The thermal conductivity for aluminium and copper current collectors were taken from literature as in batteries they appear in their pure elemental form and the thermal properties do not vary. The thermal conductivity of aluminium does not change appreciably within the operating range of the battery so the constant value of 237 in W m -1 K -1 is used. However, the thermal conductivity for the copper decreases with temperature. The dependency of thermal conductivity on temperature is fitted to a third degree polynomial to capture this change in the model (where 𝑥𝑥 is in Kelvin and in λ is in W m -1 K -1 ), see Equation S6. These measurements allow prediction of thermal inhomogeneity within a cell, but combining these values do not provide an accurate value for the overall cell thermal conductivity. This is because of the cumulative error in measuring several materials separately and by not accounting for the thermal contact resistances between the layers in a cell. For accurate 3D thermal models and to predict the performance of larger battery systems the macro-thermal properties need to be measured. Cylindrical cells are a composite and not a pure material, therefore the conductivity of each cell type has to be measured to improve prediction of the cell temperature. Effective Thermal Properties Lumped thermal models require the effective thermal properties of the jellyroll. The thermal properties of the jellyroll can be measured directly, or they can be calculated using the individual heat capacities of the components. The jellyroll is considered to be a homogenous material so it has a uniform temperature, and the thermal conductivity can be neglected. The jellyroll excludes the casing and the miscellaneous components such as the hard plastic and perforated fibrous membrane at the axial sites. An overall specific heat capacity of 887 J kg -1 K -1 (2.38•10 6 J K -1 m -3 ) was calculated using the gravimetric contributions and the heat capacities of the individual components in Table . The 2-sided electrodes relate to the whole double sided coating, including the current collector and both coated electrodes, whereas the coatings relates to the single sided coating thickness only (not including the current collector). The total specific heat capacity is similar to value reported previously, 850 J kg -1 K -1 for a jellyroll with density 2400 kg m -3 . 16 m 2702 l 876 l 2366952 l 100 l 237 l Copper foil 12 m 8933 l 383 l 3421339 l 117 l 401 l Separator (dry porous) 12