Nanometer-Scale Surface Roughness of a 3-D Cu Substrate Promoting Li Nucleation in Li-Metal Batteries

Three-dimensional Cu frameworks have been extensively investigated as the current collectors in Li electrodes. Despite their original purpose of inducing dense Li deposition inside the frameworks and mitigating dendritic growth, Li plating predominantly occurs on the protruding areas or edges of the top surface. Herein, we show that nanometer-scale surface roughness of Cu can promote Li plating at the desired position in the 3-D framework. We prepared a 3-D Cu pattern using photolithography and developed a receding area with a depth of ∼10 μm and a surface height of <10 nm through chemical etching. The etched and receding regions have high surface energy, which can enhance the wettability of an electrolyte solution and lead to more rapid Li nucleation than in the upper square-patterned region. COMSOL simulation demonstrated that a 2-fold increase in the roughness factor increases the exchange current density, which determines the concentrated local current density. In addition, the surface roughness must be increased with the increasing depth of the 3-D pattern. This study suggests a promising way for selective Li deposition in Li-metal batteries.