Engineering Active Sites of Polyaniline for AlCl2+ Storage in an Aluminum‐Ion Battery

The reversible capacity of AlCl4- intercalation/de-intercalation in conventional cathodes of aluminum-ion batteries (AIBs) is difficult to improve due to the large size of AlCl4- anions. Therefore, it is highly desirable to realize the intercalation/de-intercalation of smaller Al-based ions. Here, we fabricated polyaniline/single-walled carbon nanotubes (PANI/SWCNTs) composite films and protonated the PANI nanorods. The protonation endows PANI with more active sites and enhanced conductivity. Hyper self-protonated PANI (PANI(H+ )) exhibits reversible AlCl2+ intercalation/de-intercalation during the discharge/charge process. As a result, the discharge capacity of the Al/PANI(H+ ) battery is twice as high as that of the initial composite films. PANI(H+ )@SWCNT electrodes also have a stable cycling life with only 0.003 % capacity decay per cycle over 8000 cycles. Owing to the excellent mechanical properties, PANI(H+ )@SWCNT composite films can act as the electrodes of flexible AIBs.