High Coulombic efficiency aluminum-ion battery using an AlCl3-urea ionic liquid analog electrolyte.
basic_science · Level V
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- Record sourced from PubMed, PMID 28096353.
- Also identified by DOI 10.1073/pnas.1619795114 and PMC identifier 5293044.
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Abstract
In recent years, impressive advances in harvesting renewable energy have led to a pressing demand for the complimentary energy storage technology. Here, a high Coulombic efficiency (∼99.7%) Al battery is developed using earth-abundant aluminum as the anode, graphite as the cathode, and a cheap ionic liquid analog electrolyte made from a mixture of AlCl<sub>3</sub> and urea in a 1.3:1 molar ratio. The battery displays discharge voltage plateaus around 1.9 and 1.5 V (average discharge = 1.73 V) and yielded a specific cathode capacity of ∼73 mAh g<sup>-1</sup> at a current density of 100 mA g<sup>-1</sup> (∼1.4 C). High Coulombic efficiency over a range of charge-discharge rates and stability over ∼150-200 cycles was easily demonstrated. In situ Raman spectroscopy clearly showed chloroaluminate anion intercalation/deintercalation of graphite (positive electrode) during charge-discharge and suggested the formation of a stage 2 graphite intercalation compound when fully charged. Raman spectroscopy and NMR suggested the existence of AlCl<sub>4</sub><sup>-</sup>, Al<sub>2</sub>Cl<sub>7</sub><sup>-</sup> anions and [AlCl<sub>2</sub>·(urea)<sub>n</sub>]<sup>+</sup> cations in the AlCl<sub>3</sub>/urea electrolyte when an excess of AlCl<sub>3</sub> was present. Aluminum deposition therefore proceeded through two pathways, one involving Al<sub>2</sub>Cl<sub>7</sub><sup>-</sup> anions and the other involving [AlCl<sub>2</sub>·(urea)<sub>n</sub>]<sup>+</sup> cations. This battery is a promising prospect for a future high-performance, low-cost energy storage device.