Rational design of micro-cone array on copper host for dendrite-free sodium metal plating

• Simulate electric field distribution on micro-cone tips • Use femtosecond laser technology to obtain the desired micro-cone Cu arrays having different tip radii with high precision • Probe the surface chemistries of SEI by X-ray photoelectron spectroscopy microscope • Propose models of electrical double layers for electrodes with different tip radii using the Helmholtz capacitor theory The vertically aligned 3D structure is a promising host for dendrite-free sodium metal anodes. The distribution of electric field at the Helmholtz layer of anode surface plays a critical role in determining Na plating behavior. However, the said electric field is poorly understood, and its control remains highly challenging. Herein, we demonstrate the fabrication of vertically aligned Cu micro-cone arrays with tuned tip radii using a high precision femtosecond laser beam shaping method. Computational results confirm the advantageous effect of increasing the tip radius in promoting a widely distributed and uniform electric field. Investigations into the kinetic mechanism reveal that the uniform electric field accelerates Na ion diffusion and diminishes energy barrier, facilitating compact Na plating with suppressed dendrite growth. The Cu host having micro-cones with a large tip radius delivers excellent plating performance with exceptional high-rate capabilities. The symmetric cell presents a low overpotential of 39 mV with a negligible voltage fluctuation after 1100 h of cycle, while the full cell retains 92.1 % and 83.9 % of its specific capacities at 5C and 10C, respectively, compared to its capacity at 1C. The rational design of the micro-cone arrays with proven advantages shed new insights into the development of Na hosts for high energy density, dendrite-free Na metal batteries.