The Pitfalls in Nonaqueous Electrochemistry of Al‐Ion and Al Dual‐Ion Batteries

Abstract

The quest for cost‐effective and TWh‐scale stationary energy storage systems has caused a surge of research on novel post‐Li‐ion batteries that consist solely of abundant chemical elements. Nonaqueous Al batteries, inter alia, are appealing as an inexpensive electrochemical technology owing to the high natural abundance of aluminum. A critical assessment of the literature on Al batteries, however, points to numerous misconceptions in this field. The latter is primarily linked to the false assessment of the charge storage redox reactions occurring upon cycling of Al batteries. To ensure the constructive progress of Al batteries, in this essay, the current scientific understanding of the operational mechanisms of two commonly studied Al battery systems, Al‐ion and Al dual‐ion batteries are summarized. Furthermore, the main pitfalls in interpretation and reporting of the electrochemical performance of Al cathode materials and cell‐level energy densities of Al batteries are clarified along with core challenges currently limiting their development. Toward this end, the subject of the charge storage balancing of Al dual‐ion batteries is discussed.

Solid Electrolyte Interphase Engineering for Aqueous Aluminum Metal Batteries: A Critical Evaluation

“…[1] However, the capacity limiting and corrosive nature of aluminum chloride-containing ionic liquids (ILs) typically employed in AMBs severely limit the overall practicality of AMBs. [2,3] While desired, the exploration of alternative electrolytes has been frustrated by the ionically passivating Al 2 O 3 film natively present on Al and the low equilibrium redox potential (−1.66 V vs standard hydrogen electrode possesses both adequate ionic conductivity and a high bandgap, [16] which allow metal ion transport while deterring further decomposition of the anion and water. As previously mentioned, it is not clear whether the Al-WiSE composed of 5 m Al(OTF) 3 , [5,9,17] which has a much lower salt concentration than Li-WiSE (21 m LiTFSI) or Na-WiSE (9 m NaOTF), can reduce to form an SEI.…”

“…[ 1 ] However, the capacity limiting and corrosive nature of aluminum chloride‐containing ionic liquids (ILs) typically employed in AMBs severely limit the overall practicality of AMBs. [ 2,3 ] While desired, the exploration of alternative electrolytes has been frustrated by the ionically passivating Al 2 O 3 film natively present on Al and the low equilibrium redox potential (−1.66 V vs standard hydrogen electrode (SHE)), which promotes electrolyte decomposition. [ 1 ] These issues are especially prominent in aqueous electrolytes, as hydrogen evolution reaction readily occurs at such low potentials and water molecules act as an oxygen source for oxide film formation.…”

A Review of Emerging Dual‐Ion Batteries: Fundamentals and Recent Advances

“…Al has also attracted much attention as the metallic anode in batteries due to its low cost, environmental benignity, high SC (2980 mAh g −1 ), and volumetric capacity (8046 mAh cm −3 , Al/Al 3+ ). [ 55 ] Taking Al foil covered with aluminum nanowires (Al‐Alnw) as the anode, an aluminum‐ion‐based DIB was first presented by Lu and co‐workers using graphite materials as the cathode and Al(ClO 4 ) 3 dissolved into carbonate solution as the electrolyte. [ 54 ] During the charging process, the ClO 4 − intercalated into graphite cathode, and the Al 3+ ion deposited on the Al nanowires to form a thin layer, resulting in the more stable morphology to suppress the formation of Al dendrites; while during the discharging process, ClO 4 − and Al 3+ would release into the electrolyte (Figure 4e).…”

AlCl3‐Saturated Ionic Liquid Anolyte with an Excess of AlCl3 for Al–Graphite Dual‐Ion Batteries

“…In a search for inexpensive, large‐scale stationary storage of electricity, non‐aqueous Al‐graphite dual‐ion batteries (AGDIBs) have attracted recently much attention due to the high natural abundances of their primary constituents, the long cycle life of up to a quarter of a million cycles, the high energy efficiency of 80–90 % and facile manufacturing [1–8] . While recent research efforts on AGDIBs have been mainly focused on the judicious selection of carbonaceous cathode materials, leading to the most notable advances in the performance of AGDIBs, [9–27] the major challenge with such batteries is that they lag behind Li‐ion batteries in theoretical cell‐level energy density.…”