Abdelfattah Mahmoud

Transition-Metal Carbodiimides as Molecular Negative Electrode Materials for Lithium- and Sodium-Ion Batteries with Excellent Cycling Properties

We report evidence for the electrochemical activity of transition-metal carbodiimides versus lithium and sodium. In particular, iron carbodiimide, FeNCN, can be efficiently used as negative electrode material for alkali-metal-ion batteries, similar to its oxide analogue FeO. Based on (57)Fe Mössbauer and infrared spectroscopy (IR) data, the electrochemical reaction mechanism can be explained by the reversible transformation of the Fe-NCN into Li/Na-NCN bonds during discharge and charge. These new electrode materials exhibit higher capacity compared to well-established negative electrode references such as graphite or hard carbon. Contrary to its oxide analogue, iron carbodiimide does not require heavy treatments (such as nanoscale tailoring, sophisticated textures, or coating) to obtain long cycle life with current density as high as 9 A g(-1) for hundreds of charge-discharge cycles. Similar to the iron compound, several other transition-metal carbodiimides M(x)(NCN)y with M=Mn, Cr, Zn can cycle successfully versus lithium and sodium. Their electrochemical activity and performance open the way to the design of a novel family of anode materials.

Structure Characterization and Properties of K-Containing Copper Hexacyanoferrate

Copper hexacyanoferrate, Cu(II)[Fe(III)(CN)6]2/3·nH2O, was synthesized, and varied amounts of K(+) ions were inserted via reduction by K2S2O3 (aq). Ideally, the reaction can be written as Cu(II)[Fe(III)(CN)6]2/3·nH2O + 2x/3K(+) + 2x/3e(-) ↔ K2x/3Cu(II)[Fe(II)xFe(III)1-x(CN)6]2/3·nH2O. Infrared, Raman, and Mössbauer spectroscopy studies show that Fe(III) is continuously reduced to Fe(II) with increasing x, accompanied by a decrease of the a-axis of the cubic Fm3̅m unit cell. Elemental analysis of K by inductively coupled plasma shows that the insertion only begins when a significant fraction, ∼20% of the Fe(III), has already been reduced. Thermogravimetric analysis shows a fast exchange of water with ambient atmosphere and a total weight loss of ∼26 wt % upon heating to 180 °C, above which the structure starts to decompose. The crystal structures of Cu(II)[Fe(III)(CN)6]2/3·nH2O and K2/3Cu[Fe(CN)6]2/3·nH2O were refined using synchrotron X-ray powder diffraction data. In both, one-third of the Fe(CN)6 groups are vacant, and the octahedron around Cu(II) is completed by water molecules. In the two structures, difference Fourier maps reveal three additional zeolitic water sites (8c, 32f, and 48g) in the center of the cavities formed by the -Cu-N-C-Fe- framework. The K-containing compound shows an increased electron density at two of these sites (32f and 48g), indicating them to be the preferred positions for the K(+) ions.

Spray-Drying of Electrode Materials for Lithium- and Sodium-Ion Batteries

The performance of electrode materials in lithium-ion (Li-ion), sodium-ion (Na-ion) and related batteries depends not only on their chemical composition but also on their microstructure. The choice of a synthesis method is therefore of paramount importance. Amongst the wide variety of synthesis or shaping routes reported for an ever-increasing panel of compositions, spray-drying stands out as a versatile tool offering demonstrated potential for up-scaling to industrial quantities. In this review, we provide an overview of the rapidly increasing literature including both spray-drying of solutions and spray-drying of suspensions. We focus, in particular, on the chemical aspects of the formulation of the solution/suspension to be spray-dried. We also consider the post-processing of the spray-dried precursors and the resulting morphologies of granules. The review references more than 300 publications in tables where entries are listed based on final compound composition, starting materials, sources of carbon etc.

Li{sub x}Co{sub 0.4}Ni{sub 0.3}Mn{sub 0.3}O{sub 2} electrode materials: Electrochemical and structural studies

A B S T R A C T LiCo0.4Ni0.3Mn0.3O2 layered oxide in a member of the LiCo1� 2xNixMnxO2 solid solution between LiCoO2 and LiNi0.5Mn0.5O2. Compositions from this solid solution have attracted much attention and have been extensively studied as promising cathode candidates to replace the most popular LiCoO2 cathode material used in the commercial lithium-ion batteries (LiBs). LiCo0.4Ni0.3Mn0.3O2 positive electrode material was prepared via the combustion method followed by a thermal treatment at 900 8C for 12 h. This material was characterized by a high homogeneity and a granular shape. The Rietveld refinement evidenced that the structure of this compound exhibits no Ni/Li disorder revealing that the LiCo1� 2xNixMnxO2 system presents the ideal structure for LiBs application when x < 0.4. The electrochemical performances of the LiCo0.4Ni0.3Mn0.3O2 sample were measured at different current rates in the 2.7–4.5 V potential range. Its discharge capacity reached 178, 161 and 145 mAhg � 1 at C/20, 1C and 2C, respectively. Structural changes in LiCo0.4Ni0.3Mn0.3O2 upon delithiation were studied using ex situ X-ray diffraction. A continuous solid solution with a rhombohedral symmetry was detected in the whole composition range. This structural stability during the cycling combined with the obtained electrochemical features make this material convenient for the LiBs applications.