Combined In Situ EQCM-Raman Study of Zn Storage Mechanism in Polyaniline for Zinc-Ion Battery.

Zinc-ion batteries (ZIBs) have attracted increasing attention as safe, cost-effective, and environmentally friendly alternatives to lithium-ion batteries for large-scale energy storage. Among various cathode materials for Zn batteries, polyaniline (PANI) is a potential material that presents benefits such as high conductivity and pseudocapacitive behavior. However, it often suffers from limited cycling stability and structural degradation during repeated charge-discharge processes. Here, in situ electrochemical quartz crystal microbalance (EQCM)-Raman technique is combined to understand the Zn storage behavior in PANI wherein limited Zn insertion is observed along with detachment of the polymer from the substrate. Through anion doping of PANI, the structural stability is enhanced, and the overall Zn cycling capability is improved. Ex situ X-ray photoelectron spectroscopy (XPS) studies further reveal that doping of PANI significantly reduces the oxidation of PANI, which leads to an improved battery performance. The doped-PANI shows a high specific capacity of 310 and 235 mAh g^-1 at 0.25 and 1 A g^-1, respectively, and retains 85% of its initial capacity after 300 cycles at 1 A g^-1. These results reveal that it is important to understand the storage mechanism to develop useful strategies to improve ZIBs performance.