Document Type

Dissertation - Open Access

Award Date

2020

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering and Computer Science

First Advisor

Yue Zhou

Keywords

dendrite-free Li deposition, lithium metal battery, lithium metal surface modification, Lithium-ion battery, solid electrolyte interphase, tungsten trioxide

Abstract

The graphite-based anode material has a low theoretical specific capacity of 371 mAh g-1. The transitional metal oxides (TMOs) are considered a better choice owing to their relatively higher specific capacity. Among TMOs, tungsten trioxide (WO3) is considered promising due to a higher specific capacity of 693 mAh g-1, low cost, mechanically stable, and eco-friendly. It has been a challenge to utilize the TMOs as anode materials as they suffer from poor electronic conductivity and large electrode volume expansion during discharge/charge cycles. In our first project, we demonstrate a unique self-recovery of capacity in reduced WO3 by the incorporation of urea followed by annealing at 500 °C under the N2 environment. The reduced WO3 exhibited a unique cycling phenomenon, where the capacity was significantly self-recovered after an initial sharp decrease. This can be attributed to the activation of oxygen vacancy sites or defects, making the WO3 electrode more electrochemically active with cycling. In our second and third projects, we modify the surface of lithium metal to utilize them as anode because LIBs are approaching their theoretical energy density limit. Lithium metal anodes are expected to drive practical applications that require high energy-density storage. However, the direct use of metallic lithium causes safety concerns, low rate capabilities, and poor cycling performances due to unstable solid electrolyte interphase (SEI) and undesired lithium dendrite growth. To address these issues, in our second project, radio frequency (R-F) sputtered graphite-SiO2 ultrathin bilayer on a Li metal chips was demonstrated, for the first time, as an effective solid-electrolyte interface (SEI) layer. In the third project, we developed a facile, costeffective, and one-step approach to generate an artificial lithium metal/electrolyte interphase by treating lithium anode with an electrolyte containing tin fluoride. The development of artificial SEI on top of lithium metal anode led to a dendrite free uniform Li deposition to achieve a stable voltage profile and outstanding long hours plating/stripping compared to the bare Li. The generated SEI not only ensures fast lithiumion diffusion and suppression of lithium dendrite growth but also brings a synergistic effect of storing lithium via a reversible silicon-lithium or tin-lithium alloy formation and lithium plating.

Format

application/pdf

Number of Pages

144

Publisher

South Dakota State University

Rights

In Copyright - Educational Use Permitted
http://rightsstatements.org/vocab/InC-EDU/1.0/

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