Aluminum metal-based high efficiency energy storage system development

Abstract

Due to the low cost and high volumetric capacity, there has been a persistent endeavor to fabricate aluminum metal-based rechargeable batteries to replace existing lithium-ion batteries (LIBs). One crucial challenge in developing aluminum-ion batteries (AIBs) has been to find electrolyte-resistant substrates and Al$^{3+} ion reversible cathode materials. In Chapter 1, various metals and carbon-based materials such as pyrolytic graphite (PG) were evaluated as current collectors. In the case of metals, the presence of halide anions (Cl$^-$) in the electrolyte, (EMImCl)$_2$(AlCl$_3$)$_3$, causes corrosion within the potential range of the electrolyte. Meanwhile, PG does not exhibit such corrosion, though its upper cutoff voltage is limited to 1.7 V due to AlCl$^{4-}$ (de)intercalation. However, in the presence of Li$^+$ cations, AlCl$^{4-}$ anions are inhibited from intercalation into PG due to the strong attraction from the cations. This renders PG inactive against inadvertent anion intercalation, stabilizing its role as a promising current collector in a wide potential window. In Chapter2, a Lithium-aluminum semi-liquid hybrid battery is discussed as a new energy storage system. Vanadium redox flow batteries (VRFBs) have received considerable attention for large-scale energy storage systems because of their advantages of long-term cycle life, re-balancing capability of carrier ions, and guaranteed safety. However, they suffer from limited solubility of vanadium species, high cost of Nafion membrane, and corrosion of reactor. Here, we report a semi-liquid hybrid battery where olivine-lithium iron phosphate (LiFePO$_4$) and an ionic liquid containing AlCl$^{4-}$-Al$_2$Cl$_7$- redox couple serve as the cathode and anolyte, respectively. The electrolyte is optimized to offer a sufficient amount of Al$_2$Cl$^{7-}$ in the presence of LiCl. The redox reaction of the aluminum complex interfacing metallic aluminum is quite reversible providing a full-cell operation voltage of 1.4 V, without dendrite growth, unlike lithium metal anodes in previous lithium-polysulfide semi-liquid hybrid counterparts. Moreover, cross-reactions between carrier ions and their respective counter electrodes are infeasible, leading to suppressed self-discharge. A cost analysis suggests that the use of ionic liquids can be competitive against VRFBs that rely on costly Nafion membranes.