128 Chapter 10 Figure 11 AllCell Phase Change Composite (PCC™) material. Another method of passive cooling is through the use of a phase change material (PCM). A PCM is a material that will go through multiple physical phases when heated, generally from a solid to a liquid. That is a bit of a misnomer however as the PCM does not actually become liquid, but rather it would be more accurate to say that it softens. In these designs, the PCM is generally a block of solid material, often based on wax and graphite, which is machined or molded with locations to insert the cells.
As the cells heat up, the PCM absorbs the heat and disperses it throughout all the PCM causing the material to soften or melt. The PCM is an effective cooling methodology as it takes a lot of energy to force a material to go through a phase change. This can be a cost-effective solution, but it is still limited to being able to top out at a maximum temperature beyond which it will entirely melt and become ineffective as a cooling agent ( Figure 11 ). The biggest benefit of passive thermal management is in its cost, as there is no additional hardware required for cooling the system and cost will be lower than an air-cooled or liquid- cooled thermal management system.
The disadvantages are that it is slow to respond to high-demand applications and it is limited in its capacity to cool down only to the ambient air temperature. Temperature—Protection and Insulation Another aspect of your thermal management system is the integration of heat shields in strategic areas in order to deflect heat away from both external and internal components. Depending on the ESS design, installation location, and amount of heat generation, you may need to include some sheet steel or aluminum to protect against radiant heat and to direct it away from the lithium-ion cells.
There are also some more advanced heat shields that use a sandwich-type design where two pieces of sheet metal are separated by an insulator material in order to isolate the heat away from specific components of the system.