Ultrafast Sodium/Potassium-Ion Intercalation into Hierarchically Porous Thin Carbon Shells

The large-scale application of sodium/potassium-ion batteries is severely limited by the low and slow charge storage dynamics of electrode materials. The crystalline carbons exhibit poor insertion capability of large Na⁺ /K⁺ ions, which limits the storage capability of Na/K batteries. Herein, porous S and N co-doped thin carbon (S/N@C) with shell-like (shell size ≈20-30 nm, shell wall ≈8-10 nm) morphology for enhanced Na⁺ /K⁺ storage is presented. Thanks to the hollow structure and thin shell-wall, S/N@C exhibits an excellent Na⁺ /K⁺ storage capability with fast mass transport at higher current densities, leading to limited compromise over charge storage at high charge/discharge rates. The S/N@C delivers a high reversible capacity of 448 mAh g^-1 for Na battery, at the current density of 100 mA g^-1 and maintains a discharge capacity up to 337 mAh g^-1 at 1000 mA g^-1 . Owing to shortened diffusion pathways, S/N@C delivers an unprecedented discharge capacity of 204 and 169 mAh g^-1 at extremely high current densities of 16 000 and 32 000 mA g^-1 , respectively, with excellent reversible capacity for 4500 cycles. Moreover, S/N@C exhibits high K⁺ storage capability (320 mAh g^-1 at current density of 50 mA g^-1 ) and excellent cyclic life.