Abstracts Flexible solid-state electrochemical energy storage devices with amorphous nickel pyrophosphate microstructures and graphene nanosheets as positive and negative electrode materials have been successfully assembled. Amorphous nickel pyrophosphate microstructures have been synthesized by calcination of the ammonium nickel phosphate hydrate microstructures in air at 350°C. The device achieved a maximum volumetric energy density of 0.78mWhcm−3 which is larger than that of most of published results, and showed a long cycle life with little capacity decay even after 6000 cycles, and maintained good mechanical flexibility under a bending angle of 0–180°.