Francis Amalraj

On the Electrochemical Behavior of Aluminum Electrodes in Nonaqueous Electrolyte Solutions of Lithium Salts

We studied the electrochemical behavior of aluminum electrodes in solutions comprising ethylene carbonate (EC)-dimethyl carbonate (DMC) and lithium salts: lithium hexafluorophospate (LiPF 6 ), lithium perchlorate (LiClO 4 ), or lithium bis(oxalato)borate (LiBOB). Under anodic polarization within the potential range of 3.00-4.00 V in these solutions, aluminum electrodes demonstrate a stable behavior due to their passivation by surface films. Aluminum electrodes passivate in EC-DMC/LiPF 6 and EC-DMC/LiBOB solutions both at 30 and 60°C, whereas these electrodes remain active and corrode in EC-DMC/LiClO 4 solutions. LiBOB may decompose at anodic potentials, thus forming passive films comprising B 2 O 3 and metal-oxalate species on the aluminum electrodes polarized to 4.50-5.30 V. Li 2 CO 3 , LiF and AlPO 4 , and LiCl species were also detected on the electrodes anodically polarized in LiBOB-, LiPF 6 -, and LiClO 4 -containing solutions, respectively. At some conditions, current oscillations can be developed on aluminum electrodes upon their polarization at constant potentials. These oscillations may relate to the successive formation and dissolution of the passivating surface films formed on electrodes. The development of F 2 P(=O)O - species due to the polarization of aluminum electrodes in EC-DMC/LiPF 6 solutions was confirmed by solution NMR studies.

On the Performance of LiNi1 / 3Mn1 / 3Co1 / 3O2 Nanoparticles as a Cathode Material for Lithium-Ion Batteries

We report on the behavior of nanometric LiMn 1/3 Ni 1/3 CO 1/3 O 2 (LiMNC) as a cathode material for Li-ion batteries in comparison with the same material with submicrometric particles. The LiMNC material was produced by a self-combustion reaction, and the particle size was controlled by the temperature and duration of the follow-up calcination step. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, Raman spectroscopy, electron paramagnetic resonance, inductively coupled plasma, and atomic force microscopy were used in conjunction with standard electrochemical techniques (cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy) for characterizing the electrode materials. The effect of cycling and aging at 60°C was also explored. Nanomaterials are much more reactive in standard electrolyte solutions than LiMNC with a submicrometric particle. They develop surface films that impede their electrochemical response, while their bulk structure remains stable during aging and cycling at elevated temperatures. The use of nanomaterials in Li-ion batteries is discussed.