Pyridinic N-Dominated Hard Carbon with Accessible Carbonyl Groups Enabling 98% Initial Coulombic Efficiency for Sodium-Ion Batteries

Hard carbon (HC) has been widely regarded as the most promising anode material for sodium-ion batteries (SIBs) due to its decent capacity and low cost. However, the poor initial Coulombic efficiency (ICE) of HC seriously hinders its practical application in SIBs. Herein, pyridinic N-doped hard carbon polyhedra with easily accessible carbonyl groups and in situ coupled carbon nanotubes are rationally synthesized via a facile pretreated zeolitic imidazolate framework (ZIFs)-carbonization strategy. The comprehensive ex/in situ techniques combined with theoretical calculations reveal that the synergy of pyridinic-N and carbonyl groups promoted by the pretreatment and carbonization process would not only optimize the Na+ adsorption energy but also accelerate the desorption of Na+, significantly suppressing the irreversible capacity loss. As a result, the as-synthesized hard carbon polyhedra as an anode can deliver an unprecedented high ICE of 98% with a large reversible capacity of 389.4 mAh g-1 at 0.03 A g-1. This work may provide an effective strategy for the structural design of HC with high ICE. Pyridinic N-doped hard carbon polyhedra with easily accessible carbonyl groups and in situ coupled carbon nanotubes has been rationally synthesized via a pretreated core@shell ZIF-driven strategy, exhibiting an unprecedented initial Coulombic efficiency (ICE) of 98% with a large reversible capacity of 389.4 mAh g-1 at 0.03 A g-1 for sodium-ion batteries. image