Amorphous Ni-Mn-O Microspheres with High Energy Density and Ultralong-Term Stability up to 100, 000 Cycles for Aqueous Pseudo-Capacitors

A novel freestanding electrode of porous and amorphous NiMn1.57O4.13 microspheres is prepared for aqueous pseudo-capacitor. The NiMn1.57O4.13 microsphere has both cathodic site and anodic site so that it can be easily assembled as symmetric pseudo-capacitor (SPC), showing a great outlook for application. The SPC presents a superior stability and ability to withstand current fluctuations, which exhibits a high energy density of 122.8 Wh kg−1 with a retention of 106.1% at 5 A g−1 after 100,000 cycles. Moreover, the energy density is as high as 44.3Wh kg−1 even at the ultra-high power density of 18750.0 W kg−1, presenting an excellent charge/discharge rate.