Cointercalation of Polyaniline and Alkali-Earth Cations into V₂O₅ to Boost Aqueous Zinc-Ion Storage Performance with Superior Cycling Stability

Aqueous zinc-ion batteries (AZIBs) are considered as an attractive alternative to lithium-ion batteries. Although the vanadium pentoxide (V₂O₅) cathode exhibits high theoretical capacity of 589 mA h g^-1 for zinc-storage, it suffers from capacity decay and sluggish Zn²⁺ diffusion kinetics due to the strong electrostatic interactions with Zn²⁺, slight dissolution in aqueous electrolytes, and low electronic conductivity. Herein, the polyaniline and alkali-earth cation (Mg²⁺, Ca²⁺) cointercalated V₂O₅ composites (PVO-Mg, PVO-Ca) are fabricated to boost the zinc ion storage performance of vanadium oxide cathodes. PVO-Mg exhibits an enlarged interlayer distance of 14.15 Å and a tremelliform nanoarchitecture composed of nanosheets. The intercalated polyaniline and alkali-earth cations not only expand the Zn²⁺ diffusion channels but also form a pillar net which can improve the structural stability and electronic conductivity of the layered structure, contributing to superior electrochemical kinetics, interfacial kinetics, and Zn²⁺ diffusion kinetics. Moreover, ex situ X-ray diffraction results of PVO-Mg show a nearly constant interlayer distance during the insertion and extraction of Zn²⁺, which indicates that polyaniline and Mg²⁺ firmly support the layered framework and prevent the expansion and contraction of the interlayer distance. Ex situ X-ray photoelectron spectroscopy results of PVO-Mg reveal the highly reversible formations of Zn_x(CF₃SO₃)_y(OH)_2x−y·nH₂O on the electrode surface and Zn²⁺ inserted PVO-Mg inside the electrode, as well as a H⁺ and Zn²⁺ insertion/extraction process during which the polyaniline serves as a H⁺ reservoir and a capacity contributor. Consequently, the PVO-Mg electrode exhibits high capacity (387.0 mA h g^-1 at 0.5 A g^-1), ultrafast rate capability (199.3 mA h g^-1 at 30 A g^-1), improved cycling stability, and high reversibility and would be a promising cathode for high performance AZIBs.