Three-dimensional MnO₂ ultrathin nanosheet aerogels for high-performance Li-O₂ batteries

Abstract

Two-dimensional (2D) ultrathin nanocrystals represent a family of emerging nanomaterials with many proposed applications; however, the interlayer re-stacking between sheets greatly decreases the performance during practical operation. This work demonstrates a facile strategy to solve this challenging problem by rational assembly of 2D nanocrystals into three-dimensional (3D) aerogels, which paves the way for harvesting excellent structural properties of both nanostructures and macrostructures. The resultant 3D MnO₂ aerogel shows significantly increased discharge capacity in Li-air batteries in comparison to its powder-like counterpart (4581.4 vs. 3902.6 mA h g⁻¹), which outperforms many MnO₂ and other transition metal-based electrocatalysts. Meanwhile, the as-fabricated Li-air cell demonstrates good rate capability and cycle life. Further mechanism study reveals that the improved performance is associated with ultrathin MnO₂ nanosheets which allow highly exposed catalytic centres, as well as its excellent aerogel structure with rich porosity and a 3D continuous network that maximizes the utilization of MnO₂ species for catalytic reactions. This study may open up new opportunities for making full use of 2D nanocrystals for a number of energy storage/conversion techniques.