UPDATE: Martin Eberhard full of halibut, part 2September 2, 2007
I wrote an earlier post concerning Martin Eberhard’s critique of series hybrids, in particular the lifespan of the Chevy Volt’s battery pack. In that post, I noted that Martin incorrectly assumes that all lithium ion cells are made equal, and also incorrectly assumes that a 40 mile range correlates to 100% depth of discharge of the pack, and thus a full (and brutal) charge/recharge cycle.
GM-Volt.com confirmed recently that the 40 mile range can be achieved with only 8 kWh of the pack’s available 16kWh, and that to maximize lifespan, the generator will kick at this point of 50% charge, and stop at 80% charge. This optimized charging cycle, combined with the innate durability of lithium-iron-phosphate chemistry, will help the battery pack last for years.
Some caveats though:
1) Whether this optimization scheme will result in the ridiculous 7000+ cycle life that A123 is quoting for its proprietary LiFePO4 chemistry remains to be seen. The M1 cells that A123 makes (of which I own several) are rated at only 1000+ cycles rated at 100% DOD.
This supposedly increased lifespan might be due in part to the newer automotive-grade electrode. More likely, it might be calculated using the optimum temperature and charge conditions.
2)This optimized charging scheme assumes that there is gas in the car. Most people will, of course, but there is bound to be the person who leaves gas out to save weight, and bleeds the car battery nearly dry on a regular basis. How significantly will this reduce battery life?
Also, how will recharging the car from grid while at various states of charge affect life? For example, how will charging beyond 80% of rated capacity (which could be liberally considered “overcharging”) be bad for the cell?
The riddle for the best battery pack isn’t solved yet, but it’s becoming increasingly clear that that there is something motivating the naysayers’ rhetoric other than cold hard data. For example, both Martin and Toyota Motor Corporation are shackled to using cobalt lithium ion cells, the merits of which are increasingly being called into question. With the case of Toyota, it’s highly likely that they realize they are behind in the plug-in hybrid race, and are trying to deflect public attention from this fact. With the case of Martin/Tesla, they have spent a lot of time, sweat, and tears making a high end system to tame the cobalt cells, and they aren’t about to readily admit that this system could soon be rendered obsolete. The fact that they continue to focus on cell-level specific energy, and not on gross battery pack specific energy, also suggests that they know they need to be on the defensive.