Fig. 1: Highlights of Al-ion batteries and their performance limits.

a Scanning electron microscopy (SEM) images of a three-dimensional graphene network after supercritical CO₂ drying. Large open pores with interconnecting frameworks are clearly visible. b Cyclic voltammograms of graphene that was either supercritical CO₂ dried (G-CO₂) or dried by evaporating ethanol (G-Ethanol) (scan rate of 10 mVs⁻¹). c Plot of the specific capacity versus current density for our work (entire red block) and state-of-the-art. d Galvanostatic charge and discharge curves for devices having record-high specific capacities (200 mAh g⁻¹). The graphene cathode has a mass of 0.013 mg and density of 0.16 mg cm⁻². e Fast discharge (i_c = 100 A g⁻¹, i_dc = 100 ~ 600 A g⁻¹) leads to a quick drop in specific capacity (area of the shadow to assist the view on the amount of charging capacity). f Moderate discharge followed after a fast charge (i_c = 400 ~ 1,000 A g⁻¹, i_dc = 100 A g⁻¹) retains 85% specific capacity even when batteries were charged at 1000 A g⁻¹. g Charging voltage to maintain a decent specific capacity goes up quickly with the increase of current density. h SEM images of spotted Al islands inside surface pits of a pure Al anode after battery cells were fully charged at 400 A g⁻¹.