Zinc-Doped Polypyrrole as a Functional Protective Layer for Zinc Anodes of Zn-Ion Batteries: A Density Functional Theory Approach

The development of zinc-ion batteries (ZIBs) is hindered by the formation of zinc dendrites, which degrade battery performance and compromise safety. To address this challenge, we investigate zinc-doped polypyrrole (Zn-doped PPy) as a functional protective coating for Zn anodes by using density functional theory (DFT) calculations. We systematically analyze the intrinsic structural and electronic properties of PPy, revealing that polaron and bipolaron states significantly influence the charge distribution and coplanarity along the polymer backbone. It is found that Zn doping occurs preferentially at the nitrogen site via coordinate covalent bonding with neutral PPy providing the most stable binding environment. Electronic band structure calculations show that Zn doping reduces the bandgap from 1.77 to 0.35 eV, enhancing electrical conductivity and improving charge transport within the electrode. Furthermore, it is demonstrated that Zn-doped PPy significantly enhances nucleation site formation, with a lower binding energy (−0.104 eV) compared with undoped PPy (−0.037 eV), thereby promoting uniform Zn deposition and mitigating dendrite formation. Adhesion analysis further reveals that Zn-doped PPy exhibits stronger interactions with the Zn anode, ensuring improved coating stability and durability. These findings highlight Zn-doped PPy as a promising protective material for enhancing Zn anode stability, suppressing dendrite growth, and extending the ZIB cycle life. By offering improved conductivity, enhanced Zn nucleation, and strong adhesion, Zn-doped PPy provides a practical and scalable approach to overcoming key challenges in ZIB technology.