Ni-doping induced structure distortion of MnO2 for highly efficient Na+ storage

Manganese dioxide is a typical electrode material for supercapacitor due to its high theoretical capacitance and good environmental compatibility. However, the development of MnO2 as electrode is limited by inferior conductivity, sluggish ionic transfer kinetics and poor cycling stability. Herein, we present a structure distortion strategy via Ni doping in MnO2 to boost its Na+ storage performance. The as-obtained Ni-MnO2 can deliver a high specific capacity of 379F g−1 at 1 A g−1, excellent rate performance of 281F g−1 at 20 A g−1, and a significantly enhanced cycling stability. In situ Raman results verify that Ni-MnO2 with structure distortion can achieve a promising cycling life. Density functional theory results suggest that the structure distortion can efficiently modulate electron configuration by delocalizing electron. Furthermore, the Na+ diffusion energy barrier is remarkedly decreased in Ni-MnO2, thus accelerating ionic transport kinetics. An asymmetric supercapacitor based on Ni-MnO2 cathode exhibits a high energy density of 114.6 Wh kg−1 at a power density of 3600 W kg−1. This work verifies the efficiency of structure distortion strategy on the improvement of Na ion storage performance in MnO2, which can be extended for the optimization of other electrode materials for energy storage.