Ultrahigh Energy Density and Ultrafast Response in Symmetric Microsupercapacitors with 3D Bicontinuous Pseudocapacitance

Abstract

Achieving a high storage capability while maintaining good rate performance using symmetric microsupercapacitors (MSCs) remains challenging. Herein, a 3D symmetric MSC based on interdigitated 3D bicontinuous pseudocapacitive electrodes is proposed to simultaneously attain ultrahigh energy density and ultrafast response. The 3D electrodes comprise electrolytically active MnO2 layers conformally coated onto a 3D periodic porous Ni current collector. In this architecture, the low conductivity of MnO2 can be compensated by efficient charge transport and facile charge transfer without compromising its high capacitance. The 3D MSC with a 1‐V window exhibits an ultrahigh volumetric energy density of 15.8 mWh cm−3 with a high power density of 4.95 W cm−3, outperforming all previously reported MnO2‐based symmetric MSCs. Benefitting from its ultrafast response, the 3D MSC exhibits superiority in terms of the phase angle (−66°), areal capacitance (1400 µF cm−2), and time constant (0.6 ms) at an alternating‐current (AC) frequency of 120 Hz. By using the 3D MSC as a line‐filtering capacitor in a real circuit, the AC signal is effectively smoothed with small residual ripples (≈1.35 mV). Additionally, the device achieves excellent performance in an all‐solid‐state form.