Browsing by Subject "Anode materials"

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Li-ion and Na-ion battery anode materials and photoanodes for photochemistry
(2015-08) Dang, Hoang Xuan; Mullins, C. B.; Heller, Adam; Hwang, Gyeong S.; Fan, Donglei; Korgel, Brian A.
The current Li-ion technologies allow the popularity of Li-ion batteries as electrical energy storage for both mobile and stationary applications. The graphite-based anode is most commonly used in commercial Li-ion batteries. However, because lithium intercalation in graphite occurs very close to the redox potential of Li/Li+, accidental lithium plating is a known hazard capable of resulting in internal shorting, particularly when the battery is charged rapidly, requiring higher overpotentials to accomplish the Li-intercalation. Moreover, toward the next-generation battery, a growing interest is now on promising rechargeable Na-ion batteries. The main motivation for Na-ion alternative is that sodium is much more abundant and widely distributed on the earth’s crust than lithium. In the first part of this dissertation, we investigate safer, higher specific capacity anode materials for both Li-ion and Na-ion batteries. In a separated effort toward the efficient solar energy harvesting, the second part of the dissertation examines thin film photoanodes, active in the visible-light region, for photoelectrochemical water oxidation. This part also discusses in detail the synthesis, characterization, as well as the use of co-catalysts to improve the electrode’s photochemistry performance. The current Li-ion technologies allow the popularity of Li-ion batteries as electrical energy storage for both mobile and stationary applications. The graphite-based anode is most commonly used in commercial Li-ion batteries. However, because lithium intercalation in graphite occurs very close to the redox potential of Li/Li+, accidental lithium plating is a known hazard capable of resulting in internal shorting, particularly when the battery is charged rapidly, requiring higher overpotentials to accomplish the Li-intercalation. Moreover, toward the next-generation battery, a growing interest is now on promising rechargeable Na-ion batteries. The main motivation for Na-ion alternative is that sodium is much more abundant and widely distributed on the earth’s crust than lithium. In the first part of this dissertation, we investigate safer, higher specific capacity anode materials for both Li-ion and Na-ion batteries. In a separated effort toward the efficient solar energy harvesting, the second part of the dissertation examines thin film photoanodes, active in the visible-light region, for photoelectrochemical water oxidation. This part also discusses in detail the synthesis, characterization, as well as the use of co-catalysts to improve the electrode’s photochemistry performance.
A lithium conducting phase (Li₂Te) can obviate need for nanocrystallites in the lithiation/de-lithiation of Germanium
(2015-08) Powell, Emily Janette; Mullins, C. B.; Heller, Adam
Mainstream rechargeable lithium battery materials research of the past 20 years has focused on nano-particulate materials, where Li⁺-diffusion lengths exceeded at designated cycling rates the particle radii, and where the particles slipped rather than broke upon their expansion and shrinkage in lithiation/de-lithiation cycles. Here we show that in intrinsically rapidly Li⁺-transporting macrocrystalline germanium and even more so in a dispersion of non-cycling Li₂Te in macrocrystalline germanium it is unnecessary to use nanocrystalline materials and that Li₂Te increases the retained capacity at 1C rate after 500 cycles. Dispersions of 10-30 atom % of crystalline GeTe in 90-70 atom % crystalline Ge were synthesized by quenching from the melt followed by high energy ball milling to 1μm-5μm particle size. The particles, as well as similarly made and similarly sized pure Ge particles were incorporated in electrodes, which were galvanostatically lithiated/de-lithiated. In the initial cycle, GeTe is reduced to Li[subscript x]Ge alloys and Li₂Te. In 500 1C cycles of Li[subscript x]Ge de-lithiation/Ge lithiation the capacity of the pure Ge faded more rapidly than that of the Ge electrodes containing Li₂Te, which retained 94-96 % of their initial capacity after 500 cycles at 1C rate.