Decavanadate Doped Polyaniline for Aqueous Zinc Batteries.

Polyaniline (PANI) is a promising cathode material for aqueous rechargeable zinc batteries (ARZBs), mainly benefitting from its good electrical conductivity. The high conductivity of PANI requires high doping level, yet the introduced nonactive dopants (e.g., SO4 2- ) limit the gravimetric capacity of PANI (usually < 180 mAh g-1 ). Herein, an electro-active dopant (decavanadate anion, V10 O28 6- ) is employed to fabricate the PANI cathode (PANI-V10 O28 ) for ARZBs. The doped decavanadate anion with the sub-nanometer structure can fully expose the V-based active sites, exhibiting good electrochemical activity. Due to the steric hindrance effect as well as the strong interaction between decavanadate anions and PANI chains, the active dopants are trapped in the polymer chains, demonstrating good structural and electrochemical stability. PANI-V10 O28 achieves a record-high gravimetric capacity of 355 mAh g-1 at 0.1 A g-1 , which is significantly higher than other reported PANI cathodes. Experimental results suggest that the charge storage mechanism of PANI-V10 O28 includes reversible injection/extraction of Zn(H2 O)2 Cl4 2- ions in PANI, as well as the protonation/deprotonation of V10 O28 6- . This work enriches the doping chemistry of conducting polymer and pushes the development of organic cathodes for ARZBs to a new stage.

Protonating imine sites of polyaniline for aqueous zinc batteries.

PANI materials usually contain a certain amount of insulating components, e.g., imine (N-) and amine (-NH-) groups, limiting the electrochemical redox of PANI. Herein, we proposed a simple protonation strategy to activate the redox couples of the PANI cathode for aqueous Zn batteries, during which the insulating N- groups are partially converted to the conductive emeraldine salt (polarons -NH+-), endowing PANI more active sites and enhanced conductivity. The A-PANI electrode realizes efficient transitions of leucoemeraldine/emeraldine and emeraldine/pernigraniline, achieving a high discharge capacity of 183 mA h g-1, long life span, and good energy density of 178 W h kg-1 at the power density of 680 W kg-1. These values are significantly superior to those of the original PANI electrode, indicating the high efficiency of the proposed strategy. This simple protonation method could be applicable for many electrochemical devices, such as supercapacitors, sensors, and batteries.