LAUSR

Diffusion process at the electrode/electrolyte interphase drives the performances of the lithium-sulfur battery, and activated carbon (AC) can remarkably vehicle ions and polysulfide species throughout the two-side liquid/solid region of the interphase. We reveal original findings such as the values of the diffusion coefficient at various states of charge of the Li-S battery using a highly-porous AC, its notable dependence on the adopted techniques, and the correlation of the diffusion trend with the reaction mechanism. X-ray photoelectron spectroscopy (XPS) and X-ray energy dispersive spectroscopy (EDS) identify in the carbon derived from bio-residues heteroatoms such as N, S, O and P which can increase the polarity of the C framework. The transport properties are achieved by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT). The study reveals Li+-diffusion coefficient (DLi+) depending on the technique, and values correlated with the cell state of the charge. EIS, CV and GITT show DLi+ within 10-7-10-8 cm2 s-1, 10-8-10-9 cm2 s-1, and 10-6-10-12 cm2 s-1, respectively, dropping down at the fully discharged state and rising up upon charge. GITT allows the evaluation of DLi+ during the process and evidences the formation of lowly conducting media upon discharge. The sulfur composite delivers in Li-cell a specific capacity ranging from 1300 mAh g-1 at 0.1C to 700 mAh g-1 at 2C with S loading of 2 mg cm-2, and from 1000 to 800 mAh g-1 at 0.2C when S loading is raised to 6 mg cm-2.