δ-type manganese oxides with preintercalated sodium ions as atomic pillars for high-performance supercapacitors

Abstract

Layered δ-MnO2 (Birnessite) with interlayered H2O molecules has been considered as a promising candidate for supercapacitor application. However, severe drawbacks of δ-MnO2 owing to its structural deformation by Mn2+ dissolution and Jahn-Teller distortion cause poor durability and low capacity for energy storage. Herein, we report a δ-type Na0.16MnO2 electrode with enhanced capacitance and cycling performance synthesized by preintercalation of Na+ ions. The Na0.16MnO2 has a large amount of interlayered H2O molecules and stabilized Mn-O-Na bonds between MnO6 layers for facilitating ionic diffusion. In addition, the Na0.16MnO2 shows the homogeneously interconnected ultrathin nanosheet network for fast charge-storage kinetics, large storage capacity, and superior cycling stability. The specific capacitance of Na0.16MnO2 reaches 560 F g−1 at a current density of 1 A g−1, while maintaining constant capacity up to 10,000 cycles. The enhanced performance of Na0.16MnO2 is mainly attributed to the atomic pillars of preintercalated Na+ ions in δ-MnO2 which effectively suppress the deformation of interlayer spacing during charge/discharge processes and thus benefit the long-term stability.