The high energy density results from using air as the second reactant in the battery rather than materials like cobalt oxide or iron phosphate. The problem is that lithium is flammable and circulating air through the battery as a reactant greatly increases the risk of thermal instability.
A lot of research work remains to be done before lithium air batteries can reach their theoretical potential. IBM will use the supercomputer time for simulation and modeling of the batteries. Considering that IBM is also the manufacturer of some of the world's top supercomputers, it's not clear why the company needs to rely on DOE computing time, but hopefully this will help speed development.
[Source: Network World]