Posted: Thu Aug 07, 2008 6:24 am
If the cells are lithium technology (which seems highly likely) then they will have a terminal voltage of either 3.2V (for LiFePO4) or 3.7V (for LiCoO2 or LiMnO4), rather than the 2V that is typical for lead acid batteries.
It is this higher terminal voltage that is largely responsible for the greater energy/power density for lithium cells, together with the fact that lithium is much lighter than lead.
Typical cycle life for the best lithium technology currently available in an EV application is around 1000 to 3000 charge/discharge cycles, although this can be significantly improved by not fully discharging or charging the cells. Limiting charge to 95% (using a smart charger) will, on it's own, give a significant cycle life improvement.
Calendar life of lithium cells remains a slight problem, as lithium cells start to degrade from the date of manufacture. However, early indications are that LiFePO4 cells degrade more slowly with age than older lithium technologies. 5 years for a 30% degradation in capacity seems likely for the best cells around at the moment. 10 years seems to be stretching things a bit, as I suspect that cell capacity would be massively reduced after this period of time.
Jeremy
It is this higher terminal voltage that is largely responsible for the greater energy/power density for lithium cells, together with the fact that lithium is much lighter than lead.
Typical cycle life for the best lithium technology currently available in an EV application is around 1000 to 3000 charge/discharge cycles, although this can be significantly improved by not fully discharging or charging the cells. Limiting charge to 95% (using a smart charger) will, on it's own, give a significant cycle life improvement.
Calendar life of lithium cells remains a slight problem, as lithium cells start to degrade from the date of manufacture. However, early indications are that LiFePO4 cells degrade more slowly with age than older lithium technologies. 5 years for a 30% degradation in capacity seems likely for the best cells around at the moment. 10 years seems to be stretching things a bit, as I suspect that cell capacity would be massively reduced after this period of time.
Jeremy