Electrochemical properties of aluminum ion batteries with emeraldine base polyaniline as cathode material

Aluminum ion batteries (AIBs) are currently attracting widespread interest due to their high capacity, low price and high safety, while practical applications are severely hampered by the lack of suitable cathodes and the relatively complex and divergent energy storage mechanisms. Polyaniline has shown considerable promise for application in various rechargeable batteries, however, little research has been conducted on the applica-tion to AIBs. Here, the emeraldine base polyaniline (PANI) using a chemical oxidation method is synthesized and then assembled in an Al/PANI cell with a chloroaluminate ionic liquid as the electrolyte. Compared with the conventional protonated polyaniline cathode, the PANI cathode shows better electrochemical performance during the 0-2.4 V charging/discharging process, exhibiting a discharge specific capacity of 155 mAh g-1 at a current density of 1 A g-1and capacity retention of 80% after 2000 cycles. Meanwhile, ex-situ characterization reveals a novel conversion process of this system different from that of conventional proton-doped polyaniline materials, in which the electrolyte is spontaneously complexed with the PANI cathode. This is followed by reversible doping of the chloroaluminate anion in the -NH-group of the PANI-AlCl3 complex, yielding high reversible capacity and long cycle life. These findings have made new attempts and laid the foundation for the development of high-performance aluminum ion batteries with conducting polymers as the cathode mate-rial and further clarification of their charge storage and reaction mechanisms.