Kinetic- versus Diffusion-Driven Three-Dimensional Growth in Magnesium Metal Battery Anodes

Until now, a key barrier toward realizing a high energy density Mg2+ battery has been the limited understanding of mechanisms governing multivalent metal electrodeposition. This, compounded with recent observations of Mg dendrites, highlights the need for better fundamental insight into multivalent systems. We present a comprehensive study of electrodeposition in practical coin-cell configurations to evaluate the mechanisms of growth from common Mg(TFSI)2-based electrolytes. Our findings indicate a transition from charge-transfer-limited to diffusion-limited electrodeposition processes that govern the morphological evolution of Mg deposits. We observe the signature of cell shorting under a wide range of current densities that we attribute to 3D hemispherical growth of Mg deposits that form under mixed diffusion and kinetic control and are distinguished from traditional fractal dendrites. Our results highlight synergy with classical electrochemical theories for growth and lay groundwork for future approaches to achieve stable electroplated multivalent metal electrodes.