Nickel-hydrogen batteries characteristics

The vented-type battery needs to perform water addition in which water consumed by electrolysis is periodically added. However, in recent years, the vented-type nickel-cadmium secondary battery which has reduced the water addition frequency is produced commercially for trains and the like. The battery controls the electrolysis of the water under float charging by using the pasted-type cadmium electrode which has a high hydrogen overpotential characteristic for the negative electrode. 

The silver-cadmium (cadmium/silver oxide) battery has significantly longer cycle life and better low-temperature performance than the silver-zinc battery but is inferior in these characteristics compared with the nickel-cadmium battery. Its energy density, too, is between that of the nickel-cadmium and the silver-zinc batteries. The battery is also very expensive, using two of the more costly electrode materials. As a result, the silver-cadmium battery was never developed commercially but is used in special applications, such as nonmagnetic batteries and space applications. Other silver battery systems, such as silver-hydrogen and silver-metal hydride couples, have been the subject of development activity but have not reached commercial viability. 

The rechargeable sealed nickel-metal hydride battery is a relatively new technology with characteristics similar to those of the sealed nickel-cadmium battery. The principal difference is that the nickel-metal hydride battery uses hydrogen, absorbed in a metal alloy, for the active negative material in place of the cadmium used in the nickel-cadmium battery. 

Table 4.11 Characteristics of three types of nickel-hydrogen cells and batteries...

The iron-nickel oxide alkaline battery system has many features in common with the nickel-cadmium system discussed above. It was first developed by Edison in the USA at the turn of the century and was patented in the same year as Jungner s first nickel-cadmium US patent, 1901. Iron can be regarded as a favourable active battery material because of its low cost, high theoretical specific capacity (twice that of cadmium) and non-toxic, pollution-free characteristics. However, because its reduction potential is below that of hydrogen, and since hydrogen overvoltage is low on iron, charge retention is poor and efficiency is low. 

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. 

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