Rational Design of 2D Manganese Phosphate Hydrate Nanosheets as Pseudocapacitive Electrodes

A new class of 2D-nanosheets of nitrogen-integrated phosphate-rich ammonium manganese phosphate hydrate, (NH4MnPO4.H2O) (AMP), has been developed as pseudocapacitive electrode materials. The optimized electrodes exhibited the significant device capacitance of 48.4 and 65.4 F/g at a scan rate of 5 mVs-1 in symmetric and asymmetric devices, respectively. The devices delivered excellent energy and power (29.4 Wh kg-1 and 133 kW kg-1 for asymmetric cell, and 9.7 Wh kg-1 and 150 kW kg-1 for symmetric cell) with extra-ordinary retention of capacitance (> 93%, 100k cycles at 5 A/g for asymmetric cell and > 97%, 10k cycles for symmetric cell) that surpass most of the reported values to date. The huge pseudocapacitance of AMP is attributed to several factors including the electroactive sites containing NH4+ ions, the conductive inorganic layers, intercalated water interactions of Mn2+-H2O, redox-active phosphate ions, and the 2D nanosheets that boost both electronic and ionic transports. AMP-based all-solid-state ...