal-ion batteries, with particular emphasis on stress-induced degradations, the talk will highlight some of the important inferences gained fromour works related to real-time/operando monitoring of stress developments and phase transformations in electrode materials during electrochemical cycling. Important insights into the effects ofphase/structural transformations, presence of ‘buffer’ interlayers and SEI layer formation towards the deformation and stress development will be discussed, with reference toalloying-reaction based (Si, Sn), as well as intercalation-based (LiCoO2, graphenic carbon) electrode materials.