Improved electrochemical performance of SiO2-coated Li-rich layered oxides-Li1.2Ni0.13Mn0.54Co0.13O2

Lithium-rich layered oxides (LLOs) such as Li1.2Ni0.13Mn0.54Co0.13O2 are suitable cathode materials for future lithium-ion batteries (LIBs). Despite some salient advantages, like low cost, ease of fabrication, high capacity, and higher operating voltage, these materials suffer from low cyclic stability and poor capacity retention. Several different techniques have been proposed to address the limitations associated with LLOs. Herein, we report the surface modification of Li1.2Ni0.13Mn0.54Co0.13O2 by utilizing cheap and readily available silica (SiO2) to improve its electrochemical performance. Towards this direction, Li1.2Ni0.13Mn0.54Co0.13O2 was synthesized utilizing a sol-gel process and coated with SiO2 (SiO2 = 1.0 wt%, 1.5 wt%, and 2.0 wt%) employing dry ball milling technique. XRD, SEM, TEM, elemental mapping and XPS characterization techniques confirm the formation of phase pure materials and presence of SiO2 coating layer on the surface of Li1.2Ni0.13Mn0.54Co0.13O2 particles. The electrochemical measurements indicate that the SiO2-coated Li1.2Ni0.13Mn0.54Co0.13O2 materials show improved electrochemical performance in terms of capacity retention and cyclability when compared to the uncoated material. This improvement in electrochemical performance can be related to the prevention of electrolyte decomposition when in direct contact with the surface of charged Li1.2Ni0.13Mn0.54Co0.13O2 cathode material. The SiO2 coating thus prevents the unwanted side reactions between cathode material and the electrolyte. 1.0 wt% SiO2-coated Li1.2Ni0.13Mn0.54Co0.13O2shows the best electrochemical performance in terms of rate capability and capacity retention.This publication was made possible by NPRP Grant # NPRP11S-1225-170128 from Qatar National Research Fund (a member of the Qatar Foundation). Statements made herein are solely the responsibility of the authors. FE-SEM analysis was accomplished at the Central Laboratory Unit (CLU), Qatar University, Doha, Qatar, TEM analysis was conducted at the Core Labs., QEERI, HBKU, Qatar and XPS analysis was accomplished at the Gas Processing Center (GPC), Qatar University, Doha, Qatar.Scopu

Investigations of He ⁺ implantation and subsequent annealing effects in InP

The influence of 70 keV He + ion implantation and subsequent annealing of Cz-indium phosphide (InP) samples has been investigated using a slow positron beam-based Doppler broadening spectrometer. Three samples with ion fluences of 1 × 10 16 , 5 × 10 16 and 1 × 10 17 cm -2 were studied in the as-implanted condition as well as after annealing at 640 °C for times between 5 and 40 min. It was found that the line-shape parameter of the positron-electron annihilation peak in the implanted layer increases after 5 min annealing, then after longer annealing times it starts to decline gradually until it reaches a value close to the value of the as-grown sample. This implies that vacancy-like defects can be created in InP by He implantation followed by short-thermal annealing at T > 600 °C. Comparison of the results with a study where cavities were observed in He-implanted InP has been carried out. © 2005 Elsevier B.V. All rights reserved

Electron irradiated low-density polyethylene studied by positron annihilation lifetime spectroscopy

A study of the degree and rate of cross-linking of low-density polyethylene (LDPE) as a result of irradiation by high-energy electron beam has been performed using positron annihilation lifetime (PAL) technique. The PAL measurements were carried out at room temperature with a conventional fast-fast coincidence system. The lifetime spectra were analysed into four components using the PATFIT program to extract the positron parameters such as lifetime, mean lifetime, intensities, free volume radius, and fractional free volume. Almost all parameters exhibited differences between the unirradiated and irradiated LDPE. It can be concluded that the effect of irradiation on polyethylene results in intensive network formation, which is intensified as the electron energy is increased. The results manifest another proof of the usefulness of positron techniques in the study of the microstructure of polymers. © 2003 Elsevier Ltd. All rights reserved

Re-emission of slow positrons from tungsten at elevated temperatures

A series of measurements have been made on the dependence of the intensity and energy spectrum of slow positrons re-emitted from polycrystalline tungsten foil held at temperatures of up to 500 °C. Irrespective of target history, no sharpening of the energy spectrum of re-emitted positrons was observed as the remoderator temperature was increased. Further, a steady decrease in the apparent re-emitted positron intensity was observed, attributed primarily to the increase in positronium formation, as the temperature of the foil was increased from 20 to 500 °C. It is concluded that maintaining a moderator or remoderator at elevated temperatures in standard positron beam systems has no beneficial consequences for the quality or intensity of the beam produced. Reasons for this are discussed. © 2002 Elsevier Science B.V. All rights reserved

Positron annihilation lifetime study of helium ions implanted polyethylene blends

The structural defects of linear low density polyethylene (LLDPE) and high density polyethylene (HOPE) blends implanted with helium ions were investigated using position annihilation lifetime (PAL) technique. The positron annihilation lifetime measurements were carried out at room temperature with a conventional fast-fast coincidence system. The lifetime spectra were analyzed into four components using the PATFIT program to extract the positron parameters such as lifetime components, and their corresponding intensities. Almost all parameters exhibited a correlation with microstructure changes resulting from implantation. The results were further discussed by comparison with modifications in the morphology of implanted samples using Scanning Electron Microscope (SEM) and Differential Scanning Calorimeter (DSC). Virgin Samples of Polyethylene blends are shown to be miscible by singlet DSC melting temperatures. After ion implantation the thermal properties of blends exhibit different behaviors depending on ion fluence and blending ratio i.e. polymer structure