High Coulombic efficiency aluminum-ion battery using an AlCl ₃ -urea ionic liquid analog electrolyte

Abstract

In recent years, impressive advances in harvesting renewable energy have led to a 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 analog electrolyte made from a mixture of AlCl 3 and urea in a 1.3:1 molar ratio. The battery displays discharge voltage plateaus around 1.9 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 (positive electrode) during charge-discharge and suggested the formation of a stage 2 graphite intercalation compound when fully charged. + cations. This battery is a promising prospect for a future high-performance, low-cost energy storage device.aluminum-ion battery | urea electrolyte | ionicity | ionic liquid | energy storage C heap, high-rate (fast charge/discharge) rechargeable batteries with long cycle lives are urgently needed for grid-scale storage of renewable energy, as it is becoming increasingly important to replace fossil fuels (1). Lithium-ion batteries (LIBs) are expensive and have limited cycle life, which makes them nonideal for grid-scale energy storage. Furthermore, high-rate capability is necessary for use in the grid, under which conditions LIBs become increasingly unsafe due to the flammability of the electrolytes used. Batteries based on aluminum offer a viable alternative due to aluminum's three-electron redox properties (offers potential for high-capacity batteries), stability in the metallic state, and very high natural abundance. Furthermore, the development of these batteries based on nonflammable electrolytes of low toxicity is critical for minimizing safety hazard and environmental impact. Recently, our group developed a secondary Al battery system based on the reversible deposition/stripping of aluminum at the Al negative electrode and reversible intercalation/deintercalation of chloroaluminate anions at the graphite positive electrode in a nonflammable 1-ethyl-3-methylimidazolium chloroaluminate (EMIC-AlCl 3 ) IL electrolyte (7,8). A ratio of AlCl 3 /EMIC = 1.3 by mole was used such that Al 2 Cl 7 − was present in the (acidic) electrolyte to facilitate aluminum deposition (9). During charging, Al 2 Cl 7 − is reduced to deposit aluminum metal, and AlCl 4 − ions intercalate (to maintain neutrality) in graphite as carbon is oxidized. During discharge, this battery exhibited a cathode specific capacity of ∼70 mAh g −1 with a Coulombic efficiency (CE) of 97-98%, and ultrahigh charge/discharge rate (up to 5,000 mA g −1 ) for over 7,000 cycles. However, room for improvement exists as the parameter space for the Al battery remains largely unexplored. The three-electron redox properti...

An aluminium battery operating with an aqueous electrolyte

“…Coulombic efficiency was 97.2% after 20 cycles and decreased to 94%; energy efficiency of the CuHCF-limited cell remained at ~ 66% over > 1000 cycles, which surpasses the previously reported cycling of electrodes incorporating CuHCF [5]. The more positive voltage profile in Fig.…”

An Aluminum/Graphite Battery with Ultra‐High Rate Capability

“…[30,32] Clearly, the elevated amount of electrolyte required to sustain the electrochemical process negatively affects the attainable energy density of the Al/graphite system. The calculation indicates that for an electrolyte characterized by a higher AlCl 3 concentration, a smaller amount of electrolyte is enough.…”

“…In particular, batteries play an important role in electric mobility, and are essential for the storage of electricity produced from renewable sources like wind and solar. Among them, those using graphite cathode [23,[25][26][27][28][29][30][31][32][33][34][35] showed the best cycle life and rate capability. [1][2][3][4][5][6][7][8] Nevertheless, due to the limited resource of lithium, and of the transition metals (Co in particular) used for the realization of the battery, the long-term sustainability of such system is questioned.…”

Electrolytes for Batteries with Earth‐Abundant Metal Anodes

“…Although it seems that AlCl 4 À or Al 2 Cl 7 À have larger ionic radii, the intercalation of these anions is extremely fast. [73] (e,f). Electrolytes for aluminum-based batteries.…”