Atomic Structure of Surface-Densified Phases in Ni-Rich Layered Compounds

In this work, we report the presence of surface-densified phases (β-Ni5O8, γ-Ni3O4, and δ-Ni7O8) in LiNiO2 (LNO)- and LiNi0.8Al0.2O2 (LNA)-layered compounds by combined atomic level scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). These surface phases form upon electrochemical aging at high state of charge corresponding to a fully delithiated state. A unique feature of these phases is the periodic occupancy by Ni2+ in the Li layer. This periodic Ni occupancy gives rise to extra diffraction reflections, which are qualitatively similar to those of the LiNi2O4 spinel structure, but these surface phases have a lower Ni valence state and cation content than spinel. These experimental results confirm the presence of thermodynamically stable surface phases and provide new insights into the phenomena of surface phase formation in Ni-rich layered structures

Atomic Structure of Surface-Densified Phases in Ni-Rich Layered Compounds.

In this work, we report the presence of surface-densified phases (β-Ni5O8, γ-Ni3O4, and δ-Ni7O8) in LiNiO2 (LNO)- and LiNi0.8Al0.2O2 (LNA)-layered compounds by combined atomic level scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). These surface phases form upon electrochemical aging at high state of charge corresponding to a fully delithiated state. A unique feature of these phases is the periodic occupancy by Ni2+ in the Li layer. This periodic Ni occupancy gives rise to extra diffraction reflections, which are qualitatively similar to those of the LiNi2O4 spinel structure, but these surface phases have a lower Ni valence state and cation content than spinel. These experimental results confirm the presence of thermodynamically stable surface phases and provide new insights into the phenomena of surface phase formation in Ni-rich layered structures

Surface Structural and Chemical Evolution of Layered LiNi \u3c inf\u3e 0.8 Co \u3c inf\u3e 0.15 Al \u3c inf\u3e 0.05 O \u3c inf\u3e 2 (NCA) under High Voltage and Elevated Temperature Conditions

© Copyright 2018 American Chemical Society. This paper reports new insights into structural and chemical evolution of surface phases of LiNi0.8Co0.15Al0.05O2 (NCA) held at constant high voltages (up to 4.75 V) as well as high temperatures (60 °C) by correlating crystal structure using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) imaging with chemistry using electron energy loss spectroscopy (EELS). We also followed the Al distribution within individual NCA particles by X-ray energy dispersive spectroscopy (EDS). The progression of these phases as a function of distance from the edge shows simultaneous evolution of crystal structures and chemistry from rocksalt to layered, forming a complete solid solution. We have also observed an extended disordered phase with rocksalt (Fm3m) symmetry in which quantitative electron energy loss spectroscopy reveals it to be an oxygen deficient cation disordered phase with chemical characteristics, as determined by EELS, similar to spinel. The formation of these disordered phases with cation and oxygen vacancies has been driven by surface oxygen loss caused by reactions with the electrolyte followed by cation migration from the octahedral 3a M (M = Ni, Co, Al) layer to the octahedral 3b Li layer. These surface rocksalt phases are not fully dense as they contain Al and Li as well as a high concentration of cation and oxygen vacancies. After discharge, Li is detected within these phases indicative that Li transport has occurred through these rocksalt phases. At 60 °C and 4.75 V a very large impedance rise is observed leading to complete cell irreversibility which is caused by significant metal dissolution from the cathode and formation of surface porosity. In the near surface region of some particles, a phase transformation from R3m (O3) to P3m1 (O1) is also observed which has become thermodynamically stable from complete delithiation as well as from local Al surface depletion

UCRLJC-125296 PREPRINT Resistance Behavior of Cr-Si-O Thin Films and Chemistry and Physics of Nanostructures and Related Non-Equilibrium Materials RESISTANCE BEHAVIOR OF Cr-Si-O THIN FILMS

DISCLAIMER Thin coatings of Cr-Si-O are assessed for use as a resistor. The subrnicron thick films are sputter deposited using a ( l-x)Ar-(x)OZ working gas. Several compacts of metal and oxide powders are commercially prepared for use as the sputter targets. The deposition process yields film compositions which range from 2 to 30 at.% Cr and 20 to 45 at.% Si as measured using Rutherford backscattering. A broad range of resistivities from 10 I to 101AQ cm are found as measured through the fdm thickness between metal pads deposited onto the Cr-Si-O surface. The film structure and morphology are characterized using transmission electron microscopy from which the resistance behavior can be correlated to the distribution of metallic particles. Thermal aging reveals the metastability of the Cr-Si-O film morphology and resistance behavior

Conversion Reaction of CoO Polycrystalline Thin Films Exposed to Atomic Lithium

We have studied the reaction of 5 nm thick polycrystalline CoO films with atomic lithium as a model for the discharge of lithium-ion conversion battery electrodes. The electronic structure has been investigated with X-ray photoemission, ultraviolet photoemission, and inverse photoemission, while the morphology, crystal structure, and unoccupied states of the films have been examined with transmission electron microscopy. It is found that exposure to atomic lithium leads, at room temperature, to partial conversion with formation of Co and Li₂O, but also of a Li₂O₂ or LiOH overlayer at the surface of the sample. As full conversion was obtained at 150 °C, a comparison with room-temperature measurements enables the understanding of the kinetic limitations during lithiation

Resistance behavior of Cr-Si-O thin films

Thin coatings of Cr-Si-O are assessed for use as a resistor. The submicron thick films are sputter deposited using a (l-x)Ar-(x)O{sub 2} working gas. Several compacts of metal and oxide powders are commercially prepared for use as the sputter targets. The deposition process yields film compositions which range from 2 to 30 at.% Cr and 20 to 45 at.% Si as measured using Rutherford backscattering. A broad range of resistivities from 10{sup 1} to 10{sup 14}{Omega} cm are found as measured through the film thickness between metal pads deposited onto the Cr-Si-O surface. The film structure and morphology are characterized using transmission electron microscopy from which the resistance behavior can be correlated to the distribution of metallic particles. Thermal aging reveals the metastability of the Cr- Si-O film morphology and resistance behavior