80 Chapter 7 suffers from being less stable at higher temperatures and more reactive than other chemis- tries. This means that above about 130 °C the cell will enter the thermal runaway stage, a lower temperature than other lithium-ion chemistries. For this reason, LCO has not seen wide use in large application but continues to see use in small consumer electronics and in fact has been outright rejected by some automotive manufacturers. LCO is also a somewhat higher cost chemistry due to the high amount of cobalt, a relatively precious material that it contains.
NCA is frequently used in portable power applications but is being evaluated for automotive applications due to its high power, however, it does have some drawbacks that are keeping it from gaining a foothold in the vehicle space—high cost and low safety. Finally, LMO offers high energy and high power, however, suffers from shorter cycle life thus making it an appropriate chemistry to be used in portable power applications where you want long run time but not necessarily in automotive applications where you want long life. Anode Materials The negative side of the electrode is known as the anode.
Today, most anodes are made of a mixture of one of two materials either graphite, or soft or hard carbons. There are many different grades and types of graphite, with graphene forming the basis for most of it. But the quality and selection of the material will play a very important role in the performance of the cells (Dahn & Ehrlich, 2011). One other lithium-ion anode that is gaining a lot of interest is the lithium-ion titanate cell. An LTO cell offers the advantage that it can operate at a lower temperature than other chemistries and offers a high power density. However, LTO suffers from having a lower nominal voltage, in the range of about 2.2–2.3 V per cell.
In addition, current LTO offerings tend to be much higher cost than comparative NMC or LFP cells. This means that not only do you need more of them to achieve the desired system voltage, they will also cost more. However, there are several manufacturers that are working on improving the cost of LTO which may make it a good fit for many low energy and high power applications such as micro-HEVs and some are working hard to integrate LTO into fully EVs. There does not appear to be any technological reason that LTO will remain as a high-cost solution, as volumes begin to increase the costs should also decrease at a relatively stable rate.
Much research is being done into several different new anodes including silicon, tin, germa- nium, carbon nanotubes, and other nanocomposite materials. However, most of these are still in the laboratory and none are currently commercialized for high-volume products. As can be seen in Figure 6 below, there are some very big opportunities to increase energy density by moving to silicon, tin, or some of these other types of anode materials. There are still some