Browsing by Author "Outka, A"

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    Mechanochemically enabled metastable niobium tungsten oxides
    (American Chemical Society, 2024-04-08) Raji-Adefila, B; Wang, Y; Ding, Y; Avdeev, M; Outka, A; Gonzales, H; Engelstad, K; Sainio, S; Nordlund, D; Kan, WH; Zhou, S; Chen, DC
    Metastable compounds have greatly expanded the synthesizable compositions of solid-state materials and have attracted enormous amounts of attention in recent years. Especially, mechanochemically enabled metastable materials synthesis has been very successful in realizing cation-disordered materials with highly simple crystal structures, such as rock salts. Application of the same strategy for other structural types, especially for non-close-packed structures, is peculiarly underexplored. Niobium tungsten oxides (NbWOs), a class of materials that have been under the spotlight because of their diverse structural varieties and promising electrochemical and thermoelectric properties, are ideally suited to fill such a knowledge gap. In this work, we develop a new series of metastable NbWOs and realize one with a fully cation-disordered structure. Furthermore, we find that metastable NbWOs transform to a cation-disordered cubic structure when applied as a Li-ion battery anode, highlighting an intriguing non-close-packed-close-packed conversion process, as evidenced in various physicochemical characterizations, in terms of diffraction, electronic, and vibrational structures. Finally, by comparing the cation-disordered NbWO with other trending cation-disordered oxides, we raise a few key structural features for cation disorder and suggest a few possible research opportunities for this field. © 2024 American Chemical Society.
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    Over‐stoichiometric metastabilization of cation‐disordered rock salts
    (Wiley, 2023-12-21) Wang, Y; Outka, A; Takele, WM; Avdeev, M; Sainio, S; Liu, R; Kee, V; Choe, W; Raji‐Adefila, B; Nordlund, D; Zhou, S; Kan, WH; Habteyes, TG; Chen, DC
    Cation‐disordered rock salts (DRXs) are well known for their potential to realize the goal of achieving scalable Ni‐ and Co‐free high‐energy‐density Li‐ion batteries. Unlike in most cathode materials, the disordered cation distribution may lead to more factors that control the electrochemistry of DRXs. An important variable that is not emphasized by research community is regarding whether a DRX exists in a more thermodynamically stable form or a more metastable form. Moreover, within the scope of metastable DRXs, over‐stoichiometric DRXs, which allow relaxation of the site balance constraint of a rock salt structure, are particularly underexplored. In this work, these findings are reported in locating a generally applicable approach to “metastabilize” thermodynamically stable Mn‐based DRXs to metastable ones by introducing Li over‐stoichiometry. The over‐stoichiometric metastabilization greatly stimulates more redox activities, enables better reversibility of Li deintercalation/intercalation, and changes the energy storage mechanism. The metastabilized DRXs can be transformed back to the thermodynamically stable form, which also reverts the electrochemical properties, further contrasting the two categories of DRXs. This work enriches the structural and compositional space of DRX families and adds new pathways for rationally tuning the properties of DRX cathodes. © 1999-2024 John Wiley & Sons, Inc or related companies.