Boosting Electrochemical Capacitive of Ultrathin Shower‐Pouf Birnessite‐Type MnO ₂ for Porous High‐Mass‐Loading Energy Storage Device

Abstract High‐mass‐loading electrodes are critical for the economic viability and practicability of energy storage devices. Here, shower‐pouf‐like birnessite (SPB) with dense‐core‐free nanostructures are synthesized via a cost‐effective strategy, which significantly reduces the content of electrochemical dead mass caused by insufficient ion diffusion. Ascribed to the F ⁻ (from NH ₄ F) adsorbed on the (001) crystal plane of birnessite, the thickness of ultrathin birnessite films is regulated to ≈3 nm, providing abundant electrochemical active sites. By constructing high‐speed electronic transfer routes with conductive carbon black (CCB) and carbon nanotubes (CNTs), an SPB/CCB/CNTs electrode delivers a high capacitance of 278.6 F g ⁻¹ with an optimal high mass loading of 15.3 mg cm ⁻² . Based on the optimized slurry, the power‐law b ‐values, Ohmic resistance and cycling stability can be improved dramatically with increasing mass loading. Hence, a high‐mass‐loading asymmetric supercapacitor, assembled by SPB/CCB/CNTs nanostructure and hierarchical porous carbon composites (HPC/CCB/CNTs), delivers a capacitance of 1.75 F cm ⁻² and a record areal energy density of 0.97 mWh cm ⁻² (39.6 Wh kg ⁻¹ ). Moreover, A PV‐SC (photovoltaic‐supercapacitor) system driven mechanical vehicle achieves a travel distance of 4.8 m after being charged for 60 s in sunlight, highlighting the practical application prospect of SPB based high‐mass‐loading electrodes.