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

Abstract

The application of MnO2 cathodes in aqueous zinc-ion batteries (AZIBs) is limited because of the poor intrinsic conductivity and easy phase transition of MnO2. To address these problems, we prepared polyaniline (PANI)-intercalated δ-MnO2 (PMO) nanosheet as a promising cathode material for AZIBs. Through a series of characterizations, such as X-ray diffraction (XRD) and Raman spectroscopy, it was found that the introduction of PANI effectively increased the interlayer spacing of MnO2 and facilitated the transport of ions into the interlayer. Even more surprising, it was found via scanning electron microscopy (SEM) that PANI intercalation did not change the morphology of MnO2, clearly demonstrating the structural stability of the prepared PMO samples. In addition, because of the excellent conductivity of PANI, the PMO electrode exhibited an ion diffusion coefficient of 10−6−10−9.7 cm2 s−1. X-ray photoelectron spectroscopy (XPS) indicated the complexation between PANI and MnO2, and the decrease in the oxidation state of manganese alleviated the distortion of MnO2. Moreover, the ex-situ XRD analysis confirmed the role of PANI as a pillar between MnO2 layers, with good reversibility. Therefore, the prepared PMO cathode had an excellent cycle life of 2000 cycles, a superior capacity of 250 mAh g−1, and an outstanding capacity retention rate of 76%. Through mechanism analysis, this study also revealed the mechanism of the co-insertion process of H+ and Zn2+ into the PMO electrodes. Additionally, ZnSO4(OH)6•nH2O (ZSH) and ZnMn2O4 byproducts were generated, which prevented a high capacity. This work thus demonstrated a method of developing manganese-based electrode materials for AZIBs by intercalation.

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