Vacancy Diffusion during Stripping of Metal Electrodes

Abstract The formation of voids at the interface between metal (Li or Na) electrodes and solid electrolytes has critical implications for the development of robust solid-state batteries. Here, we examine vacancy diffusion in a metal electrode during electrochemical stripping to assess its role in the nucleation and growth of such voids. We develop one-dimensional solutions for the vacancy distribution within the electrode for an imposed stripping current. To develop a non-equilibrium vacancy concentration within the electrode, we assume that the redox reaction at the electrode/electrolyte interface imposes a vacancy flux into the electrode that is a fraction of the stripping current. Consequently, the vacancy concentration within the electrode can increase significantly above its initial equilibrium value and these vacancies might coalesce to form voids. However, there is a large energy cost to this non-equilibrium vacancy concentration in apparent violation of the Onsager/Rayleigh principle of the least dissipation of energy. Further, work is needed to understand if and how the redox reaction may provide the extra energy required to increase the vacancy concentration.