Polyaniline intercalated layered VOPO₄·2H₂O: An organic-inorganic hybrid cathode for high performance aqueous zinc-ion batteries

Considering the mechanism of charge intercalation, an optimized tuning of the interlayer spacing and microstructure is vital for realizing enhanced Zn²⁺ storage performance of the inexpensive two-dimensional (2D) layered vanadyl phosphate, VOPO₄·2H₂O (VP). Herein, we report a facile development of an organic-inorganic conductive polyaniline (PA) intercalated hybridized cathode (PA-VP) by pre-intercalating aniline monomers and subsequent in situ polymerization within the VP layers. The electrostatic interactions between the V[sbnd]O/P[sbnd]O layer and Zn²⁺ can be efficiently lessened owing to the distinctive π-conjugated structure and the “pillars” effects of PA. More significantly, the conjugated conductive intercalant PA could intrinsically prompt electron transport to lower vanadium chemical valence states, which is crucial for improving electronic conductivity. Furthermore, the resulting PA-VP microstructure provides rich active sites for Zn²⁺ intercalation and facilitates contact with the electrolyte. Correspondingly, the PA-VP cathode with an interlayer d-spacing of 14.6 Å delivers a maximum specific capacity of 223.9 mAh g⁻¹ at 0.1 A g⁻¹ and outstanding cycling performance of 86.7 % capacity retention after 500 cycles. Thus, our approach offers a practical solution to slow Zn²⁺ diffusion kinetics and unsatisfactory stability of layered VOPO₄·2H₂O, and also provides insight into the principle of interlayer chemistry for realizing superior zinc ion batteries (ZIBs).