Atomically dispersed Ni induced by ultrahigh N-doped carbon enables stable sodium storage

Building phase interface with enough solid-phase contact is of great importance for improving chemical reaction kinetics and depth. High dispersion of electrode materials, especially at the atomic-level, are known for high interface contact, yet their potential application in batteries is restricted due to low loading. Herein, the atomically dispersed metal Ni (Ni in Ni–N–C is 54.9 wt %) with high loading was achieved by ultrahigh N-doping carbon (N/N–C:29.5 wt %) during the discharging process of nickel sulfide, leading to good reversibility and high-capacity maintenance owing to ultrahigh phase contact during long cycling for sodium-ion batteries. It delivers a stable cycling life (0.061% capacity decay per cycle) compared with the poor cyclability (0.418%) for the Ni agglomeration electrode with lower N-doping. The assembled pouch cells achieve robust stability (92.1% after 50 cycles). DFT calculations reveal that ultrahigh N-doping and electrochemically formed Na2S can provide thermally stable Na2S/Ni/NC structures, inhibiting Ni agglomeration during cycling.