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 nanoparticles (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. Our work paves the way for utilization of 3D printed metal-fluorides to enhance the electrochemical performance of the sodium metal anodes.

Lithium metal has been considered one of the most promising anodes for next-generation rechargeable batteries, but its practical application is largely hindered by the uncontrollable dendrite growth and infinite volume change. Here, inspired by superior catalytic effects of single-atom catalysts, carbonsupported single atomic Co with asymmetric N, O-coordination (Co-N/O) is developed for Li metal battery. Experimental results and theoretical calculations indicate that single atomic Co atoms with asymmetric N, O-coordination present enhanced binding ability toward Li in comparison with N-coordinated atomic Co site and isolated O site, enabling uniform Li plating/stripping. Moreover, the asymmetric N, O-coordination around Co atoms induces co-activation effects, lowering the energy barriers toward Li⁺ to Li⁰ conversion and largely promoting the deposition kinetics. When used as a Li deposition host, the Co-N/O achieves a high average coulombic efficiency of 98.6% at a current density of 1 mA cm⁻² and a capacity of 2 mAh cm⁻², long cycling life of 2000 h in symmetrical cells, and excellent rate performance (voltage hysteresis of 23 mV at 8 mA cm⁻²). This work provides a comprehensive understanding of single atomic metals with asymmetric heteroatom coordination in the design of Li metal anode.

Regarding the reverse process of materials growth, etching has been widely concerned to indirectly probe the growth kinetics, offering an avenue in governing the growth of two-dimensional (2D) materials. In this work, interface-driven anisotropic etching mode is demonstrated for the first time to be generally applied to 2D heterostructures. It is shown that the typical in-plane graphene and hexagonal boron nitride (h-BN) heterostructures follow a multi-stage etching behavior initiated first along the interfacial region between the two materials and then along edges of neighboring h-BN flakes and finally along central edges of h-BN. By accurately tuning etching conditions in the chemical vapor deposition process, series of etched 2D heterostructure patterns are controllably produced. Furthermore, scaled formation of graphene and h-BN heterostructures arrays has been realized with full assist of as-proposed etching mechanism, offering a direct top-down method to make 2D orientated heterostructures with order and complexity. Detection of interface-driven multi-staged anisotropic etching mode will shed light on understanding growth mechanism and further expanding wide applications of 2D heterostructures.