Rechargeable metal hydrides

Zhang, P. W. Yokoyama, T. Itabashi, O. Wakui, Y. Suzuki, T. M. Inoue, K. Recovery of metal values from spent nickel-metal hydride rechargeable batteries. J. Power Sources 1999, 77, 116-122. 

A nickel-metal hydride rechargeable battery for laptop computers is based on the following chemistry ... 

In the case of metal hydrides, recharging the system requires the chemical heat of reaction between the metal and the hydride to be removed (via an in-tank heat exchanger). Large tanks, as used on the German Class 212 submarine, require long recharge times, of the order of one day. 

Combining the nickel cadmium and nickel-hydrogen systems technologies has given rise to the nickel-metal hydride rechargeable battery, one of the most advanced rechargeable systems commercially available and an environmentally friendlier alternative to nickel-cadmium batteries. The cell and its reaction may be written ... 

Engineering applications such as hydrogen storage in metal hydrides, the nickel-metal hydride rechargeable battery (Ni-MH), and the proton exchange membrane fuel cell (PEMFC) are basically dependent on the surface properties and characteristics. 

Characteristic of Nickel-Metal-Hydride Rechargeable Batteries... 

Nickel-iron (conven- tional) Nickel-zinc Zinc/silver oxide (silver-zinc) Cadmium / silver oxide (silver-cadmium) Nickel- hydrogen Nickel- metal hydride Rechargeable primary types, Zn/Mn02 lithium ion systems ... 

G.M. Weng, C.Y.V. Li and K.Y. Chan, High voltage vanadium-metal hydride rechargeable semi-flow battery, J. Electrochem. Soc. 160,2013, A1384-A1389. 

Hydrogen-storage alloys (18,19) are commercially available from several companies in the United States, Japan, and Europe. A commercial use has been developed in rechargeable nickel—metal hydride batteries which are superior to nickel—cadmium batteries by virtue of improved capacity and elimination of the toxic metal cadmium (see BATTERIES, SECONDARYCELLS-ALKALINe). Other uses are expected to develop in nonpolluting internal combustion engines and fuel cells (qv), heat pumps and refrigerators, and electric utility peak-load shaving. 

One of the problems with early hydride systems was decrepitation of the alloy. Each time the metal hydride storage tank was recharged the particles would break down and eventually the particles became so small that they began to pass through the 5-p.m sintered metal filter which kept the hydride inside the tank. Addition of 0.5% manganese, which caused the decrepitation process to cease once the particles reached a size of about 10 p.m, solved this problem. 

GM began offering more expensive nickel-metal hydride batteries as an option. These batteries extended the range to 75 to 130 miles, but also took slightly longer to recharge. 

Compared with nickel-cadmium and nickel-metal hydride systems RAM cells exhibit very low self-discharge, making them ideal for intermittent or periodic use without the need to recharge before using, even in hot climates. Figure 6 shows a comparison of the temperature characteristics, for various battery systems in the form of Arrhenius diagrams. 

Battery technology continues to advance at a steady pace. Lithium batteries and nickel-metal-hydride batteries are now commonplace. These new rechargeable batteries eliminate the need for toxic cadmium and store more energy per unit mass. The detailed chemistry that underlies the newest advances in battery technology involves principles that are beyond the scope of an introductory course. 

Gamburtzev S., Velev O.A., Danin R., Srinivasan S., Appleby A.J. Performance of an improved design of metal hydride/air rechargeable cell . In Batteries for portable application and electric vehicles. C.Holmes, A.Landgrebe ed. Pennington Electroch. Soc, 1997, 726-33. 

The three generic classifications of hydrogen storage materials are reversible metal hydrides, non-reversible chemical hydrides, and adsorbent materials. Reversible metal hydride materials and adsorbents can be recharged with hydrogen without removing them from the vehicle, while non-reversible chemical hydride materials must be removed from the vehicle in order to be recharged. 

Those rare-earth AB -type hydrides were quickly utilized in rechargeable nickel metal hydride batteries where electrochemical hydrogen charging and discharging take place at ambient temperature. Such electrochemical hydrogen storage is reversible, when the negative hydride electrode (anode) is combined with the positive Ni electrode (cathode) in the battery cell.. 

As a matter of fact, the first hydrides with practical hydrogen storage capacities were realized in rechargeable nickel metal hydride batteries. For more information on electrochemical hydrogen storage in rechargeable batteries a reader can be referred to several recent reviews on this subject [71-73]. 

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