Date on Master's Thesis/Doctoral Dissertation

5-2019

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physics and Astronomy

Degree Program

Physics, PhD

Committee Chair

Sumanasekera, Gamini

Committee Co-Chair (if applicable)

Jayanthi, Chakram S.

Committee Member

Jayanthi, Chakram S.

Committee Member

Yu, Ming

Committee Member

Sunkara, Mahendra K.

Author's Keywords

lithium-sulfur; battery; li-s battery; lithium molybdate; titanium oxide; lithium

Abstract

Rechargeable energy storage systems play a vital role in today’s automobile industry with the emergence of electric vehicles (EVs). In order to meet the targets set by the department of energy (DOE), there is an immediate need of new battery chemistries with higher energy density than the current Li- ion technology. Lithium–sulfur (Li–S) batteries have attracted enormous attention in the energy-storage, due to their high specific energy density of 2600 Wh kg-1 and operational voltage of 2.0 V. Despite the promising electrochemical characteristics, Li-S batteries suffer from serious technical challenges such as dissolution of polysulfides Li2Sx (3 ≤ x ≤8) in the electrolyte and the shuttling of polysulfide between the sulfur cathode and the lithium metal anode hindering cycling efficiency and life. There is also an immediate need to replace lithium metal (as the anode in Li-S batteries) with a suitable material. To improve the cyclability of Li-S battery, a novel method is described using mesoporous TiO2 to prevent the loss of active material from the sulfur cathode. Herein, the surface adsorbance of TiO2 for lithium polysulfides is used to prevent the leaking of soluble polysulfides into the electrolyte. Hence, cyclability with high specific capacity is achieved. The mesoporous TiO2 (titania) coated carbon-sulfur cathodes exhibit a retention capacity of 980 mAhg-1 over 100 cycles at C/3 rate (433 mA g -1) vs lithium metal anode. Further, pre-lithiated α-MoO3 is investigated as a state-of-the art anode material for Li-S batteries. α-MoO3 demonstrates lithiation potential of ~0.2 V with a specific capacity of ~1000 mAh g-1. Herein, α-MoO3 are synthesized by two different techniques; direct synthesis by Hot Wire CVD (HWCVD) technique and 40% H2/Ar reduction of impure MoO3. The initial specific charge capacities of these material are found to be over 1000 mAh g-1. The α-MoO3 electrodes of different morphologies are then assembled with mesoporous TiO2 coated sulfur cathode to make S-Li1.33Mo0.66O2 full cell, achieving initial capacity of 905 mAh g-1 at C/10 rate and 635 mAh g-1 at C/3 rate. Finally, a novel cell design is demonstrated, allowing manufacture of high energy density lithium molybdate-sulfur batteries in one step process. In this dissertation, high energy density cathodes based on mesoporous titania coated sulfur and pre-lithiated anodes based on α-MoO3 are developed for Li-S batteries by analyzing their electrochemical properties. Finally, these electrode materials are used to manufacture commercially viable Li-S pouch cells with >300 Wh kg-1 energy density over 100 cycles as the outcome of this dissertation.

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