Engineering Active Sites of Polyaniline for AlCl 2 + Storage in an Aluminum‐Ion Battery

The reversible capacity of AlCl 4 − intercalation/de‐intercalation in conventional cathodes of aluminum‐ion batteries (AIBs) is difficult to improve due to the large size of AlCl 4 − 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 AlCl 2 + 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.