In Situ Measurements of Stress-Potential Coupling in Lithiated Silicon

An analysis of the dependence of electric potential on the state of stress of a lithiated-silicon electrode is presented. Based on the Larché and Cahn chemical potential for a solid solution, a thermodynamic argument is made for the existence of the stress-potential coupling in lithiated silicon; based on the known properties of the material, the magnitude of the coupling is estimated to be ∼ 60 mV / GPa in thin-film geometry. An experimental investigation is carried out on silicon thin-film electrodes in which the stress is measured in situ during electrochemical lithiation and delithiation. By progressively varying the stress through incremental delithiation, the relation between stress change and electric-potential change is measured to be 100–120 mV/GPa, which is of the same order of magnitude as the prediction of the analysis. The importance of the coupling is discussed in interpreting the hysteresis observed in the potential vs state-of-charge plots and the role of stress in modifying the maximum charge capacity of a silicon electrode under stress.