A. Hightower

Electrochemical Studies on LaNi5 − x Sn x Metal Hydride Alloys

Electrochemical studies were performed on LaNi(sub 5-x)Sn(sub x) with 0(less than or equal to)x(less than or equal to)0.5. We measured the effect of the Sn substituent on the kinetics of charge transfer and diffusion during hydrogen absorption and desorption, and the cyclic lifetimes of LaNi(sub 5-x)Sn(sub x) electrodes in 250 mAh laboratory test cells. We report beneficial effects of making small substitutions of Sn for Ni in LaNi(sub 5) on the performance of metal hydride alloy anode in terms of cyclic lifetime, capacity and kinetics. The optimal concentration of Sn in LaNi(sub 5-x)Sn(sub x) alloys for negative electrodes in alkaline rechargable secondary cells was found to lie in the range 0.25(less than or equal to)x(less than or equal to)0.3.

Irreversible Capacities of Graphite in Low‐Temperature Electrolytes for Lithium‐Ion Batteries

Carbonaceous anode materials in lithium-ion rechargeable cells exhibit irreversible capacity, mainly due to reaction of lithium during the formation of passive surface films. The stability and kinetics of lithium intercalation into the carbon anodes are determined by these films. The nature, thickness, and morphology of these films are in turn affected by the electrolyte components, primarily the solvent constituents. In this work, the films formed on graphite anodes in low-temperature electrolytes, i.e., solutions with different mixtures of alkyl carbonates and low-viscosity solvent additives, are examined using electrochemical impedance spectroscopy (EIS) and solid-state ^(7)Li nuclear magnetic resonance techniques. In addition, other ex situ studies such as X-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy were carried out on the graphite anodes to understand their microstructures.

Electron energy-loss spectrometry on lithiated graphite

Transmission electron energy-loss spectrometry was used to investigate the electronic states of metallic Li and LiC6, which is the Li-intercalated graphite used in Li-ion batteries. The Li K edges of metallic Li and LiC6 were nearly identical, and the C K edges were only weakly affected by the presence of Li. These results suggest only a small charge transfer from Li to C in LiC6, contrary to prior results from surface spectra obtained by x-ray photoelectron spectroscopy. Effects of radiation damage and sample oxidation in the transmission electron microscopy are also reported.

Mechanical alloying of Fe and Mg

Abstract We performed mechanical alloying of Fe and Mg powders with a wide range of compositions and characterized the as-milled alloys with X-ray powder diffractometry, rotating sample magnetometry, density measurements, and Mossbauer spectrometry. Alloys with less than 20 at.% Mg were single phase bcc with enlarged lattice parameters, indicating that Mg atoms were substitutional on the bcc lattice. Mossbauer spectrometry showed these alloys to have large chemical heterogeneties, however. Likewise, it appears that the Mg-rich hcp phase contains some Fe, but the Fe atoms are probably clustered together.

Electrochemical Properties of LaNi5–xGex Alloys in Ni-MH Batteries

Electrochemical studies were performed on LaNi5–xGex metal hydride alloys with 0 <= x <= 0.5. We carried out single-electrode studies to understand the effects of the Ge substituent on the hydrogen absorption characteristics, the electrochemical capacity, and the electrochemical kinetics of hydrogen absorption and desorption. The electrochemical characteristics of the Ge-substituted alloys are compared to those of the Sn-substituted alloys reported earlier. LaNi5–xGex alloys show compositional trends similar to LaNi5–xSnx alloys, but unlike the Sn-substituted alloys, Ge-substituted alloys continue to exhibit facile kinetics for hydrogen absorption/desorption at high solute concentrations. Cycle lives of LaNi5–xGex electrodes were measured in 300 mAh laboratory test cells and were found to be superior to the Sn-substituted LaNi5 and comparable to a Mm(Ni,Co,Mn,Al)5 alloy. The optimum Ge content for LaNi5–xGex metal hydride alloys in alkaline rechargeable cells is in the range 0.4 <= x <= 0.5.

Electrochemical Studies on LaNi(sub 5-x)Sn(sub x) Metal Hydride Alloys

Electrochemical studies were performed on LaNi(sub 5-x)Sn(sub x) with 0(less than or equal to)x(less than or equal to)0.5. We measured the effect of the Sn substituent on the kinetics of charge transfer and diffusion during hydrogen absorption and desorption, and the cyclic lifetimes of LaNi(sub 5-x)Sn(sub x) electrodes in 250 mAh laboratory test cells. We report beneficial effects of making small substitutions of Sn for Ni in LaNi(sub 5) on the performance of metal hydride alloy anode in terms of cyclic lifetime, capacity and kinetics. The optimal concentration of Sn in LaNi(sub 5-x)Sn(sub x) alloys for negative electrodes in alkaline rechargable secondary cells was found to lie in the range 0.25(less than or equal to)x(less than or equal to)0.3.

Electrochemical Evaluation of LaNi(sub 5-x)Ge(sub x) Metal Hydride Alloys

We report a detailed evaluation of Ge-substituted LaNi_5 for electrochemical application as a negative electrode in alkaline rechargeable cells. Alloys with small substitutions of Ge for Ni show operating pressures, chargeability, cyclic lifetime, and kinetics for hydrogen absorption and desorption all superior to those found in many other substituted LaNi_5 alloys. These improved properties were achieved with a minimal reduction in hydrogen storage capacity.

LaNi/sub 5-x/M/sub x/ alloys in rechargeable batteries: factors affecting cycle lifetimes

We have studied the effect that solute chemistry has on the cyclic lifetimes of AB/sub 5/ alloys in rechargeable cells. The results of a large number of measurements of cycle lifetimes of LaNi/sub 5-x/M/sub x/ electrodes are compiled. Correlations are made between the lifetimes, characterized by an exponential decay, and properties of the alloys and their constituents. It is found that the lifetimes show a strong dependence on the formation enthalpy of La with Ni/sub 1-x/5/M/sub x/5/ and a weak dependence on alloy volume expansion on hydriding.

LaNi/sub 5-x/M/sub x/ metal hydride alloys for alkaline rechargeable cells

This work centers on making alloy modifications to LaNi/sub 5/ by replacing Ni with various metal elements. The primary goal of the alloy modifications is to stabilize the alloy during electrochemical cycling in an alkaline medium. The reasons that some elements promote cyclic stability are explored, and the relative magnitude of their effect is Ge>Sn>Si>Ga>Al>In>Ni. Other properties are determined for each alloy, such as maximum capacity, charge transfer kinetics, hydrogen diffusion, charge overpotentials, and charge efficiency. Alloy microstructural information is measured by X-ray diffraction, and gas-phase.

Electrochemical Evaluation of LaNi5 − x Ge x Metal Hydride Alloys

We report a detailed evaluation of Ge-substituted LaNi_5 for electrochemical application as a negative electrode in alkaline rechargeable cells. Alloys with small substitutions of Ge for Ni show operating pressures, chargeability, cyclic lifetime, and kinetics for hydrogen absorption and desorption all superior to those found in many other substituted LaNi_5 alloys. These improved properties were achieved with a minimal reduction in hydrogen storage capacity.