Schematic of the impact of the surface energy on the Gibbs free energy (a) and voltage (b) profile of an insertion material exhibiting a first-order phase transition upon (de)lithiation. A difference in surface energy leads to a different free energy that scales with the particle surface area. The consequences are a change in the chemical potential and hence in voltage plateau and a shift in the solubility limits. A distribution in particle sizes leads to a distribution of voltages as shown by the dotted voltage profile.^[7]