High-energy SWCNT cathode for aqueous Al-ion battery boosted by multi-ion intercalation chemistry

The aqueous Al-ion battery has achieved great progress in recent years. It now shows comparable performance to that of even non-aqueous Al-ion batteries. However, it also shows relatively low energy output and there is limited general understanding of the mechanism behind this restriction to its practical application. Thus, the development of a high-performance cathode material is in great demand. Herein, a high-capacity single-walled carbon nanotube (SWCNT) is developed as a cathode for the water-in-salt electrolyte-based aqueous Al-ion battery, which provides an ultra-high specific capacity of 790 mAh g^–1 (based on the mass of SWCNT) at a high current density of 5 A g^–1 even after 1000 cycles. Moreover, the SWCNT/Al battery shows a complicated multi-ion intercalation mechanism, where AlCl₄^–, Cl^–, Al³⁺, and H⁺ can function at the same time, improving the battery output. Beyond recently revealed H⁺ and metal ion co-intercalation, the Cl-assisted intercalation of Al³⁺ ions mechanism is also studied by experimental characterization and modeling for the first time, which significantly boosts the Al³⁺ storage capacity. This multi-ion intercalation mechanism combines the high-voltage anion deintercalation and the high-capacity cation intercalation, and thus, benefits the development and application of high-energy Al-ion batteries in the future.