A High Efficiency Aluminum-Ion Battery Using an AlCl3-Urea Ionic Liquid Analogue Electrolyte

TL;DR

This paper reports a high-efficiency aluminum-ion battery with nearly 99.7% coulombic efficiency, using an AlCl3-urea ionic liquid analogue electrolyte, demonstrating promising stability, capacity, and insights into the electrochemical mechanisms involved.

Contribution

It introduces a novel AlCl3-urea electrolyte for aluminum-ion batteries, achieving high efficiency and stability, with detailed spectroscopic analysis of intercalation and deposition pathways.

Findings

Coulombic efficiency of ~99.7% achieved.

Stable operation over 150-200 cycles demonstrated.

Spectroscopic evidence of intercalation and deposition mechanisms.

Abstract

In recent years, impressive advances in harvesting renewable energy have led to 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 analogue electrolyte made from a mixture of AlCl3 and urea in 1.3 : 1 molar ratio. The battery displays discharge voltage plateaus around 1.9 V 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 in the cathode side during charge/discharge and suggested the formation of a stage 2 graphite intercalation compound when fully charged. Raman spectroscopy and nuclear magnetic resonance suggested the existence of AlCl4-, Al2Cl7- anions, and [AlCl2. (urea)n]+ cations in the urea/AlCl3 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.