3D printed MgF₂/reduced graphene oxide monolith: A multifunctional platform for stable and dendrite-free sodium metal anodes

The notorious growth of sodium dendrites and significant volume fluctuations have posed substantial challenges to the practical application of sodium metal anodes. In this work, an aerogel composed of MgF₂ nanoparticles (NPs) onto a three-dimensional (3D) printed reduced graphene oxide (rGO) (MgF₂/rGO) monolith was employed as a scaffold for sodium metal anodes. During the initial discharge process, the MgF₂ NPs underwent an electrochemical in-situ conversion into NaF and sodiophilic Mg NPs, which act as the Na metal nucleation centers and contribute to the formation of a stable solid electrolyte interface (SEI) layer. Benefiting from these synergistic effects, the 3D printed MgF₂/rGO electrode exhibits a high Coulombic efficiency of 99.49% after 1200 cycles at 0.5 mA·cm⁻² with 1 mAh·cm⁻². It also shows a long cycle lifespan of 2500 h with a high capacity of 10 mAh·cm⁻² at 5 mA·cm⁻². Moreover, when assembled into a full cell with a Na@MgF₂/rGO anode and a Na₃V₂(PO₄)₃@C-rGO cathode, the cell delivers an extended cycle life of 3500 cycles at 1 C, preserving a reversible capacity of 86.98 mAh·g⁻¹. This work paves the way for utilization of 3D printed metal-fluorides to enhance the electrochemical performance of the sodium metal anodes.