UCLA

Lithium-ion batteries are essential energy storage devices for modern-day technology and for creating a more sustainable future. One limitation is the energy density. This dissertation describes materials to increase the energy density of batteries, design principles to encourage reversibility, and examines how the structure changes with lithiation and delithiation. The first part focuses on nanoporous tin antimonide (NP-SbSn) as an anode material. NP-SbSn performs well with only 1% capacity fade after 100 cycles. To make structure-property relationships, we use a combination of transmission x-ray microscopy (TXM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). We compare these results with previous results on nanoporous tin to show that the use of an intermetallic stabilizes the structure and discover that the mechanism of lithiation involves amorphization, unlike bulk SbSn. Because of the increased stability of SbSn vs Sn, NP-SbSn is cycled with sodium, a harder material to cycle with. There is more structural degradation, but we obtain 85% capacity retention of after 100 cycles, To increase structural stability, a surface coating of aluminum oxide was added resulting in less structural damage under sodiation when compared to uncoated NP-SbSn. The second part of the dissertation focuses on nanoporous antimony (NP-Sb). NP-Sb is used to study the effects of non-crystalline intermediates when cycling because we observed amorphization during lithiation of NP-SbSn. Unusually, Sb cycles similarly with sodium as with lithium. When cycled against lithium, NP-Sb has crystalline intermediates and amorphous intermediates, when cycled against sodium. Through XRD and TXM, we show how crystalline changes can have large effects on macro- and meso-scale structure. Also, we reveal synergistic effects when amorphous intermediates are combined with mesoporosity. Lastly, we synthesize novel, icosahedral boron clusters as a cathode material through solid-state methods, atypical for boron cluster syntheses. These clusters are cross-linked with disulfides, resulting in redox active sulfur and clusters. The cluster’s role is two-fold: the cross-linked nature prevents sulfur dissolution and provide capacity. We observe solid-state redox of the cluster, for the first time, and sulfur with reversible cycling. Cluster and sulfur redox are confirmed with operando Raman spectroscopy.