A comprehensive picture of the current rate dependence of the structural evolution of P2-Na<inf>2/3</inf>Fe<inf>2/3</inf>Mn<inf>1/3</inf>O<inf>2</inf>

Cathodes that feature a layered structure are attractive reversible sodium hosts for ambient temperature sodium-ion batteries which may meet the demands for large-scale energy storage devices. However, crystallographic data on these electrodes are limited to equilibrium or quasi-equilibrium information. Here we report the current-dependent structural evolution of the P2-Na2/3Fe2/3Mn1/3O2 electrode during charge/discharge at different current rates. The structural evolution is highly dependent on the current rate used, e.g., there is significant disorder in the layered structure near the charged state at slower rates and following the cessation of high-current rate cycling. At moderate and high rates this disordered structure does not appear. In addition, at the slower rates the disordered structure persists during subsequent discharge. In all rates examined, we show the presence of an additional two-phase region that has not been observed before, where both phases maintain P63/mmc symmetry but with varying sodium contents. Notably, most of the charge at each current rate is transferred via P2 (P63/mmc) phases with varying sodium contents. This illustrates that the high-rate performance of these electrodes is in part due to the preservation of the P2 structure and the disordered phases appear predominantly at lower rates. Such current-dependent structural information is critical to understand how electrodes function in batteries which can be used to develop optimised charge/discharge routines and better materials

Structure-Electrochemical Evolution of a Mn-Rich P2 Na<inf>2/3</inf>Fe<inf>0.2</inf>Mn<inf>0.8</inf>O<inf>2</inf> Na-Ion Battery Cathode

The structural evolution of electrode materials directly influences the performance of sodium-ion batteries. In this work, in situ synchrotron X-ray diffraction is used to investigate the evolution of the crystal structure of a Mn-rich P2-phase Na2/3Fe0.2Mn0.8O2 cathode. A single-phase reaction takes place for the majority of the discharge-charge cycle at ∼C/10, with only a short, subtle hexagonal P2 to hexagonal P2 two-phase region early in the first charge. Thus, a higher fraction of Mn compared to previous studies is demonstrated to stabilize the P2 structure at high and low potentials, with neither "Z"/OP4 phases in the charged state nor significant quantities of the P′2 phase in the discharged state between 1.5 and 4.2 V. Notably, sodium ions inserted during discharge are located on both available crystallographic sites, albeit with a preference for the site sharing edges with the MO6 octahedral unit. The composition Na∼0.70Fe0.2Mn0.8O2 prompts a reversible single-phase sodium redistribution between the two sites. Sodium ions vacate the site sharing faces (Naf), favoring the site sharing edges (Nae) to give a Nae/Naf site occupation of 4:1 in the discharged state. This site preference could be an intermediate state prior to the formation of the P′2 phase. Thus, this work shows how the Mn-rich Na2/3Fe0.2Mn0.8O2 composition and its sodium-ion distribution can minimize phase transitions during battery function, especially in the discharged state

Using in situ synchrotron X-ray diffraction to study lithium-and sodium-ion batteries: A case study with an unconventional battery electrode (Gd<inf>2</inf>TiO<inf>5</inf>)

Designing materials for application as electrodes in sodium-ion batteries may require the use of unconventional materials to realize acceptable reversible sodium insertion/extraction capabilities. To design new materials simple electrochemical methods need to be coupled with other techniques such as in situ X-ray diffraction (XRD) to correlate the influence of electrochemical performance on a parameter that can be modified, e.g., the crystal structure of the material. Here we use in situ synchrotron XRD data on Gd2TiO5-containing cells to show the minor changes in reflection positions during discharge/charge that illustrates minimal volume expansion and contraction due to insertion/extraction reactions. These small changes correlate to the Gd2TiO5 anode material in both lithium-and sodium-ion batteries showing reversible capacities of ∼45 and ∼23 mA h/g after 20 cycles, respectively. Analysis of sodium location in the crystal structure shows a preference for sodium in the smaller channels along the c axis direction during the first discharge before moving to the larger channels at the charged state. Therefore, in this work, in situ studies highlight minimal structural changes with respect to volume expansion during electrochemical cycling and illustrate where sodium ions locate within the Gd2TiO5 structure

Using in situ synchrotron x-ray diffraction to study lithium- and sodium-ion batteries: A case study with an unconventional battery electrode (Gd2TiO5)

