Metal Electrode Surfaces Can Roughen Despite the Constraint of a Stiff Electrolyte

Roughening of metal electrodes in batteries is detrimental as it can lead to metal dendrites. Such dendrites can cause short circuits when they grow from the metal electrode to the other one, as can happen during battery operation when metal is plated onto the surface of an electrode. It has been suggested that solid electrolytes of sufficient elastic stiffness can suppress electrode surface roughening and dendriting, although experimental evidence is now emerging that this possibility is not valid. To investigate whether metal electrode surfaces will roughen during battery charging we carry out a linear perturbation analysis. Our calculations explore whether an electrode surface with one-dimensional sinusoidal roughness will experience growth of its amplitude. We assess a linear elastic electrolyte that is a single ion conductor bonded to a metal electrode being plated by a cathodic ionic current. We find that long wavelength perturbations will always increase in roughness. High current densities during battery charging are found to permit growth of the amplitude of small wavelength roughness. The stiffness of the solid electrolyte is found to play a role in limiting the growth of roughness, but its effect can always be overcome at high current densities and for long wavelength protrusions.