Cathode Electrolyte Interface Studies of Li-S batteries.

FRANCISCO J. GARCIA-SORIANO; VICTORIA BRACAMONTE; GERMAN LENER; CEPPI, S. A.; GUILLERMINA LUQUE; G. STUTZ

Jeju

Congreso; 72º Annual International Society of Electrochemistry Meeting; 2021

Among the many potential energy storage systems, lithium-sulfur batteries are one of the most attractive due to their high theoretical specific capacity and energy (with lithium), of 1672 mAh g-1 and 2600 W h kg-1, respectively[1]. In addition, sulfur is abundant on the earth-crust, non-toxic, and relatively cheap. However, the widespread application of these batteries is challenged by some problems associated with this system such as: the insulating nature of sulfur and Li2S, the volumetric expansion of the cathode during lithiation, and the migration of intermediate products (Li2Sn, n ≥ 4) to the anodic side of the cell, resulting in the so-called shuttle effect. Despite the great advances that have been achieved, including long-term cyclabilities, high active material utilization, and high sulfur loading, the overall understanding of the system[2] is still limited specially the functioning of the cathode electrolyte interface (CEI). In this work, sulfur mixed with super P carbon black was used as cathode for lithium-sulfur batteries. Also, to promote the formation of S-O species, 2 wt% of a natural clay was added to the cathode. Sulfur K-edge X-ray XANES spectra were collected in total electron yield mode on SXS (XAS) beamline in the Laboratorio Nacional de Luz Sincrotron (LNLS). Furthermore, S2p X-ray photoelectron spectroscopy (XPS) were performed on both modified and unmodified cathodes in fully lithiated and delithiated states at cycles 3th and 20th. The S2p and XANES spectra showed that the clay promotes the formation of COSO2-/SO32- species on the cathode surface. These species can help to immobilize sulfur atoms and therefore serve as mediators to retain and confine polysulfides in the cathode[3]. Depth-profiling XPS analysis were also measured, these experiments revealed that the formation of S-O species are mostly limited to the cathode surface. Electrochemical studies of ciclability were carried out for both cathodes, showing that the modified cathode has a grater specific capacity and Coulombic efficiencies. In this manner, through a simple modification we systematically investigated the influence of S-O species on the formation process of the CEI layer on sulfur cathode by X-ray experiments.