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High Coulombic efficiency aluminum-ion battery using an AlCl 3 -urea ionic liquid analog electrolyte

2017; National Academy of Sciences; Volume: 114; Issue: 5 Linguagem: Inglês

10.1073/pnas.1619795114

1091-6490

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

Advancements in Battery Materials

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.