All Two-Dimensional Pseudocapacitive Sheet Materials for Flexible Asymmetric Solid-State Planar Microsupercapacitors with High Energy Density.

With the rapid development of portable devices and wireless protocols, miniaturized energy storage units have become an important prerequisite. Although in-plane microsupercapacitors are emerging as competitive candidate devices, their practical applications have been severely hindered by their low energy density. Here, employing pseudocapacitive active materials working in complementary voltage windows, namely, manganese oxide (MnO2) and titanium carbide (Ti3C2), both in the two-dimensional sheet morphology, a flexible asymmetric interdigitated solid-state microsupercapacitor was assembled. Profiting from the perfect voltage complementarity of the two types of sheets, the high exposure of electrochemically active sites and the maximized utilization of the sheets due to the planar ion transport, the designed device achieved excellent electrochemical performance even when using a gel electrolyte. In particular, the device obtained a high specific capacitance of 106 F g-1 (295 mF cm-2), a wide potential window (2 V), an ultrahigh rate performance (retaining 83% even with a 20-fold in current density to 20 A g-1), an excellent cycling stability (87% retention after 104 cycles at 10 A g-1), and a competitive energy density of 58 W h kg-1 (162 μW h cm-2) that are even comparable to those of some microbatteries, while maintaining a high power density of 985 W kg-1 (2.7 mW cm-2). Importantly, this outstanding electrochemical performance was also stably maintained under various bending conditions. These results indicate that two-dimensional pseudocapacitive sheet materials have a plethora of possibilities for constructing flexible and wearable devices.