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

Manganese phosphate nanosheets (Mn-3(PO4)(2)center dot 3H(2)O NSs) with similar to 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(PO4)(2)center dot 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 mu Wh cm(-2) at 0.5 A g(-1) (1.3 A m(-2)) and a power density of 46 mu W 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(PO4)(2)center dot 3H(2)O NSs, high conductivity and surface areas of graphene NSs.