Boosting Electrochemical Capacitive of Ultrathin Shower-Pouf Birnessite-Type MnO₂ for Porous High-Mass-Loading Energy...

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 NH₄F) 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.