Single Nanorod Devices for Battery Diagnostics: A Case Study on LiMn₂O₄

Yang, Yuan,Xie, Chong,Ruffo, Riccardo,Peng, Hailin,Kim, Do Kyung,Cui, Yi American Chemical Society 2009 NANO LETTERS Vol.9 No.12

<P>This paper presents single nanostructure devices as a powerful new diagnostic tool for batteries with LiMn<SUB>2</SUB>O<SUB>4</SUB> nanorod materials as an example. LiMn<SUB>2</SUB>O<SUB>4</SUB> and Al-doped LiMn<SUB>2</SUB>O<SUB>4</SUB> nanorods were synthesized by a two-step method that combines hydrothermal synthesis of β-MnO<SUB>2</SUB> nanorods and a solid state reaction to convert them to LiMn<SUB>2</SUB>O<SUB>4</SUB> nanorods. λ-MnO<SUB>2</SUB> nanorods were also prepared by acid treatment of LiMn<SUB>2</SUB>O<SUB>4</SUB> nanorods. The effect of electrolyte etching on these LiMn<SUB>2</SUB>O<SUB>4</SUB>-related nanorods is investigated by both SEM and single-nanorod transport measurement, and this is the first time that the transport properties of this material have been studied at the level of an individual single-crystalline particle. Experiments show that Al dopants reduce the dissolution of Mn<SUP>3+</SUP> ions significantly and make the LiAl<SUB>0.1</SUB>Mn<SUB>1.9</SUB>O<SUB>4</SUB> nanorods much more stable than LiMn<SUB>2</SUB>O<SUB>4</SUB> against electrolyte etching, which is reflected by the magnification of both size shrinkage and conductance decrease. These results correlate well with the better cycling performance of Al-doped LiMn<SUB>2</SUB>O<SUB>4</SUB> in our Li-ion battery tests: LiAl<SUB>0.1</SUB>Mn<SUB>1.9</SUB>O<SUB>4</SUB> nanorods achieve 96% capacity retention after 100 cycles at 1C rate at room temperature, and 80% at 60 °C, whereas LiMn<SUB>2</SUB>O<SUB>4</SUB> shows worse retention of 91% at room temperature, and 69% at 60 °C. Moreover, temperature-dependent <I>I</I>−<I>V</I> measurements indicate that the sharp electronic resistance increase due to charge ordering transition at 290 K does not appear in our LiMn<SUB>2</SUB>O<SUB>4</SUB> nanorod samples, suggesting good battery performance at low temperature.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2009/nalefd.2009.9.issue-12/nl902315u/production/images/medium/nl-2009-02315u_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl902315u'>ACS Electronic Supporting Info</A></P>

Ultrathin Spinel LiMn₂O₄ Nanowires as High Power Cathode Materials for Li-Ion Batteries

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>

Manganese-cobalt hexacyanoferrate cathodes for sodium-ion batteries

Pasta, Mauro,Wang, Richard Y.,Ruffo, Riccardo,Qiao, Ruimin,Lee, Hyun-Wook,Shyam, Badri,Guo, Minghua,Wang, Yayu,Wray, L. Andrew,Yang, Wanli,Toney, Michael F.,Cui, Yi The Royal Society of Chemistry 2016 Journal of materials chemistry. A, Materials for e Vol.4 No.11

<P>Prussian Blue analogues (PBAs) have shown promise as electrode materials for grid-scale batteries because of their high cycle life and rapid kinetics in aqueous-based electrolytes. However, these materials suffer from relatively low specific capacity, which may limit their practical applications. Here, we investigate strategies to improve the specific capacity of these materials while maintaining their cycling stability and elucidate mechanisms that enhance their electrochemical properties. In particular, we have studied the electrochemical and structural properties of manganese hexacyanoferrate (MnHCFe) and cobalt hexacyanoferrate (CoHCFe) in an aqueous, sodium-ion electrolyte. We also studied manganese-cobalt hexacyanoferrate (Mn-CoHCFe) solid solutions with different Mn/Co ratios that combine properties of both MnHCFe and CoHCFe. The materials have the characteristic open-framework crystal structure of PBAs, and their specific capacities can be significantly improved by electrochemically cycling (oxidizing and reducing) both the carbon-coordinated Fe and the nitrogen-coordinated Co or Mn ions.<I>In situ</I>synchrotron X-ray diffraction studies and<I>ex situ</I>soft X-ray absorption spectroscopy combined with an in-depth electrochemical characterization provide insight into the different electrochemical properties associated with the Fe, Co, and Mn redox couples. We show that cycling the C-coordinated Fe preserves the crystal structure and enables the outstanding kinetics and cycle life previously displayed by PBAs in aqueous electrolytes. On the other hand, the N-coordinated Co and Mn ions exhibit a slower kinetic regime due to structural distortions resulting from the weak N-coordinated crystal field, but they still contribute significantly towards increasing the specific capacity of the materials. These results provide the understanding needed to drive future development of PBAs for grid-scale applications that require extremely high cycle life and kinetics.</P>

A study on cobalt substitution in sodium manganese mixed-anion phosphates as positive electrode materials for Na-ion batteries

Ryu, Soojy,Wang, Ji Eun,Kim, Joo-Hyung,Ruffo, Riccardo,Jung, Young Hwa,Kim, Do Kyung Elsevier 2019 Journal of Power Sources Vol.444 No.-

<P><B>Abstract</B></P> <P>Sodium polyanionic materials provide various structural frameworks compared to their lithium counterparts, leading to diverse studies on novel polyanion-based electrode materials for sodium ion batteries. Na<SUB>4</SUB>M<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB>P<SUB>2</SUB>O<SUB>7</SUB> (M = Mn, Fe, Co, Ni, and Mg) is a new class of mixed-anion phosphates combined with two polyanion groups, (PO<SUB>4</SUB>)<SUP>3−</SUP> and (P<SUB>2</SUB>O<SUB>7</SUB>)<SUP>4−</SUP>. It is an attractive electrode candidate because of its stable cyclability and low volume changes upon cycling. Although Mn-based mixed-anion phosphate materials have shown a high redox potential of 3.8 V vs. Na<SUP>+</SUP>/Na, they have suffered from low electrical conductivity and structural distortion upon oxidation. Partial substitution of Mn by other divalent cations is an efficient strategy to suppress lattice distortion and to affect the phase transition process during electrochemical cycling. Here we study the cation substitution effect of the Mn-based mixed-anion phosphates on the phase stability and the kinetics of the electrochemical reaction. The electrochemical reversibility was found to be improved by certain cation substitution. In particular, Co substitution not only increased the operating voltage but also enhanced both cyclability and rate capability. Furthermore, we investigate the phase changes upon cycling using <I>in situ</I> synchrotron X-ray diffraction, supporting the positive effect of the mixed-anion phosphate structure through cation substitution.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Co substitution on Mn-based mixed-anion phosphate by solution combustion synthesis. </LI> <LI> Substituted Co alleviated structure distortion and lowered phase transition barrier. </LI> <LI> Enhanced operating potential and half-cell performance of mixed-anion phosphate. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>