Integration of Micro-encapsulated Phase Change Materials into Thin Coatings for a Passive Battery Thermal Management System

Exploiting the heat energy storage capability of phase change materials is emerging as a potential new strategy for managing Li-ion cell temperature changes during cycling. Phase change materials present a solution that is lighter and more energy efficient than current active battery thermal management systems.  However, deploying phase change materials for battery thermal management is currently held back by the leaking of material when melted, incongruent melting, and low thermal conductivity. In order to solve these problems, micro-encapsulation, the formation of a core-shell capsule, has been used in this work. Encapsulation protects against leakage and the shell properties can be used to increase thermal conductivity. In this work, micro-encapsulated octadecane (C18H38) comprising a carbon composite-based shell made up of graphene oxide and carbon nanotubes, was selected to maintain a temperature of 27 °C. The synthesised capsules were formulated into a coating and applied onto the exterior of cylindrical,1.6 Ah, Li-ion cells. The coating delivered a heat storage capacity of 100 J·g-1, and thermal imaging of cells showed that the average peak increase in cell temperature during galvanostatic cycling was reduced by 8 °C when the coating was applied. The optimum coating thickness was found to be 3 mm, increasing the cell mass by 10-15%. Furthermore, the coatings delivered a cell temperature reduction of 4 °C during a modified European drive cycle, highlighting good functionality towards practical cell usage.