Certainly, it isn’t because of low-cost. Lithium ion (Li-ion) is much more expensive than the nickel-metal hydride (NiMH) battery technology it is replacing. However, both specific energy and energy density of a lithium-ion battery pack is much greater than NiMH, saving weight and space in automotive applications. These considerations are not trivial in today’s world, as motorists clamor for more room in the car, and weight reduction is equated with increased fuel economy.
There are a number of different types of lithium ion batteries being used in current EVs and PHEVs. The major difference between them is the materials used to construct the cell’s positive electrode. Higher energy cells (such as those used in consumer electronics) use lithium cobalt oxide and tend to be intolerant to overcharging and other abuse. When these cells overheat, the electrode releases oxygen into a flammable organic electrolyte, which can lead to thermal runaway. If you’ve ever witnessed a laptop computer fire, this is likely what caused it.
There is ongoing development taking place on lithium ion electrodes that are more stable, but this generally results in a less powerful battery. For instance, the Chevrolet Volt has used a lithium manganese spinel based electrode which is less energetic but much more manageable than its cobalt oxide cousin. GM has now licensed nickel manganese cobalt (NMC) technology from the Argonne National Laboratory that further improves the Volt’s battery performance at every level. The combination of improved battery chemistry and more effective thermal management makes HV battery packs progressively safer and longer-lived for the EVs of the future.
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