All-solid-state high-energy planar asymmetric supercapacitors based on all-in-one monolithic film using boron nitride nanosheets as separator

Fast development of smart electronics requires urgently integrated energy storage devices, but conventional supercapacitors, using two substrates, suffer from weak flexibility, low energy density and inferior integration. Here we demonstrate a printable construction of all-solid-state high-energy planar asymmetric supercapacitors (EG//MP-PASCs) based on all-in-one monolithic films of stacked-layer pseudocapacitive MnO2/poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (MP) nanosheets as positive electrode, highly ionic conductive boron nitride nanosheets as ultrathin separator (~ 2.2 μm), and capacitive electrochemically exfoliated graphene (EG) nanosheets as negative electrode integrated on single substrate. Notably, EG//MP-PASCs are free of conventional separators, additives, binders, and metal-based current collectors, significantly simplifying the device fabrication process. EG//MP-PASCs can be operated reversibly at high voltage of 1.8 V at polyvinyl alcohol/LiCl gel electrolyte, and exhibit volumetric energy density of 8.6 mW h cm−3, much higher than those of conventional asymmetric supercapacitors based on two substrates (3.1 mW h cm−3), planar symmetric supercapacitors based on EG//EG (0.64 mW h cm−3), MP//MP (2.5 mW h cm−3). Further, EG//MP-PASCs display robust mechanical flexibility with ~ 98.8% of initial capacitance even bended at 180°, and applicable scalability on various substrates. Remarkably, EG//MP-PASCs can be readily self-interconnected in series and parallel, without usage of metal-based interconnections and contacts, to tailor the voltage and current output for integrated circuits.