Hollow amorphous-crystalline hybrid MnO2 nanoflower spheres for high-performance rechargeable aqueous zinc ion batteries

Manganese dioxide (MnO2), a commonly employed cathode material in aqueous zinc ion batteries (ZIBs), presents numerous advantages including a high theoretical capacity, abundant reserves, and environmental friendliness. The material, however, experiences sluggish reaction kinetics and rapid degradation in battery capacity due to its inherent poor electrical conductivity and significant volume changes during charge and discharge processes. Herein, we demonstrate the rational synthesis of a hollow MnO2 nanoflower sphere material with a well-defined δ-MnO2/amorphous MnO2 structure (named as HMS) and evaluate its potential as a cathode material for ZIBs. The three-dimensional (3D) nanoflower spheres with an amorphous structure possess a large specific surface area, accumulating numerous structural defects that enhance ion diffusion kinetics. Furthermore, the hollow nanostructures can provide a larger number of active sites and shorter ion transfer pathways in electrochemical processes, thereby promoting reaction kinetics and mitigating volume expansion during cycling, ultimately leading to significantly enhanced cycling performance. The synthesized HMS composite demonstrates remarkable synergistic advantages, exhibiting an outstanding capacity of 375 mAh g−1 at 0.1 A g−1 and an impressive rate performance of 225 mAh g−1 at 2 A g−1, and maintains 84% of its initial capacity after 1000 cycles. This work provides a novel approach for developing high-performance aqueous ZIBs.