Designing materials for application as electrodes in sodium-ion batteries may require the use of unconventional materials to realize acceptable reversible sodium insertion/extraction capabilities. To design new materials simple electrochemical methods need to be coupled with other techniques such as in situ x-ray diffraction (XRD) to correlate the influence of electrochemical performance on a parameter that can be modified, e.g., the crystal structure of the material. Here we use in situ synchrotron XRD data on Gd2TiO5-containing cells to show the minor changes in reflection positions during discharge/charge that illustrates minimal volume expansion and contraction due to insertion/extraction reactions. These small changes correlate to the Gd2TiO5 anode material in both lithium- and sodium-ion batteries showing reversible capacities of ∼45 and ∼23 mA h/g after 20 cycles, respectively. Analysis of sodium location in the crystal structure shows a preference for sodium in the smaller channels along the c axis direction during the first discharge before moving to the larger channels at the charged state. Therefore, in this work, in situ studies highlight minimal structural changes with respect to volume expansion during electrochemical cycling and illustrate where sodium ions locate within the Gd2TiO5 structure. © 2014 Materials Research Societ

Cystallographic Evolution of P2 Na<inf>2/3</inf>Fe<inf>0.4</inf>Mn<inf>0.6</inf>O<inf>2</inf> Electrodes during Electrochemical Cycling

The development of new insertion electrodes requires an in-depth understanding of the structure-function relationships in order to rationally develop better electrodes. Sodium layered oxides such as P2 Na2/3Fe1/2Mn1/2O2 and Na2/3Fe2/3Mn1/3O2 are particularly interesting due to their performance, price, and low toxicity. Using in situ synchrotron X-ray diffraction during electrochemical cycling of P2 Na2/3Fe0.4Mn0.6O2, changes in the phase composition, lattice parameters, and critically sodium content within the crystal structure are determined. Approaching the charged state, there is an increase in the interlayer distance, brought about via a subtle two-phase region that maintains the structure type as P2. Interestingly, this appears to stabilize the P2 structure in the charged state and inhibits the formation of the highly disordered and typically unfavorable "Z" or OP4 phases up to 4.2 V at 20 mA/g. At the discharged state, at least three phases are present, including P′2 and two subtly different P2 phases. This structural evolution and these parameters are critically assessed in light of data from other compositions in the P2 Na2/3Fe1-yMnyO2 system. This study represents a method for performance optimization by tuning the Fe:Mn ratio

Los tipos de cultura y su relación con la rotación organizacional

La rotación de personal es una de las grandes preocupaciones del entorno empresarial. Uno de los factores que merece la pena estudiar para evitarla es la cultura organizacional. En este artículo se presenta una revisión de literatura y una propuesta de modelo que permitirán abordar aspectos clave en cuanto a la retención de personal a nivel organizacional

Sodium uptake in cell construction and subsequent in operando electrode behaviour of Prussian blue analogues, Fe[Fe(CN)6]1−x·yH2O and FeCo(CN)6

The development of electrodes for ambient temperature sodium-ion batteries requires the study of new materials and the understanding of how crystal structure influences properties. In this study, we investigate where sodium locates in two Prussian blue analogues, Fe[Fe(CN)6]1-x·yH2O and FeCo(CN)6. The evolution of the sodium site occupancies, lattice and volume is shown during charge-discharge using in situ synchrotron X-ray powder diffraction data. Sodium insertion is found to occur in these electrodes during cell construction and therefore Fe[Fe(CN)6]1-x·yH2O and FeCo(CN)6 can be used as positive electrodes. NazFeFe(CN)6 electrodes feature higher reversible capacities relative to NazFeCo(CN)6 electrodes which can be associated with a combination of structural factors, for example, a major sodium-containing phase, ∼Na0.5FeFe(CN)6 with sodium locating either at the x = y = z = 0.25 or x = y = 0.25 and z = 0.227(11) sites and an electrochemically inactive sodium-free Fe[Fe(CN)6]1-x·yH2O phase. This study demonstrates that key questions about electrode performance and attributes in sodium-ion batteries can be addressed using time-resolved in situ synchrotron X-ray diffraction studies. © 2014 Royal Societies of Chemistr

A short review of symbol grounding in robotic and intelligent systems

This paper gives an overview of the research papers published in Symbol Grounding in the period from the beginning of the 21st century up 2012. The focus is in the use of symbol grounding for robotics and intelligent system. The review covers a number of subtopics, that include, physical symbol grounding, social symbol grounding, symbol grounding for vision systems, anchoring in robotic systems, and learning symbol grounding in software systems and robotics. This review is published in conjunction with a special issue on Symbol Grounding in the Künstliche Intelligenz Journal