Asymmetric supercapacitors with high energy density based on helical hierarchical porous Na x MnO2 and MoO2.

Helical hierarchical porous Na x MnO2/CC and MoO2/CC, which are assembled from nanosheets and nanoparticles, respectively, are fabricated using a simple electrodeposition method. These unique helical porous structures enable electrodes to have a high capacitance and an outstanding cycling performance. Based on the helical Na x MnO2/CC as the positive electrodes and helical MoO2/CC as the negative electrodes, high performance Na x MnO2/CC//MoO2/CC asymmetric supercapacitors (ASCs) are successfully assembled, and they achieve a maximum volume Csp of 2.04 F cm-3 and a maximum energy density of 0.92 mW h cm-3 for the whole device and an excellent cycling stability with 97.22% Csp retention after 6000 cycles.