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Nolis, Gene M.,Adil, Abdullah,Yoo, Hyun Deog,Hu, Linhua,Bayliss, Ryan D.,Lapidus, Saul H.,Berkland, Lisa,Phillips, Patrick J.,Freeland, John W.,Kim, Chunjoong,Klie, Robert F.,Cabana, Jordi American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.8
<P>In this report, the feasibility of reversible Ca<SUP>2+</SUP> or Zn<SUP>2+</SUP> intercalation into a crystalline cubic spinel Mn<SUB>2</SUB>O<SUB>4</SUB> cathode has been investigated using electrochemical methods in an aqueous electrolyte. A combination of synchrotron XRD and XANES studies identified the partial structural transformation from a cubic to a tetragonally distorted spinel Mn<SUB>3</SUB>O<SUB>4</SUB>, accompanied by the reduction of Mn<SUP>4+</SUP> to Mn<SUP>3+</SUP> and Mn<SUP>2+</SUP> during discharge. TEM/EDX measurements confirmed that practically no Ca<SUP>2+</SUP> was inserted upon discharge. However, non-negligible amounts of Zn were detected after Mn<SUB>2</SUB>O<SUB>4</SUB> was reduced in the Zn<SUP>2+</SUP> electrolyte, but through the formation of secondary phases that, in some cases, appeared adjacent to the surface of a cathode particle. This report aims to identify bottlenecks in the application of manganese oxide cathodes paired with Ca or Zn metal anodes and to justify future efforts in designing prototype multivalent batteries.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2018/jpccck.2018.122.issue-8/acs.jpcc.7b12084/production/images/medium/jp-2017-12084c_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b12084'>ACS Electronic Supporting Info</A></P>
Kim, Chunjoong,Adil, Abdullah A.,Bayliss, Ryan D.,Kinnibrugh, Tiffany L.,Lapidus, Saul H.,Nolis, Gene M.,Freeland, John W.,Phillips, Patrick J.,Yi, Tanghong,Yoo, Hyun Deog,Kwon, Bob Jin,Yu, Young-Sang American Chemical Society 2018 Chemistry of materials Vol.30 No.5
<P>Oxides undergoing reversible electrochemical cycling of Mg<SUP>2+</SUP> ions would enable novel battery concepts beyond Li<SUP>+</SUP>, capable of storing large amounts of energy. However, materials showing this chemical reactivity are scarce. Suitable candidates require small particles to shorten transport lengths, together with chemically complex structures that promote cation mobility, such as spinel. These goals pose a challenge for materials chemists. Here, nanocrystals of spinel-type Mg<SUB>0.5</SUB>Mn<SUB>2.5</SUB>O<SUB>4</SUB> were prepared using colloidal synthesis, and their electrochemical activity is presented. Cycling in an aqueous Mg<SUP>2+</SUP> electrolyte led to a reversible transformation between a reduced spinel and an oxidized layered framework. This reaction involves large amounts of capacity because of the full oxidation to Mn<SUP>4+</SUP>, through the extraction of both Mg<SUP>2+</SUP> and, in the first cycle, Mn<SUP>2+</SUP> ions. Re-formation of the spinel upon reduction resulted in enrichment with Mg<SUP>2+</SUP>, indicating that its insertion is more favorable than that of Mn<SUP>2+</SUP>. Incorporation of water into the structure was not indispensable for the transformation, as revealed by experiments in non-aqueous electrolytes and infrared spectroscopy. The findings open the door for the use of similar nanocrystals in Mg batteries provided that electrolytes with suitable anodic stability are discovered, thereby identifying novel routes toward electrode materials for batteries with high energy.</P> [FIG OMISSION]</BR>