Mohd Faiz Hassan

Ultra-fine porous SnO2 nanopowder prepared via a molten salt process: a highly efficient anode material for lithium-ion batteries

Ultra-fine porous SnO2nanoparticles for lithium ion batteries were prepared by a simple, easily scaled-up molten salt method at 300 °C. The structure and morphology were confirmed by X-ray diffraction and transmission electron microscopy. The as-prepared SnO2 had a tetragonal rutile structure with crystal sizes around 5 nm. The electrochemical performance was tested compared with commercial nanopowder and previously reported nanowires. The as-prepared nanoparticles delivered a significantly higher discharge capacity and better cycle retention. The nanoparticle electrode delivered a reversible capacity of 410 mAh g−1 after 100 cycles. Even at high rates, the electrode operated at a good fraction of its capacity. The excellent electrochemical performance of the ultra-fine porous SnO2 can be attributed to the ultra-fine crystallites (which tend to decrease the absolute volume changes) and the porous structure (which promotes liquid electrolyte diffusion into the bulk materials and acts as a buffer zone to absorb the volume changes).

SnO2–NiO–C nanocomposite as a high capacity anode material for lithium-ion batteries

Carbon-coated SnO2–NiO nanocomposite was successfully synthesized via the molten salt route, using SnCl2·H2O and NiCl2·6H2O as the starting materials, with a molten salt composition of H2O2 : LiOH·H2O : LiNO3 as a solvent at 300 °C. The synthesis was followed by a carbon layering process. The phases and morphology of the as-prepared samples were examined by X-ray diffraction and transmission electron microscopy. Electrochemical investigation was carried out by using a series of complementary techniques, including galvanostatic charge–discharge, cyclic voltammetry, and impedance spectroscopy. The results confirmed that the carbon-coated SnO2–NiO nanocomposite has higher discharge capacity, better rate capability, and excellent cycling performance in comparison to the uncoated SnO2–NiO nanocomposite. The carbon-coated SnO2–NiO nanocomposite electrode exhibited a reversible capacity of about 529 mA h g−1 at 800 mA g−1, and 265 mA h g−1 at 1600 mA g−1, even after 500 cycles. The excellent electrochemical performance of the SnO2–NiO–C nanocomposite can be mainly attributed to the combined effects of the nanostructure, the carbon layering on the SnO2 and NiO nanoparticles, and the ultra-fine carbon matrix, because the three factors would contribute to high electronic conductivity, reduce the traverse time of electrons and lithium ions, and also prevent high volume expansion during cycling. Due to its excellent electrochemical performance, the SnO2–NiO–C nanocomposite could be considered as a promising anode material for future lithium-ion batteries to be used in electric vehicles and hybrid electric vehicles.

Nanocrystalline porous α-LiFeO2–C composite—an environmentally friendly cathode for the lithium-ion battery

A novel nanocrystalline porous α-LiFeO2–C composite with a high surface area of around 115 m2 g−1 has been synthesized by a simple molten salt method, followed by a carbon coating process. The structure and morphology were confirmed by X-ray diffraction, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). FE-SEM observations demonstrated that the morphology consists of α-LiFeO2–C nanoclusters composed of very tiny nanoparticles joined together by a porous architecture. TEM investigations revealed that amorphous carbon was incorporated into the pores among the nanoparticles and that some nanoparticles were covered by a thin layer of carbon as well. Electrochemical measurements showed that the α-LiFeO2–C nanocomposite delivered a significantly higher reversible capacity and excellent cycle stability (230 mA h g−1 at 0.5 C after 100 cycles). Even at the high rate of 3 C, the electrode showed more than 50% of the capacity at low rate (0.1 C). The excellent electrochemical performance of the α-LiFeO2–C nanocomposite electrode can be attributed to the porous conductive architecture among the nanoparticles, which not only has benefits in terms of decreasing the absolute volume changes and increasing the mobility of lithium ions, but also offers conductive pathways along the whole interconnected wall in the structure, which is favourable for the transport of electrons, promotes liquid electrolyte diffusion into the bulk materials, and acts as a buffer zone to absorb the volume changes.

Nanorods of vanadium compounds: Synthesis, characterisation, and application in electrochemical energy storage

The synthesis and characterisation of nanorods of vanadium pentoxide, VO, vanadium trioxide, VO, vanadium dioxide, VO (B), and vanadium nitride, VN, are presented, and their application in electrochemical supercapacitors and lithium-ion batteries is outlined. Specifically, a novel method for the preparation of VO nanorods is discussed. It involves ball milling as a first step and controlled annealing as a second step. Nanorods of VO can be converted into those of other vanadium-relatedphases by simple chemical reduction treatments Such chemical transformations are pseudomorphic and often topotactic, that is, the resulting nanorods belong to a different chemical phase but tend to retain the original morphology and preferential crystal orientation dictated by parent VO crystals The corresponding properties of nanorods for their prospective application in electrochemical energy storage (lithium-ion batteries and electrochemical supercapacitors) are discussed. The synthesised VO nanorods possess a stable cyclic behaviour when they are used in a cathode of a lithium-ion battery and are suitable for use in an anode. VN nanorods synthesised by NH reduction of VO were found to possess pseudocapacitive properties in aqueous electrolytes.