Sodium/Potassium‐Ion Batteries: Boosting the Rate Capability and Cycle Life by Combining Morphology, Defect and Structure Engineering

TLDR

Carbon-based anodes are attractive for sodium‑ and potassium‑ion batteries because of their stability, conductivity, and environmental friendliness, yet the large ionic radii of Na⁺ and K⁺ make achieving high capacity, long cycle life, and fast rates difficult. The authors fabricated N‑doped 3D mesoporous carbon nanosheets with ultrathin sheets, hierarchical pores, high pyridinic/pyrrolic N content, and expanded interlayer spacing to accelerate Na⁺/K⁺ intercalation, shorten diffusion paths, and accommodate volume changes. These N‑CNS electrodes deliver 239 mAh g⁻¹ at 5 A g⁻¹ after 10 000 cycles for SIBs and 321 mAh g⁻¹ at 5 A g⁻¹ after 5 000 cycles for PIBs, with first‑principles calculations attributing the performance to charge‑density modulation by the high N doping.

Abstract

Carbon-based materials have been considered as the most promising anode materials for both sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs), owing to their good chemical stability, high electrical conductivity, and environmental benignity. However, due to the large sizes of sodium and potassium ions, it is a great challenge to realize a carbon anode with high reversible capacity, long cycle life, and high rate capability. Herein, by rational design, N-doped 3D mesoporous carbon nanosheets (N-CNS) are successfully synthesized, which can realize unprecedented electrochemical performance for both SIBs and PIBs. The N-CNS possess an ultrathin nanosheet structure with hierarchical pores, ultrahigh level of pyridinic N/pyrrolic N, and an expanded interlayer distance. The beneficial features that can enhance the Na-/K-ion intercalation/deintercalation kinetic process, shorten the diffusion length for both ions and electrons, and accommodate the volume change are demonstrated. Hence, the N-CNS-based electrode delivers a high capacity of 239 mAh g-1 at 5 A g-1 after 10 000 cycles for SIBs and 321 mAh g-1 at 5 A g-1 after 5000 cycles for PIBs. First-principles calculation shows that the ultrahigh doping level of pyridinic N/pyrrolic N contributes to the enhanced sodium and potassium storage performance by modulating the charge density distribution on the carbon surface.