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Origin of unusual spinel-to-layered phase transformation by crystal water.


ABSTRACT: It is well known that many layered transition metal oxides can transform into a spinel structure upon repeated battery cycling, but a phase transition in the opposite direction is rare. Recently, the transformation from spinel Mn3O4 to layered MnO2 was observed during the operation of a Mg battery in aqueous conditions, resulting in high performance Mg batteries. We hereby use ab initio calculations to unveil the mechanism by which crystal water plays a critical role in this unique transformation. Once inserted into the spinel form, a water molecule donates an electron, offering a key structural and thermodynamic driving force to initiate the transformation process. These crystal water molecules then get favorably clustered into a planar form in the layered structure and act as a stabilizing agent for birnessite. Kinetically, the inserted crystal water dramatically promotes the necessary rearrangement of Mn during the transition by lowering the activation barrier by >2 eV. The present structural, thermodynamic and kinetic understanding of the crystal water-driven phase transition provides novel insights to further the design of related low dimensional hydrated materials for multi-valent cathodes.

SUBMITTER: Yang E 

PROVIDER: S-EPMC5868318 | biostudies-other | 2018 Jan

REPOSITORIES: biostudies-other

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Origin of unusual spinel-to-layered phase transformation by crystal water.

Yang Eunjeong E   Kim Heejin H   Kim Sangryun S   Kim In I   Kim Jaehoon J   Ji Hyunjun H   Choi Jang Wook JW   Jung Yousung Y  

Chemical science 20171024 2


It is well known that many layered transition metal oxides can transform into a spinel structure upon repeated battery cycling, but a phase transition in the opposite direction is rare. Recently, the transformation from spinel Mn<sub>3</sub>O<sub>4</sub> to layered MnO<sub>2</sub> was observed during the operation of a Mg battery in aqueous conditions, resulting in high performance Mg batteries. We hereby use <i>ab initio</i> calculations to unveil the mechanism by which crystal water plays a cr  ...[more]

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