Designing of Birnessite/Polyaniline Composite for Improving Cyclability as Cathode Material for Zinc Ion Batteries Based on Insights into the Reaction Mechanism

Abstract Aqueous Zn/MnO 2 batteries (ZIBs) have high application value and development prospects in large‐scale energy storage. However, the cyclability of MnO 2 is poor and its reaction mechanism is still controversy. Here, we revealed the zinc storage mechanism was Zn 2+ /H + intercalation and conversion mechanism rather than Zn 2+ and H + co‐insertion reaction mechanism of birnessite (δ‐MnO 2 ) electrode, and cycle fading was mainly caused by bad reversibility of ZnMn 3 O 7 ⋅ 2H 2 O which was formed during conversion reactions by combining with X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy analyses and so on. On this basis, appropriate polyaniline (PANI) was intercalated to the layer of δ‐MnO 2 to stabilize its structure. The composite electrode exhibited higher capacity of 105 mAh/g after 250 cycles at 1 C rate, while δ‐MnO 2 electrode had capacity of 86 mAh/g at same condition. Therefore, PANI intercalation can improve the cycle performance of the ZIBs to some extent. This work is believed to provide new strategy for further research on MnO 2 cathode in ZIBs.