Structural, thermodynamic and electrochemical properties of over-stoichiometric La1-y(Ni1-zSnz) 5+2y hydride forming compounds

The structural properties of four tin substituted La1-y(Ni 1-zSnz)5+2y compounds have been investigated by X-ray powder diffraction (XRD) and microprobe analysis as a function of both tin amount (z) and over-stoichiometry (y). Their thermodynamic behaviour toward hydrogen gas absorption/desorption has been measured up to 1MPa. Their electrochemical capacities and cycle lives have been determined. From these analyses, the different behaviour observed for these materials have been correlated to their structural and thermodynamic properties

In situ Raman analysis of gas formation in NiMH batteries

In this paper Raman spectrometry is introduced in the field of sealed battery research for in situ gas-phase analysis and for long-term measurements. For this purpose, a new method was successfully applied in order to model battery behavior without interfering with operation. It is shown that oxygen, hydrogen, and nitrogen are responsible for the pressure increase that occurs during overcharging. The relative contribution of the different gases depends on the current imposed on the battery as well as the operating temperature. Reproducible and stable signals could be obtained even under severe conditions such as high pressure and elevated temperature. Oxygen and hydrogen are produced in side reactions taking place during battery operation. However, as nitrogen is unlikely to be a reacting gas inside the battery, the change in its partial pressure can be attributed to electrode expansion and a change in the electrolyte volume

Secondary batteries - nickel systems : nickel–metal hydride : metal hydrides: Metal Hydrides

Many scientists and even policy-makers are nowadays openly speculating about the future hydrogen economy for which it is believed that hydrogen-driven fuel cells are going to play a dominant role in transportation, thereby replacing conventional and inefficient internal combustion engines. To enable such beneficial economy it has been argued that safe and efficient storage of hydrogen gas is one of the crucial aspects to be solved. However, it has generally not been realized that our society has already entered the hydrogen economy a few decades ago with the development of nickel-metal hydride (Ni-MH) batteries. Advantageously, this battery system is indeed based on the smallest energy carrying chemical particle shuttling between the two electrodes. Storage of hydrogen in the negative electrode of Ni-MH batteries has been accomplished efficiently, which is safe and at low pressures in the form of metal hydrides (MH). Since its discovery, this battery type has become widely accepted to power our portable electronics, due to their high storage capacity, excellent rate capability, and environmental friendliness. Its popularity is currently further boosted resulting from the large-scale introduction in hybrid electrical vehicles (HEVs) for which Ni-MH batteries are exclusively used and it is to be expected that this expansion is further amplified in the near future into the direction of plug-in (hybrid) electrical vehicles (P(H)EV). This battery system can, therefore, be considered as the first commercial success toward a fully developed hydrogen era. In this article the basic electrochemical principles underlying Ni-MH operation are first outlined and then the materials research, which has enabled this successful battery system, is reviewed. Finally, more recent developments in materials research, which may lead to a new generation of high-energy density Ni-MH batteries in the near future, are described

High energy density strategies: From hydride-forming materials research to battery integration

Two different strategies are outlined to develop both high energy density and space-efficient batteries, including the most widely applied rechargeable nickel-metal hydride (NiMH) and Li-ion batteries. The hydrogen storage capacity of fluorite-structured Mg-containing compounds are shown to have a reversible electrochemical storage capacity of more than four times that of the commonly used MischMetal-based AB5 compounds in NiMH, i.e. 1500mAh/g (5.6wt.%). The formation of octahedral sites within the crystal lattice is argued to be very crucial for the improved kinetics of hydrogen absorption and desorption. It is shown that the fluorite-structure can be conserved with both precious Sc and the less expensive Ti up to a Mg content of 80at.%. Both thermodynamic and kinetic data are presented in relation to the materials composition. In addition, the development of preshaped batteries, as the first step to battery integration, has contributed to a much higher level of design freedom for portable electronic equipment. The manufacturing process of preshaped batteries will be described together with their electrochemical characteristics. Advantageously, the mechanical stability is provided locally by polymer rivets, allowing to get rid of heavy metallic casings and to make use of a much wider range of battery shapes