Ultrathin Polyaniline-Coated Single-Crystalline Mn₂O₃Nanoporous 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 Mn₂O₃covered 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 Mn₂O₃surface. 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 Mn₂O₃dissolution 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.