Unusual Inside–Outside Li Deposition within Three-Dimensional Honeycomb-like Hierarchical Nitrogen-Doped Framework for a Dendrite-Free Lithium Metal Anode

Lithium (Li) metal batteries have attracted massive research interest as candidates for a high energy density system. However, the instability and dendrite issue of Li metal have substantially hindered their practical applications. Therefore, we proposed a well-designed three-dimensional honeycomb-like hierarchical nitrogen (N)-doped framework (HHNF) as a matrix for Li deposition. Many Li ions can be distributed and reduced uniformly through the strong adsorption of N-containing functional groups in the HHNF. Metallic Li deposition on the HHNF follows an "inside–outside" mechanism, and the deposited Li spreads evenly on a flat surface when the internal porous space is filled completely. In this work, homogeneous Li deposition and the avoidance of Li dendrite formation are demonstrated by in situ optical microscopy and in situ Raman spectroscopy. The HHNF performs a high and stable Coulombic efficiency (98.5%) within 400 cycles and an ultralong lifespan of 1000 h at 0.5 mA cm–2 with a low potential polarization (23.8 mV) according to the symmetric cell test. In addition, full cells based on HHNF@Li anodes and LiFePO4/sulfur cathodes exhibit outstanding reversible capacities and rate performance (144.1 mAh g–1 for LiFePO4 after 150 cycles and 676.2 mAh g–1 for sulfur after 100 cycles at 0.5 C).