Date of Award

2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering

Department

Chemical Engineering

First Advisor

Arijit Bose

Abstract

Lithium ion batteries (LIBs) with high power and energy density are desirable for use in portable electronics and electric vehicles. Silicon (Si) and tin (Sn) are among the most promising candidates for LIB anodes owing to their high theoretical specific capacity. However, both Si and Sn suffer from a dramatic volume change during lithiation/delithiation. Extensive efforts have been made using nanostructures to overcome this issue and improve the electrochemical performance of Si and Sn anodes. Carbon black (CB) is usually added to either electrode in LIBs to provide electrical conductivity. Because CB does not contribute to capacity, minimizing its use can lower the mass of battery to further increase the energy density. Due to the high aspect ratio and excellent electrical conductivity, sheet-like material reduced graphene oxide (RGO) is able to form a conducting network at much lower volume fractions than CB based on the percolation theory.

In this work, Si and Sn based anodes were prepared respectively using an emulsiontemplating strategy where active material nanoparticles were confined in the oil phase of the formed emulsions. CB stabilized these emulsions and formed a conductive network. We reduced the total carbon loading of Si anode by replacing a small amount of CB with RGO. In Si anode with a lower total carbon content, the formation of a conducting network consisting of CB and RGO contributed to a good cycle performance, which is comparable to the anode with double carbon loading but no RGO. We also studied the influence of the oil on the structure and electrochemical behavior of emulsion-templated Sn based anode. Density and vapor pressure of the oils affected the creaming and drying rates of the emulsions, which in turn affected the structures of dried emulsions and anode performance. Emulsion droplet size also had an impact on the drying process. Sn anode prepared with hexadecane that had a smaller density than water and a low vapor pressure along with smaller oil droplet showed the highest capacity and capacity retention which were attributed to the smooth and dense morphology with no cracking. Aqueous suspensions of CB and mixtures of CB and RGO were also examined. It was found that the concentrations of CB and pH conditions played major roles in determining the rheological properties and microstructures of the suspensions. The combinations of optical microscopy, cryogenic and conventional scanning electron microscopy, transmission electron microscopy were used to characterize the structures of fresh emulsions, dried emulsions (anodes) and suspensions throughout this dissertation.

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