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Choi, Ji Ung,Park, Yun Ji,Jo, Jae Hyeon,Kuo, Liang-Yin,Kaghazchi, Payam,Myung, Seung-Taek American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.48
<P>Layered Na<SUB>2/3</SUB>MnO<SUB>2</SUB> suffers from capacity loss due to Jahn-Teller (J-T) distortion by Mn<SUP>3+</SUP> ions. Herein, density functional theory calculations suggest Na<SUB>2/3</SUB>[Fe<SUB><I>x</I></SUB>Mn<SUB>1-<I>x</I></SUB>]O<SUB>2</SUB> suppresses the J-T effect. The Fe substitution results in a decreased oxygen-metal-oxygen length, leading to decreases in the <I>b</I> and <I>c</I> lattice parameters but an increase in the <I>a</I> lattice constant. As a result, the capacity retention and rate capability are enhanced with an additional redox pair associated with Fe<SUP>4+/3+</SUP>. Finally, the thermal properties are improved, with the Fe substitution delaying the exothermic reaction and reducing exothermic heat.</P> [FIG OMISSION]</BR>
Kim, Heejin,Kim, Dong Jun,Seo, Dong-Hwa,Yeom, Min Sun,Kang, Kisuk,Kim, Do Kyung,Jung, Yousung American ChemicalSociety 2012 Chemistry of materials Vol.24 No.6
<P>The Na0.44MnO2 structure is a promising cathode material for sodium ion batteries due to a high capacity (similar to 130 mAh/g) and good cycle performance. In this work, we present the results of density functional theory (DFT) calculations on the structural and electrochemical properties of Na0.44MnO2, combined with experiments. Seven intermediate phases and the two-phase reactions among them were found, where the calculated voltage profile agreed well with experiments. We found that the S-shaped tunnel is not empty in the deintercalated Na0.22MnO2 structure but has a partial occupancy of sodium ions. The new sodium sites were found in a limited sodium composition range (x = 0.44-0.55) which is attributed to the electrostatic interactions between sodium ions and manganese atoms. The asymmetric lattice evolution in Na0.44MnO2 as a function of sodium insertion/deinsertion is shown to be due to the Jahn-Teller effects. On the basis of this interpretation, we suggest that the Cr substitution will reduce the volume change significantly.</P>
Lee, Hyun-Wook,Muralidharan, P.,Ruffo, Riccardo,Mari, Claudio M.,Cui, Yi,Kim, Do Kyung American Chemical Society 2010 NANO LETTERS Vol.10 No.10
<P>Ultrathin LiMn<SUB>2</SUB>O<SUB>4</SUB> nanowires with cubic spinel structure were synthesized by using a solvothermal reaction to produce α-MnO<SUB>2</SUB> nanowire followed by solid-state lithiation. LiMn<SUB>2</SUB>O<SUB>4</SUB> nanowires have diameters less than 10 nm and lengths of several micrometers. Galvanostatic battery testing showed that LiMn<SUB>2</SUB>O<SUB>4</SUB> nanowires deliver 100 and 78 mAh/g at very high rate (60C and 150C, respectively) in a larger potential window with very good capacity retention and outstanding structural stability. Such performances are due to both the favorable morphology and the high crystallinity of nanowires.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-10/nl101047f/production/images/medium/nl-2010-01047f_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl101047f'>ACS Electronic Supporting Info</A></P>