High Capacity Adsorption—Dominated Potassium and Sodium Ion Storage in Activated Crumpled Graphene

Structurally and chemically defective activated-crumbled graphene (A-CG) is employed to achieve unique synergy of large reversible potassium (K) and sodium (Na) ion storage capacity with fast charging and extended cyclability. A-CG synthesis consists of low temperature spraying of graphene oxide slurry, followed by partial reduction annealing and air activation. For K storage, the reversible capacities are 340 mAh g⁻¹ at 0.04 A g⁻¹, 261 mAh g⁻¹ at 0.5 A g⁻¹, and 210 mAh g⁻¹ at 2 A g⁻¹. For Na storage, the reversible capacities are 280 mAh g⁻¹ at 0.04 A g⁻¹, 191 mAh g⁻¹ at 0.5 A g⁻¹, and 151 mAh g⁻¹ at 2 A g⁻¹. A-CG shows a stable intermediate rate (0.5 Ag⁻¹) cycling with both K and Na, with minimal fade after 2800 and 8000 cycles. These are among the most favorable capacity—rate capability—cyclability combinations recorded for potassium-ion battery and sodium-ion battery carbons. Electroanalytical studies (cyclic voltammetry, galvanostatic intermittent titration technique, b-value) and density functional theory (DFT) reveal that enhanced electrochemical performance originates from ion adsorption at various defects, such as Stone–Wales defects. Moreover, DFT highlights enhanced thermodynamic stability of A-CG with adsorbed K versus with adsorbed Na, explaining the unexpected higher reversible capacity with the former.