title: High Coulombic efficiency aluminum-ion battery using an AlCl3-urea ionic liquid analog electrolyte.
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 AlCl3and 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-1at a current density of 100 mA g-1(∼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 AlCl4-, Al2Cl7-anions and [AlCl2·(urea)n]+cations in the AlCl3/urea electrolyte when an excess of AlCl3was present. Aluminum deposition therefore proceeded through two pathways, one involving Al2Cl7-anions and the other involving [AlCl2·(urea)n]+cations. This battery is a promising prospect for a future high-performance, low-cost energy storage device.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305.
authors.forename: Michael
authors.initials: M
authors.lastname: Angell
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305.|Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan.
authors.forename: Chun-Jern
authors.initials: CJ
authors.lastname: Pan
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305.
authors.forename: Youmin
authors.initials: Y
authors.lastname: Rong
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305.
authors.forename: Chunze
authors.initials: C
authors.lastname: Yuan
authors.affiliation: College of Electrical Engineering and Automation, Shandong University of Science and Technology, Qingdao 266590, People's Republic of China.
authors.forename: Meng-Chang
authors.initials: MC
authors.lastname: Lin
authors.affiliation: Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan.|National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: Bing-Joe
authors.initials: BJ
authors.lastname: Hwang
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305; hdai1@stanford.edu.
authors.forename: Hongjie
authors.initials: H
authors.lastname: Dai
keywords: aluminum-ion battery; energy storage; ionic liquid; ionicity; urea electrolyte