Amine–Aldehyde Condensation‐Derived N‐Doped Hard Carbon Microspheres for High‐Capacity and Robust Sodium Storage

Hard carbon is generally accepted as the choice of anode material for sodium‐ion batteries. However, integrating high capacity, high initial Coulombic efficiency (ICE), and good durability in hard carbon materials remains challenging. Herein, N‐doped hard carbon microspheres (NHCMs) with abundant Na+ adsorption sites and tunable interlayer distance are constructed based on the amine–aldehyde condensation reaction using m‐phenylenediamine and formaldehyde as the precursors. The optimized NHCM‐1400 with a considerable N content (4.64%) demonstrates a high ICE (87%), high reversible capacity with ideal durability (399 mAh g−1 at 30 mA g−1 and 98.5% retention over 120 cycles), and decent rate capability (297 mAh g−1 at 2000 mA g−1). In situ characterizations elucidate the adsorption–intercalation‐filling sodium storage mechanism of NHCMs. Theoretical calculation reveals that the N‐doping decreases the Na+ adsorption energy on hard carbon.