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 MnO 2 layers conformally coated onto a 3D periodic porous Ni current collector. In this architecture, the low conductivity of MnO 2 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 MnO 2 ‐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.