Ultrathin Polyaniline-Coated Single-Crystalline Mn₂O₃ Nanoporous Ellipsoids with High Energy Density and Cyclability for Low-Cost Zinc-Ion Batteries

Secondary Zn-ion batteries (ZIBs) using aqueous electrolytes are very promising for safe and large-scale energy storage in the future. However, we still lack suitable cathode materials with high energy density and durability for Zn2+ storage. Herein, a three-dimensional nanoporous microellipsoid Mn2O3 covered with an ultrathin layer of polyaniline (PANI) composite (Mn2O3/PANI) is developed for advanced ZIBs. The synthesis of Mn2O3/PANI is quite easy: nanoporous Mn2O3 (which is obtained from the pyrolysis of MnCO3) is immersed into aniline, and the subsequent self-initiated polymerization of PANI will cover the Mn2O3 surface. The bicontinuous nanoporous structure with a pore size of ∼30 nm facilitates ion diffusion and provides an active interface for fast zinc-ion storage. Moreover, the uniformly coated ultrathin PANI cover not only inhibits Mn2O3 dissolution and protects the structural integrity but also provides a fast electron transport network during charge/discharge. Consequently, the designed Mn2O3/PANI achieves a high energy capacity, a high rate performance, and a much longer lifetime (86.6% capacity retention over 2000 cycles at 1 A g–1), outperforming those of most reported cathode materials. Detailed electrochemical studies and characterizations demonstrate that the H+ and Zn2+ coinsertion mechanism and the PANI cover can enlarge the Zn-ion diffusion coefficient. This work introduces a facile route to develop 3D bicontinuous nanoporous Mn2O3/PANI composites for highly reversible ZIBs.