Substrate Integrated Nickel–Iron Ultrabattery with Extraordinarily Enhanced Performances

A substrate-integrated nickel–iron ultrabattery is realized using nickel oxide (NiO) nanoflakes and hematite (α-Fe₂O₃) nanorods as electroactive materials for its positive and negative electrodes, respectively. Direct growth of electroactive materials on a highly conductive stainless steel substrate enhances the mechanical stability of the system together with reducing its internal resistance. The proposed nanoarchitectural design of the electroactive materials provides a large number of interaction sites for the electrolytic ions with the electrode materials in conjunction with short ion-diffusion paths, which significantly improve the capacitive performance of individual electrodes and hence of the fabricated ultrabattery. As a consequence, the as-assembled ultrabattery exhibits a specific capacity value of ∼36 mAh/g (94 F/g and volumetric capacitance ∼0.77 F/cm³) at a current density of 0.5 A/g in a potential window between 0 and 1.4 V, with capacitance retention of ∼60% of its original value even when the load current density is increased 20 times.