Here 𝑐𝑐 𝑠𝑠 and 𝑐𝑐 𝑒𝑒 refer to lithium concentration in the solid lattice and electrolyte, respectively, 𝑐𝑐 𝑠𝑠,𝑚𝑚𝑡𝑡𝑚𝑚 is the maximum concentration in the electrode particles and 𝑐𝑐 𝑒𝑒0 is the reference concentration in the electrolyte. The parameter 𝑘𝑘 0 is the reference current of the reaction. As shown in Figure , the exchange current density for the NMC811 positive electrode was measured at 25 °C between 0.5•10 -4 A cm -2 and 3.0•10 -4 A cm -2 with a mean value of 2.01•10 -4 A cm -2 . For the graphite-SiOy electrode the exchange current density was measured at 25 °C between 2.0•10 -5 A cm -2 and 9.0•10 -5 A cm -2 with a mean value of 7.1•10 -5 A cm -2 . The observed trends are similar to the results reported by Ecker et al. who reported a value of 2.23•10 -4 A cm -2 and 7.05 10 -5 A cm -2 corresponding to x=0.5 in Lix(Ni0.4Co0.6)O2 and LixC6. The Butler-Volmer equation (Eq. [13]) fits the negative electrode exchange current density vs stoichiometry well, this fit is worse for the positive electrode (R 2 =0.63) and a semi-ellipse with an exchange current value of 0 at stoichiometries at ~ 0.2 and 0.9 (at 25 °C) provides a better fit (R 2 =0.9, Fig ). The question arises whether using the stoichiometry of 0 to 1 to represent degree of lithiation with respect to the molar lithium concentration within the crystal structure is the correct assumption to use in the model. There is most probably 'inactive' or non-mobile lithium below x=0.2 in this case as observed in Figure , where it is impractical for LixNi0.8Mn0.1Co0.1O2 to be delithiated further due to collapse of the crystal structure. There is little sensitivity in this particular parameter, and therefore have assumed Butler-Volmer kinetics over the entire lithium stoichiometry in this work which is consistent with the model inputs.