Solid-state and intercalation chemistry of nickel-tellurate positive electrodes for lithium and sodium secondary batteries




Grundish, Nicholas Spencer

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Current cathode chemistries for lithium and sodium secondary batteries are pushing their theoretical limit. Materials exploration on novel structures and compositions is essential to discover new phenomena that can guide the design of next-generation cathodes for these systems. The phase chemistry of the alkali-ion nickel-tellurates has been largely unexplored, with only four materials being presented in the literature. Of these four materials, only three of them have been electrochemically characterized. In this dissertation, the solid-state and intercalation chemistry of the alkali-ion nickel-tellurates is explored further for lithium and sodium secondary batteries. The structural nuances of many of the synthesized materials required both bulk and localized techniques. X-ray diffraction paired with solid-state nuclear magnetic resonance spectroscopy were used to meet this requirement. Once the structure of each composition was fully understood, the electrochemical intercalation/deintercalation process was assessed to evaluate the relationship between the structure of the material and its electrochemical intercalation chemistry. The sodium nickel-tellurates could always be synthesized in the layered structure and showed promising structural features that led to the suppression of vacancy ordering in the interlayer space, and of the layered-layered phase transitions common in Na [subscript x] MO₂ layered oxides, leading to voltage-composition curves that are reminiscent of LiMO₂ layered oxides. The lithium nickel-tellurates in this work were more structurally diverse, but only a partially disordered rock salt phase could be synthesized directly via solid-state synthesis owing to the similarity in ionic radius between Li⁺ and Ni²⁺. To obtain layered nickel-tellurate structures with lithium, ion-exchange with the sodium analogue compositions was necessary; the ion-exchange procedure led to unusual site occupation for lithium in the layered structure motif. Among other factors, electrochemical performance of the lithium phases was always hindered by Ni²⁺ transfer to vacant lithium sites that blocked the diffusion pathway of lithium for the insertion/extraction process


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