drees wrote:[*]LiMn (as used in the LEAF/Volt) has horrendous cycle/calendar life at temperatures of 30C+ compared to say LiCo (as used by Tesla). LiCo is even better than LiFe (A123).
[*]Additives can have a very strong effect on coulombic efficiency (and thus durability)[/list]
Thanks drees. Marvelous informative video. Everyone that wants to understand lithium ion batteries should watch this
The truly horrendous coulombic efficiency of the LiMn battery as used by the LEAF and Volt does raise interesting questions about why Nissan and GM went that way.
LiMn does have advantages, but it is primarily in safety, markedly lower run away potential.
There haven't been any LEAF HV pack related fires, and only the one post accident Volt fire, where no one did the right thing and failed to remove the fire potential post accident.
Who would leave gasoline in a damaged vehicle
While Tesla with 18650 commodity cells, which they took extensive efforts to protect and eliminate fire hazard, have still encountered a couple of unfortunate post road hazard / post accident fires.
And use of LiCo on an airplane (which in my own personal opinion was ill advised and which the FAA should still take a much harder look at) had serious problems.
Time will tell if Boeing has fixed the problem and adequately minimized the hazard.
GM did take the approach of providing temperature management for their LiMn version, which as the professor acknowledges in the video has resulted in much better capacity retention than the LEAF.
The real question is whether you can tweak the electrolyte chemistry with the right combination of trace additives to get a reasonable capacity life in a LiMn battery without a temperature management system
Nissan may be correct that not having a temperature management system is the right design approach.
As Dr. Edward Buiel of Coulometrics pointed out in his presentation to the Chattanooga Engineers Club recently, a battery temperature management system can be a huge energy drain. Research on an electric bus a few years back showed the battery temperature management system taking as much energy as what the bus was using for propulsion
But not having a temperature management system is only the right cost effective design approach if you have a battery that can maintain capacity for 100,000+ miles (and while being sufficiently safe). Nissan did NOT get the capacity side of the question correct for the product they have been selling in 2011 / 2012 / 2013 / early 2014. We can only hope they have come up with the magic five or more part additive for the electrolyte to get there with the HOT battery. And that they will offer it to buyers of the early defective HV pack LEAFs at a reasonable pro-rated / variable cost only price, and to the people they are now attempting to sell used LEAFs to that are coming off of lease. If they don't, they may have destroyed the Nissan EV brand