LiNi0.5Mn0.5O2, a promising cathode material for lithium-ion batteries, is synthesized by a novel solution-combustion procedure using acenaphthene as a fuel. The powder X-ray diffraction (XRD) pattern of the product shows a hexagonal cell with a=2.8955Å and c=14.1484Å. Electron microscopy investigations indicate that the particles are of sub-micrometer size. The product delivers an initial discharge capacity of 161mAhg−1 between 2.5 and 4.6V at a 0.1C rate and could be subjected to more than 50 cycles. The electrochemical activity is corroborated with cyclic voltammetric (CV) and electrochemical impedance data. The preparative procedure presents advantages such as a low cation mixing, sub-micron particles and phase purity.

Cobalt coatings were applied over lanthanum process-rich MmNi2.38Al0.82Co0.66Si0.77Fe0.13Mn0.24 alloy particles by an autocatalytic electroless deposition process. Electrode characteristics such as electrochemical capacity and cycle life were studied for the uncoated and coated alloys. The structure and morphology of the surface modified samples were characterized with XRD and SEM/EDAX techniques. The cobalt coating forms a thin layer on the surface of the core material and the coated alloys exhibit a 15% improvement in performance over the bare alloy. A comparison of the electrochemical impedance behaviour of the bare and cobalt-coated metal hydride electrodes at different states-of-charge reveals that the relaxation period is distinct for different SOCs. The cobalt microencapsulations influence the apparent activation energy of the dehydriding process. The calculated equivalent rate constant (keq) values confirm the improvement in reversibility for the cobalt-coated alloy as compared to the bare alloy.

Electroless coatings of Ni–P, Co–P and Cu were applied on the surface of non-stoichiometric MmNi3.25Al0.35Mn0.25Co0.66 (Mm: misch metal) metal hydride alloy. Elemental analysis was made with Energy Dispersive X-ray Analysis (EDAX). The structural analysis of bare and coated alloys was done by X-ray diffraction (XRD) whereas surface morphology was examined with scanning electron microscope (SEM) and transmission electron microscope (TEM). The electrode characteristics inclusive of electrochemical capacity and cycle life were studied at C/5 rate. Superior performance is obtained with copper coated alloy. Microstructure observations indicate that the observed excellent performance could be attributed to uniform and efficient surface coverage with copper. Also, lanthanum surface enrichment in samples during Cu coating leads to improvement in performance. It is inferred from electro analytical investigations that copper coatings act as microcurrent collectors with alterations in hydrogen transport mechanism and facilitate charge transfer reaction on the alloy surface without altering battery properties. Moreover, supportive first time TEM evidence of existence of such copper nano current collectors (about 8 nm in diameter and length about 20 nm) is reported.

The use of Nickel–Metal Hydride (Ni–MH) batteries for traction application in electric and hybrid vehicles is on the rise. High-rate charge/discharge characteristics are important parameters for electric vehicle applications. The ability to reduce charging time is essential in these traction applications. In this paper, the performance of assembled Ni–MH batteries (1.2V, 0.5Ah specimen cells) when subjected to different charging rates is described. Changes in battery voltage during charging were monitored with a particular emphasis on the quest for fast recharge characteristics. The charging curves reveal the formation of different types of phases. Hydrogen evolution resulted in flat charge profile after certain amount of overcharging. The changes in discharge level after different rates of charging are insignificant. This paper describes the fast rechargeability of assembled Ni–MH cells under various fast-charge regimes.

The heat of hydride formation is a crucial parameter in characterizing a hydrogen storage alloy for battery applications. Novel AB5-type, non-stoichiometric, lanthanum-rich MmNi3.03Si0.85Co0.60Mn0.31Al0.08 (Mm: Misch metal) hydrogen storage metal hydride alloy electrodes are prepared. Electrochemical hydrogen absorption/desorption and electrochemical impedance measurements are carried out at various temperatures in conjunction with sintered nickel hydroxide positive electrodes. The specific capacity of the prepared metal hydride electrodes decreases from 283mAhg−1 at 303K to 213mAhg−1 at 328K. Electrochemical pressure–composition–temperature (PCT) isotherms are constructed from galvanostatic discharge curves and the change in enthalpy (ΔHe°) and the change of entropy (ΔSe°) of the metal hydride alloy electrodes are evaluated as −41.74kJmol−1 and 146.28Jmol−1K−1, respectively. Kinetic parameters are obtained by fitting the electrochemical impedance spectrum performed at different temperatures. The charge-transfer resistance decreases with temperature, whereas exchange current density and diffusion coefficient parameters increase with temperature. It is concluded that the deterioration in capacity is due to enhanced surface activity at higher temperatures.

The cyclic voltammetric behavior of MmNi3.03Si0.85Co0.60Mn0.31Al0.08-based metal hydride electrode was studied in alkaline electrolytes at various temperatures (303, 308, 318 and 328K). Electrochemical parameters such as limiting current density and corrosion potential were determined at these temperatures. The corrosion potential became more negative with increasing temperature. Hydrogen diffusivity was also found to increase with increasing temperature. From electrochemical discharge experiments, it was concluded that the charge transfer process was the rate-determining step.

Capacity fade, generally observed in metal-hydride electrodes of nickel metal-hydride batteries with prolonged cycling, is a problem of concern. To investigate the capacity fade, electrochemical impedance spectroscopy (EIS) measurements were performed in lanthanum rich mischmetal alloy (MmNi3.6Al0.4Mn0.3Co0.7) electrodes. The impedance measurements were conducted during charging at different stages of cycle life. A novel approach was made to get reaction resistances and limiting currents from impedance data based on an equivalent circuit for finite spherical hydrogen diffusion. The main cause of the capacity fade occurring in metal-hydride electrodes with number of cycles was due to particle pulverization and consequent poor hydrogen desorption kinetics, thereby making it more difficult for hydrogenation to occur because of passivation and resistance of electron conduction between the alloy particles.

AB 5 -type MH alloys with Mm (Misch metal) as the A part (with varied rare earth contents in Mm) were investigated for rare earth by XRF analysis and battery performance by life cycle tests with an objective of understanding the influence of rare earth content on electrochemical hydrogen storage. The La/Ce ratio was found to vary from 0.51 to 18.73. The capacity output varied between 179 and 266 mAh g −1 . The results show that the La/Ce ratio has a strong influence on the performance, with the best performance realized with samples having an La/Ce ratio of around 12. La enhancement facilitates easy activation due to refinement in grain size and interstitial dimensions. Also, an orderly influence on crystalline structure could be seen. The study demonstrates that the rare earth content is an essential factor in determining the maximum capacity output because of its influence on crystal orientation as well as an increase in the radius of the interstitials, lattice constants and cell volumes.

In order to improve the electrochemical performance, the alloy represented by the composition ZrMn0.2V0.2Fe0.8Ni0.8 was microencapsulated with Cu, Ni and Pd. Microencapsulation was done prior to test electrode preparation by electroless plating method. The electrode characteristics such as electrochemical capacity and cycle life were studied for the uncoated and coated alloys. It was found that the coated alloy showed higher discharge capacity and lower activation time in comparison to the uncoated alloy. The phase composition of the alloys was characterized using X-ray diffraction (XRD) and surface morphology was studied using scanning electron microscope (SEM). It was found that the surface microencapsulation of alloy powder was effective in improving the electrode discharge capacity and in reducing the activation time.