Date of Completion

9-25-2019

Embargo Period

9-24-2020

Keywords

Battery, Supercapacitor, Manganese oxides, Transition metal sulfides, Porous

Major Advisor

Dr. Steven L. Suib

Associate Advisor

Dr. James Rusling

Associate Advisor

Dr. S. Pamir Alpay

Associate Advisor

Dr. Mark Aindow

Associate Advisor

Dr. Alfredo Angeles-Boza

Field of Study

Materials Science

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

Lithium ion batteries have predominated the market of energy storage since 1990 due to their large energy density, high discharging plateau, and good cyclability. However, the safety issues caused by the flammable organic electrolyte used in lithium ion batteries limits the battery market and customers. The solution to the flammable electrolyte problem is to focus on aqueous energy storage systems. Two storage systems which have attracted the most attention are aqueous supercapacitors and aqueous batteries.

Porous metal chalcogenides are the best electrode candidates in aqueous supercapacitors and batteries since they possess rich active sites, high surface area, large pore volume, simple synthetic methods, and low cost. Mesoporous metal sulfides exhibit better performance than metal oxides in supercapacitors due to better electronic conductivity. Binary metal sulfides such as meso-NiCo2S4 have enhanced electron transfer between the two metals and exhibit high capacity (1350 F g-1 at 10 A g-1), as well as stable cyclability (70.3% capacity retention after 10,000 cycles).

For aqueous battery systems, zinc-ion batteries (ZIBs) are the most promising candidates since they have a high anodic storage limit of 819 mAh g-1. Studies on ZIB cathodes have focused on tunneled manganese oxides with cation-host structures. Manganese dioxides with large tunnels allow fast Zn2+/H+diffusion during cycling resulting in high capacity at the beginning. But the structures change rapidly and lead to capacity fading. Manganese dioxides with small tunnels have low capacity limited by small tunnel sizes. Although manganese dioxides with middle tunnel sizes exhibit the best ZIB performance, the structure is still not stable during cycling. Our studies prove that amorphous manganese oxides can convert to the active and stable ZnMn2O4 phase with better ZIB performance than tunneled manganese dioxides.

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