Battery thermal management is vital to consider during pack design. With the difficulty of accurate thermal modeling of cells, experimental methods can assist in optimizing battery packs, managing thermal stress, and informing models. Many packs are designed with a bottom cooling system, thus knowing the thermally conductive behavior along the length of cylindrical cells is necessary. This value allows for assessment of the efficacy of bottom cooling for various cells and more accurate cell temperature values for thermal management. The effect tested is longitudinal axis of heat flow on a cylindrical cell, however the effect is expected to meaningfully affect thermal conductivity in both pouch cells and cylindrical cells using graphite anodes. It is currently postulated that the LiC24 to LiC12 to LiC6 lithiation phase transitions of graphite are responsible for the significant thermal conductivity shifting with SOC%.
- Design, build and test a fixture to determine the thermal conductivity of cylindrical cells along the longitudinal axis
- Experimentally determine thermal conductivity of various cells
- Observe the relationship between state of charge and thermal conductivity
The dominant thermal conduction longitudinal pathway is through the copper and aluminum current collector foils. In the measurements performed at higher SOC%, a higher fraction of the Graphite is in LiC6 phase, which exhibits meaningfully improved thermal conduction than LiC12 and LiC24 graphite intercalation phases.