Ordered nano-structured mesoporous CMK-8 and other carbonaceous positive electrodes for rechargeable aluminum batteries

Abstract

The chloroaluminate ion storage properties of various carbonaceous electrodes, namely soft carbon (SC), hard carbon (HC), activated carbon (AC), and ordered mesoporous carbon CMK-8, are investigated. The effects of carbon crystallinity, surface area, and pore size are systematically examined. Due to their non-ideal graphitic structures, the charge–discharge capacities of SC and HC electrodes are unfavorable for practical applications, although SC, with its relatively high crystallinity, outperforms HC. The high-surface-area AC and CMK-8 exhibit reversible capacities of 59.0 and 100.5 mAh g−1, respectively, at 300 mA g−1. Pore size and geometry play important roles in determining the electrochemical properties. The CMK-8 framework not only serves as an electronic conduction pathway but also provides interpenetrating three-dimensional open channels for electrolyte accessibility and complex AlCl4− anion transport. The charge storage mechanism of the CMK-8 electrode, confirmed by electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry, has a capacitive contribution and a diffusion-controlled intercalation/deintercalation contribution. Based on this unique mechanism, great rate capability, and excellent cyclability of the CMK-8 electrode are demonstrated.