Optimizing the electrons/ions diffusion kinetics in -MnO₂ for realizing an ultra-high rate-capability supercapacitor

delta-MnO2 nanosheets are promising cathode candidates for supercapacitors because of their cost-effective, environmental protection, and high theoretical capacity. Unfortunately, the commercial application of delta-MnO2 is hindered by the challenging issues of sluggish diffusion kinetic and poor rate-capability. It is urgent to optimize its kinetics behavior to improve the ion diffusion ability and electronic conductivity. Herein, one-step and one-phase synthesis of few-layer defective delta-MnO2 nanosheets (named delta-MnO2-CTAB) has been developed via a redox reaction between cetyltrimethylammonium bromide (CTAB) and KMnO4, and the kinetics storage mechanisms are investigated by DFT calculations. The migration barrier energies of Na in the surface or interlayer of delta-MnO2 (001) are reduced significantly with the reduction of layer-number (0.32 eV of 3 layers and 0.04 eV of 2 layers), which is conducive to the Na ion diffusion. Moreover, the generation of defects increases the density of states at the Fermi level of delta-MnO2, indicating the improvement of electronic conductivity. Therefore, when the current density is increased 50-fold (1 A g(-1) to 50 A g(-1)), the rate-capability of delta-MnO2-CTAB is as high as 77%, exhibiting ultra-high rate-capability. This work unveils the kinetics storage mechanisms in few-layer delta-MnO2 with defects nanosheets for ultra-high rate-capability supercapacitors.