Boosting hybrid capacitive-intercalative Al-ion storage with N-F doped nanocarbon electrodes

Aluminum-ion (Al-ion) storage with carbon cathode provides a lightweight and cost-effective alternative to lithium-ion batteries due to the hybrid charge storage mechanism, combining intercalation of aluminum ions (Al 3+ ) and polyatomic ions (Al 2 Cl 7 − ) with the inherent capacitive behavior of carbon. This study explores the influence of gas doping on the structural and electrochemical properties of nanoporous carbon (NPC). Pristine doping with nitrogen (N) and argon (Ar) results in NPC with limited surface porosity, while N-F doping significantly improves structural characteristics, yielding NPC with a high surface area of 3048 m 2 g −1 and uniformly distributed pores (25–130 nm). This enhanced porosity provides abundant active sites for hybrid charge storage, facilitating both ion intercalation and pseudocapacitive mechanisms. The Al-ion device (Al|AlCl 3 -EMImCl|N-F doped NPC) achieves a specific capacity of 197 mAh g −1 at 0.5 A g −1 , with 97 % coulombic efficiency over 25 cycles. This performance arises from efficient ion adsorption and partial redox reactions involving Al 3+ and Al 2 Cl 7 − ions. Pseudocapacitive behavior is particularly evident at low frequencies, where the phase angle (φ) approaches 90° and cyclic stability challenges persist due to Al 3+ ion trapping at the NPC-electrolyte interface. • N-F doping enhances NPC's electronegativity, improving Al-NPC electrode pairing. • Doping yields uniform pores, achieving 197 mAh/g at 500 mA/g with 97 % efficiency. • Microscopic analysis shows limited cycle life due to trapped Al 3+ ions and instability. • At low potentials, adsorption dominates; at high potentials, intercalation prevails.