First Principle characterization and experimental validation of the Solid-Solid Interface in a Novel Organosulfur Cathode for Li-S Battery.

Organosulfur silanes grafted on aluminium current collector have been proposed and demonstrated to function as a sulfur source in cathode for a lithium sulfur battery. Bis[3-(triethoxysilyl) propyl] disulfide silane (TESPD) and Bis[3-(triethoxysilyl) propyl] tetrasulfide silane (TESPT) are typical examples of organosulfur complexes used for the study. These organosulfur silanes act as an insulator. Formation of polysulfides (LiS) which is a major bottleneck in the case of elemental sulfur can be eliminated using this novel cathode. In the absence of charge-carrying polysulfide species, the role of insulating TESPD/TESPT in the charge conduction pathway is an open question. Insight into the interface between the aluminium current collector and grafted TESPD/TESPT at an atomic level is a prerequisite for addressing the charge conduction pathway. The systematic theoretical methodology is developed based on electronic structure calculations and ab-initio molecular dynamics simulations to propose the realistic cathode model for Li-S battery. A cluster model is developed to predict the reduction potentials of TESPD/TESPT discloses the reduction reaction with Li resulting in the intramolecular S-S bond breaking which is validated by experimental cyclic voltametry measurements. The realistic interface model between aluminium current collector and TESPD/TESPT is also proposed to mimic the experimental conditions where Al surface was exposed to O and HO. The top few layers of Al is transformed into α-AlO and covered with HO molecules in the vicinity of grafted TESPD/TESPT. The structural models are further validated by comparing simulated S-2p binding energies with experimental X-ray photoelectron spectroscopy studies.