| dc.description.abstract | Rechargeable aluminum batteries (RABs) are extensively developed due to their cost-effectiveness, eco-friendliness, and low flammability and the earth abundance of their electrode materials. However, the commonly used RAB ionic liquid (IL) electrolyte is highly moisture-sensitive and corrosive. To address these problems, a 4-ethylpyridine/AlCl3 IL is proposed. The effects of the AlCl3 to 4-ethylpyridine molar ratio on the electrode charge–discharge properties are systematically examined. A maximum graphite capacity of 95 mAh/g is obtained at 25 mA/g. After 1000 charge–discharge cycles, 85% of the initial capacity can be retained. In situ synchrotron X-ray diffraction is employed to examine the electrode reaction mechanism. In addition, low corrosion rates of Al, Cu, Ni, and carbon-fiber paper electrodes are confirmed in the 4-ethylpyridine/AlCl3 IL. When opened to the ambient atmosphere, the measured capacity of the graphite cathode is only slightly lower than that found in a N2-filled glove box; moreover, the capacity retention upon 100 cycles is as high as 75%. The results clearly indicate the great potential of this electrolyte for practical RAB applications.
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, respectively, at 300 mA/ g. 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.
Self-discharge plays as a critical subject for RABs industrial application. In this work, in order to investigate the phenomenon of RAB self-discharge, two different kind of graphite was used as positive material for comparison. Variations in open-circuit potential of natural graphite and expanded graphite electrode have been investigated as a function of the storage time. The OCP of the natural graphite showed a plateau at about 2.16 V after 12 h, while expanded graphite only maintained at 2.07 V. EG, possessing larger d spacing and higher surface area, will result in more channel, high utilization and thus high specific capacity of electroactive sites, however it is difficult for holding AlCl4 anion at high potential, leading to more serious self-discharge. Almost the self-discharge capacity loss attributed to the upper plateau capacity fading and it could be recovered. The self-discharge mechanism of the graphite electrode was confirmed by electron microscopy, energy-dispersive X-ray spectroscopy, in-situ XRD, and corrosion test of Al anode. | en_US |