Acylation-assisted N, O dual-doped hierarchical porous hard carbon with enhanced kinetics for Na-ion and K-ion storage

Abstract

Hard carbon (HC) is perceived as an anode candidate for sodium-ion batteries and potassium-ion batteries due to its disordered structure and cost-effectiveness, yet its capacity is restricted by limited active sites. Heteroatom-induced defect engineering of HC is commonly applied for enhancing its reversible capacity, but high heteroatom doping (> 14 at%) is challenging due to the absence of heteroatoms in most biomasses. Not only that, the heteroatom doping strategy is also bothered with high diffusion barriers toward Na⁺/K⁺. Herein, based on a rationally selected low-cost precursor (sodium alginate–melamine–NaCl), a new HC with high-level N, O heteroatom dopants (21.4 at%) and well-regulated porous structure has been constructed via acylating and controllable pore engineering. Experimental proof and theoretical calculations have been conducted to clarify the influence of heteroatom dopants and porous structures on the ion storage behavior of the designed HC. The rich N, O co-doping could enable efficient Na⁺/K⁺ adsorption and enhanced electron transfer behavior. Besides, benefiting from the hierarchical porous structures (micro to macropores), the interfacial reaction kinetics and electrochemical behavior can be boosted. Particularly, the optimized N, O dual-doped hierarchical porous HC (NO-HPHC-1, 0.285 mol L⁻¹ NaCl in precursor) with abundant defects from macropores and moderate micropores make it exhibit excellent Na⁺ storage: 127 mAh g⁻¹ at 0.5 A g⁻¹ even after 2000 cycles. Meanwhile, the superiority of NO-HPHC-1 can be well maintained for K⁺ storage with a reversible capacity of 199 mAh g⁻¹ at 0.1 A g⁻¹. More importantly, the diverse Na⁺/K⁺ storage behaviors have been elucidated.

Graphical abstract