Phase change materials (PCM's) will undoubtedly be used as part of the Volt's battery management system. The phase change material (a paraffin wax) is encapsulated in a graphit composite matrix. Blocks of individual cells are then wrapped in this material in order to passively cool the cells and maintain a more constant temperature distribution in the pack. This thermal management technique is used in conjunction with the active cooling system of the BMS to ensure the Volt's Lithium pack will last at least 10 years.

http://www.sae.org/mags/aei/8094