Origin of unusual spinel-to-layered phase transformation by crystal water. Issue 2 (8th November 2017)

• Record Type: Journal Article
• Authors: Yang, Eunjeong; Kim, Heejin; Kim, Sangryun; Kim, In; Kim, Jaehoon; Ji, Hyunjun; Choi, Jang Wook; Jung, Yousung
• Is Part Of: Chemical science. Volume 9:Issue 2(2018)
• Page Start: 433
• Page End: 438
• Publication Date: 2017-11-08
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c7sc04114d
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Crystal water mediated phase transition: the underlying thermodynamic and kinetic role of crystal water is investigated using ab initio calculations. 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 Mn3 O4 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.