Semi-coherent cation-rich Mn-Cu oxides heterostructures as cathode for novel aqueous potassium dual-ion energy storage devices.

In this work, combining both advantages of aqueous energy storage systems (ESS) and conventional dual-ion ESS, a novel aqueous dual-ion ESS is developed based on K and OH electrochemistry by employing semi-coherent KMnO-CuO (sc-Mn-Cu) cathode. Profting from the elaborate design, the electrolyte and cathode simultaneously act as source of cations. In the novel aqueous dual-ion ESS configuration, the dependence of the performance on the electrolyte salt concentration is reduced and the sc-Mn-Cu cathode can host OH with lower working potentials by conversion mechanism. Furthermore, based on the sc-Mn-Cu cathode and freestanding VO-VC (fs-VO-VC) anode, we developed a flexible quasi-solid-state device. Remarkably, it exhibits an ultrahigh energy density of ~39.9 μW h cm together with high power density of carbon-based devices, which outperforms most previously reported flexible storage devices to our knowledge. These results indicating that the unique mechanism of the sc-Mn-Cu cathode opens up a promising direction for low-cost and high-performance novel aqueous ESS.