Inceptive high-performance flexible aqueous aluminum-ion batteries derived from pre-intercalated copper hexacyanoferrate cathode

Abstract

Aqueous aluminum-ion batteries (AAIBs) have increasingly been regarded as inexpensive, non-toxic, environmentally benign, and safe energy storage devices that can replace lithium-ion batteries (LIBs) because of their potential to achieve a high energy density. They might be integrated into future technologies, such as grid storage or flexible electronics, aligning with their advantages. While the commercialization of AAIBs is challenging, as the three-electron transfer reactions of Al³⁺/Al are difficult to realize and its charge transfer mechanism is still debated, the use of intercalation materials such as copper hexacyanoferrate (CuHCFe) stands out as an appealing strategy to enhance their electrochemical performance. Building on this approach, we successfully developed CuHCFe intercalated with Al³⁺ ions and utilized the resulting material to fabricate, for the first time, a flexible aqueous aluminum-ion battery full cell where a sol-gel synthesized MoO₃ anode has been incorporated. The fabricated device shows a specific capacity of 66.84 mAh g⁻¹ at a current density of 0.5 Ag⁻¹. It maintained a coulombic efficiency of 96.77 % over 150 cycles, with almost no capacity fading. The flexibility of the device was studied by testing bending angles of 60°, 90°, and 180°. At 0.5 Ag⁻¹, the battery exhibited specific capacities of 65.38, 56.78, and 52.93 mAh g⁻¹ at 60°, 90°, and 180° bending conditions, respectively, highlighting its remarkable flexibility with 79.2 % capacity retention after 180° bending.