Lithium-ion technology is regarded as the logical successor to the nickel hydride battery packs which are still widely used. But while lithium-ion cells have been used successfully in light duty applications like mobile phones since the nineties, they start to look expensive when you build them for high current applications. Nevertheless, Li-ion turns in a better performance than NiMH under virtually all conditions, though unfortunately its particular strength is low-current systems.
Memory effect is not a problem with Li-ion, and self-discharge is much less of a problem than with most NiMH cells.
But there are problems. Operating life is not good, with cell capacity diminishing steadily in use — and this is more of a problem in high-current applications. High temperatures accelerate a cell’s deterioration, and these temperatures can be generated by charging, high-load discharge or even by hot weather. Modern laminated types of Li-ion cell disperse heat more effectively that traditional cylindrical cells, but cooling is still critical. Automotive Li-ion batteries (and some NiMH packs) use pumped liquid cooling.
Part of the ageing process for a Li-ion battery is that internal resistance steadily climbs. This means that cell voltage under load drops. Additionally, Li-ion cells suffer from thermal runaway if they are overheated by high current drain or by charging at excessive voltage. In extremis, this can result in explosion.
If you deep-discharge a Li-ion pack, it could be irreversibly damaged. Commercial Li-ion batteries are fitted with protective circuitry that prevents deep-discharging or over-voltage charging in normal use,
but there is still a risk of the pack becoming deep-discharged if it remains unused for some time.
Some of the problems with Li-ion batteries could be overcome using lithium-air technology, though this is not likely to happen in the short term.
NiMH battery pack in BMW Active Hybrid X6.
Li-ion battery pack in BMW Active Hybrid 7 using conventional cylindrical cells.
Laminar Li-ion cell produced by Nissan. These are assembled into small batteries...
A small battery of Li-ion cells. Several small batteries are assembled as a complete battery pack...
Nissan Li-ion battery pack, used in Nissan and Renault vehicles.