Tuning defect chemistry of vertical graphene arrays toward highly stable and dendrite-free sodium metal anodes

Abstract

Vertical graphene (VG) arrays, characteristic of particularly porous microscopic structures, are one promising host to accommodate Na deposition, relieve the formidable volume change and eliminate uncontrolled dendrite growth, by decreasing the local current density. However, in practice, the prepared VG arrays possess superabundant defect sites in the local tip positions, which would guide the accumulation of rampant Na-ion flux concentration on these tip defect sites, and thus result in strong local electric field distribution and the divisional dendritic growth. Herein, a novel reconstruction strategy is proposed to re-build the edges and stacking of VG, by removing some unstable carbon defects and changing turbostratic stacking structure of VG to a Bernal stacking mode of the graphited VG, which enables to guide the comparatively smaller and stable interface with Na. Benefiting from the synergistic effect of microscopic structure and defect chemistry design, the re-build VG achieves a long-term reversible Na plating/stripping over 6400 h at an areal capacity of 8 mAh cm−2 in half cell, as well as a long cycle life of up to 3300 h at 1 mA cm−2 with a plating capacity of 4 mAh cm−2 in symmetric cells. Concomitantly, the density functional theory calculations demonstrate that Na atoms tend to nucleate and grow into lateral Na plating on the re-build VG arrays at an atomic level. As a result, the full cell coupled with a P2-Na2/3Ni1/3Mn1/3Ti1/3O2 cathode has a predominant improved cycling stability. This microscopic structure/defect chemistry engineering strategy provides new insight into guiding the uniform deposition of Na metal for high-performance sodium metal battery.