Effect of surface energies and nano-particle size distribution on open circuit voltage of Li-electrodes

Surface free energies become increasingly important in affecting voltage profiles and solubility limits of first-order phase transformations as electrode particles approach nanometer dimensions. Here, we show that the presence of a distribution in crystallite sizes at nanometer dimensions (<100 nm) can qualitatively modify the voltage profile around a first-order phase transformation. The plateau voltage of a first-order phase transformation depends on crystallite dimensions and a distribution of crystallite sizes leads to a spectrum of transformation voltages that produces a sloping voltage profile similar to that of a solid solution. This suggests that the voltage profile of a collection of nano-electrode particles can be tailored not only by modifying chemistry, but also with surface treatment and through control of particle size distribution.