Wow, it's been well over a year since my last post!

So much has happened, but as usual I've run out of time to talk about it.  I'm adding the following documentation in hopes that google scrapes this site, so other battery hackers can learn from my tinkering with a Chevy Volt battery.

I couldn't find any information on manually charging the 2013-2014 Chevy Volt's LiNiMnCoO2 battery, so after reading a bunch of research papers and verifying the data with some empirical measurements, I present the following charge/discharge advice:

The 2013-2014 Volt's battery is made up of three parallel LG Chem 15 Ah cells per segment.  While the cell can handle up to 4.5 V peak, the lifetime is considerably shortened (less than 100 cycles) under these conditions, and voltages much higher can cause thermal events (i.e. a fire).  At 4.4 V, the lifetime increases to 125 cycles, which isn't much better.  The main reason for shortened lifetime is the carbon dioxide evolution and Mn dissolution into the electrolyte.  I've defined lifetime as the point where less than 60% of the original charge remains... which is a lot of lost charge (I'm being generous).  In short, don't overcharge lithium cells!

And thus we must charge to lower voltages and give up the additional storage capacity.  At 4.3 V, we're up to 300 cycles.  At 4.24 V we're up to 500 cycles or so.  At 4.1 V we're somewhere around 1000 cycles.  Cycle life continues to drastically increase for a couple hundred more mV, but then it levels off.

In short, I've chosen to CV charge each cell to 4.08 V to maximize lifetime.  Once 4.08V is hit at 1C, there's an additional 2.5 or so Ah (~5% of nominal capacity) if you hold the voltage constant and regulate current.  I'm building a BMS that'll just cutoff the charge at 4.08 V, as using a smaller section of the overall SOC also helps increase battery lifetime.

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Cycle life is also greatly reduced by over-discharging cells.  There's not much energy left below 3.4 V, so it's certainly not worth the decreased lifetime to drag them all the way down to 3.0 V.  I found less than 2 Ah between 3.0 and 3.4 V (less than 5% nominal capacity).  Considering the decrease in lifetime is exponential once you drop below 3.2 V, it's just not worth the sacrifice milking every last Ah.

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tl;dr: For maximum lifetime @ 1C:
-CV charge the Chevy Volt's LiNiMnCoO2 cells to 4.08V,
-then CC to C/50 (1 A) if you want an additional 5% capacity.
-Discharge the cell no less than 3.3 V, or 3.2 V if you want that last 5%.