Novel Electrode Material for Aluminum Batteries

Abstract

The need of sustainable and efficient energy storage devices is an urgent need of modern society. The renewable energy production is characterized by an intermittent power output, and needs, for large scale applications, an improvement on the capability of energy storage (currently less than 1% of the energy production can be stored) 1. The development of low cost and environmentally friendly electrochemical storage systems characterized by high performances is of fundamental importance for a sustainable energy economy. The currently most mature battery technology is the lithium ion battery, considered the one of most appealing candidate as power source for electric vehicle application. Unfortunately, the large scale application of lithium ion batteries is nowadays under discussion, due to the limited amount of lithium resources2. Several other metal anodic materials such as sodium3, potassium4, calcium5, magnesium6 and aluminum7, characterized by a higher abundance with respect to lithium, have been considered as suitable candidates for electrochemical storage devices in replacement of lithium systems. In particular aluminum, the most abundant metal element in the earth’s crust, is considered a promising candidate for application in stationary electrochemical storage systems. The light weight of aluminum and its ability to exchange three electrons during the electrochemical process (Al3+ + 3e- ↔ Al) grant both, a high gravimetric and volumetric capacity density of 2.98 Ah g-1 and 8.04 Ah cm-3, respectively, the latter value being four times higher as compared to a lithium metal anode. Additionally, the aluminum can be handled in open air leading to enormous advantages in the cell fabrication and an extreme improvement of the safety level of electrochemical storage systems employing this electrode material. In our work we propose the use of a Al2(WO4)3 as an alternative cathode material for the application in aluminum batteries. This material is characterized by a theoretical capacity of 202 mAh g-1 for complete de-intercalation of the aluminum from the structure. Electrochemical tests have been performed employing 1-ethyl-3-methylimidazolium chloride (EMImCl) ionic liquid and AlCl3 in a molar ratio of EMImCl:AlCl3 1:1.5 as the electrolyte. The suitability of the electrolyte media against aluminum metal has been evaluated by means of impedance spectroscopy as well as of cyclic voltammetry, revealing the reversibility of the electrochemical process of stripping and deposition of the aluminum in the employed cell configuration. The reversibility of the electrochemical intercalation of the Al3 + ion in the Al2(WO4)3cathode material has been demonstrated by cyclic voltammetry as well as galvanostatic cycling tests that reveal a good electrochemical performance of the investigated material.