Access Type

Open Access Dissertation

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemical Engineering and Materials Science

First Advisor

Simon Ng

Second Advisor

Steven O. Salley

Abstract

Ni nanoparticles has been investigated as a carbon-free cathode material for dissolved polysulfide Li-S battery. A series of Ni nanoparticles with nominal particle size of 20, 40, and 100 nm have been used as electrocatalysts, and the effect of particle size on Li-S battery performance has been investigated. In addition, graphene has been chosen as a support to anchor the Ni nanoparticles, and the synergetic effect of carbon material and Ni nanoparticles on Li-S battery electrochemical performance has been studied. The results indicated there is a strong particle size effect. Ni/graphene electrode exhibits a capacity of 753 mAh g-1 sulfur after 40 cycles due to its high conductivity and electrocatalytic activity toward polysulfide reduction reaction. This capacity is significantly higher than similar studies.

Based on the understanding of the electrocathalytic effect of Ni and capacity fading mechanism, transition metal nitrides has been investigated as a new class of cathode materials. Titanium nitride (TiN) nanoparticle was studied as a novel cathode material for Li/dissolved polysulfide batteries. In addition, X-ray photoelectron spectroscopy (XPS) analysis was used to obtain a deeper understanding of the mechanism underlying polysulfide conversion reactions with TiN cathode, and during charge and discharge processes. TiN exhibited a superior performance in a Li/dissolved polysulfide battery configuration.

Knowing the superior performance of TiN, the study was expanded to different transition metal nitrides to investigate the role of surface composition and morphology in enhancing the electrochemical performance of Li-S batteries. WN, Mo2N, and VN were synthesized and the electrochemical performance, surface composition, and oxidation/reduction mechanism of these cathodes electrodes were studied for lithium sulfur batteries.

Understanding the fading mechanisms of dissolved polysulfide system for metal nitride cathodes, It was tried to enhance Li-S battery cycling stability. The effect of TiN nanotube size and length on cyclability of Li-S battery has been studied. A series of TiN nanotube with the average nanotube size of 20, 50, and 80 nm were growth and synthesized on Ti foil using anodization method. The electrochemical performance and capacity retention of these nanotubes with different length were studied.

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