High-Performance All-Solid-State Supercapacitor Based on the Assembly of Graphene and Manganese(II) Phosphate Nanosheets

Manganese phosphate nanosheets (Mn 3 (PO 4 ) 2 ·3H 2 O NSs) with ∼2 nm thickness were prepared by exfoliating the bulk material in dimethylformamide (DMF) under ultrasonication. They can spontaneously form face-to-face stacked assemblies with exfoliated graphene NSs in DMF. The assemblied Mn 3 (PO 4 ) 2 ·3H 2 O and graphene NSs at the mass ratio of 1:10 (M 1 G 10 ) revealed a specific capacitance of 2086 F g –1 at 1 mV s –1 . These M 1 G 10 assemblies were used to fabricate all-solid-state supercapacitor (M 1 G 10 -ASSS) on the basis of PVA/KOH solid polymer electrolytes, which exhibited a specific capacitance of 152 F g –1 (or 40 mF cm –2 ) at 0.5 A g –1, an energy density of 0.17 μWh cm –2 at 0.5 A g –1 (1.3 A m –2 ) and a power density of 46 μW cm –2 at 2 A g –1 (5.3 A m –2 ). M 1 G 10 -ASSS also showed excellent cycling stability and nearly 100% capacitance retention was achieved after 2000 galvanostatic charge–discharge cycles at 2 A g –1 . Such extraordinary properties were attributed to the synergistic effect of high pseudocapacitance of Mn 3 (PO 4 ) 2 ·3H 2 O NSs, high conductivity and surface areas of graphene NSs.