LAUSR

At present, the replacement of fossil fuels by alternative CO2-emission-free energy sources, such as solar and wind, is substantially hindered by the lack of low-cost and large-scale energy storage technologies. Although lithiumion batteries (LIBs) represent the most mature and widely deployed electrochemical energy storage technology for mobility and portable electronics, the uneven worldwide distribution of known lithium reserves and the high production costs greatly reduce the economic appeal of LIBs for large-scale stationary storage. In this regard, inexpensive Al−graphite dual-ion batteries (AGDIBs) have attracted great attention over the past few years. With energy densities of 30−70Wh kg−1, AGDIBs are suitable for stationary storage. The constituents of AGDIBs include highly abundant elements (H, O, N, C, and Al) and are easy to manufacture. While recent research efforts on AGDIBs have been mainly focused on testing various graphite cathodes, further progress of this technology is inherently limited by the low charge storage capacity of the chloroaluminate ionic liquids used as anolytes (often but incorrectly called electrolytes). In this Viewpoint, we discuss the critical interplay between the capacity of the anolyte and the energy density of AGDIBs along with their measurements at different current densities. The basic configuration of an AGDIB contains a graphite cathode, AlCl3-EMIMCl (1-ethyl-3-methylimidazolium chloride) ionic liquid anolyte, and metallic aluminum current collector, as demonstrated in Figure 1a. AGDIBs operate as an electrochemical energy storage system by employing the reversible intercalation of AlCl4 − anion species into the positive graphite electrode upon charging (i.e., the oxidation of the graphite network). Concurrently, the aluminum electroplating reaction takes place on the negative side of AGDIBs. The working principle of AGDIBs can be represented by the following cathodic and anodic half-reactions during charging: