Energy_Storage_Technologies.pdf

With almost as long of a history and market

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With almost as long of a history and market penetration as lead acid batteries are nickel-electrode cells, in particular, nickel cadmium. These devices have a high specific energy and require little maintenance, but have high costs and a somewhat low cycle life. In general, these devices can better-endure more extreme conditions and full discharges without sacrificing loss of capacity, lifetime, or efficiency than lead acid batteries [3]. As of 2009, the largest battery installation in the world was a NiCd array providing 40 MW for 7 minutes, in Fairbanks, Alaska [7]. How it Works This device operates based on the principles of simple electrochemical cells, described in Section 2.1. Each cell has a positive electrode assembly composed of nickel hydroxide Ni(OH) 2 , and the negative electrode is the distinguishing feature in each of the designs described below. The electrolyte is typically potassium hydroxide KOH(H 2 O) [1]. Variations There are a wide variety of chemistries within this category, the most prevalent of which is nickel-cadmium. Nickel-cadmium (NiCd) As the most common nickel-electrode system in utility-use today, this chemistry is fairly tolerant of abuse and compared with lead acid batteries these systems have higher energy density, longer cycle life, and require less maintenance [2]. This basic chemistry comes in a number of designs including vented industrial nickel-cadmium, vented sintered-plate nickel-cadmium, and sealed nickel-cadmium [1]. Nickel-iron (NiFe) This is the oldest type of this genre of battery, and is quite durable, able to deal with physical and operation abuse (including overcharging, over-discharging, being open-circuited for long periods of time, and being short circuited) without shortening its lifetime significantly. The downside of these systems is that their performance is significantly affected by changes in temperature, the are unable to retain charge, have low power density and produce significant levels of gas while operating [2]. Nickel-hydrogen (NiH 2 ) A hybrid system with features similar to both batteries and fuel cells and in this design the negative electrode is gaseous hydrogen, and the positive electrode is nickel oxyhydroxide [2]. Although this design is highly reliable, with very long expected lifetime, and requiring little maintenance, this device is the most costly of this genre [2]. Nickel-metal hydride (NiMH) In this configuration, the negative electrode is hydrogen, but the hydrogen is absorbed into a metal alloy [2]. This technology has longer cycle lifetime and does not lose capacity as easily has NiCd, but it is sensitive to overcharge and high-rate discharge [2]. Nickel-zinc (NiZn) A relatively new technology that has not shown itself to be outshine other chemistries, however advances in this design could be commercially promising due to its high specific energy [1].
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