Browsing by Author "Ojwang, DO"

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    Influence of synthesis routes on the crystallography, morphology, and electrochemistry of Li2MnO3
    (American Chemical Society, 2020-02-05) Menon, AS; Ojwang, DO; Wilhammar, T; Peterson, VK; Edström, K; Gomez, CP; Brant, WR
    With the potential of delivering reversible capacities of up to 300 mAh/g, Li-rich transition-metal oxides hold great promise as cathode materials for future Li-ion batteries. However, a cohesive synthesis–structure–electrochemistry relationship is still lacking for these materials, which impedes progress in the field. This work investigates how and why different synthesis routes, specifically solid-state and modified Pechini sol–gel methods, affect the properties of Li2MnO3, a compositionally simple member of this material system. Through a comprehensive investigation of the synthesis mechanism along with crystallographic, morphological, and electrochemical characterization, the effects of different synthesis routes were found to predominantly influence the degree of stacking faults and particle morphology. That is, the modified Pechini method produced isotropic spherical particles with approximately 57% faulting and the solid-state samples possessed heterogeneous morphology with approximately 43% faulting probability. Inevitably, these differences lead to variations in electrochemical performance. This study accentuates the importance of understanding how synthesis affects the electrochemistry of these materials, which is critical considering the crystallographic and electrochemical complexities of the class of materials more generally. The methodology employed here is extendable to studying synthesis–property relationships of other compositionally complex Li-rich layered oxide systems. © 2020 American Chemical Society
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    Synthetic pathway determines the nonequilibrium crystallography of Li- and Mn-rich layered oxide cathode materials
    (American Chemical Society, 2021-02-10) Menon, AS; Ulusoy, S; Ojwang, DO; Riekehr, L; Didier, C; Peterson, VK; Salazar-Alvarez, G; Svedlindh, P; Edström, K; Gomez, CP; Brant, WR
    Li- and Mn-rich layered oxides show significant promise as electrode materials for future Li-ion batteries. However, an accurate description of its crystallography remains elusive, with both single-phase solid solution and multiphase structures being proposed for high performing materials such as Li1.2Mn0.54Ni0.13Co0.13O2. Herein, we report the synthesis of single- and multiphase variants of this material through sol–gel and solid-state methods, respectively, and demonstrate that its crystallography is a direct consequence of the synthetic route and not necessarily an inherent property of the composition, as previously argued. This was accomplished via complementary techniques that probe the bulk and local structure followed by in situ methods to map the synthetic progression. As the electrochemical performance and anionic redox behavior are often rationalized on the basis of the presumed crystal structure, clarifying the structural ambiguities is an important step toward harnessing its potential as an electrode material. Copyright © 2021 The Authors. Published by American Chemical Society.