Lithium Based Batteries.

Lithium is the battery technology of choice for applications from laptop batteries to electric vehicle batteries for two important reasons: Lithium is relatively cheap, and, more importantly, Lithium is very light.  The lightest metal known to man has the potential of producing the highest energy density batteries possible. 

Energy density is of primary importance in portable and electric vehicle applications.  In utility applications it is no more than a 'nice to have' feature.  For utility applications, Lithium batteries generally come up short in a couple of key feature requirements, low cost and long cycle life.

Most Lithium batteries degrade quickly on repeated full cycling of their capacity, many becoming useless after only a few hundred 100% depth of discharge cycles.  In addition, many Lithium batteries lose capacity as a factor of time, regardless of cycling.  Add to this costs that are generally in excess of $1 million / MWh without power conditioning, and you can see why Lithium batteries are not generally considered a viable product in the utility space.  For a more detailed explanation as to the general non-viability for plate-type batteries in utility applications, see the battery overview.

Not All Lithium Batteries Are the Same
A few plate batteries have high enough cycle life to be of value in utility applications.  One example is the Nano Titanate technology championed by Altair-Nano.  In this technology, the active material is contained in a spherical crystalline form that does not change morphology (shape or size) during the charge discharge cycle, removing that important path for cycling degradation.  The result is a highly increased cycling capability.

For different (and somewhat arcane) reasons, the lithium chemistry of Lithium Iron Phosphate (LiFePO4) has a much higher cycle life than other lithium chemistries, providing for as much as 7000 100% DOD cycles.  The most well known manufacturer using this chemistry is A123 Systems, who is widely expected to be a major player in future electric vehicle battery, HEV, and PHEV markets.

Both of these technologies are relatively expensive, but because of their advantages over other plate batteries are being marketed for utility applications.  Altair Nano is actively marketing into frequency regulation utility applications, and A123 Systems has proposed a large scale 8MW/32MWh battery for Southern California Edison.

In addition, an important note for Lithium is that IBM announced in August of 2009 a major effort to develop a Lithium-Air battery, which has the potential of producing 'serious' electric vehicle batteries, batteries with an energy density sufficient to power a car for 400 miles.  While it is unlikely that this will produce a cost effective utility scale battery, it is an effort worth following. 

This would be a pure Lithium metal battery, as opposed to the Lithium complexed batteries noted above, which sacrifice energy density for safety, manufacturability, reduced corrosion and other issues.  Pure Lithium metal, while electrochemically the best, is so highly reactive as to be a safety issue.  IBM will have to create an air membrane that passes Oxygen freely while denying even a trace of water vapor to the Lithium metal.

It has been suggested that a solution to renewable energy integration will be to use either new or well-used EV and PHEV batteries as dispatchable utility storage. Note that, if the utility were to schedule dispatching of stored energy in batteries from, for example, 5000 PHEV owners, the value of the batteries in the cars would decrease faster than the value of the stored energy could compensate for.  Car owners would be unlikely to allow the utility to degrade the value of their cars without compensation. 

The use of used Lithium PHEV batteries is possible, but consider the issue of connecting, maintaining, monitoring, and properly charging the hundreds of PHEV batteries it would take to create a minimally useful utility energy storage of, say, 10MWh.