Non-woven carbon paper as current collector for Li-ion/Li2S system: Understanding of the first charge mechanism

Abstract

The use of porous 3D current collectors, especially carbon-based ones, has already been demonstrated as a concept of choice as alternative to standard 2D aluminium foil in sulfur positive electrodes. In this study, we investigated non-woven carbon (NwC) as a 3D current collector for Li2S positive electrodes. Improved charge and discharge capacities, and capacity retention were obtained, as compared with electrodes containing Al-foil current collector. However, irrespective of the current collector used, the initial charge presents a particular and weakly reproducible voltage shape. By applying GITT and XRD measurements an electrochemical mechanism was proposed to explain the initial charge profile, in terms of equilibrium potential and polarization phenomenon. During the 1st charge, competitive oxidation reactions can be evoked involving both Li2S and long polysulfide intermediates (Li2Sn), in the main part of the charge process. While the oxidation of Li2S is thermodynamically favorable over the oxidation of Li2Sn, the kinetics of the latter is much more rapid.