Intercalation Effect of Polyaniline in Δ-Mno2: Optimizing the Interlayer Spacing and Ion Transport Capacity

Abstract

The application of MnO2 cathodes in aqueous zinc-ion batteries (AZIBs) has been hampered by the intrinsically poor conductivity and proneness to phase transition of MnO2. To surmount these obstacles, we synthesized polyaniline (PANI)-intercalated δ-MnO2 (PMO) nanosheets as promising cathode materials for AZIBs. Through X-ray diffraction (XRD) and Raman spectroscopy characterization, it was ascertained that introducting PANI effectively enlarges the interlayer spacing of MnO2, facilitating ingress of ions into the interlayer. Scanning electron microscopy revealed that PANI intercalation did not alter the morphology of MnO2, unequivocally confirming the structural stability of the fabricated PMO samples. Furthermore, owing to the outstanding conductivity of PANI, the ion diffusion coefficient of the PMO electrode range from 10–6–10–10 cm2 s–1. X-ray photoelectron spectroscopy suggested that PANI complexes with MnO2, reducing the oxidation state of manganese and thus mitigating the distortion of MnO2. Ex-situ XRD analysis further corroborated that PANI forms stabilizing pillars between the MnO2 layers with excellent reversibility. Consequently, the fabricated PMO cathode exhibited an outstanding cycle life (2000 cycles), a remarkable capacity (250 mAh g–1), and an impressive capacity retention rate (76%). An in-depth mechanism analysis revealed that H+ and Zn2+ are co-inserted into the PMO electrodes. Two byproducts, ZnSO4(OH)6•nH2O (ZSH) and ZnxMnO(OH)2 (ZMO) were found to limit the capacity. This intercalation-based approach is a new direction for the development of manganese-based electrode materials for AZIBs.

Keywords: δ-MnO2, aqueous zinc-ion battery, polyaniline, intercalated