Design of Electroactive Materials and Mechanistic Investigations of Metal (Li, Na, Mg)-Sulfur Batteries

Abstract

The thesis entitled “Design of Electroactive Materials and Mechanistic Investigations of Metal (Li, Na, Mg)-Sulfur Batteries’’ deliberates on some of the important issues impeding the progress of metal sulfur battery (Li/S, Na/S, Mg/S) and discusses possible materials design as well as alternative cell configuration strategies to alleviate them. The major factor hindering the practical applications of metal sulfur battery is the dissolution of intermediate polysulfides into the ether-based electrolyte during the battery cycling. The present thesis discusses in detail the usage of conductive additive in sulfur cathode as one of the important strategies for the confinement of intermediate polysulfides at the S-cathode. This chemical design strategy is highly effective for both Na/S and Li/S batteries. Apart from the polysulfides dissolution, volume expansion and safety concerns are the other challenges in practical applications of metal sulfur battery. To alleviate such issues, an alternative cell configuration has been proposed. Instead of the sulfur element cathode, fully expanded state of polysulfides viz. lithium sulfide (final discharge product of S8  Li2S) is used as the cathode and lithium metal is replaced by lithiated anatase TiO2. The various stages of redox reaction occurring in the metal-sulfur battery have been extensively investigated using various operando and ex-situ spectroscopic techniques. Apart from the design strategy of the S-cathode, the present thesis also discusses the major challenges associated with electrolyte in bivalent metal sulfur battery system viz. the Mg/S system. Majority of the literature reports the Mg/S battery performance with TEGDME and THF solvent-based electrolyte. However, the persistent concern regarding the lower current density and poor cyclability of TEGDME and higher volatility of THF put Mg/S on the backfoot for practical applications. The present thesis discusses a new class of electrolyte using 1,3-Dioxalane (DOL)/1,2-Dimethoxyethane (DME) binary solvent in Mg/S battery. Like Li/S and Na/S battery system, various intermediate polysulfides formation take place in the Mg/S system as well. The present thesis discusses in detail the polysulfide confinement mechanism in the Mg/S system using operando and ex-situ spectroscopic techniques.