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.