Experimental characterization of thermal conductance across the separator-shell interface in dry cylindrical lithium ion batteries

Although Lithium ion batteries offer numerous advantages (e.g. energy density, efficiency, etc.) over other types of batteries, recent accidents involving consumer electronics have necessitated a deeper understanding of the thermal behavior of these batteries. Thermal transport across the multilayer stacks that form prismatic and spiral-wound batteries generally hinders heat removal from the system. In cylindrical batteries, most commonly found in laptops, electric vehicles and power banks, heat must conduct to the metallic shell through many layers of the anode-separator-cathode structure, which is of low effective thermal conductivity. This work presents thermal conductance and thermal conductivity measurements of dry 18650 cells using infrared microscopy. Two-dimensional temperature maps are captured and are averaged in the direction normal to the heat flow for analysis of the one-dimensional temperature profiles. Interfacial temperature jumps indicate thermal resistances and can be separated from the thermal gradients due to conduction within a single material. We measure both cross-plane thermal conductivity of the battery stack and interfacial thermal conductance. Interfacial thermal conductance and the thermal conductivity in active batteries is expected to be higher, due to the presence of a liquid electrolyte. This work demonstrates that the low cross plane thermal conductivity of the plastic separator material is one of the limiting factors in heat dissipation.