Beyond Lithium-ion: Reaction Mechanisms of Low-Cost Rechargeable Zinc/Manganese Dioxide and Lithium/Sulfur Batteries

Abstract

New rechargeable batteries beyond lithium-ion have attracted increasing interest due to their potential in commercializing various applications, including grid storage, electric vehicle (EV), etc. These new batteries hinge upon the respective storage/conversion mechanisms suitable for the particular application purposes. For instance, the stationary energy storage applications necessitate batteries to possess high cycling stability and, in some cases, high power densities, while high volumetric and gravimetric energy densities are critical for EV applications. Most importantly, all need to be cost competitive. Rechargeable zinc/manganese dioxide (Zn/MnO2) batteries are very promising for the stationary energy storage owing to their low cost, environmentally benign constituents, excellent safety, and relatively high energy density. Their usage, however, is largely hampered by the fast capacity fading. The complexity of the reactions has resulted in long-standing ambiguities of the capacity fading of Zn/MnO2 system. In this thesis, we find that both H+/Zn2+ intercalation and conversion reactions occur at different voltages in Zn/MnO2 and that the rapid capacity fading can clearly be ascribed to the rate-limiting and irreversible conversion reactions at a lower voltage. By limiting the irreversible conversion reactions, we successfully demonstrate ultrahigh power and long life that are superior to most of the reported zinc-ion batteries (ZIBs) or even some lithium-ion batteries (LIBs). As for the application of batteries in the EV market, lithium/sulfur (Li/S) batteries hold great promise as the next-generation energy battery. Their practical application, however, is hindered by the rapid capacity fading associated with the dissolution of lithium polysulfides (LiPSs) into the organic electrolytes. By anchoring thiol (-SH) functional groups to the nonpolar surface of a mesoporous carbon host, we successfully impede these losses. This new strategy increases the surface polarity of conductive carbons and traps LiPSs inside cathodes. By utilizing various spectroscopic methods, we investigate the mechanisms of LiPS trapping, which originate from the electrostatic and covalent interactions of the thiol functional groups with Li+ from the electrolyte and with S from the LiPS chains. The fundamental insight on the thiol functionality suggests a further rational design of multifunctional interfaces to achieve better Li/S performance.