Lithium-Ion and Other Cell Chemistries 73 Nickel Cadmium Nickel cadmium (NiCd) batteries are most commonly used in portable power applications such as consumer electronics, portable power, telecommunications, uninterruptible power supplies and most frequently in train and rail car applications. In fact, about 40% of all NiCd batteries end up in one or another train-based application providing power from lighting to air conditioning to powering switchgear equipment and many other electrical power loads on the train (Erbacher, 2011).
The two biggest challenges, as mentioned above, that NiCd faces are that when compared to lithium-ion, it has a relatively low energy density ( 40–60 Wh/kg) and the “memory effect” that NiCd faces. The memory effect occurs when a battery gets used to working within a certain duty cycle range. After time this will be the only range that the cell can operate within as it will modify its electrical properties to adjust to the new operational profile. For these reasons NiCd has not found a large market in automotive application and is gener- ally not appropriate for automotive electrification applications.
However, NiCd has proven very suitable to consumer electronics and light rail type applications. Nickel Metal Hydride Nickel metal hydride (NiMh) gained initial market acceptance in portable power applications but really found a good home with the introduction of the automotive HEV. The HEV is a very good application for NiMh, as NiMh offers about twice the energy and power density of lead acid at about half the size. Typical NiMh cells will range between 30- and 80-Wh/ kg-energy density. Some early EV applications, such as the General Motors EV1, adopted NiMh batteries to power these EVs thereby offering significant improvements over the lead acid alternatives.
However, with the introduction of lithium-ion chemistries with much higher energy density, NiMh became a less viable solution for full electrification. NiMh requires about twice the space as lithium-ion (higher volumetric energy density of lithium-ion) at about twice the weight (higher gravimetric energy density of lithium-ion). On the other hand, NiMh offers about half the size and weight of a comparative lead acid battery solution. But NiMh has found a good home in the high-volume automotive HEV applications such as the Toyota Prius which now has well over 7 million HEV vehicles on the road globally with this technology since the launch of their first generation Prius (Holmes, 2014).
Addition- ally, with the growth of stationary power and telecom power applications, NiMh offers many benefits over what has traditionally been a lead acid application market. Yet as the cost of lithium-ion comes down more companies are beginning to evaluate other chemistries.