Study of sulfur-based electrodes by operando acoustic emission

Abstract

The mechanical degradation upon cycling of sulfur-based electrodes is investigated by operando acoustic emission (AE). The AE response of S-based electrodes using two different binders, polyvinylidene difluoride (PVdF) and carboxymethylcellulose (CMC), as well as two different current collectors, usual aluminum foil and porous non-woven carbon paper (CP), are compared. In all cases, AE signals are mainly detected during the 1st plateau of the 1st discharge, related to the initial dissolution of elemental sulfur into the electrolyte, causing a collapse of the electrode network. At the end of charge, the formation of micrometric sulfur on the surface of the electrode can be acoustically detected, in particular in the case of the CMC/Al formulation, where signals are also detected during subsequent cycles. This is believed to be a result of the good adhesion of CMC-based electrode to the current collector, which allows acoustic waves to propagate through the electrode to the AE sensor more easily. However, with CP current collector, no AE activity is detected upon charge, reflecting a lower mechanical stress attributed to a more homogeneous growth of the S particles in the electrode. It is also noted that inefficient electrode formulation/elaboration can be detected via AE, as AE signals are emitted at the end of the discharge when the cell polarizes more than usually observed. The use of CP as a current collector greatly improves the electrochemical performance of the cells, especially when combined with the better adhesion/cohesion strengths of CMC binder, reaching an initial capacity of 1180 mAh g−1 (∼4.5 mAh cm−2) stabilizing around 860 mAh g−1 after 50 cycles.