Regulated Electrodeposition of Na Metal in Monolithic ZIF-Pillared Graphene Anodes

Sodium (Na) metal batteries receive increasing attention because of their high energy densities and low costs that are enabled by the abundant Na resources. However, dendritic growth and low efficiency of Na-metal anodes limit the practical applications of Na-metal batteries. Here, we propose a three-dimensionally pillared structure in which carbonized nanoparticles of zeolite imidazolate framework-8 (ZIF-8) are sandwiched between reduced graphene oxide (rGO) sheets (ZIF-8-C@rGO). Such a pillared structure enables two advantages over rGO. First, the sodiation products of ZIF-8 (NaZn13, Na2O, and N-doped carbon) have a strong chemical affinity to Na metal, thereby inducing favorable nucleation of Na metal to guide Na deposition. Second, the pillared structure could facilitate the diffusion of Na ions through rGO sheets and help homogenize the current distribution, leading to a uniform deposition of Na metal. As a result, ZIF-8-C@rGO exhibits a dendrite-free morphology during Na plating/stripping and excellent cycling stability with high Coulombic efficiency of over 99.8% for at least 2000 h. A symmetric cell could maintain more than 4000 h with a stable average overpotential of only 30 mV at a capacity of 1 mA h cm-2. This work demonstrates that the design of a ZIF-pillared structure could combine thermodynamic and kinetic regulating factors to offer an alternative solution to the development of durable Na electrodes for high-performance Na-metal batteries.