High Coulombic efficiency aluminum-ion battery using an AlCl3-urea ionic liquid analog electrolyte

Michael Angell, Chun Jern Pan, Youmin Rong, Chunze Yuan, Meng Chang Lin, Bing Joe Hwang, Hongjie Dai

Research output: Contribution to journalArticlepeer-review

248 Citations (Scopus)


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 AlCl3 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-1 at 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 AlCl3 was 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.

Original languageEnglish
Pages (from-to)834-839
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number5
Publication statusPublished - Jan 31 2017
Externally publishedYes


  • Aluminum-ion battery
  • Energy storage
  • Ionic liquid
  • Ionicity
  • Urea electrolyte

ASJC Scopus subject areas

  • General


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