Suppressing passivation layer of Al anode in aqueous electrolytes by complexation of H2PO4− to Al3+ and an electrochromic Al ion battery

Aqueous aluminum ion batteries (AIBs) are attractive alternatives for post-lithium energy storage systems. However, the short lifespan seriously limits the development of AIBs, arising from the formation of a passivation layer on the Al electrode surface as well as the strong electrostatic interaction between bulky Al3+ ions and host materials. Herein, we developed a hybrid electrolyte based on aluminum trifluoromethanesulphonate (Al(TOF)3) and H3PO4 which can effectively alleviate the passivation and exhibit superior stability. A full aqueous AIB based on this electrolyte and polyaniline (PANI) cathode exhibits a record-breaking lifespan of 3850 cycles and superior rate capability. Mechanism study suggests that Al3+ ions are bonded to both the H2PO4− and TOF− to form complex ions Al(H2PO4−)x(TOF−)y+(H2O)n, which can mitigate the strong charge densities of trivalent Al3+ and contribute to fast reaction kinetics. Besides, the ex-situ study reveals that PANI cathode experiences a co-intercalation/deintercalation process of Al(H2PO4−)x(TOF−)y+(H2O)n, TOF−, and H+ during the charging/discharging process with high reversibility and stability. As a proof of concept, an electrochromic Al//PANI battery is fabricated, which combines both electrochromism and energy storage and delivers a higher coloration efficiency of 84 cm2 C−1 at a wavelength of 630 nm. This work presents an effective and facile strategy to developing long-life aqueous Al//PANI batteries and may promote the application of AIBs with electrochromic function.