An aluminium battery operating with an aqueous electrolyte

The consumption of renewable energy, excluding hydropower, has grown almost exponentially over the past 20 years [ 1 ]. Most of this growth has come in the form of distributed solar PV and wind power which can cause a number of problems for electricity grids. For example, cloud cover can cause output from solar PV plants to be subject to large voltage and power fluctuations. This can be alleviated through use of low energy but high power, high cycle life and fast response energy storage systems [ 2 ]. Given suitable electrode materials, the high conductivity of aqueous electrolytes mean aqueous intercalation batteries may be capable of providing these characteristics in addition to being safe, non-toxic and potentially low-cost when compared to non-aqueous systems, such as ionic liquids. This communication reports on the construction and testing of a fully functional aqueous Al-ion cell. It should be noted that the majority of Al-ion research focusses on room temperature ionic liquid electrolyte systems (RTILs) theoretically allowing the utilisation of aluminium metals high capacity through reversible deposition [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. The primary research aim becomes the identification of positive electrode materials that will not severely limit cell capacity. Table 1 provides an overview of RTIL-based Al-ion systems reported in the literature to date. Cycle life varies from just 50 to 7500. Applied currents also vary considerable between reported electrodes, from 12 up to 5000 mA g −1 . The majority of studies use AlCl 3 /EMICl (1-ethyl-3-methylimidazolium chloride) or AlCl 3 /BMICl (1-butyl-3-methylimidazolium chloride) as the electrolyte. Given a suitable positive electrode, a high capacity and energy density cell could be constructed. The best-performing cell to date, with a natural graphite positive electrode, has achieved a capacity of c.a. 100 mA h g −1 when cycled at 198 mA g −1 . However, the expense and corrosiveness of RTILs are significant disadvantages of such a battery system.