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 cm(2) 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.

Automated summary

This study presents a hybrid electrolyte based on Al(TOF)(3) and H3PO4 for aqueous aluminum ion batteries (AIBs) which exhibits superior stability and a record-breaking lifespan of 3850 cycles. The Al//PANI battery with this electrolyte shows high reversibility and stability during the charging/discharging process, and delivers a higher coloration efficiency of 84 cm(2) C-1 at a wavelength of 630 nm.