Modulating electronic structure with heteroatom dopants in porous hard carbon towards ultralong lifespan sodium-ion batteries

Hard carbon (HC) has been recognized as one of the most mature and commercialized anode materials for sodium-ion batteries (SIBs). However, it still faces problems such as low reversible capacity, poor rate capability and cycling stability for commercial applications. Herein, we propose a systematic investigation into heteroatom-doped engineering for tailoring the electronic structure of N-doped carbon by integrating heterogeneous atoms (S/P) into 3-dimensional (3D) interconnected porous HC. Thus-fabricated N/P dual-doped HC (NPDC) exhibits improved electronic conductivity and expanded interlayer spacing, which endows high rate capability and prolonged cycle life over 28,000cycles for SIBs (1400 h lifespan at 5.0 A/g). Theoretical and experimental results unravel that the electron-donating ability of P atoms with unmatched p orbital slightly change the spin density optimizes the adsorption energy and electronic structure to balance the Na+ adsorption/intercalation in NPDC. The "adsorption/intercalation" mechanism of Na+ in the NPDC is also illustrated by a detailed correlation analysis between electrochemical kinetics analysis and spectral information. Moreover, the corresponding pouch full battery delivers a high energy density of 254.7 Wh kg−1 with excellent rate capability and outstanding cycle stability (89.0% capacity retention) after 500cycles at 1.0C. This work provides a feasible approach to finely modulate the electronic structure of porous HC and facilitate the future design of printable carbon-based SIBs anodes.