The current collectors also make a notable proportion of the cell mass (>7%) so the variability of the specific heat capacities can also be captured to better predict local inhomogeneities in temperature. The heat capacities across the normal temperature operating range of a battery for aluminium and copper were taken from literature and fitted to third order polynomials to capture the parameter-dependency using Debye theory (where 𝑇𝑇 is in Kelvin and units are J kg -1 K -1 ). These relationships are outlined in Equations [S4] and [S5]. The decreasing NMC specific heat capacity above 80 °C could be due to decomposition of the binder within the sample, as there are no phase transitions within this range. However, this is beyond the normal operating range of a battery cell so this information would not be captured by the simulations.