Michael Talianker

Stabilizing nickel-rich layered cathode materials by a high-charge cation doping strategy: zirconium-doped LiNi0.6Co0.2Mn0.2O2

Ni-rich layered lithiated transition metal oxides Li[NixCoyMnz]O2 (x + y + z = 1) are the most promising materials for positive electrodes for advanced Li-ion batteries. However, one of the drawbacks of these materials is their low intrinsic stability during prolonged cycling. In this work, we present lattice doping as a strategy to improve the structural stability and voltage fade on prolonged cycling of LiNi0.6Co0.2Mn0.2O2 (NCM-622) doped with zirconium (+4). It was found that LiNi0.56Zr0.04Co0.2Mn0.2O2 is stable upon galvanostatic cycling, in contrast to the undoped material, which undergoes partial structural layered-to-spinel transformation during cycling. The current study provides sub-nanoscale insight into the role of Zr4+ doping on such a transformation in Ni-rich Li[NixCoyMnz]O2 materials by adopting a combined experimental and first-principles theory approach. A possible mechanism for a Ni-mediated layered-to-spinel transformation in Ni-rich NCMs is also proposed.

Identification of the structure of a new Al-U-Fe phase by electron microdiffraction technique

The particles of an unknown intermetallic phase with the approximate composition Al10Fe2U were observed in a ternary Al–Fe–U alloy. The structure of this phase was investigated in a transmission electron microscope using a microdiffraction technique based on analysis of the symmetry and relative positions of reflections in the zero-order and high-order Laue zones. The phase has an orthorhombic C-centered unit cell with lattice parameters a=8.900, b=10.190 and c=8.993 A; its crystal symmetry can be described by the Cmcm space group.

Non-equilibrium microstructures in TiAl–2Fe alloy

Abstract Microstructure evolution in Al-49.6 at% Ti-1.9 at% Fe alloy during cooling from 1400 and 1300°C leading to non-equilibrium structure is presented and discussed. ©

High loading of short W(Mo)S2 slabs inside the nanotubes of SBA-15. Promotion with Ni(Co) and performance in hydrodesulfurization and hydrogenation.

Abstract Layered nanoslabs of a M0S2 and WS2 phases with a well-defined hexagonal crystalline structure were inserted into the nanotubular channels of SBA-15 at loadings up to 60 wt%. Sonication of a slurry containing SBA-15 in a W(Mo)(CO)6-sulfur-diphenylmethane solution yielded an amorphous W(Mo)S2 phase inside the mesopores that was transformed into hexagonal crystalline W(Mo)S2 nanoslabs by further sulfidation. The nanoslabs were distributed exclusively inside the mesopores in a uniform manner (HRTEM, local quantitative microanalysis), without blocking the pores (N2-sorption). The Ni(Co) promoters were introduced into the W(Mo)S2/SBA-15 composites by impregnation from an aqueous solution of nickel (cobalt) acetate. The activity (based on the volume of the catalyst loaded into reactor) of the optimized Ni-W-S/SBA-15 catalyst in hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrogenation (HYD) of toluene was 1.4 and 7.3 times higher, respectively, than that of a sulfided commercial CO-MO/Al2O3. The HDS activity of Co-Mo- S/SBA-15 catalyst was 1.2 times higher than that of commercial catalyst. After promotion with Co, the directly introduced M0S2 slabs and M0S2 slabs prepared by sulfidation of Mo- oxide monolayer spread over SBA-15 displayed similar HDS performance.

The stability of structures with icosahedral local order in Al-based alloys with transition metals

Abstract The paper considers the stability of the phases formed in alloys of aluminum with transition metals (TM) in terms of the theory of coordination compounds. The structural stability is related to the degree of distortion of the first-neighbor coordination icosahedra commonly found around TM atoms. Changes in the symmetry of coordination polyhedrons are explained in terms of the Jahn–Teller theorem. The stability of the structures may be correlated with the effective charge of the TM atom and with the electronegativity of its neighbors: the phase transforms to the structure with lower symmetry when the electronegativity or effective charge decrease.

Ion-Beam Induced Formation of Nanoparticles with Predicted Structure

The ab initio approach is developed that allows predicting structural changes, which can be induced by Plasma Immersion Ion Implantation (PIII) of Ag ions into Mg based alloys. The calculations are performed in the framework of the density functional theory. The approach is based on the assumption that the electronic properties of the irradiated parent phase predetermine the structural characteristics of a new implantation-induced phase. It is presumed that penetration of the implanted ions into the host lattice leads, firstly, to “immediate” excitation of the electronic subsystem of the parent phase. Then this initial stage is followed by changes of the atomic configuration so that the electronic subsystem transfers to the relaxed state. To characterize and to quantify how the initial non-equilibrium state is far from the quasi-relaxed state of the system, the energy parameter ΔE is proposed. The behaviour of ΔE plot vs. different concentrations of implanted ions correlates with the conditions of formation of the new phase. The correctness of the proposed approach was corroborated by ab-initio analysis of the experimentally observed phase transitions Mg + Agions → MgAg and Mg17Al12 + Agions → Mg54Al28Ag18 induced by PIII treatment.

Understanding the Role of Minor Molybdenum Doping in LiNi0.5Co0.2Mn0.3O2 Electrodes: from Structural and Surface Analyses and Theoretical Modeling to Practical Electrochemical Cells

Doping LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode material by small amount of Mo6+ ions, around 1 mol %, affects pronouncedly its structure, surface properties, and electronic and electrochemical behavior. Cathodes comprising Mo6+-doped NCM523 exhibited in Li cells higher specific capacities, higher rate capabilities, lower capacity fading, and lower charge-transfer resistance that relates to a more stable electrode/solution interface due to doping. This, in turn, is ascribed to the fact that the Mo6+ ions tend to concentrate more at the surface, as a result of a synthesis that always includes a necessary calcination, high-temperature stage. This phenomenon of the Mo dopant segregation at the surface in NCM523 material was discovered in the present work for the first time. It appears that Mo doping reduces the reactivity of the Ni-rich NCM cathode materials toward the standard electrolyte solutions of Li-ion batteries. Using density functional theory (DFT) calculations, we showed that Mo6+ ions are preferably incorporated at Ni sites and that the doping increases the amount of Ni2+ ions at the expense of Ni3+ ions, due to charge compensation, in accord with X-ray absorption fine structure (XAFS) spectroscopy measurements. Furthermore, DFT calculations predicted Ni-O bond length distributions in good agreement with the XAFS results, supporting a model of partial substitution of Ni sites by molybdenum.

Observation of ε′-Ag17 Mg54 phase induced by plasma immersion ion implantation

This paper provides a confirmation of the effectiveness of the recently suggested ab initio approach to the theoretical prediction of phase transformations which may be induced in metallic alloys by metal plasma immersion and ion implantation processing. The approach is based on an assumption that at certain concentrations of the implanted species, the relaxation of the exited electronic state of the implanted structure should be accompanied by the rearrangement of atoms leading to the formation of a new phase. Recently, on the basis of density functional theory calculations of the energetic characteristics of the electronic subsystems of the implanted Mg–Ag system, it was predicted that concentrations of the implanted Ag ions within the range from ∼18 to 23 at% Ag, favor transition to the phase ε′-Ag17Mg54. Our transmission electron microscopy observations and electron diffraction analysis of the Mg-based alloy subjected to the implantation of Ag ions at dose of ∼5×1015 ion/cm2 confirmed that the formation of the ε′-Ag17Mg54 phase indeed takes place.